How much boost can i make

[JD_countryboy]

How much boost will a stock GM 3 turbo make at stock fuel settings? I have a new ip from walt, and he gave me the instuctions to turn up the fuel, but i havent yet. I kept looking at 1100* egt at hard accel, soi figured pulling a load it would be that high or higher. I wired my waste gate shut, At WOT 90+ mph, boost will reach 11.5 or close to. Hard accel, 10 psi, at lower rpm, i don't have a tach so not sure the rpms, it climbs to 10 and stays there thru the whole rpm and accel speed range. Normal accel, 6 psi. Crusin its now 2-4psi. Before the waste gate was wired shut egts at hard accel were 1000 or more, dependin on outside temp. yesterday befroe wastegate wired shut, 1000-1050*. punched to floar and hold till 60mph. Afetr wireing shut, 850-900*. Decrease in egts and increased boost was the only thing i noticed. Now i'm debating adding fuel, but not sure if i can make the turbo add any more air. Was aiming for around 12 psi boost. No intercooler yet. but after an intercooler, if $ comes around, id'd be aiming for 15 -17 psi. Thanks

[grancito]

you have a turbo or wastegate problem, wired shut should blow something, like 20 psi.

[JD_countryboy]

So what do i check next? i know watse gate is as shut as i can get, i moved it back and forth with pliers, so i know its free. Its as far closed as i can get. thats where its wired. I constantly am checkin gauges, those are the numbers i normally see, nothing higher.

[grancito]

Is your gage accurate? exhaust or cat not blocked? intake not restricted? turbo OK? If the boost has been low for some time and you have a catalytic convertor, it will be full of carbon.

[jifaire]

First, you aren't gonna make huge pressure with a GM-3. There's a reason why they replaced that model of turbo.

When you do finally get it to hold pressure, it should do 10-14, but your IATs are gonna climb; it's just not a real efficient design.

--Did you change the downpipe? The stock 93 downpipe sucks, adn will prevent your turbo from spooling right up
--Did you change the crossover? The stock 93 crossover has a history of collapsed corners (it's double-wall, and the inside layer often got bulged during bending, restricting the pipe)
--Did you remove the snorkle and open the airbox to remove the intake air restriction? If you can't get air in, you can't get exhaust out, and your turbo will suck, not blow.

Now... about making things work. Wiring the wastegate shut is not healthy... you're better off to put a helper spring on it for now, and get or build a TurboMaster later. Turning up the IP a bit will help you by generating more heat energy adn exhaust volume. If you turn it up and get black smoke, you have too much fuel and your EGTs will rise, but as long as you can keep the air volume up, you should be ok.

If you do all the stuff above, and have no black smoke, you can safely turn up your IP and see what happens.

[grancito]

I don't agree with removing the snorkle, it supplies clean cool air under pressure from the front and causes 1/8 psi drop in pressure in the intake, the filter causes 1/4 psi drop in pressure.

[JD_countryboy]

ok. Heartthrob exhaust from walt, no muffler. no cat.
upgraded crossover at same time. ya, both are MUCH better than oe design.
New bully dog gauges. Air filter looks ok, least 10,000 miles on it. paper element from napa. Air filter box is about as open as you can get. Cut open at largest diameter top and sides. basically all thats left is enough to bolt it to the fender liner. and protect the filter sides.
whats the difference wiring the wastegate shut and puting a bigger spring on it? if you set the spring tension real high for maximum boost, then the wastegate won't move anyway? I am going to make a mechanical wastegete, just havent yet, decided to try the wiring it shut to see what kinda boost i could make.
How can tell if the turbo is good/bad? any kinda test procedure?
When i first mash the pedal to the floar i get just a bit more than a puff of black smoke, but soon as the boost starts to rise its gone. You have to be looking at the exhast in the miror when you mash it to see the puff, or else its gone by the time you look back.

[jifaire]

I don't agree with removing the snorkle, it supplies clean cool air under pressure from the front and causes 1/8 psi drop in pressure in the intake, the filter causes 1/4 psi drop in pressure.

Your call. It's not about pressure though, it's about mass airflow (volumetric solution rather than barometric)

Kennedy has a write-up on his website under 'Tech Tips' on how to do it. Everybody I know with a 92-95 chev has done this mod with great results. Makes about as much difference as changing the downpipe on a 95..

[ChevyCowboy]

thats about as much smoke as my 93 makes, is it posble to put a newer style turbo on that year of truck to create more boost and whats really the differenc in a GM3, GM4 and a GM 8. im assuming the only real good way to see if the turbo is working correct is a boost gauge right

[surreysinner]

Wow, you tow at 90mph? :eek:

[JD_countryboy]

nope. i wasnt towing at 90mph. i was trying to see what the max pressure i get the turbo to push at WOT propelling the truck. Figured i would never see that rpm while pulling anyway.

ok so i hauled a load of scrap inthe the scrapyard today. 6.5td almost impressed me. Not sure what the truck weighed, full of diesel, trailer empty weight 4,000 or a touch more, net on trailer 4,500. weight slip didnt show gross weight though. just net on it. So i was pulling 8,500lbs. No problem for my truck. Held 55-60 mph at will. Carried the speed up and down the hills too. Steepest hill I pulled today was froma dead stop. Peak 14psi boost, 1,050egt with my foot basically floared was at 55 at top of hill. Length of hill i can't say cause i was glancing at all the other gauges other than odometer. Took it much better than my 350 gasser ever did. Crusin kept around 6 psi, 600-700 egt 55-60 mph. on normal accel from stoplight, would get to 900-1050 egt 12-14 psi boost till it got to 55-60 mph. then I'd just kep it crusin. Wastegate is still wired shut. MPG i don't know. Took remote state routes till I got about 5 miles fromt the scrapyard. Filled truck up close to home on my way back. But When i left my house, gauge read 1/2. After the 55 mile trip to the yard the gauge still read almost a 1/2 tank.

FYI i passed two city cops with no muffler. Both times it was taking off from a stoplight. Normal accel, I wasn't brave enough to just mash it and see what the responce I would get from them, but they never even looked my way. One was getting in his car, beside me and never looked up. and this town in know for pulling you over for loud exhaust. So either i was lucky, or my truck isn't really all that loud.

Whats the difference in wiring the wastegate shut, or crankin a turbomaster to make 14 psi? either way the wastegate is gonna have to be shut to make that kinda boost with this turbo. Or is my turbo on its way out?

[grancito]

I guess you have no cat if there is no muffler, so 14 psi boost is probably OK if the exhaust is clear.

[JD_countryboy]

ehaust is clear as i can see. after inital puff. but i never increased fuel yet. That is probly next step. and with more fuel comes more egts, and possibly more boost? or if 14 psi is all the turbo is capable of making what will happen with more fuel, more egts and exhaust flow? I sure don't want to grenade a turbo :eek: that wouldn't be good at all. Turbomaster is on my to do list this week. that and probly increase fuel.

[jifaire]

Whats the difference in wiring the wastegate shut, or crankin a turbomaster to make 14 psi? either way the wastegate is gonna have to be shut to make that kinda boost with this turbo. Or is my turbo on its way out?

It's hard to get it wired shut so it stays shut... anything in the gate causes it to lose seal. A spring, on the other hand, 'flaps' and seals.

At least, that's how it was explained to me. A buddy tried to wire his shut, and then had much better results with a turbomaster.

He had a GM-3, too. First, he built his own TM by cutting the cannister in half and replacing the spring with one that was stronger, then he just bought a TM from USDieselparts in Montana. He says the actual TM works better than his home-made one.

I just bought one, never tried to make one.

[JD_countryboy]

Your right on the hard to wire it completely shut. I think i have it though. can't get the wire any tighter thats for sure. I've been debating making my own turbomaster or buying one. Probly try makining one first though. So yes I overlooked your point. If somethings keepin the wasgegate open just a touch then your losin some.

If I turn up the fuel, which will create more egts, and exhaust flow, what will happen to my turbo and boost? I'm was pushin 12-14psi on hard accel at stock fuel setting. Will my turbo make more boost? or will it come apart?

[jifaire]

If I turn up the fuel, which will create more egts, and exhaust flow, what will happen to my turbo and boost? I'm was pushin 12-14psi on hard accel at stock fuel setting. Will my turbo make more boost? or will it come apart?

Should make more boost like crazy... more fuel = 'way more exhaust = more turbo pressure. It won't blow your turbo up, just watch the gauges and lift your foot if either your EGT or Boost starts looking too high. I'd feel a lot better if your turbo was adjustable first, though, just so you can keep the boost pressure down. With a GM-3, more boost will raise your IATs considerably, so you have to find that balance point "sweet spot" where the fuel and boost pressure adjustments are balanced right.

In your case, all you can adjust is the fuel, by turning up the IP. If you had a TurboMaster, you could also adjust the boost.

[JD_countryboy]

ok. adjustable boost controller is first on the list before more fuel. The wiring the wastegate shut was more for turbo testing than long term performance mod. Since it seems that my turbo is making boost as it should, unless everyone thinks its not making enough since it is wired shut, now im gonna add a turbomaster.

If i was gonna swap my turbo for a different one, which model would fit as a direct bolt on replacement? GM-4 or GM-8. I'm gonna guess that the 8 is the newest and greatest for these trucks, but is it nessesary to go to it? Would a 4 be sufficiant? Thanks for the advice.

[jifaire]

ok. adjustable boost controller is first on the list before more fuel. The wiring the wastegate shut was more for turbo testing than long term performance mod. Since it seems that my turbo is making boost as it should, unless everyone thinks its not making enough since it is wired shut, now im gonna add a turbomaster.

If i was gonna swap my turbo for a different one, which model would fit as a direct bolt on replacement? GM-4 or GM-8. I'm gonna guess that the 8 is the newest and greatest for these trucks, but is it nessesary to go to it? Would a 4 be sufficiant? Thanks for the advice.


A GM-8 is a good choice... I have a GM-4, and it has similar IAT issues with the GM-3.

[JD_countryboy]

Was the GM-8 a stock turbo on trucks? Any ideas what years, if so, that they were used. Maybe i could find a good used one off a wrecked truck from a scrapyard. Hopefully cheap. And low mileage. In great shape.

[jifaire]

Was the GM-8 a stock turbo on trucks? Any ideas what years, if so, that they were used. Maybe i could find a good used one off a wrecked truck from a scrapyard. Hopefully cheap. And low mileage. In great shape.

Yeah, it was stock... I *think* from about 97 on...

They have a little plate or stamp on 'em with the model number.

[JD_countryboy]

Thank you

[Oldsmoke]

Hey Countryboy! Sounds like you are getting pretty good power!! I think my truck might do a little better with the chip and mods I've done but I am worried about blowing up my tranny now.

[JD_countryboy]

My tranny aint goin nowhere. weakest part, (so i'm told) is the indirect clutch. Which is used in 4th and reverse. With shift kit its 300% stronger. according to shift kit manufacture. It wont move ideling in reverse. gotta rev it just a slight bit to move, but hang on, it will GOOOOO. My truck is making good power for a 6.5. but i think with a bit more tuning, it will make more power, and get better fuel economy while doing so. That is what i'm after. I'm not driving it much cause its so cold out now. just wheni'm pulling something, or longer drives. Its only 2 miles to work for me, so that s horrible on a diesel in winter. Thats why i kep my gas plow truck for for my winter daily driver. plus, the gasser heats up MUCH faster. Diesel will put out better heat, but takes longer.

[torque454]

GM-8 is actually 96+ im pretty sure, mine hasa GM-8 and its the factory turbo.

[JD_countryboy]

Thanks Guys.

[DieselFreak]

GM-8 is actually 96+ im pretty sure, mine hasa GM-8 and its the factory turbo.

Hey Torque,

How can I tell which turbo I have? Truck is a '97, so according to you, it should be a GM-8, right?

Thx

[JD_countryboy]

There is a small tag riveted to the compressor side of the turbo. Gives serial number, & model of turbo.

[DieselFreak]

Thanks, JD :)

[backcountryburban]

If you have the cold air intake, 80hp chip, 3" downpipe,4" exhaust, full guages,marine injectors and full cooling upgrade, in other words most of Walt's suggested goodies:
What is the best step by step testing and observation procedure to make sure your turbo and all related hardware is running at 100% operational correct capacity?
What should we be seeing in terms of PSI numbers and at what specific rpms.
This would greatly help me once and for all.
I ask this because I think my turbo is not running 100%, it just seems very slow to spool up and not very responsive. From idle upwards it seems delayed in showing boost on the quage.
Or maybe I am just expecting to much from these stock turbo's.
After all I do realize we are not building racing cars, but it would be nice to know once and for all that my turbo is as good as it is going to get.The truck Hauls but at higher speeds and rpms, but just seems to be lacking low end take off or punch off the line.
Cheers!

[DieselFreak]

I have the 80 hp chip, 3" downpipe, 4" exhaust, SSD intake, full gauges. I get around 15 PSI when hauling approximately 7500 lbs. Turbo starts spooling up immediately - just off idle. Hauls great ! :-)
Update:
Just went mudding around today, and boost peaks are now @ 18 PSI, dropping to 15 and stays there, when I _REALLY_ put my foot into it. Turbo sounds better than ever now, when I release throttle at high boost pressures, it sounds exactly as if I had installed a blow-off value ;-)) niiiiiice

[Oldsmoke]

Boost comes up almost instantly and will hold 14psi as long as I keep my foot down.

[backcountryburban]

With the vehicle in park or neutral, I start to increase the rpms from idle you can definately hear the turbo start to build it's pressure. While watching the boost guage the needle confirms what I am hearing from the turbo and engine. The question is what psi numbers should I be witnessing on the quage and at what corresponding rpm? ie 1000 rpm=_____ psi, 2000 rpm=____ psi etc? I understand everyones guages will read somewhat differently, but I just want to know I am in the ballpark!

Under full throttle while driving the boost guage climbs quite high but fluctuates and does not stay at a constant pressure. Is this normal?

Has anyone ever found a blowoff valve for the GM turbos? If so, is there any mechanical benefit, or is it really just for a cool effect?:o

[Oldsmoke]

For boost to hold steady you need a constant load on the motor. For instance if you are under full throttle but then reach the rev limit boost will drop off. You might not reach as high a boost level while accelerating downhill as you will accelerating uphill. It is a function of the load or power demand on your motor and the resulting throttle application. Hook onto a good heavy trailer and get on an uphill pull or into a headwind. You boost should stay high and steady anywhere over 10psi.

[DieselFreak]

Has anyone ever found a blowoff valve for the GM turbos? If so, is there any mechanical benefit, or is it really just for a cool effect?:o

I never found one yet, thought I was in the market for one, but now my turbo sounds as if I already had one installed. :-)
Supposedly the benefit should be faster depressurerizing allowing turbo to spool up again faster. I'm not a mechanic or anything, so maybe someone else can give the exact explanation?

[962500]

If I had 18:1 Pistons, could i up the boost pressure higher then 15 psi?

[backcountryburban]

I will continue to do some more tests and get some actual recorded data.
Thank You Old Smoke!:)

As for the blow off valve, I guess mine is quite loud as it is now, I can hear it very well in the cab with all windows closed, so it must be loud outside! I will get someone else to drive the truck by me and let off the pedal to hear how loud it is for bystanders.

[backcountryburban]

Is the GM-8 a true direct bolt onto a 95 with no extra mods?
Will it make a huge improvement, or am I just wastin my time and money??

I am quite sure I only have the GM-3. If I am unable to read or locate the small ID tag, can the Vin confirm the type of turbo presently in the truck??
Cheers!

[Chevylover]

You should have a GM-4 due to your truck is a 1995 model.

-93 = GM-3
94 + 95 = GM-4
96-= GM-8

Just have a short look at SS Diesel Supply site !

Cu,
Sven

[backcountryburban]

Thanks Sven!

[backcountryburban]

Correct it is a GM-4.
Can I still mount a Gm-8 directly, and will there be any advantages?
The SS site clearly states that the 8 is for 96 and up.
Has anyone tried to mount the 8 to a truck that had a GM -4?

[grancito]

With the vehicle in park or neutral, I start to increase the rpms from idle you can definately hear the turbo start to build it's pressure. While watching the boost guage the needle confirms what I am hearing from the turbo and engine. The question is what psi numbers should I be witnessing on the quage and at what corresponding rpm? ie 1000 rpm=_____ psi, 2000 rpm=____ psi etc? I understand everyones guages will read somewhat differently, but I just want to know I am in the ballpark!

Under full throttle while driving the boost guage climbs quite high but fluctuates and does not stay at a constant pressure. Is this normal?

Has anyone ever found a blowoff valve for the GM turbos? If so, is there any mechanical benefit, or is it really just for a cool effect?:o

Does your boost pressure drop at high revs when it fluctuates? If so, you have a rocker problem, mine does that at 2500 rpm and has worn push rods and rockers. The new ones have just arrived for cylinders 5 and 7, the usual ones to fail, will put them in, in the the next few days.

[JD_countryboy]

I asked two different sellers on direct bolt on fit, GM-3, 8, are direct bolt replacements. One listing on ebay that saw did list that GM-4, and 8 would also direct fit, but i never inquired anywhere else about that. But as for core credit, you may get 1/2 or less back if you return a different model than you buy.

[backcountryburban]

I have to hit the highway again tomorrow and will pay close attention to my readings ie boost pressures, rpms and most importantly fluctuations of the needle.
I will post what I observe.

After that I hopefully will get some further feedback from all.

[backcountryburban]

Has anyone replace a GM 4 with a GM-8???
What happened, good or bad?

[DieselFreak]

Has anyone ever found a blowoff valve for the GM turbos? If so, is there any mechanical benefit, or is it really just for a cool effect?:o

Blow-Off Valves here :
http://www.sportcompactonly.com/Blow-Off-Valves/Forced-Induction/Performance/performance-parts_c-52.htm

(hope it's ok to post the link, Garth :o )

[backcountryburban]

While driving in 4th gear on highway at 110km, boost reading was 4-5psi.
After driving away from a stop sign I nailed the pedal to the floor, the boost spiked to 17psi on the guage, but dropped off almost right away once the truck took off.
Is this normal, or should the boost not stay up at a higher reading as long as my foot is to the floor?
I get the feeling that I am loosing boost pressure way too early.
Does this confirm I do have a problem with my vacumn pressure?
Possibly at the pump itself or the boost selenoid.
I will take more reading again and run the diagnostic tree test I posted already.
PLEAESE ANYONE HELP ME!

[Oldsmoke]

Doesn't sound right! At 17psi you are almost getting excessive boost. Does it drop back to about 14 or 15 and then hold there as long as your foot is down? It could be you are initially overboosted then the ECM is cutting you back to what it is programmed for.

[torque454]

Doesn't sound right! At 17psi you are almost getting excessive boost. Does it drop back to about 14 or 15 and then hold there as long as your foot is down? It could be you are initially overboosted then the ECM is cutting you back to what it is programmed for.

He's got the 80hp ECM. I too initally thought he had too much boost, but then i noted hes got the 80hp ECM, in his signature. 17 might be about right in that case.

[grancito]

I just got the burb going today with new push rods and rockers on cylinders 6 and 8 and reconnected the vacuum wastegate system and getting the same problem, good boost till 2500 rpm then drops low. Still a pulse in the intake so it must be lifter problems that caused the ware on those parts.

[torque454]

That bites, grant. Time for new lifters?

[Sasquatch]

Sounds like a good time to replace timing parts too (gears, chain, cam, and lifters since you will be that far in. Save an extra trip into the motor. Didn’t you have similar problems about a year ago?

[grancito]

Don't have to go in far to change the lifters, they are accessable once the rocker cover is off, but the intake manifold and turbo needs to come off, not to mention a heap off other small parts. Need someone to describe what the lifter removal tool looks like, will have to make one. Took 3 hrs to remove the bits to change the rockers and all day to put it back together.

[Oldsmoke]

Is there a simple test for a worn valvetrain or do you just get under the valve covers and try to measure how much the valves are moving? I can see how this could cause all kinds of performance problems.

[grancito]

I'm getting a clack sound that is from the bad lifters, otherwise you need to remove the rocker cover and turn the engine over to see the amount of valve movement and check for loose rocker movement when the valve is shut.

[backcountryburban]

Are you telling us that your spiking to 18psi and if you let off a little, your boost still only drops to 15 or so and stays at this level without dropping below until you let off your foot completely? If so, I mus have some kind of a problem. Especially since we have simiar set ups.

[grancito]

Are you telling us that your spiking to 18psi and if you let off a little, your boost still only drops to 15 or so and stays at this level without dropping below until you let off your foot completely? If so, I mus have some kind of a problem. Especially since we have simiar set ups.

Are you replying to me? I didn't see those pressures posted.

[DieselFreak]

Are you telling us that your spiking to 18psi and if you let off a little, your boost still only drops to 15 or so and stays at this level without dropping below until you let off your foot completely? If so, I mus have some kind of a problem. Especially since we have simiar set ups.

If you're replying to me, then yes and no - when hauling a load and foot on the floor, peaking @ 18 (the highest I've noticed), with foot still on the floor in drops to around 15. When letting off a little, it drops even further.

When empty and foot on the floor, it very quickly drops to some 10-14 psi and doesn't peak quite as high.

[Garth J]

I think you better change the boost sensor on top of the intake those pressures are way too high...Garth