Back pressure guage anyone?
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Sure did, thanks CFI-EFI, I'll probably order one, then get some braided line and an adapter for the 02 bung. Just think it would be a nice tool, but not at the prices they want that I saw $116. plug for an actual back pressure guage.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by rick lambert
Sure did, thanks CFI-EFI, I'll probably order one, then get some braided line and an adapter for the 02 bung.
Originally Posted by rick lambert
Just think it would be a nice tool, but not at the prices they want that I saw $116. plug for an actual back pressure guage.
RACE ON!!!
Last edited by CFI-EFI; Jul 25, 2006 at 06:22 PM.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
Originally Posted by AKS Racing
How much power do you think is left on the table at just under 6 psi?
This reading was at 6K in 2nd Gear WOT. I have no cats, but full exhaust with mufflers. I have known this to be a problem for some time, but have not attempted to resolve.
This reading was at 6K in 2nd Gear WOT. I have no cats, but full exhaust with mufflers. I have known this to be a problem for some time, but have not attempted to resolve.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by bjankuski
6 PSI is alot of backpressure,
RACE ON!!!
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Looking back in my FSM, Tom said his stated you can check it at the A.I.R. Pipe, he is correct, you can check it at both..but the specs are the same. engine at idle should not exceed 1 1/4 psi. Accelerate engine to 2000 RPM, reading should not exceed 3 psi.If backpressure exceeds at either RPM a restricted exhaust system is indicated.
Wonder why they checked your at 6000 RPMs?
And bjankuski, sound like you really exceed 3 psi. of course I'm referring to specs for an 87..don't know if yours would be the same..check your FSM.
Wonder why they checked your at 6000 RPMs?
And bjankuski, sound like you really exceed 3 psi. of course I'm referring to specs for an 87..don't know if yours would be the same..check your FSM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Safety Car
Joined: Apr 2001
Posts: 3,525
Likes: 2
From: Houston TX
Originally Posted by bjankuski
6 PSI is alot of backpressure, my guess is you are giving up 30 to 50 HP with that much backpressure. If you were to reduce the backpressure and retune the car I would expect a significant power increase.
A guy on the forum was selling 2" primary "home-built" headers and tru dual 3" exhaust. I did not bite because the back half of the exhaust is really no better than where I am today.
If I sell some more car parts, I would like to get some of the EM 1 7/8" headers and then try a single 4.5" oval center pipe into 3.5" Flowmasters. I would think this is a step in the right direction.
Aaron
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by rick lambert
Wonder why they checked your at 6000 RPMs?
Originally Posted by AKS Racing
This reading was at 6K in 2nd Gear WOT.
Originally Posted by CFI-EFI
my car was being revved in neutral, which generates a lesser volume of exhaust gases than when under load, at WOT, at 6000 rpms in second gear.
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
After reading this thread, I decided to check the back-pressure on my '92.
I bought two brass fittings at Lowe's, one 1/2" female pipe to 1/4" female pipe and one 1/4" male pipe to a 1/4" barb fitting for my gauge. Cost, about $3.
My A.I.R. check valves were easy to remove.
Even with the Northstar coil pak for the Delteq on the left valve cover, I didn't have to remove anything to take the check valves out.
Taking one check valve out at a time, it took about 10 minutes each to check the back-pressure.
The highest reading at about 3K rpm was less than 1.
My cats aren't plugged at 88K miles.
Tom Piper
I bought two brass fittings at Lowe's, one 1/2" female pipe to 1/4" female pipe and one 1/4" male pipe to a 1/4" barb fitting for my gauge. Cost, about $3.
My A.I.R. check valves were easy to remove.
Even with the Northstar coil pak for the Delteq on the left valve cover, I didn't have to remove anything to take the check valves out.
Taking one check valve out at a time, it took about 10 minutes each to check the back-pressure.
The highest reading at about 3K rpm was less than 1.
My cats aren't plugged at 88K miles.
Tom Piper
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
Originally Posted by Tom Piper
After reading this thread, I decided to check the back-pressure on my '92.
I bought two brass fittings at Lowe's, one 1/2" female pipe to 1/4" female pipe and one 1/4" male pipe to a 1/4" barb fitting for my gauge. Cost, about $3.
My A.I.R. check valves were easy to remove.
Even with the Northstar coil pak for the Delteq on the left valve cover, I didn't have to remove anything to take the check valves out.
Taking one check valve out at a time, it took about 10 minutes each to check the back-pressure.
The highest reading at about 3K rpm was less than 1.
My cats aren't plugged at 88K miles.
Tom Piper
I bought two brass fittings at Lowe's, one 1/2" female pipe to 1/4" female pipe and one 1/4" male pipe to a 1/4" barb fitting for my gauge. Cost, about $3.
My A.I.R. check valves were easy to remove.
Even with the Northstar coil pak for the Delteq on the left valve cover, I didn't have to remove anything to take the check valves out.
Taking one check valve out at a time, it took about 10 minutes each to check the back-pressure.
The highest reading at about 3K rpm was less than 1.
My cats aren't plugged at 88K miles.
Tom Piper
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
Originally Posted by bjankuski
Did you check it at WOT? You need to check for plugged CATS at WOT because that is when you are moving large amounts of exhaust, no load conditions do not move much exhaust.
I have no intention of WOT in neutral for any length of time.
If that isn't enough, I won't be doing any more.
Tom Piper
Melting Slicks
Joined: Mar 2003
Posts: 2,898
Likes: 0
From: Oklahoma City Oklahoma
Originally Posted by rick lambert
I guess you and I are the only one old enough to remember JC Whitney
CFI-EFI
but that is interesting, I'll look.
CFI-EFI
but that is interesting, I'll look.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
Originally Posted by Tom Piper
Just a brief blip to 3K at WOT.
I have no intention of WOT in neutral for any length of time.
If that isn't enough, I won't be doing any more.
Tom Piper
I have no intention of WOT in neutral for any length of time.
If that isn't enough, I won't be doing any more.
Tom Piper
Check the pressure at WOT while your driving the car, not in netural. Get on the highway pick a gear that is a safe speed and go to WOT from 2000 to 5000 RPM and see what the backpressure is. I quick blip to 3000 RPM in netural will not give you an accurate reading.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
There is no question that a blip in neutral will not supply the volume of exhaust gases that a WOT run will, but that is how the muffler shop determined that I needed a cat. I wasn't in the car and I couldn't see the tach, but they did not rev it unmercifully. I would guess that 3000-3500 was about it. I was told that 3 psi back pressure indicated a cat was needed. Tom Piper observed less than 1 pound. My car had 15 psi. No wonder it had lost a second in the 1/4 mile.
RACE ON!!!
RACE ON!!!
Last edited by CFI-EFI; Aug 2, 2006 at 10:33 AM.