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Let's talk turbo... GM-x with homemade TM vs ATT setup

K

knkreb

The Bus Driver is here!
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So, finished fabricating the homemade turbo master on the 'burb. Thanks to all who created a thread for the DIY guys to home grow their own. Mine is kind of a hybrid between ideas... will post on that later....

So, got all the parts installed, and went to adjust. With boost gauge installed (through the driver's window for test purposes) I closed in on 11 or 12 psi, and then the SES light came on... okay... so backed it down a bit. Reset code... drew it down to about 9 psi... sustained about 9-10 psi, then de-fueled no SES light. I'm assuming it was IAT was way too high (90°F here)...

soooo... I backed it down to 8 psi. I can gun it all day long, no smoke, no defueling, up to 80+MPH.

Now for question one... for those of you running the ATT, and other varieties of turbos... what is the difference between running a lower boost pressure (reducing exhaust turbine restriction in a GM-x turbo) and higher boost with higher IAT's vs the ATT setup?

And for question two... if you go above the IAT temps allowed by stock computer, it just defuels with no SES light? No scanner or other goodies to chit chat with Mr. Microchips. It just defuels until key cycle? Wondering out loud about this and how the computer handles it? Will it return to normal fuel levels should the IAT's come back into a "normal" range?
 
Question 1:
From my understanding ATT can run 15-20 psi if you get enough fuel in your egine to get there but the IAT remains low because of the lower backpressure.

With GMX turbos the high backpressure with high boost can just cause a restriction because the engine is working to turn your turbo the turbo but doesn't produce enough air to make it beneficial. This hard work causes a high IAT and EGT which becomes limiting anyways because of the risk of melt down. (WMI and IC solves this to a degree)

Question 2: Just get a reflash and forget about it! I think you can make a boost fooler to get by w/o a defuel if a reflash is out of the picture. Not sure about defueling and not throwing a code though.
 
This is where I have a problem understanding this...backpressure... Ok.... IAT heat is generated by the inlet turbine or what? I understand heat is generated by compressing air, but if we are compressing air into the same volume (intake) and using the same CFM (lbs of air) into same displacement engine, then how is it different from turbo to turbo?

Help me understand these finer points.
 
No no, you have to read the 200 page replacement thread.

J/K, with a more efficient, larger turbine less heat is transferred from the turbine and housing to the compressor and housing. The more backpressure the more work the engine has to do and more heat is transferred to the housings.

If I were going to only drive empty and only travel up to 75mph then there wouldnt be much need for the ATT. If I tow, or drive loaded a lot, or want to make a 130mph run then the engine is way more happy with the ATT because it keeps IATs a little lower and less backpressure (which is opposition to the movement of the piston).

Also, dont confuse CFM and lbs of air, one is a volume flow and one a pressure, neither taking into account mass.
 
Buddy is attempting to say:

"Also, dont confuse CFM and lbs of air, one is a volume flow and one a pressure, neither taking into account mass."
Air expands like 47 times when heated. This is why the pressure in a hot tire rises.

So you can have 14 PSI of 500 degree F air or 14PSI of 200 Degree F air. You loose a % of engine power for every 10 degree rise in temperature on N/A engines for example. Suppose 300 additional degrees kills some power...

Yes the turbo run out of it's efficiency bounds can cheerfully provide 500 degree intake air. This is useful for burning the oil out of the inside of the tubes... :D

Exhaust "drive" pressure is an indication of the 'small' turbo being too small. Spools quick but chokes the engine at higher RPM and load due to high exhaust back pressure. High exhaust pressure also leaves more exhaust in the cylinder. Then the intake pressure has to over come this leftover exhaust air on the intake stroke.
 
Attempted to say huh, I just got tired of trying to explain it to everyone else, and you didnt hit on the reason you lose power for the temperature rise, because as temperature increases volume and pressure can increase, but mass decreases, less density, less oxygen.
 
I can spike 12-1300 on an accelerating uphill run with lots of throttle...that's unloaded. Doesn't stay there, but it's better to know when to back off.

Get an egt gauge if you plan to play with the loud pedal much.
 
Since I don't have a pyro, and I don't have a fixed boost gauge (I was testing through the window only) maybe ya'll can learn me somethin' here. ;)

Okay, boost and EGT Question:
Let's say we are burning dead on the money. We don't have any excessive boost, and we are not under burning poorly and smoking either. With a GM-x turbo... do your EGT's go down with more boost, OR do they stay the same, OR go up with more boost?

I was thinking that the EGT's go down with more air being introduced. Then I was thinking about the backpressure to run the turbo. True or not? Don't have gauges to prove either way. What has your experience been? And is your pyro pre or post turbo?

Running boost above and beyond what is needed to burn clean... it that going to rob extra power from the engine to
a) produce extra air not "needed" for complete combustion
b) reduce cylinder temperature and heat for the power stroke
c) just increases the load on the engine to compress all that extra air?

I'm still wrapping my brain around all these turbo concepts.
 
I think the answer is all of the above, its very dynamic. It is increasing load to boost more than you need, but its hard to tell what too much is, because even though you dont have smoke doesnt mean some of the fuel isnt burning. So once you hit the no smoke point I think you need like another psi of boost. I also do believe EGTs can go down by overboosting, but you have to be set up right with large exhaust, large air filter, and a decent timing curve to make it very high in boost and still hold true to that.
 
buddy said:
If I were going to only drive empty and only travel up to 75mph then there wouldnt be much need for the ATT.
Click to expand...

Buddy, I almost never disagree with you but my ATT is going to pay for itself in fuel savings alone. I don't tow as much as a lot of you guys but I plan on keeping my truck for quite a while.
 
Thats just my experience, didnt notice any mileage difference in my 45-65mph drives to work. On the intestate when I would go 75-80mph for long distances seemed to be a bit more economy. You have similar vehicle, doesnt run very high revs at all with 3.42 gears and tall tires, which you also have. It all depends how you have it set up though, and I assume since you have been keeping track of the mileage the turbo was the only change to the vehicle. For people with lower gearing that spin higher revs it might be a greater economy gain too if you cruise at higher RPMs.
 
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