Boost Pressure in M939A2?

Mos68x

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Seligman,AZ
Does anyone who has a boost gauge in their truck know what the peak boost pressure is? I need to know so that I can size the water/methanol injection nozzles properly.

I cannot drive my truck until I get the w/m injection system in it since I built a replacement intake manifold and got rid of the aftercooler. I want better control over my EGTs, and a cooler intake charge. Instead of having a controller that is sketchy I’ll be running mine off of a Teensy microcontroller (more powerful version of an arduino). I’ll run two water circuits for injection, 1 for pre-turbo injection for wet compression and it will be based on rpm and boost, and it will only be for replacing the aftercooler or an intercooler. The second circuit will be post-turbo, and it will be based only on exhaust gas temps. The whole purpose of this is to get better control over EGTs, not to gain any HP or Tq, but it would be nice.
 

FullSpecial

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Tacoma WA
I have a modest tune. 150ml delivery to 180ml. Cross math comes out to 285HP. Larger muffler, K&N air filter and a lot less piping.
I drive my gauges and see 32 pounds with foot buried in the floor.
 

Mos68x

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Seligman,AZ
I have a modest tune. 150ml delivery to 180ml. Cross math comes out to 285HP. Larger muffler, K&N air filter and a lot less piping.
I drive my gauges and see 32 pounds with foot buried in the floor.
Thanks! Any upgrades to the engine? Like new valve springs or head studs? Happen to know your EGTs when you run at 32# boost?
 

simp5782

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Thanks! Any upgrades to the engine? Like new valve springs or head studs? Happen to know your EGTs when you run at 32# boost?
We saw 26lbs on Profos camper all the way to California. It is intercooled though. Max of 1200 degrees no matter how big the hill. That was at around 50,000lbs
 

Mos68x

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We saw 26lbs on Profos camper all the way to California. It is intercooled though. Max of 1200 degrees no matter how big the hill. That was at around 50,000lbs
Thanks Wes! That is quite hot for EGTs, I’m hoping to keep mine maxed at 800-900, but we shall see what will happen. But at least with this info I can properly size my nozzles. It will still be a guessing game with nozzles to a degree since I’ll have two separate water circuits, but at least this will help with a total size.
 

Mos68x

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I just sent an email to Snow Performance with some info looking for a better idea for nozzle selection, right now I’m thinking of a single 100-175ml nozzle for pre-turbo, and then twin 100 nozzles post-turbo.
 

MAdams

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San Dimas, CA
I have my truck set at 26psi right now. I have had it as high at 36psi but it doesn't really make more power, just heat. Where is your air compressor going to pull its air from? You'll need to move it from the head, to before your 1st water injector.
 

simp5782

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Thanks Wes! That is quite hot for EGTs, I’m hoping to keep mine maxed at 800-900, but we shall see what will happen. But at least with this info I can properly size my nozzles. It will still be a guessing game with nozzles to a degree since I’ll have two separate water circuits, but at least this will help with a total size.
That is with a stock H1E turbo. An HX50 will do you alot better. Intercooler will as well. You do not need water injection. Bad things happen with that. 6CTA maxes out in the 1250 egt range.
 

Mos68x

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Seligman,AZ
I have my truck set at 26psi right now. I have had it as high at 36psi but it doesn't really make more power, just heat. Where is your air compressor going to pull its air from? You'll need to move it from the head, to before your 1st water injector.
Crap, I forgot about that! Thanks for reminding me
 

Lukes_deuce

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Long Island, NY
Max boost I see is 35psi. I have the fuel turned up high and she has a lot more pep. I run a 4in straight pipe and a TMG air filter. She will get hot, have to keep an eye on the EGTs. I can hit 1300F pretty easily. I like to keep it below 1200. I need an intercooler!
 

Lukes_deuce

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Long Island, NY
Thanks Wes! That is quite hot for EGTs, I’m hoping to keep mine maxed at 800-900, but we shall see what will happen. But at least with this info I can properly size my nozzles. It will still be a guessing game with nozzles to a degree since I’ll have two separate water circuits, but at least this will help with a total size.
You do know that these trucks stock will hit 1200 if you bury the throttle for any period of time? Im interested to see your results with W/M injection, but I highly doubt you will lowered the EGTs that much. Why not try running the truck the way it is? Ive always wanted to see some numbers, EGT mainly, with no aftercooler.
 

74M35A2

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Others have posted about 900F pre-turbo, stock, which makes sense. You had 1200F before and after turning up the fuel?
 

Lukes_deuce

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Others have posted about 900F pre-turbo, stock, which makes sense. You had 1200F before and after turning up the fuel?
My motor always ran stronger than other stock trucks I drove. Theres a tag on it from Ft. Carson, not sure what they did. All the safetys were still on the motor when I bought it. I was surprised when I installed the EGT gauge in. I could hit 1200F and more completely stock with a load. I turned it up and can hit 1200F easily now, loaded, empty, uphill, down hill etc. Just have to keep an eye on the gauge. She sure does move now!
 

Mos68x

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Seligman,AZ
Once I get my fuel delivery issue resolved I might try to see what my EGTs are, although I think I’ll most likely wait until after I get the water injection setup in place so that I don’t risk destroying this engine again. That way I can turn it on if it gets too hot
 

Jbulach

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I finally got my gauges installed on my stock, the way I got it from Uncle Sam 8.3.

I only had a chance for a short, empty test run up to about 50 mph. I’m seeing 24psi of boost, and about 1215F pre turbo EGT, kind of scary! Now I cant wait to load it up for a proper test, and see just how hot I’ve been running the past few years loaded to around 50k on the highway, and also see if I have my top end power loss problem solved.
 
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Jbulach

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Hauled a couple 12ton loads of stone today, max boost was right at 25psi.

Air temp was 80F, coolant temp 195, uphill, lugging 4th down to 1600rpm would spike EGT up to 1275-1300, just before transmission would downshift and bring EGT right back under control.
 

Floridianson

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Hauled a couple 12ton loads of stone today, max boost was right at 25psi.

Air temp was 80F, coolant temp 195, uphill, lugging 4th down to 1600rpm would spike EGT up to 1275-1300, just before transmission would downshift and bring EGT right back under control.
Myself if I am driving by the EGT gage I shift the automatic transmission myself before I let transmission do it. Same with a manual if you watching you temps then keep the RPM up higher than what you cruse at. If my temps don't run cool at close to the governor I turn down the fuel.
 

Jbulach

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Yep, just wanted to see the worst I could do. Now that I’ve got a gauge and my baseline, I might start tweaking on her knobs.
 
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