930 engine rebuild start-up- hot engine-too hot?
 

I have a friend in New Mexico who builds 911 engines but this is his first turbo. He's not on this board yet but will be soon,until then I'm going to quote the email I just got from him and see what you guys think. I'll forward the answers you give to him and personally take full credit for all your great ideas (just kidding..)

"We just started the '86 turbo that we modified: Ted Robinson removed
0.035" from the heads and the cam was ground to 964 specifications by
Elgin's. I timed the cams as per the turbo shop manual, which I believe
was about 0.8 mm intake lift at overlap. The owner also removed the
ceramic from the catalytic converter and removed the air injection system.
After building oil pressure, and timing the engine, we ran for about 10
minutes at 2500 - 3000 RPM to insure good oiling to the camshafts and new
rocker arms. The engine compartment above the catalytic converter shell
got very, very hot, to the point where we feared the paint would burn on
the engine mount bar; the turbo was hot to the touch almost an hour later.
The ambient temperature was about 80 F.
I have little experience with 930's. My reasons for this apparent high
temperature are no air flow over the forward oil cooler, and no insulation
benefit from the ceramic in the catalytic converter. I can measure the
temperatures; can you give me some guidance regarding what I should expect
from one of these engines so modified?
I am also embarrassed to say the the owner disconnected the engine
without taking notes. The shop manual seems a poor guide to checking the
various connections, which I would like to do. Is there another reference
of merit?"

My experience with these motors is that heat is always a factor, is the cat the main problem here? The oil cooler is going to be of little help at lower rpm and no air flow over the cooler even though there is little air flow to that cooler anyway. My suggestion is to dump the cat if possible and go to a B&B type exhaust or put an insulated cat back on. What do you guys think. Thanks

Bruce Herrmann

You don't mention the oil temperature.
The first modification made to a 930 engine should be the exhaust. Without a free flowing exhaust no other mod will work. A euro unit is a less expensive alternative to the sky-high SS systems, if this is an issue.

As you know, many things can cause extreme heat. Exhaust restriction, incorrect timing, detonation, lean mixtures, cooling system maladies, etc.

I can think of a couple of reasons why a freshly rebuilt engine will run hot.
1. The engine is still tight. The friction losses are high in a fresh engine. Give it more time to break in.
2.The mixture is off. I rebuilt my 930 with higher compression and 964 cams and it was running lean with its original setting. The mixture had to be fattened up.
How hot is too hot? You gave no real numbers, only indicators of a hot running engine. It may not be running as hot as you think. I think it's a misconception that street turbos run hot in general. They should run as hot (or even cooler with lower compression)as a normally asperated engine. The only time an additional heat load is imposed on the engine is under boost. A street engine is under boost very short periods of time.

My 89 always generates a lot of heat. The rear bumper gets warm enough to make the kids jump back when they touch it, no burns just hot.

The heat on engine shroud over the cat causes it to rust out, it also hardends and cracks the rubber shroud seal. If the shroud and seal are shot much of your cooling air is being sucked right past the cat and muffler.

The housing on a turbo is thick cast iron, it will take a long time to disipate the heat thats generated, couple hours after shutting down it can still be pretty hot.

I got rid of the cat and went to a B&B it did help cool things down a bit.

Todd

For a starter, his valve timing is retarded for 964 cams, as the value in BA 2nd ed. p. 157 is 1.16 to 1.36 mm.

Without numbers to work with, who knows whether there is an overheating problem or not!
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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 07-20-2001).]