I get ~5 psi accelerating by 2200 rpm and can make 10-15 psi around 2500 rpm pushing it but cruising I get ~ 5 psi @2500 rpm.

Anyone elso care to post their boost numbers at RPM's for a campre and contrast?

My turbo is a GM-4 in my '94

Please note if you have the GM-8

When are you going to get around to getting us the corresponding back pressure readings? Just drill a small hole in your crossover pipe and "tee" in another gauge.

I'll let you know in a few days. I will be getting a new boost gauge as mine broke. Don't ask!Censored

It depends on speed and hills.
If you have 4.10 gears, you probably won't have as much boost at the same rpm as someone with 3.73 or 3.42 because the actual load on the engine will be different.
If I remember right, 2500 RPM on mine is about 75 MPH and about 8-10 PSI. If I hit a small hill, it will go to about 12-14.

When are you going to get around to getting us the corresponding back pressure readings? Just drill a small hole in your crossover pipe and "tee" in another gauge.
I'd like to do this before I put on any different turbos, so it is still on my mind.

New Canadian WG contoler, tweeked.

11-12 psi cruising @ 75 MPH 2300-2400 rpm

16-17 PSI WOT (needs more tweaking)

EGBP coming when time permits.

91 acclaim ready for the road again! -:t

Freebies + shipping...

2000 tuna can - 180,000 km's
61010 Used belt - Same
Used WG selonoid - Can't remember but not 180,000 km's
Toasted Vac pump - still works, just noisy as hell - Good Pulley - Can remove pulley and send separate.

All items 100% satifaction assured.... until you touch it! :D

Try to keep the back pressure down to get the most power. Low back pressure will also boost your fuel economy and lower your EGTs.

Bigger turbine housing with high AR ratios will also lower back pressure.

It will also increase turbo lag. Have to find a good balance for your engine.

Same size turbine with higher A/R will lower back pressure..................

Nobody here knows what the back pressure is.

Hey Diesepro.......How much backpressure do you have? I think I've got the same turbo as you, the 300 hp from Peninsular. I sure don't have any lag in mine.

3-5 psi at 70 mph

3-5 psi at 70 mph
I think you would notice a huge difference if you are able to bump your boost a little.

I gaged it - pegs a 20psi gage at first, then tapers back to about 15psi at 8psi Boost at 2200rpm, and rising.........

That was b4 the 83mm3 chip and charge-air cooler, but pump was at +8.5deg, and -1.50deg TDCO

I think you would notice a huge difference if you are able to bump your boost a little.
Actually my boost will top at about 15 psi under WOT but at cruising speed it stays fairly low unless accelerating or going uphill.. I have a 10K pot that I can actually turn up to get about 19-20 but until I get the IC installed I'm afraid of getting too much heat in there with the higher pressures.

Until I installed the pot I was not getting any boost while cruising at 70 mph. And I could only top out at 7-8 under WOT, which then would drop back to 5-6 after about 2 seconds.

What does it read as the tach passes 2200 RPM WOT? and at what RPM do you see 10-12 psi during the same acceleration?

I still think a 10* turbine clip would solve all the flowing issues the GM series turbos have....

2200rpm cruise I see 1psi, if I get into it from 2200 but not let it shift it will run up to 7psi. If I nail it from a standing stop, the boost never exceeds 5psi....

4.10s

Your PCM is performing as designed............
Your turbo is performing as commanded.............

I've some further insight into this. I was looking at the garret m25 a/r60 and yes, it's smaller than the gm-4, In the process of comparing the two I noticed my turbine shaft was sloppy, as in completly wornout. I switched in a new center cartridge and did some more WOT tests after to see what a difference a free spinning turbine shaft might have. WOT dead stop to 2500 rpm, Boost hits 5 psi by 2200 and 10 psi by 2500. I picked up ~400lbs of broken sidewalk and on the 70 mile ride home I noticed that when I shifted to 4th and the TCC locked I was at 2000 rpm~55 mph. Stepping into it, but not hard enough to have the tranny downshift as I was going up a steep overpass I hit 10 psi at 2000 rpm and held 10 psi 'till 2350 rpm where it climbed passed 12 psi. I was able to repeat this three times but only under those circumstances. I also hit 15 psi @ 2500 and 18 psi at 2900 rpm.

CR, the worn out shaft wouldn't make more than 15 psi anymore. Check yours out.

I'm not to concerned about making boost, i was just noting since my woofing started i've lost boost along with the woofing and miss. Even with no boost it should still be running without the missing in the engine. I thank you for your input though.

Keep pushing that boost QM, you'll be woofing right along with me.... lol

When you had that cracked piston did you notice a difference in sounds like mine?

I had a cracked piston for 40,000 miles and knew about it. It did make some strange noises as the compression went into the crankcase, like a Rut rut thuuut! rut rut but when it finally when all the way it was unmistakeable that something was wrong, with the miss being felt like a hard thump! through the engine/truck/brakepedal.
0 psi on the cracked cylinder too.

WOT I hit 18psi and drop to 16psi. Cruising at 60 I am at 4-5 psi. And when I give her all the throttle I can without downshifting I can hold 15 psi.

Cant say enough about the 3bar map and 4in SS diesel exhaust. And all this is done with the factory vacuum setup. And YES, I do carry a spare vacuum pump and wastgate solenoid with me at all times. When I use up my current setup and spares...then I will look into aftermarket spring setups...or make my own.

Did some readings while driving with the scanner. Max fuel rate sustained 64.5mm3 at 75% APP, (79-99% aap yeilds 59.9mm3, I'd guess from the optical bump, you get that TEX?).
It takes 40mm3 fuel rate to make 10 psi at 2200 rpm in 4th uphill and at 70 mph/2500 rpm on flat ground. I saw IAT's jump from 62*C to over 120*C in five seconds at 15+ psi, ambient ~42*F

I was kind of disappointed with my boost. I need to adjust my turbomaster more, but at 70 and ~2400rpm I hold at 9psi and can't get it above 10 on hard acceleration. SO i will be toying with it a little.