thedusterridesagain

so here is my set up. 340 with mild cam. 727 with b&m transpak. 8 3/4 with 3:55. now i have a full 3 in dynomax system with full length hooker headers. now my old 318 had only 2.5 in pipes and was a hell of alot snappier then my 340....... is the 3 in pipes to big for a small block ? like i said my old 318 would damn near rip the fillings out of your head. this car for some reason is a bit more tame but from what i have as far as documentation has the best of everything. help is welcomed. thank you.

78D200

What are all of the performance upgrades that you have done to the motor and tranny?

Without know what other upgrades you have done, I would say yes, the exhaust to too large. 3" is great for a big block build, whether its only a small build or mild. A good rebuild with a lot of performance parts should get 3.5" on a big block.

With a small block, you'll only want 3" exhaust if you have gone all out with it (cam, intake, carb, dizzy, bored out cylinders, port and polished heads, etc.). 2.5" exhaust is a better choice because it give you backpressure that the motor needs to build lower RPM power. I'd be willing to bet that your car moves pretty well at teh higher RPMs.

mr340

2.5" max on the exhaust will give you all the power you can use fron the 340, as stated above unless you go to an all out race motor, then the 3" would be better.

thedusterridesagain

yeah your right. at high rpms this bitch moves like its the end of days. like high i mean between 3500 and 5000. sounds good and has power she doesnt float or knock ...... i know the motor has a mild cam with edelbrock performer intake. its bored .030 over and im unsure the head work.... everything to this car was done in the early 90s. the trans is just a 727 with transpak kit and governor on it......so yeah i was thinkin 3 in might be too much. thanks alot.

67 GTX

agreed
i have a 440 with 2.5 exhaust, and its fine
you dont wanna do too big with exhaust, because then you will lose more torque

mr340

I'm running a .030 over 340 with a mild cam backed up by a 4 speed in my Duster, and I use a factory exhaust with no problems. The car doesn't seem to need anything more than that.

67 GTX

Mr. 340
do you have the original manifolds on it?

thedusterridesagain

rock nuts guys. thank you for your input. now once i get some money and i can change it over ill let you know the outcome. to bad theres no black friday sales at local exhaust shops huh?

mr340

I am running the original manifolds and a completely stock exhaust. I purchased a repop exhaust ( built and bent to the factory specs) from a place in Fla called Kepich Exhaust it ran about 250 complete with all the pipes hangers and mufflers and clamps. It fits like a glove and not a leak or squeek anywhere.

67 GTX

Wow! Do you have any pinging problems?
What octane do you run?

mr340

No problems with pinging, it'll run just fine on 87/89 octane pump gas. It's not really beat on too hard ( well, maybe once or twice) the only drawback is that the guy that did the motor work (previous owner) didn't bother to have the valve seats changed and now I need some major head work.....

67 GTX

is your compression still 10 to 1?
Where are you located?

mr340

Honestly don't remember the compression specs, I have to find my paperwork. I bought this thing in '95, and just don't remember all the small details. I'm in western NJ, on the PA border.

67 GTX

Huh, i think if it is original, the compression should be around 10 to 1
did you have to retard the timing to run on lower octane?