If you ever wondered how much power you are leaving on the table with a restricted exhaust then listen up. I just swapped my exhaust and gained almost 40rwhp!!! Learn from my mistake and do your exhaust right the 1st time. It costs less than doing it wrong and having to redo it anyway.

Last year I swapped my tired 350 TPI for a carbed 383. Didn't have much money left over after buying the engine to really do the exhaust so I cheaped out and got a pair of budget shorty headers with 1.5" primaries and had an exhaust shop run what I thought were dual 2.5" inch pipes (later discovered they were 2.25") with crush bends, universal cats and dynomax mufflers. It sounded great, felt a lot faster and dynoed at 282rwhp. Estimating 20% loss through my automatic I figure roughly 350hp at the flywheel.

A couple months ago I took it to the track for the 1st time just to see what the car would run and was disappointment I ran a 13.8 but even more pissed that I lost to a mustang who ran 13.5 in the quarter.

Fast forward to last week and I replaced the entire exhaust. This time I went with long tube headers with 1.75" primaries, dual 3" with an x-pipe and mandrel bends, cherry bomb vortex mufflers.

The results are a very noticeable jump in power across the rpm range. Yes it is louder but I expected that after everything I've read about 3" pipes on TGO. The interesting thing is I also expected a loss in low end torque because I've heard the myth about backpressure but that did not happen at all. Dyno test with the new exhaust was 320rwhp. I'm figuring roughly 400 at the flywheel now.

 

Quick question just to verify: Same dyno?

 

Whats the 383 combo look like for heads cam intake?

Engine is a system, everything needs to match. Dual 3" is overkill for what you have there but i think it can be abit better to be slightly to large than too small for exhaust. Depends on applications but full length exhaust, dont worry about torque loss from to large diameter. Longer runs of pipe should be abit larger imo.

 

Yes same dyno and same Guy operating it. He was kind of surprised because he said alot of people make a change and expect 20 or 30 HP and only to get 5 HP.

 

Aluminum heads 64cc combustion chamber 10.4:1CR. Cam is 224/230 .525 lift 110 LSA. Intake is dual plane weiand speed warrior.

I have pics of the before and after exhaust and dyno sheet but haven't figured out how to upload them up yet. This was my first new thread.

 

Sounds like solid gains to me. I have virtually the same exhaust on my car with a .060"over 350 nonetheless. I don't think it's too large at all. Fwiw mine went a 10.98 @ 123.5 and 6.96 @ 98.4 with a 1.48 60' on 275's this weekend.

 

Full exhaust setup is great. Even when I installed headers I felt a big step up in power pull.

 

Not sure who is doing your math but a 20% loss resulting in 282hp is just at 302 at the crank, not 350.. and your looking at 340 after the exhaust not 400.

 

Your math isn't so good Take 350x .8 (1-.2) (100%-20%=80% or .8)

That will give you 280 my friend - stay in school.. JK or 320rwhp is 400fwhp with a 20% drivetrain loss.

 

No loss in low end tq, huh?
I know A LOT of people that would love to argue with you on this.
(I'm not one of them tho lol)

Nice gain, a good exhaust is important an should be mandatory for any build/budget.