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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
_________________________

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

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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: 11775
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: 11775
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.
_________________________
[image][/image]

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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: 9856
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)
_________________________
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.
_________________________
69 Dart

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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)
_________________________
1969 'Cuda 446ci, best 9.96@133.9 in 1990
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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