Good morning!

Several years back as a way of easing back into the RWD pool I built a '74 Duster with a 5.9 Magnum. One of the goals was to look fairly stock under the hood but after yesterdays track results that is getting tossed out the window.

In 2010 the car was taken to the track with the following combo-

1994 5.9 with Enginequest 1.88 intake heads, 360 windage tray, Performer RPM intake, 625 AFB and a cam with the following specs.

Crane Compucam 2020

112 lobe separation
Valve Lift with 1.6 rocker .434 int./ .458 exh.
Valve Lift with 1.7 rocker .461 int / .486 exh.
Gross Duration 250/260 with 1.6 rocker

This cam was run with *1.7* HS roller rockers.

The rest of the combo was '74 904 trans with 3.55's out back with a 24.5 slick x 10" Exhaust system is 2.5" mandrel bent with H-pipe.

The car ran 14.2's at 94 mph which for a 3600 lb car I thought was a fair first outing with such a mild combo. Too mild in my opinion. I had gone a little to conservative on cam choice as I wanted more of a cruiser the wife could drive than something rowdy.

Did I mention stock looking under the hood? As "still has exhaust manifolds" stock looking? We will get back to that in a minute.

Flash forward to yesterday..

Since 2010 the car has been updated with a new cam with the following specs-

Comp Cams CRS XR265R-14

114 lobe separation
216 intake duration at 50
224 exhaust duration at 50
Gross Duration 265/273

.506 intake lift
.506 exhaust lift

Installed with STOCK 1.6 rockers.

Also installed is a 44RH overdrive transmission with better first gear (2.74 vs 2.50) and a tuned 750 AFB that is no longer being used on my GTX (which ran 11's with this carb)

The car is MUCH more lively with the cam, carb and transmission combo. I expected at least mid-13's without much problem.

2010 14.2 at 94 mph
2015 14.1 at 95 mph (2.08ST)

Exhaust manifolds are going in the trash. I'm astounded on how badly they are throttling the combo. I beat on the car yesterday like it owed me money. Adjusted slick pressures up/down and trying different launch techniques and the best I could get out of the car was a 2.08 short time. Made about a dozen passes with the same results.

Aside from headers I'm thinking about pulling the lockup converter and replacing it.

The shop sent what I feel is a stocker even though I was clear on all specs of the combo particularly the cam specs. It pulls on car when at a stop light fairly bad. I got the whole "oh sorry about that" song and dance after it was installed and told "just send it back" like I have nothing better to do..

Thoughts? Headers are a no brainer.

I know that in a dyno test with a 300 hp Mopar crate motor that mainifolds gave up 30 hp to cheap headers but I didn't think it would be this bad.

Gary

A converter would be beneficial as well as headers.Why such a wide LSA on the cam?
I would still have expected more with 3.55 gears and a 24.5 slick though.That comes out to 3.91's for actual gear ratio as a guess.

Did you play with shift rpm's to see if it help/hurt?

Some more head flow wouldn't hurt either.

What intake are you running? The stock kegger will limit your rpms to around 4500. If you have the stock one, an M1 would be the first thing I would change.

It was what was available at the time and several Dakota/Durango owners reported good results. The cam does work far better than the old one via "seat of the pants."

Both cams are roller by the way, it was a major factor in running a magnum motor.



I thought so as well, hell my GTX ran mid 12's on 3.23's with on a 28" tall slick. 440 does make a touch more torque though.



I did not as there isn't a tach currently installed in the car, the 44RH was allowed to shift by itself with overdrive in the off position. Shifts are around 4800 rpm which while a touch low with the manifolds killing the exhaust flow there might not be much advantage to shifting higher till the headers are installed.

Next outing I'll pop in a shift light and try different rpm points.

Edelbrock RPM with a 750 Carter Comp series AFB carburetor.

Best and last pass of the day was with my son Kyle on board. We had lined up against a 392 Challenger and I took him out on the tree and he never caught up in time even though at the traps he had 15 mph more speed!

Was flipping great!

Have you tried to flash the conv...it sounds like
you have a tight stock conv if it wants to pull at
idle... the thing with the lock up conv is they dont
have the space in them to make a good conv... thats
why I changed the pump and input shaft to allow me to
use a high stall conv on my Rampage... watch your rpm
(when you put a tach in) and see how long it takes to
get the rpm up to where the peak torque should be
EDIT
next I would drop the back of the exhaust to see how
bad it is.. could be very restrictive

Yes, I tried a few different ways to launch the car from walking it out the hole to standing on the brakes for dear life while mashing the pedal to flashing it.

The car seemed to like flashing it slightly best but there wasn't a huge difference.



I'm considering this as well since I stopped using the lockup feature some time ago. Only drops off about 100 rpm or so (tach installed temporarily for testing after getting the trans in)

Change the input shaft and get a stouter converter while keeping the overdrive. I'm open to suggestions on brand and specs. The car is on the stout side at 3750 (I'm guessing as it was 3600 even with just me on board and a 904) with my son and a 44RH its just going to be more on the porky side.



I'll try and do an in-car video, the car winds up in a hurry hence my surprise at the track results.



Possible, but with a 2.5" mandrel bent system with an h-pipe and decent mufflers I suspect those tiny 318 outlets with 2"? headpipes are sucking wind first. When I throw the headers on I think I'll take the opportunity to throw some dumps in at the same time.

I don't see how in the world you could make SB duster weigh 3600lbs. you couldn't do that if you put 500lbs in the trunk

1974 Duster.

Door crash beams, bumpers have extra steel backing front and rear and in the back has bumper shock setup for good measure and that is with a 220 lb driver.

Exhaust manifolds don't help either.

Later cars have a lot of extra steel due to bumper/crash regulations that went into effect.

I have owned 2-73's and 1-74 none of them weighed over 3200lbs soaking wet

1) 73 is different than 74. 73 doesn't have the steel behind the bumpers nor the rear shock setup nor the front bumper guards (they were optional I think in '73)

2) Car has been on two different scales, 3600 lbs back in 2010 is accurate with the 904 installed with driver. The car is also an a/c car with power steering, disc brakes, bench seat, fold down rear seat and exhaust manifolds. And slicks on steel rims with cast aluminum front wheels.

Call it 3380 without driver in 2010 if you like but the car doesn't make it down the track by itself.

The car is porky, it is what it is. It didn't get any lighter with my 120 pound son on board nor the swap to 44RH.

MPH didn't change a whit with him in the car for three passes so it does point to something else limiting the car.

I definitely think you would gain by raising you shift points to at least 5500 rpm.
For a point of reference by 69 dart has run a best of 13.7 at 102mph with the following,
340, stock stroke
Stock 2.02 heads
Ld4b intake
600 edelbrock carb
Stock bottom end, pistons etc.
3.23 open rear
Street cooper cobra tires, 215/60/14
My 60 ft is around 2.15
727 with stock convertor that stalls at less than 2000
Cam is a racer brown, hydraulic, non roller, 266 total duration, .220@50, 460 lift, 110 lsa.
I shift at about 6000rpm.

Everything is very mild so there is no reason you can't pick up significantly from where you are now.
I also run stock manifolds and exhaust is original to the car.

Question (and this might be a loaded question but take a stab at it)

My friend has a 1970 440 Duster with aluminum heads, power steering, bench seat, 9 inch ford rear, steel wheels, headers, frame connectors, steel bumpers, flat factory hood and a 518 overdrive trans with an ultra-bell, fuel cell and four wheel disc brakes.

Car to guess how much it weighs? It was done on the same scales last rear before he installed 50 pounds of roll bar last week.

He ran 11.1 yesterday with a 1.58 short time, I think the best mph was 121.

I looked, but can't find the article, but there was a comparison between 340 exhaust manifolds, Magnums, and headers and the conclusion was that the cast irons flowed really well compared to headers.

If it's a stock Magnum bottom end, these things are barely 9:1 compression, so, I think low compression is the bottle-neck.

Otherwise, the HP Calculator shows you at 250 at the back wheels, which sounds about right for what you've done to it. You've picked up about 70hp from a stock Magnum which is pretty good if you ask me.

Dyno results with a 300 hp crate engine-

http://www.hotrod.com/how-to/engine/mopp-0307-mopar-crate-engine-exhaust/

318 manifolds- 311 hp, 403 torque.
340 manifolds- 315 hp, 409 torque.
Hooker headers- 319 hp, 424 torque.

I'm tossing away at least 20 ft/pounds and they did testing with 2.25" pipe off the manifolds, I think I have 1 7/8" or 2" (what ever the stock 318 pipe is) The manifolds were suppose to be temporary but ended up being on the car for 5 years as I have been tied up with other projects.

FYI- I don't dispute shift points being a factor on ET, just so I am being clear. I did consider shifting manually but with no tach did not feel comfortable running through "by ear" and should have had no to little impact on mph on the big end.

Matter of fact adding my 120 lb son to the car, a different automatic, a different cam or a different carburetor had zero impact on MPH.

The car ran 95 mph in 2010 and ran 95 mph in 2015.

I was really tempted to wind out first to see if I could improve the short time but decided to play around with different launch techniques first.

So the bottleneck on mph is in the exhaust, the compression or somewhere else. I'm inclined to think the exhaust as I have run 115 mph with an 8:1 440 in a GTX.

Could be in the stock 340 air cleaner with rear flapper, but I suspect if that was a bad bottleneck people would have noticed by now.

Your terminology is confusing. Do you have a 2.5" mandrel bent system (which includes the "head pipe"), or is the system 2". Or are you saying that you have 318 manifolds that have a 2" outlet?

A good hp manifold system can easily support more power than you are making. I always recommend changing mufflers frequently, as they can be serious power suckers, especially older ones that might have an internal failure.

And

Shift rpm matters a lot and will effect mph. You need a tach. It is frankly a little silly to be spending money chasing hp and you are running the car without a tach.

Off the manifolds is 2" and then opens up to 2.5" at the bellhousing. The plan was to install 340 manifolds and to run the 318 units till then.



The point of the car is it is a stab and steer vehicle, there are plenty of people running cars without tachs for one reason or another.

Going back in 2 weeks, timeslip will tell the tale. Will try different shift points after a shakedown pass or two.

Yes there are cars without a tach.. but run a shift
light.. if you feel you cant hear/feel the engine then
get a tach