Opinions, please, on exhaust question

[ramcharger_440]

I am trying to decide between Spitfire, Hedman Tight Tubes, or 340 exhaust manifolds for my 1974 Dart Sport.

Rebuilt 318 mildly built for performance, just enough to make it a little more fun to drive. Will retain power steering, A/C, floor shift automatic. In case it matters, it will have a Comp XE262 cam, Weiand stealth intake, 600 CFM carb, 9.5:1 compression and Magnum heads with cast pistons. 3.55 gears.

TTIs are out of the question and I don't want the headers to hang below the linkage.

I am concerned with clearance and the best power. The issue of obtaining the Spitfires is resolved if I decide I want them and they are what I am leaning towards.

Thanks for your help.

[dwc43]

We run hookers and Hedmans in ours. 1 5/8 tube is all you need. Your carbs too small though. Get a thermoquad. Also wrap your headers to reduce under hood temps and to save your plug wires. Use an X pipe between the headers and the flowmasters to get a nice gain in tq and hp.

[plymouth360]

I also run 1 5/8" Hooker Comp headders on my small block, but one or two of the left side pipes hang below the steering components... They seem to make good power though!

Not to disagree with dwc43, but I go low 13's through mufflers and an air cleaner in a 3500 pound car on a 625 cfm carter...my advice would be to get some times with the 600 then borrow a larger carb (if you can) to see if it will drop your times! Just my two cents!

[440Ramcharger]

Ditto on the Hooker Comps. Mine is a 340 4 speed Duster. One pipe runs around the steering rod. Good power and no leaks.

[pishta]

I would go with the 340 manifolds and a 2.5 inch "H" dual system if you can afford them. I dont think that cam and carb will benefit a whole lot from tubular headers. And the pain factor with headers is evident with clearance, gasket burn, higher underhood temps and the resonance. I had a little hotter than stock cam (Chet Herbert stage 1) and a TQ on my first 340 and it was a great sounding car with those 340 exhaust manifolds. I went to Super Comps and cut and wedged those in there and I never realized the gains that headers could produce becasue the rest of the motor wasnt built for it. I embarrased a few people with that docile sounding car, including a 396 powered Nova. It would pull hard from a stand still until about 4500. I would be so far ahead of his "cammed" 396 that I would shut down and let him fly by. He knew he had been beat in the 1/8 but I would never take him in the 1/4. My humble opinion.

[gthomas]

Originally Posted by plymouth360

I also run 1 5/8" Hooker Comp headders on my small block, but one or two of the left side pipes hang below the steering components... They seem to make good power though!

Not to disagree with dwc43, but I go low 13's through mufflers and an air cleaner in a 3500 pound car on a 625 cfm carter...my advice would be to get some times with the 600 then borrow a larger carb (if you can) to see if it will drop your times! Just my two cents!

Go to this site for carb calculations:

http://www.classictruckshop.com/garage/shopmathcfm1.asp

If your 318 is only spinning at 6500 and your engine is running at 100% volumetric efficiency, (in theory) you should be fine with a 600cfm.

[dwc43]

Originally Posted by gthomas

Go to this site for carb calculations:

http://www.classictruckshop.com/garage/shopmathcfm1.asp

If your 318 is only spinning at 6500 and your engine is running at 100% efficiency, (in theory) you should be fine with a 600cfm.

Charts are nice, but this has never worked in the real world. The TQ will give you much more throttle response and the correct amount of cfm the engine needs.

[gthomas]

Originally Posted by dwc43

Charts are nice, but this has never worked in the real world. The TQ will give you much more throttle response and the correct amount of cfm the engine needs.

Yes, I agree that a TQ set up right is the best way to go. Basically the small primaries give you good bottom end response and correctly adjusted secondaries will give you good top end with out bogging even if its an 800+ cfm on a small block 318.

And IMHO a 625cfm on a low rpm 318 may be better than a 600cfm if set up correctly. Especially if it has vacuum secondaries. On the other hand if it doesn't have vacuum secondaries, the volumetric air speed through the carb will be poor at wide open throttle.

I see so many GM guys with extra large carbs the cause bogging as well as 8 inch x 2 inch air cleaners that will not supply enough air, but at least they look "cool". I regularly see many big block GM's with tiny aircleaners that obviously will not flow much CFM.