Too much boost for too long? (non-intercooled)

[Big Red Suburban]

Maybe someone can help me understand why boost can be too high or sustained for too long IF you constantly watch the EGT? On my recent trip I saw spikes up to 14 psi, and sustained 12 psi up the long hills. I never saw over 750F EGT. I was only towing about ~3000 lbs.

If I understand it correctly, an intercooler helps to keep the IAT down (more power) which in turn helps keep the EGT down. However, if the EGT never approaches the limit, it is not necessary? BTW, what is the limit on EGT? 900F-1000F?

I also got to thinking of where I installed my pyro probe, it is in the downpipe, however it is located after the bend which makes the pipe parallel to the ground (maybe 20" after turbo flange). I wonder how much cooler it is reading just because it is that far away from the turbo?

[rjschoolcraft]

Increased boost, even without an intercooler, helps to lower EGT. I saw the same gains you mentioned before installing the IC. However, sustained boost above 12 psi will generate high intake air temperatures that will cause the computer to pull fuel and reduce power. This lowers boost and usually causes EGT to climb. At least that's what I expereienced in June 2003 towing to California and back.

[Billman]

If I had to guess, I'd say that your Pyro location was not the best choice.

How much does EGT cool off from the turbo outlet to where you have it is a Huge question. I wouldn't even guess on that one.

Mine is PRE-TURBO in the L/S Exhaust Manifold. I can safely see 1100-1200*. Post-turbo can see 1000*.

I don't think you're seeing an accurate EGT reading. But your ECM is seeing accurate IAT's. Once they climb too high ~225*, It will pull back on the fuel and prevent itself from destructing.

[DennisG01]

Regarding where your EGT probe is and based on my experience with it closer to the turbo, I think your number is pretty accurate. I towed 6,000lbs with about 14psi sustained and temps got to about 875 on a long hill. I don't think the temp would change much in 20 inches.

[Big Red Suburban]

So once the IAT reaches roughly 225F, the ECM will pull fuel (reduce power) to ensure no engine damage occurs? Does the SES light only remain on during the high IAT event or does it remain set until restart?

Therefore, as long as your IAT stays below 225F and your EGT remain ok (which someone said was 1000F?), your boost can be as high as you want. Obviously, the more boost, the higher the IAT, so you would probably be limited by IAT temp (assuming a decent exhaust system). Thus the reason for an intercooler, to allow more boost with the IAT below 225F.

I'm starting to understand everything.