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#2380976 - 10/02/17 09:46 PM 408 help needed
Mirada 408 Offline
member

Registered: 08/10/15
Posts: 14
Loc: West Virginia
Trying to figure out what is holding it back from better et's. Car is a 1981 Dodge Mirada. If I had to guess weight is 3500lbs, never weighed it. 8 3/4 with 3.55s running mt et street radials 275/60r15s , 904 low gear set and 3500 stall foot brake to 2500 launch. Engine is 408ci. eagle crank and rods, kb hyper pistons, comp cam hydraulic roller xr-292hr-10 duration 242/248 lift .545, 1.6 ratio rockers, edlebrock rpm heads, airgap intake, and 750 Holley dp. Car is consistently 12.20-12.30 @108-110mph. That's shifting at 5800 rpms, which is what it liked. I was happy with it, but wanted to go faster. therefore send the heads out and have them cnc ported and 2.08 intake valves put in. put the engine back together and car is still 12.20s-30s. Thinking I should look into a 950 carb. Am I looking in the right direction?

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#2380984 - 10/02/17 09:58 PM Re: 408 help needed [Re: Mirada 408]
MR_P_BODY Offline
Master

Registered: 06/13/03
Posts: 50192
Loc: Romeo MI
Whats the cam installed at and yes it needs
more carb...there are a couple of things I
would change but that car is heavy.. I would
think closer to 3900#
wave
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#2380988 - 10/02/17 10:04 PM Re: 408 help needed [Re: Mirada 408]
scottb Offline
pro stock

Registered: 02/26/05
Posts: 1263
Loc: New Smyrna Beach FL
More carb and more convertor

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#2380995 - 10/02/17 10:17 PM Re: 408 help needed [Re: scottb]
pittsburghracer Online   content
Slowride

Registered: 02/02/05
Posts: 11772
Loc: PA.
A higher stall convertor, gasket matched Victor intake (not super Victor), a higher stall convertor, and did I say a higher stall convertor. I went 9.80's with a 520 lift cam and a 750 Holley at 2700 pounds so a big carb isn't a must have. These engines love high stall so how fast do you want to go
_________________________
1970 Duster
Edelbrock headed 408
6.143@110.89 mph
9.73@135.05 mph shifting at 6700 RPM
422 Indy headed small block
6.004@113.27mph
9.56@137.89

https://flic.kr/p/WjECmg

[img]http://i.imgur.com/Z4SvNU4.jpg?1[/img]



Untitled by John Cadamore, on Flickr





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#2380997 - 10/02/17 10:19 PM Re: 408 help needed [Re: pittsburghracer]
pittsburghracer Online   content
Slowride

Registered: 02/02/05
Posts: 11772
Loc: PA.
That air gap intake can go fast with some simple mods so if you are happy in the 11's dont ditch it
_________________________
1970 Duster
Edelbrock headed 408
6.143@110.89 mph
9.73@135.05 mph shifting at 6700 RPM
422 Indy headed small block
6.004@113.27mph
9.56@137.89

https://flic.kr/p/WjECmg

[img]http://i.imgur.com/Z4SvNU4.jpg?1[/img]



Untitled by John Cadamore, on Flickr





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#2381033 - 10/02/17 11:16 PM Re: 408 help needed [Re: Mirada 408]
A/MP Offline
mopar

Registered: 10/09/08
Posts: 489
Loc: East Coast
That stroker is doing what it is supposed to do, make torque. Your moving that sled but with the 3.55 you can't reach the potential of that motor. That stroker will pull hard to at least 6700.I have a similar short block with RT heads and a 1.94 intake, 750 DP, 10.60/121, launching at 3 and shifting at
6300.

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#2381058 - 10/02/17 11:57 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
I'd take it to a chassis dyno and see what the upper end of the power curve looks like(and where it ends).

Hyd rollers with 1.6 rockers and high rpm don't always go hand in hand.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2381152 - 10/03/17 09:03 AM Re: 408 help needed [Re: Mirada 408]
sgcuda Offline
master

Registered: 01/28/05
Posts: 3494
Loc: Charlotte, North Carolina
I would compare time slips before and after the head work and look at the different intervals. Even though the et is the same I would look to see where you are gaining and losing, and determine issues from there.
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#2381159 - 10/03/17 09:11 AM Re: 408 help needed [Re: Mirada 408]
B3422W5 Offline
master

Registered: 01/20/03
Posts: 9854
Loc: Portage,michigan
Sounds like low cylinder pressure, low compression. And definately more convertor.
Doubt the carb is hurting more than a tenth.
How far in the hole are the pistons?
What is the cam lsa?


Edited by B3422W5 (10/03/17 09:12 AM)
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69 Dart GTS, performance upgrades in progress
11.26@ 118.40 best so far. Stock 360 shortblock with eddie heads.

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#2381466 - 10/03/17 08:22 PM Re: 408 help needed [Re: Mirada 408]
intenseneon Offline
member

Registered: 06/24/06
Posts: 73
Loc: georgia
My 408 hated the 950 I put on it, so I put a 750 back on and picked it back up. Carb would be last on my list.
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#2381496 - 10/03/17 09:28 PM Re: 408 help needed [Re: Mirada 408]
rb446 Offline
member

Registered: 10/17/15
Posts: 169
Loc: UK
Looking at some numbers for an 1981 Mirada it says 3501lbs curb for the 5.2V8 version, so if we only add 150lbs for driver = 3650 at the line approx. 110mph is 395 track hp@crank, which is only 30 more than my old stock '71 340 motor made with a Holley strip Dom int./MP.590 solid ft cam and an 850DP, (750DP lost 2/10ths) that ran 12.39@108+ at 3550lbs+, had a 4200stall/4.30's/10x28's and trapped at 6300.

With those tyres/gears your only trapping at around 5000 with slip, not enough. Adding 2.08's and CNC work added hp, but not usable hp with the chassis set up hence the same ET/mph. A Solid ft cam matched to the heads would be better in my opinion, 4.30's and at least a 4200 stall depending on cam choice would be good, it needs to trap at 6000+ and it'll pick up no end, an 850DP could be worth trying if you can borrow 1 and tune it.

As an example I picked up 1 sec and almost 8mph going from a 302track hp set up to 365hp with the spec mentioned above, thats 60hp which is around 4>5 ths, the rest came from going to 4.30's from 3.55's and a 4200stall from a 3500stall, 60ft is ET.

my 2c's.


Edited by rb446 (10/03/17 09:42 PM)
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1971 340 'Cuda, best 11.01@122.8 in 1987

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#2381504 - 10/03/17 09:41 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
An 8.2cr 360 Mirada with 200cfm 1.88 valve heads, stock intake, TQ, and about a .420 lift cam will run 11.70's in nhra Stock.

It doesn't seem like at low 12's you're getting the most out of a 408, ported aftermarket heads, hyd roller and 1.6 rockers.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2381507 - 10/03/17 09:45 PM Re: 408 help needed [Re: Mirada 408]
rb446 Offline
member

Registered: 10/17/15
Posts: 169
Loc: UK
not over here it won't smile
_________________________
1969 'Cuda 446ci, best 9.96@133.9 in 1990
1971 340 'Cuda, best 11.01@122.8 in 1987

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#2381512 - 10/03/17 09:54 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
A couple guys buy a used I/SA car, no motor.

Order up some pistons, rings, cheater cam, Schubek lifters.......they send me the heads to go through, get a block machined, crank turned and balanced........bolt it together, no test stand run in, no dyno session.....just put it in the car with an 8" converter and tti headers.

The carb is junk.......it still runs 11.70's at an nhra event.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2381522 - 10/03/17 10:05 PM Re: 408 help needed [Re: fast68plymouth]
Mirada 408 Offline
member

Registered: 08/10/15
Posts: 14
Loc: West Virginia
Thanks for all the input thus far guys, given me some more to think about, and wont forget to get a higher stall converter. but...
Originally Posted By fast68plymouth
An 8.2cr 360 Mirada with 200cfm 1.88 valve heads, stock intake, TQ, and about a .420 lift cam will run 11.70's in nhra Stock.

It doesn't seem like at low 12's you're getting the most out of a 408, ported aftermarket heads, hyd roller and 1.6 rockers.
This is the actual issue I'm trying to fix. The engine itself just seems to be underperforming. I tried shifting at higher rpms, but at 6400 it nosed over. Once I get the engine pulling like it should, then I probably will throw lower gears and a convertor at it.

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#2381523 - 10/03/17 10:08 PM Re: 408 help needed [Re: Mirada 408]
rb446 Offline
member

Registered: 10/17/15
Posts: 169
Loc: UK
A couple guys buy a used I/SA car, no motor.

Order up some pistons, rings, cheater cam, Schubek lifters.......they send me the heads to go through, get a block machined, crank turned and balanced........bolt it together, no test stand run in, no dyno session.....just put it in the car with an 8" converter and tti headers.



You make it sound very simple and easy, but we all know that ain't quite the full story...don't know the I/SA min weight but thats 440ish hp from that mild set up. up


Edited by rb446 (10/03/17 10:09 PM)
_________________________
1969 'Cuda 446ci, best 9.96@133.9 in 1990
1971 340 'Cuda, best 11.01@122.8 in 1987

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#2381528 - 10/03/17 10:13 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
Well, I'm sure it wouldn't be anywhere near 440hp.

It's not even that quick for I/SA.

I looked through some old qualifying sheets...... ran 11.804, qualified #103(.494 under).

Another better I/SA car was there that same day running 11.30's.

My friend was there with his Firebird, qualified #22, 1.03 under.

Invariably, a common theme with these threads is how hard it is to make a car run quick in nhra Stock legal trim(at least when compared to the typical street strip or mild bracket build)....... and yet at many events throughout the country, all season long, there will often be fields of over 100 cars doing what apparently is nearly impossible.

IMO, instead of looking at the way those cars run and thinking it's magic, it's better to look at them as a lesson on what's important in terms of getting a good ET, and seeing if you can apply some of that to your program.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2381545 - 10/03/17 10:32 PM Re: 408 help needed [Re: Mirada 408]
J_BODY Offline
I Live Here

Registered: 04/30/03
Posts: 11075
Loc: aZLiViN
depending on how much you want to "ruin" your car, my old ride was 3380 with me in it. 80 J, RB/stage VI, gutted interior with single Jazz bucket, full cage. I did keep all the factory glass including the pwr windows. Front bumper and brackets removed. If I would have kept the car it would have been treated to a tube K, rack steering and coil overs. Would have removed/relocated tons of weight getting rid of those gawd awful X torsion bars.

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#2381746 - 10/04/17 11:05 AM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
The min weight, with driver for an 80 mirada 360-4 in Stock is 3410, if run in "I".

I is 12.00 lbs per factored hp, the hp factor for that combo is 270.
270*12= 3240, then you add 170 for the driver.

That has no bearing on what the OP's car actually weighs, but is an indicator that they aren't really "tanks".

If you're strictly looking for good ET's out of these "milder" combos, and you assume certain things are a "given", meaning..... It will hook, it will have an adequate fuel system, and the appropriate gearing to get the most out of the motor, and obviously the motor has to be mechanically sound, meaning good ring seal and good valve seal....... Then for the most part it comes down to the "three c's", as it was told to me by an old(er) timer racer in Stock.
-cam
-carb
-converter(or clutch)

If those 3 things are "right", along with the "givens", the car will ET pretty well, without anything exotic in the car.

Even a fairly mediocre Stocker(say, .2-.4 under the index......so, pretty far down the qualifying sheet), still puts up a relatively impressive ET compared to a typical street/strip or bracket equivalent.

20+ years ago when my friend decided he wanted to run Stock instead of brackets we took his old trw piston street short block, found a set of suitable head cores, an intake manifold, and q-jet carb.
I rebuilt the heads, and called lunati for a cam(they were one of the more popular Stocker cams at the time), and we just had them send us what was the current top dog for that motor combo(350hp 400 Pontiac).
Put the motor together, dynoed it, stuck it in the car with the same converter that he was using behind the bracket motor(8" Dynamic).
At the time the car was in "E", and the index back then was 12.00.

The car wouldn't even run the index. It ran 12.20's, with 3670lbs min weight.

As poor as that was for Stock, it was still just as quick as the car was when he was racing it as a street/strip combo.
And that had ported heads, .540 lift solid cam, aftermarket manifold, ported Holley 3310...... All of that on the same short block.

Several cams later, send the converter back to be adjusted for the stocker combo, and get the carb working a little better had the car running high 11's consistently...... Which was still way down on the qualifying sheet.
A few years later the car got converted to a 4 speed(we were never happy with the way the converters were working in it, and a few different ones were tried), and that was about .4 improvement right off the bat.
Got another carb...... That worked way way better than the one we had been running...... And a few more cams were slid in, and we finally got something we felt was what we were looking for.
At that point the car was running 11.30's in decent(but not at all mine shaft) air.
We had picked up about one full second and 8-10mph from that first outing.

Pretty early on in the process of sorting through this combo, and this was prior to running the Schubek lifters, I think it was cam #4..... We found a nice gain with that cam...... But it was pretty hard on rocker arms. It wouldn't go very many passes before poking a pushrod through a rocker.
That cam ran 11's, but we needed something that was easier on parts.
The next cam that was tried was something totally different than what we had used up til that point.
It was what the cam grinder recommended, as we were told the philosophy we were trying to follow just wasn't what that motor combo liked.
Well...... That cam just sucked. The car was back into the 12.20's and 30's.

So, as an experiment....... To see if chasing the cam was worth spending time on or not, the old solid that was run when it was a street/strip cam got slid in.
Wow!!! Did that ever wake it up....... 11.68.
At least we knew the car could run solidly in the 11's if we could get a legal cam to run close to that one.
It took about 4 or 5 more cams to get there, and it was during that series of cams that the Schubek lifters were installed, which allowed for much higher spring loads, which allowed the motor to finally pull clean all the way to the finish, which resulted in a couple extra mph at the stripe.
A nice by product of not running the valvetrain hard into float every pass(which was just the way it was with the std lifters), is the valve job wasn't all beat to he11 at the end of the season.

_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2381767 - 10/04/17 11:39 AM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
Quote:
Once I get the engine pulling like it should, then I probably will throw lower gears and a convertor at it.


IMO, that's not the best way to approach it.

If ET's are more of a priority that street manners, then put the appropriate gear and converter in the car now.

If you're trying to keep it as street friendly as possible, then understand less stall and gear will yield slower ET's....... And that's the compromise you're making.

The dual purpose car is much much harder to get to live up to the "on paper" potential of the combo than something that can be optimized without concern for street worthiness.

I still feel a trip to the chassis dyno would be worthwhile place to start.
This does a couple of things......
-let's you see what the fuel curve of the carb looks like
-gives you an idea of what the upper limit of the usable power band is, which helps with converter and gear selection
-gives you some hp/tq numbers you can if into some calculators to see what the car "could" run
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2381772 - 10/04/17 11:49 AM Re: 408 help needed [Re: Mirada 408]
EV2Bird Offline
On Vacation

Registered: 06/23/14
Posts: 2662
Loc: Kansas Roads Between 0 and 140...
Looking at this...Engine is 408ci. eagle crank and rods, kb hyper pistons, comp cam hydraulic roller xr-292hr-10 duration 242/248 lift .545, 1.6 ratio rockers, edlebrock rpm heads, airgap intake, and 750 Holley dp. Car is consistently 12.20-12.30 @108-110mph.

You have a very very mild entry level cookie cutter stroker, your 2.08 heads are probably not helping you yet.


So you have a mild motor that happens to have a 4 inch crack, a much lesser motor as you found can easily equal that.

Id start at the big red flag to me and dump the hydro roller cam for a better "performance" cam, turn up the rpms to use the heads you have.

But as many has mentioned, when you start down the faster road, how fast is fast enough for you and how often do you like to drive the car?

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#2381789 - 10/04/17 12:26 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
Quote:
...don't know the I/SA min weight but thats 440ish hp from that mild set up.


That car runs around 111mph, min weight is 3410.
At 3450 the Moroso chart shows 362hp.

If the car were really way overweight, you'd just run it in the next class down (H, 12.5lbs/factored hp), which would be 3545 min weight.

There is someone who does run that combo in "H", and that car has run 11.40's.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2381819 - 10/04/17 01:03 PM Re: 408 help needed [Re: B3422W5]
Crizila Offline
master

Registered: 10/31/03
Posts: 7447
Loc: Az
Originally Posted By B3422W5
Sounds like low cylinder pressure, low compression. And definately more convertor.
Doubt the carb is hurting more than a tenth.
How far in the hole are the pistons?
What is the cam lsa?
iagree Double check the CR to be sure. Whats the cranking compression. Ran a very similar set up to yours ( engine and car weight )in my 79 300 for a while. Ran a little larger cam and 3.90 gears. Think my CR was around 10.7:1. My car ran consistent 11.80's and a best of 11.53 with speeds in the 118 - 119 range. Yours should be able to do that.


Attachments
2006-08-02 14.53.10.jpg


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#2381825 - 10/04/17 01:11 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
Too late to undo it now, but I would have just done a nice mild clean up on the heads, kept the 2.02 valves(keeping the ports for the most part, as small as possible), swapped to a solid lifter cam, went for 4.10's and a 4500 converter.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2381832 - 10/04/17 01:38 PM Re: 408 help needed [Re: fast68plymouth]
B3422W5 Offline
master

Registered: 01/20/03
Posts: 9854
Loc: Portage,michigan
Originally Posted By fast68plymouth
Too late to undo it now, but I would have just done a nice mild clean up on the heads, kept the 2.02 valves(keeping the ports for the most part, as small as possible), swapped to a solid lifter cam, went for 4.10's and a 4500 converter.



That advice sounds familiar Dwayne..... lol
Just bought me a nice 904 with low gear, billet drum and A&A brake.
Still need convertor and driveshaft, will swap over in the offseason. Also going to install my hemi dart glass hood and paint it to match. Hoping to get her to threaten the 10's.
_________________________
69 Dart GTS, performance upgrades in progress
11.26@ 118.40 best so far. Stock 360 shortblock with eddie heads.

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#2381879 - 10/04/17 03:53 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
There is no mention of the cr by the OP, but assuming 10.2-10.5:1, ported rpm's, that sized cam, intake, carb, on a 408...... Should be right in the 500hp range(if the valvetrain is stable enough to allow the motor to reach its natural peak).
And it should be over 500tq.

Assuming it weighs as much as my heap did when I first slid my 383 in it(3670 w/driver), if I apply the "90% rule"(the car should be able to run within 10% of the dyno crank hp, using the Moroso slide as the reference)......that's just shy of 117mph(450hp@3670).

If you had a 4500(or higher) converter, it's likely going to have some amount of slippage..... Seems like 7% is fairly typical.
Then if you have it geared right to use up all of what the motor has to offer, running a 28" tire...... 4.30's look about right.
4.30's, 28" tire, 7% slip, 117mph...... Works out to just under 6500 through the lights.

I'd be surprised if the current motor combo would actually "pull" through to 6500.

Each little step you take away from that scenario is ET you're probably not going to get back.

As a motor comparison, we did a 410 last year.
10.5cr, rpm's with mild clean up(265-ish), easy on parts sold roller, victor intake, qft-850 carb, pump gas.........538hp/524tq.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2382033 - 10/04/17 05:36 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
Quote:
I was happy with it, but wanted to go faster. therefore send the heads out and have them cnc ported and 2.08 intake valves put in.


Just curious...... Who did you end up having the cnc porting done by?
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2382156 - 10/04/17 09:39 PM Re: 408 help needed [Re: Mirada 408]
gregsdart Offline
master

Registered: 01/21/03
Posts: 8060
Loc: Frostbitefalls (Rocky&Bullwink...
What kind and brand valve springs are you running? A cheap straight spring might kill power and limit usable rpm you need to keep the motor up in the power band.
I just dynoed a very similar 408 with Airgap intake EQ heads and similar cam, made 504 up, 500 hp from 5700 to 6100. Torque was 520 at 4600. Something is definitely holding you back. If this is going to be a strip only car I would go with a 5,000 to 5200 stall converter. Get it to pull to over 6,000 so you can shift at 6,000( actual shift will be about 6200!)


Edited by gregsdart (10/04/17 09:50 PM)
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Educated at SHK U
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528 cubic inch alky injected 440-1 wedge, 3055 race weight.
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#2382161 - 10/04/17 09:46 PM Re: 408 help needed [Re: Mirada 408]
Mirada 408 Offline
member

Registered: 08/10/15
Posts: 14
Loc: West Virginia
I will try and answer some of the more asked questions. the cr is right around 10.7:1. The car started out with the goal as more of a street/strip car, with emphasis more on street manners. But over time its being turned into more of a strip/street car. Granted, its still full interior etc etc. And currently have no plans of gutting the car. I'm more of the Test and Tuner racer, I hit the track maybe 6 times a year and have some fun. As far as street driving it'll go out maybe a dozen times or so. And realistically if in my last outing the car would've picked up to say as fast as Crizila, 11.80's then I would've been content for the time being. The cnc porting was done by Hughes Engines. And other than more gear/convertor it seems as though many are saying camshaft. Is this the logical step in getting more rpms to be able to use the heads? If so would a solid roller be the way to go?

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#2382168 - 10/04/17 09:55 PM Re: 408 help needed [Re: Mirada 408]
B3422W5 Offline
master

Registered: 01/20/03
Posts: 9854
Loc: Portage,michigan
If your compression is indeed 10.7 to 1, and the heads are at least decent, by far the biggest thing to fix is the convertor.
Nothing else even close.
_________________________
69 Dart GTS, performance upgrades in progress
11.26@ 118.40 best so far. Stock 360 shortblock with eddie heads.

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#2382170 - 10/04/17 09:57 PM Re: 408 help needed [Re: gregsdart]
Mirada 408 Offline
member

Registered: 08/10/15
Posts: 14
Loc: West Virginia
Originally Posted By gregsdart
What kind and brand valve springs are you running? A cheap straight spring might kill power and limit usable rpm you need to keep the motor up in the power band.
I just dynoed a very similar 408 with Airgap intake EQ heads and similar cam, made 504 up, 500 hp from 5700 to 6100. Torque was 520 at 4600. Something is definitely holding you back. If this is going to be a strip only car I would go with a 5,000 to 5200 stall converter. Get it to pull to over 6,000 so you can shift at 6,000( actual shift will be about 6200!)
Springs are Engine Pros, Dual with damper. And since you brought springs up, it reminded me. Hughes did tell me the springs seemed a little weak to them. could it be something as simple as the springs?

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#2382203 - 10/04/17 11:01 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
It's not just the springs.
But.......it could be the springs, along with the converter and gears.

I've had one set of the sb rpm's in my shop that had the Hughes cnc porting.

Just an observation on my part, with no actual testing on an engine to see if it makes any difference or not.......but I don't care for the way they do the intake short turn on those heads.
It's as flat as a pancake.

Perhaps your cam and Gregs look somewhat similar on paper, but they are from fairly different lobe families, with yours being the more aggressive one, which would also tend to make it less rpm friendly.

Until you get some data(like from the chassis dyno), you're somewhat shooting in the dark.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2382355 - 10/05/17 10:19 AM Re: 408 help needed [Re: Mirada 408]
Crizila Offline
master

Registered: 10/31/03
Posts: 7447
Loc: Az
Originally Posted By Mirada 408
I will try and answer some of the more asked questions. the cr is right around 10.7:1. The car started out with the goal as more of a street/strip car, with emphasis more on street manners. But over time its being turned into more of a strip/street car. Granted, its still full interior etc etc. And currently have no plans of gutting the car. I'm more of the Test and Tuner racer, I hit the track maybe 6 times a year and have some fun. As far as street driving it'll go out maybe a dozen times or so. And realistically if in my last outing the car would've picked up to say as fast as Crizila, 11.80's then I would've been content for the time being. The cnc porting was done by Hughes Engines. And other than more gear/convertor it seems as though many are saying camshaft. Is this the logical step in getting more rpms to be able to use the heads? If so would a solid roller be the way to go?
I ran a Hughes HEH4650 AL ( .606 / .614 246 / 250 108 LSA ) Hyd cam with 1.6 rockers. Fully ported J heads W/ 2.02's.
_________________________
Fastest 300

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#2382377 - 10/05/17 11:02 AM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
I guess if someone else who's looked at the heads has already mentioned the springs are a little light...... That may not be a bad place to start, but it will only affect the power curve above the point where the current springs are allowing some float(if that's even happening at all).

You could have a couple of the ones currently on the heads tested if Hughes didn't provide that info to you.
I'd shoot for 150-ish on the seat, 350-375 open.

Then, if your goal is just high 11's, start with more stall(4200-ish), and if that doesn't get you quite where you want to be, put some 4.10's in it.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2382418 - 10/05/17 12:23 PM Re: 408 help needed [Re: Mirada 408]
Guitar Jones Offline
master

Registered: 12/18/09
Posts: 8746
Loc: in a cattle trailer down by th...
No mention of what you have for a fuel system or what it flows?
_________________________
W5 408 cid, 1.324, 6.155 @ 110.34, 9.756 @ 134.67 with a broken converter hub. Oh yeah, it's all Mopar too, 904 trans and an 8.75 rear!!

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#2382454 - 10/05/17 01:00 PM Re: 408 help needed [Re: Guitar Jones]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
Originally Posted By Guitar Jones
No mention of what you have for a fuel system or what it flows?


Good point.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2382466 - 10/05/17 01:13 PM Re: 408 help needed [Re: fast68plymouth]
pittsburghracer Online   content
Slowride

Registered: 02/02/05
Posts: 11772
Loc: PA.
Heck I had a 440 with two 750's on a tunnelram go high 9's with a Holley blue pump. I'm betting in todays world he has a better pump than that, BUT WHO KNOWS.
_________________________
1970 Duster
Edelbrock headed 408
6.143@110.89 mph
9.73@135.05 mph shifting at 6700 RPM
422 Indy headed small block
6.004@113.27mph
9.56@137.89

https://flic.kr/p/WjECmg

[img]http://i.imgur.com/Z4SvNU4.jpg?1[/img]



Untitled by John Cadamore, on Flickr





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#2382994 - 10/06/17 01:18 PM Re: 408 help needed [Re: pittsburghracer]
Guitar Jones Offline
master

Registered: 12/18/09
Posts: 8746
Loc: in a cattle trailer down by th...
Two carbs in that kind of application actually require less fuel flow to keep up because the jets are smaller. I know sounds weird.
_________________________
W5 408 cid, 1.324, 6.155 @ 110.34, 9.756 @ 134.67 with a broken converter hub. Oh yeah, it's all Mopar too, 904 trans and an 8.75 rear!!

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#2383051 - 10/06/17 03:14 PM Re: 408 help needed [Re: Guitar Jones]
pittsburghracer Online   content
Slowride

Registered: 02/02/05
Posts: 11772
Loc: PA.
Originally Posted By Guitar Jones
Two carbs in that kind of application actually require less fuel flow to keep up because the jets are smaller. I know sounds weird.



I should have added it to my post but before I ran the tunnelram I ran it for 3 years with a 1050 dominator. Same pump
_________________________
1970 Duster
Edelbrock headed 408
6.143@110.89 mph
9.73@135.05 mph shifting at 6700 RPM
422 Indy headed small block
6.004@113.27mph
9.56@137.89

https://flic.kr/p/WjECmg

[img]http://i.imgur.com/Z4SvNU4.jpg?1[/img]



Untitled by John Cadamore, on Flickr





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#2383074 - 10/06/17 04:39 PM Re: 408 help needed [Re: Mirada 408]
Cab_Burge Offline
Too Many Posts

Registered: 08/23/03
Posts: 29377
Loc: Bend,OR USA
You improve the airflow into the motor and it ran the same as before, did you improve the fuel supply ?(not pressure,volume) work
I would look at that and IF you can jet the carb. rich enough to slow the MPH down in the 1/4 mile. If you can you have enough fuel supply to feed your motor in its current condition scope up
When changes don't help or the results don't make since, there is usually a reason for that work


Edited by Cab_Burge (10/07/17 12:34 AM)
_________________________
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

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#2383259 - 10/06/17 11:15 PM Re: 408 help needed [Re: Mirada 408]
rb446 Offline
member

Registered: 10/17/15
Posts: 169
Loc: UK
Blue pump on my '69 440 brkt car, 850DP, stock 906 heads, best 11.2@118, made just 1 NA run with new 2.14/1.81 ported 906's with HS rockers, no other changes, 10.7@125....people give those pumps away for free these days don't they?
_________________________
1969 'Cuda 446ci, best 9.96@133.9 in 1990
1971 340 'Cuda, best 11.01@122.8 in 1987

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#2383278 - 10/07/17 12:38 AM Re: 408 help needed [Re: Guitar Jones]
Cab_Burge Offline
Too Many Posts

Registered: 08/23/03
Posts: 29377
Loc: Bend,OR USA
Originally Posted By Guitar Jones
Two carbs in that kind of application actually require less fuel flow to keep up because the jets are smaller. I know sounds weird.

If the motor makes more power with two carbs., and what Mopar V8 doesn't, it has to use more fuel, correct work
It takes X amount of fuel to make each HP, increase the HP output and the fuel consumption has to increase to make that power shruggy
_________________________
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

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#2383300 - 10/07/17 03:09 AM Re: 408 help needed [Re: Cab_Burge]
Guitar Jones Offline
master

Registered: 12/18/09
Posts: 8746
Loc: in a cattle trailer down by th...
Originally Posted By Cab_Burge
Originally Posted By Guitar Jones
Two carbs in that kind of application actually require less fuel flow to keep up because the jets are smaller. I know sounds weird.

If the motor makes more power with two carbs., and what Mopar V8 doesn't, it has to use more fuel, correct work
It takes X amount of fuel to make each HP, increase the HP output and the fuel consumption has to increase to make that power shruggy


True but you now have 4 float bowls each using less fuel than just two. If the systems flow was near or at capacity with two bowls it should be slightly less taxed with 4 bowls. Its not necessarily the pump either. Where you could get by feeding each carb on a tunnel ram with 5/16 line you may need 3/8 or 1/2 for a single carb.

I know my 2 BG 750's use a lot.


Edited by Guitar Jones (10/07/17 03:48 AM)
_________________________
W5 408 cid, 1.324, 6.155 @ 110.34, 9.756 @ 134.67 with a broken converter hub. Oh yeah, it's all Mopar too, 904 trans and an 8.75 rear!!

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#2383313 - 10/07/17 08:00 AM Re: 408 help needed [Re: Guitar Jones]
B1MAXX Offline
mopar

Registered: 05/07/05
Posts: 666
Loc: Apollo, PA.
Originally Posted By Guitar Jones
Two carbs in that kind of application actually require less fuel flow to keep up because the jets are smaller. I know sounds weird.


2 750'S jetted square with 8 #79 jets and no power valve is .052 sq.in total jet area.

a single 1050 jetted 88 square no power valve is .034 sq. in. total jet area.

you also have to keep 4 bowls at set level...all comes down to total jet restriction.


Edited by B1MAXX (10/07/17 08:06 AM)

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#2383327 - 10/07/17 08:50 AM Re: 408 help needed [Re: Cab_Burge]
MR_P_BODY Offline
Master

Registered: 06/13/03
Posts: 50192
Loc: Romeo MI
Originally Posted By Cab_Burge
Originally Posted By Guitar Jones
Two carbs in that kind of application actually require less fuel flow to keep up because the jets are smaller. I know sounds weird.

If the motor makes more power with two carbs., and what Mopar V8 doesn't, it has to use more fuel, correct work
It takes X amount of fuel to make each HP, increase the HP output and the fuel consumption has to increase to make that power shruggy


Rule of thumb is it takes .5 lbs of fuel for
every HP
wave
_________________________

W-9 8.94 @ 151 NOW ON E-85
Mike "Raff"...(180)Watching over us
CAR IS FOR SALE

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#2383343 - 10/07/17 09:30 AM Re: 408 help needed [Re: Mirada 408]
Guitar Jones Offline
master

Registered: 12/18/09
Posts: 8746
Loc: in a cattle trailer down by th...
I guess I stated incorrectly. What I meant was each carb of a tunnel ram application uses less fuel than a single carb would. TR carbs don't typically use a power valve either. Some carbs have PV's in both the front and rear and the size of the PV orifice must also be taken into consideration. They are not all the same. So 4 bowls don't empty nearly as fast as 2 will. While you should be able to maintain the fuel bowls full all the way through a pass it could get by with less by the end of the pass. You could be giving up some MPH that way and never know it.

Sorry for the confusion.

Either way none of this is helping the OP, we still don't know what he has for a fuel system. Anytime I hear someone say their car is nosing over at higher RPM's my first thought is fuel supply, second thought is valve float.

BTW I feed my carbs with blue pumps, one for each carb with -8 to the regulators and -6 at the bowls.
_________________________
W5 408 cid, 1.324, 6.155 @ 110.34, 9.756 @ 134.67 with a broken converter hub. Oh yeah, it's all Mopar too, 904 trans and an 8.75 rear!!

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#2383382 - 10/07/17 11:06 AM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
I went 10.60's @3670lbs with a Carter mech fuel pump, a $4 wix fuel filter, and the rest of the original 5/16" fuel line from the tank to the pump.

It doesn't take hardly anything for a fuel system to run deep into the 11's.

The only way I can see this really being the issue for the lack of performance in the OP's combo is if there is just a straight up "problem" with what he's running.

A Summit mech pump(used with a moly coated eccentric) with the rest of the plumbing all stock would be enough for his goals........ Provided the line isn't kinked somewhere and the pick-up sock isn't plugged.
_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2383433 - 10/07/17 12:37 PM Re: 408 help needed [Re: fast68plymouth]
Guitar Jones Offline
master

Registered: 12/18/09
Posts: 8746
Loc: in a cattle trailer down by th...
What gets me is he says the ET didn't change at all. You would think something would change for better or worse. That's what makes me think there is something wrong with the fuel system. There was probably more in the original combo but something is holding it back and what ever that was it's also limiting the new combo.

And I have never been able to squeeze those kind of numbers out of a nearly stock fuel system. laugh2 The heat here is probably a factor in that though.

I tend to over build my fuel systems just so I know there is enough. I used those same two blue pumps and 3/8 lines when I ran a single 950 with each pump feeding one bowl.
_________________________
W5 408 cid, 1.324, 6.155 @ 110.34, 9.756 @ 134.67 with a broken converter hub. Oh yeah, it's all Mopar too, 904 trans and an 8.75 rear!!

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#2383435 - 10/07/17 12:44 PM Re: 408 help needed [Re: Mirada 408]
Guitar Jones Offline
master

Registered: 12/18/09
Posts: 8746
Loc: in a cattle trailer down by th...
Just thinking, he didn't say whose converter was in it either did he? There are plenty of crappy converters out there. I had a Hughes in my Duster then bought a Turbo Action and picked up 7 tenths. Apples to oranges I know, the Hughes was a 9.5 inch and the T/A was an 8 inch. Still goes to show what the correct converter can do.
_________________________
W5 408 cid, 1.324, 6.155 @ 110.34, 9.756 @ 134.67 with a broken converter hub. Oh yeah, it's all Mopar too, 904 trans and an 8.75 rear!!

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#2383456 - 10/07/17 01:58 PM Re: 408 help needed [Re: Mirada 408]
fast68plymouth Offline
I Live Here

Registered: 01/20/03
Posts: 10221
Loc: So. Burlington, Vt.
IMO, the converter is way way up on the list of things that need to be "right".

When my friend was racing his gto as a bracket car, running low 11's at around 120mph, he thought maybe it was time to upgrade from the factory fuel line and Carter street/strip mechanical pump.

He went with a Mallory 140 pump/regulator, matching filter, and upgraded to a 1/2" line from pick-up to regulator.
Then 2 #6 lines to the carb.

Zero difference in performance.

I'm not advocating the use of marginal fuel systems...... But at the same time, you only need what you need...... And having more fuel system capacity than that won't improve your ET.


_________________________
68 Plymouth Satellite, 383, stock 906's, 3550lbs, 11.18 @ 123, 1.51 60' PRH is a Comp Cams W/D......competitive pricing on entire line. Custom cams available. ** dealer for Indy Cylinder Heads **

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#2383574 - 10/07/17 06:56 PM Re: 408 help needed [Re: Cab_Burge]
gregsdart Offline
master

Registered: 01/21/03
Posts: 8060
Loc: Frostbitefalls (Rocky&Bullwink...
Originally Posted By Cab_Burge
Originally Posted By Guitar Jones
Two carbs in that kind of application actually require less fuel flow to keep up because the jets are smaller. I know sounds weird.

If the motor makes more power with two carbs., and what Mopar V8 doesn't, it has to use more fuel, correct work
It takes X amount of fuel to make each HP, increase the HP output and the fuel consumption has to increase to make that power shruggy

The deal with feeding a tunnelram is you can do it with a lot less pressure because you are feeding the bowls with four needle and seats, twice as much area for flow. I bet it is also better as far as not aireating the fuel in the bowls as well , If you keep the pressure down some. I ran a tunnelram many years ago and got away with 3.5 psi. That is all one blue pump and the junk I had would deliver in the traps. More pressure from a second pump didn't change the mph.


Edited by gregsdart (10/07/17 07:05 PM)
_________________________
GREG
Educated at SHK U
Measure with yardstick
mark with chalk
cut with torch!



528 cubic inch alky injected 440-1 wedge, 3055 race weight.
8.779 at 153.16 mph. 1.289 60 ft. density altitude 1617 feet. Best 60 ft 1.24

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#2383793 - 10/08/17 09:48 AM Re: 408 help needed [Re: gregsdart]
B1MAXX Offline
mopar

Registered: 05/07/05
Posts: 666
Loc: Apollo, PA.
I wonder how much if at all that the cnc portwork opened up the chamber. Could it be that the compression ratio was dropped. I had a pair of B1BS heads ported, the chamber went from 65cc to 85cc. To the OP was there chamber work done? If so how much? If this was already covered someone say so. I didn't read all 6 pages.

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#2384076 - 10/08/17 06:10 PM Re: 408 help needed [Re: Mirada 408]
Mirada 408 Offline
member

Registered: 08/10/15
Posts: 14
Loc: West Virginia
Fuel System consists of stock tank, original lines 5/16, Holley Blue pump and regulator run with 7lbs pressure. Never thought of pick-up sock, so good call on that. The converter is a PTC. Heads got milled so that i wouldn't lose compression.

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