Anti-boost
Thread Starter
Melting Slicks
Joined: Jun 2002
Posts: 3,060
Likes: 3
From: Dublin CA
Anti-boost
Connected boost gauge to exhaust. Drilled & tapped pipe before cats, ran copper tube up near brake master for boost gauge connector.
zero psi at idle. 15psi at WOT on passenger side. It's near 100* outside, I'm on a beer break, will test drivers side later.
15psi sounds high, but I have nothing to compare it to. What should it be?
zero psi at idle. 15psi at WOT on passenger side. It's near 100* outside, I'm on a beer break, will test drivers side later.
15psi sounds high, but I have nothing to compare it to. What should it be?
Instructor
Joined: Jun 2004
Posts: 190
Likes: 0
From: CA
Originally Posted by blu00rdstr
Connected boost gauge to exhaust. Drilled & tapped pipe before cats, ran copper tube up near brake master for boost gauge connector.
zero psi at idle. 15psi at WOT on passenger side. It's near 100* outside, I'm on a beer break, will test drivers side later.
15psi sounds high, but I have nothing to compare it to. What should it be?
zero psi at idle. 15psi at WOT on passenger side. It's near 100* outside, I'm on a beer break, will test drivers side later.
15psi sounds high, but I have nothing to compare it to. What should it be?
Why did you connect it to your exhaust? It's supposed to measure manifold pressure...
-DC
Burning Brakes
Joined: Mar 2002
Posts: 1,040
Likes: 1
From: Knoxville TN
he is checking the backpressure in his exhaust system. backpressure kills hp and that sounds like a lot of backpressure, blu. I am probably in the same boat as you are. I've been thinking about building a custom 3" exhaust with Borla xr's, 2 chamber flowmasters or warlock mufflers. with that kind of backpressure, I would think the change would be good for at least 20hp.
Thread Starter
Melting Slicks
Joined: Jun 2002
Posts: 3,060
Likes: 3
From: Dublin CA
Originally Posted by QuickSilver2002
2x boost is the most you want to see on a turbo manifold, but that is a totally different deal.
I'm guessing that 15psi is way too high, but I have nothing to back it up.
I'm guessing that 15psi is way too high, but I have nothing to back it up.
Part of why I took a beer break is the car threw codes at me and lost power. But if I think about it, I didn't plug both 1/4" lines, just hooked one up to the boost gauge. I cleared the codes but maybe it's an O2 sensor unhappy with sniffing clean air.
Pro
Joined: Jul 2000
Posts: 580
Likes: 0
From: Washington, USA
This is a pretty free-flowing exhaust setup I put together. Of course I've still got the stock cats, but it's after there that it's all wide open / straight through design. Check out the video / sound clip to see how quiet it still is.
http://forums.corvetteforum.com/showthread.php?t=869319
http://forums.corvetteforum.com/showthread.php?t=869319
Burning Brakes
Joined: Oct 2002
Posts: 797
Likes: 1
From: Sunny Earthquake Country, USA On the Left Coast (which is becoming more Right!)
I don't have the answer as to how much is typical, however you now have your baseline, now get a set of LT's w/high flow cats and a good set of mufflers, check again and you (we) will have the answer! 
I like that you look into these things with gusto-I wish I had your spunk!
Good luck,
Roy
I like that you look into these things with gusto-I wish I had your spunk!
Good luck,
Roy
Thread Starter
Melting Slicks
Joined: Jun 2002
Posts: 3,060
Likes: 3
From: Dublin CA
Ramcharger, looks pretty cool! I think my problem is cats forward. A previous tuner couldn't get it right and it ran pig rich for a weeks' worth of driving. I was worried pig rich was bad for the cats. I don't think it looks ricer, the tips aren't big enough.
Supervette, it's a curse that I dig into problems! I waste so much time trying to outsmart myself that I end up below the average curve. If I only were a normal consumer and ignorant of the detail of how things worked, life would be much easier (on me).
That being said, I wonder if there's any backpressure with cut-outs? (Hmm, he says, and wanders off with the cord of a die-grinder trailing behind him).
Supervette, it's a curse that I dig into problems! I waste so much time trying to outsmart myself that I end up below the average curve. If I only were a normal consumer and ignorant of the detail of how things worked, life would be much easier (on me).
That being said, I wonder if there's any backpressure with cut-outs? (Hmm, he says, and wanders off with the cord of a die-grinder trailing behind him).
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Pro
Joined: Jul 2000
Posts: 580
Likes: 0
From: Washington, USA
Cool cats.
Originally Posted by blu00rdstr
A previous tuner couldn't get it right and it ran pig rich for a weeks' worth of driving. I was worried pig rich was bad for the cats.
Keep in mind that it's the whole setup that determines what your backpressure is. Did your pressure gage peak at 15psi and drop or did it stay there? It'd be interesting to see on the street (or dyno) what it does after you get your exaust flowing through the pipes. Of course it'll be very different under load than simply taking the engine to redline in your driveway or on jackstands.
Thread Starter
Melting Slicks
Joined: Jun 2002
Posts: 3,060
Likes: 3
From: Dublin CA
Backpressure goes up and down with rpm if under load. If it's partial throttle pressure varies from 2-5psi.
Yesterday passenger side pressure went to 15psi@5,000rpm, today drivers' side went to 10psi@5,000rpm. I think they're probably closer but today I had issues with the A4.
Yesterday passenger side pressure went to 15psi@5,000rpm, today drivers' side went to 10psi@5,000rpm. I think they're probably closer but today I had issues with the A4.
Melting Slicks
Joined: Mar 2002
Posts: 2,931
Likes: 2
From: Tx
Originally Posted by blu00rdstr
Me neither. What is too much pressure? Does a 'free-flow' exhaust have no backpressure? And if there's 15psi in the exhaust pipe, what does that mean for the cylinder(s)?
Part of why I took a beer break is the car threw codes at me and lost power. But if I think about it, I didn't plug both 1/4" lines, just hooked one up to the boost gauge. I cleared the codes but maybe it's an O2 sensor unhappy with sniffing clean air.
Part of why I took a beer break is the car threw codes at me and lost power. But if I think about it, I didn't plug both 1/4" lines, just hooked one up to the boost gauge. I cleared the codes but maybe it's an O2 sensor unhappy with sniffing clean air.
Thread Starter
Melting Slicks
Joined: Jun 2002
Posts: 3,060
Likes: 3
From: Dublin CA
Originally Posted by QuickSilver2002
If you can think of a quick and easy way to hook up a fitting to an 02 bung I'll run a test on mine. I really don't want to poke another hole in my collector. I guess you also have to use some type of metal tubing for the first foot or two. ( I would imagine rubber or plastic melting pretty fast)
Edit: I checked your profile, LG Pro LT headers
I went to ACE hardware and got two setups of; 1) 1/8male-1/4 flare adapter, 2) flare nut with ring, 3) 1/8 plug (for after testing) and 4) 10' box of 1/4" copper tubing. From the auto parts store I bought some 1/8" and 5/16" rubber caps to cap off the open ports.
I drilled 3/8" holes just before cats, and tapped those. Screwed the adapter in, ran the tubing down from the master cylinder, slid the nut and ring over the end of the tube, and attached that.
The boost sensor is connected the top end of the tubing with about a foot of rubber hose. I could've just used one tube and moved it underneath, but it was easier to move the hose between tubes up top.
Last edited by blu00rdstr; Jul 26, 2004 at 07:15 PM.
Pro
Joined: Jul 2000
Posts: 580
Likes: 0
From: Washington, USA
Originally Posted by QuickSilver2002
I had an 02 bung cap at one time, but I cannot find it now. I'll rig it up if I can find something cheap. I remember them charging me over $10 for the cap last time.