Turbo temp question

[cruiser_guy]

Today coming back from El Salvador the hose on the intake manifold popped off (it's under pressure from the turbo all the time) while climbing a hill. We instantly noticed it (and the loss of power) and I knew what the problem was (I had no boost reading at that point). I had glanced at the pyro just before the hose popped and we were running about 1200 F. As soon as the hose popped my wife noticed the pyrometer spike to over 1400 F.

Why are we concerned about keeping the pyro down to under 1200 F with the turbo if it easily spikes WAY beyond that without the pressure from the turbo?

I'm not planning to change and run hotter but I am curious.

 

[The Dude]

most metel starts to melt around 1250 I believe. I have spiked my duramax around 1500 before...not good but for a few seconds, it prob won't hurt.

plus things like oil start to break down faster, coolant works harder etc...

 

[Waggoner5]

The reason it spiked to 1400 without the boost pressure is that the injection pump is set up to deliver the correct amount of fuel when under boost conditions, so at 0 boost the pump is putting a large amount of fuel into the combustion chamber to compensate for the extra air. That mixture will most definately cause high EGT. Doesn't the AXT kit come with a boost compensation valve? With it, when under boost, the valve will cause the injection pump put out more volume/pressure acording to boost levels. On my HJ61, which has a 12HT in it, I wanted a little more power after going with 35s. I added gauges first for a baseline and after turning the boost up from 7 to 10.5 psi max., the EGTs actually went down. I had intentions of also adjusting the boost comp valve, but it seems that someone had already changed the pump timing adding more total fuel and so I left the BCV alone. It smokes a little less and max EGT is now around 1100, at high altitude running about 2700 rpms. Diesels will continue to make power the more air and more fuel you add right up until it melts something. A long living engine is one that maxs out EGTs at 1200 pre turbo. A short spike of 1400 should not have hurt anything, but I completely understand the OH sh*t factor.
Gary

 

[cruiser_guy]

The reason it spiked to 1400 without the boost pressure is that the injection pump is set up to deliver the correct amount of fuel when under boost conditions, so at 0 boost the pump is putting a large amount of fuel into the combustion chamber to compensate for the extra air. That mixture will most definately cause high EGT. Doesn't the AXT kit come with a boost compensation valve?
Gary

Negative on the boost compensation valve. The AXT kit doesn't come with anything like that and I haven't turned up the fuel from the naturally aspirated setting. I think the wire is still on the adjustment screw. I know lots of folks turn their fuel up but if you've dropped a pre-cup as I have you tend to be cautious.

I'm told that naturally aspirated, the 3B regularly reaches 1400 F and more. I don't know since I didn't have a pyrometer when I was still naturally aspirated. All I can say is it spiked fast cause I backed out right away.

fwiw, my pyrometer is located between the head and the turbo (tapped into the manifold).

 

[gifu]

I added gauges first for a baseline and after turning the boost up from 7 to 10.5 psi max., the EGTs actually went down.

Hey Gary,

guick question: so... your 12HT maxes it's boost at 10.5PSI? Do DI motors use less boost then IDI? I (finally) put a boost gauge on my Onan, and was surprised it was hitting 14.5PSI. It's an IDI 3.4L straight six.

My other question... did you turn the boost up by adjusting the wastegate spring somehow? I don't plan on turning my boost up, it seems quite high already, but I'm just curious how for helping a friend with his 12HT.

Also, with your setup (HJ61, SOA, 35's, auto, 4.10's?), what kind of mileage do you eek out of it?

thanks,

~Brian