exhaust flow tuning

[dsmdojo]

I was reading some other threads on turbo flow & boost & I started thinking(always a bad thing). So boost is a measure of the engine's resitance to flow. Has anyone put a boost guage on the exhaust to measure its efficiency? If I put one before the muffler, I expect I would want it to be as close to 0lbs as possible & still move the air. If I put one further up, like on the downpipe, we would want some boost to keep the air warm & moving, but how much? Is this something you could actually do, set up your exhaust & tune it with a boost guage? or am I thinking too much again?

[whiteGSX]

Actually, there's this tool that measures backpressure. I'm sure it's the same idea, and it's used to check for clogged cats. Not sure where you'd find it tho.

I'd think it'd be overkill and a waste of money to actually manitor and "tune" your exhaust. Exhaust pieces on our cars is pretty simple, so there's not too much variety other than the size of piping...which only comes in 2.5 and 3 inch anyway.

[JustDSM]

Just for the records.. Greddy makes a twin pressure gauge which can be used to measure back pressure as well as other things. Check it out...

http://www.greddy.com/products/electronics.htm#8TPG

[rcm1061]

I have a pressure gauge on my exhaust and it is a very useful tool. I bought an old 0-15 psi fuel pressure gauge at a swap meet for five bucks and plumbed it with copper tubing to my exhaust pipe. (It is temporarily zip tied to my e-brake handle.) Port one is on the DP just before the cat\con and port two is after the cat\con but I can only measure one at a time.

At port #1 with my old original press bent 2 1\2" and 2 1/2" cat\con I measured 6 1\2 psi at WOT with a 14B!! Dropping the cat brought it down to 4 psi (Isn't that what a test pipe is for?!!) I have since trashed the pressbent and installed my own mandrel 2 1\2" cat back with a Dynomax 2 1\2" muffler.

With several other engine mods (Still a 14B)it has dropped to 2-2 1\2" (no cat\con). You're not going to get much better than that without getting loud. The performance increase from 2 1\2psi down to about zero are probably minimal.

Real testing and tuning will bring better results than just slapping on some parts because someone thinks it works good.

Rick - '91 GSX Now it really blows!!

[dsmdojo]

I like the greddy gauge, a little big, but it's the first greddy product I like.
rcm1061, thats what I'm talking about. It seems to have worked well for you. & Now if you upgrade your turbo, you'll be able to tell if your outflowing your exhaust, or what boost you can run until you start outflowing your exhaust. People here upgrade turbos all the time, It might be worth it to see if you really need that 3" downpipe or confirm that what you got is working. & a boost gauge is only like $25($15 from jc whitney)