Alot of people have the misconception of back pressure vs exhaust escape velocity....
The problem that indeed you are seeing is restriction of sorts..... what is your a/f ratio?....And the timing?....What kind of injectors/o2 sensors are you running?.......
And also have you done a boost leakdown test?

 

I'm measuring boost in the intake manifold. What is a boost leakdown test?

 

just some random #'s for you Mike. Not sure whether they are relative or not to your situation, but your questions are some that i hope to be solving for myself this coming weekend with my new exhaust.

My current setup = 496c.i. force fed with a (struggling) 2.3L intercooled whipple with stock exhaust and peak #1 cylinder timing of 16* @ 6psi on 93 octane pump gas.

This engine is "extremely" sensitive to timing. While 16* peak timing @ 6psi will sometimes get a blip of KR (maybe .2 - .3*)......17* of peak timing @ 6psi will net me 10x that amount or 2.0 - 3.0* of KR. Luckly for me, this engine (lately) responds better to more timing, than it does more boost. When I go to the track, i wll generally stop by and throw some 118 octane in the tank, and when mixed with the 93 octane probably balances out to somewhere in the 110 octane neighborhood i guess. With that combo, i can run 17.5* of timing @ 6psi with no knock (and i may push it a little next time too). I am very curious to see how a more free flowing exhaust will change my timing/boost formula.

I do know that one problem with this engine is how it looses quite a bit on the top end. Through the first 1/8 mile it runs strong as hell, but the last 1/8 it struggles a bit. Yea, yea...i know the best thing for it would be some better heads and CAM, but then I know this 2.3L whipple would be using more than its giving at that point. I am hoping to gain a little top end with the exhaust, i will keep you posted. Good luck.

Is ther some generic calculation to determine the flow capabilities of a "STOCK" exhaust?

 

Still waiting, when are you going to get that new exhaust installed already?!

 

LOL....well i came home from work today to find 1 box in front of the garage. It was the muffler...Well yippidy DO!....I might need the pipes to go along with that ya think? So I called the people i bought it from and they said sometimes the 2 boxes get separated, but the box with the pipes should be there tomorrow. So I am hoping to have it on and running by the weekend with some pics and audio clips for you guys.

 

.............oh, and its a 2bar MAP speed density tune and i think the 8.1L has a 9.1 CR.