how much boost is too much

[Jim P]

I was playing with my homemade wastegate controler tonight. I ran the nut in a little farther to tighten the spring. I took it for a drive and when I pound it the boost will jump to 20psi. Will it hurt it to leave it like this. I don't have an intercooler but I do have the 18:1 compression. I got to get a pyrometer.

I sure hate to back it off. It runs so nice. :D

Jim P.

[pannhead]

due to physics that others can explain better than i, there is a point where additional boost without extra fuel is worthless....just my opinion, i think 20 psi is too much....although i can see the temptation :D

[Jim P]

I know that I need to turn up the fuel. I want to try a different calibration resistor or a potentiometer but my pmd is still mounted to the pump and I can't get to it without taking off the intake. I know my truck has a #3 resistor now. I probably shouldn't mess with fuel until I get a pyrometer either.

Jim P.

[rjschoolcraft]

I agree with pannhead to a point.

It is true that without adding fuel, you're not getting all of the combustion that you could; however, it seems that more boost pressure is good for these engines simply because it helps them breathe better. The intake ports and combustion chambers don't seem to be designed for efficient flow and higher boost pressure helps overcome the inefficiencies.

Kennedy runs 20 psi + on his 18:1 engine. I think the Project Truck runs similar numbers IIRC. Keep in mind that the higher the boost pressure, the hotter the intake temperature...without the charge air cooler. I would highly recommend installing one. It has helped my truck a bunch.

I installed the TD Max chip before installing the intercooler. The increased boost (12-13 psi max) helped the truck in a couple of areas: 1) more power (fuel was added too), 2) lower EGT because of more efficient scavenging of the combustion chamber. It is really cool to get more power with lower EGT...really makes you wonder why they didn't do that from the factory. :rolleyes:

With your truck at 18:1, you should have no mechanical issues with 20 psi. Get a set of gauges so you can see what's going on, though.

[patrick m.]

i believe the physical design of the turbo is the limiting factor. the exhaust pressure pre-turbo becomes greater than the air charge to be beneficial.
since you have a 95 model, i suppose you have a GM-4 turbo, which is what i have. I feel like 12 psi boost is the max for this configuration.
As far as exhaust temps, in my case, more boost = lower pyro readings (up to 12 psi more than that does not help or hurt). low boost= high pyro readings, and no boost= pyro climbs like a rocket

for more boost, we need a better turbo. from what i have read here kennedy has the answer to this dilema. :D

[charliepeterson]

With no Intercooler I wouldn't spike past low teens and hold no more than ten. After the Intercooler swap I would hold low teens and spike high teens.
The only way to add more fuel is to get into the computer. The "chip" in the FSD is not a contributing factor in the fuel curve.
A stock OBD I computer program only gives 63mm of fuel at WOT. You can get HO "chips" for the computer to increase the fuel to 80mm at WOT. Now add more air and hold on to the wheel!!!
Some of these new chips also help the Transmission handle this extra power much better than the stock programming.