knock at operating temp.

[zachsgn]

Lately I have been getting knock (2 yellow lights on knock gauge) after the engine has reached operating temp at WOT. No knock at WOT when the engine is cool/cold. Any ideas why?

 

[NJTurbo]

What kind of fuel, how much boost.

 

[dsa87gn]

what are you considering "operating temp" ?

 

[zachsgn]

93 octane, 15 # boost,

I don't have a water temp. gauge but the car does not appear to be running hot. It runs great for the first 5 to 10 minutes then the knock problems start.

 

[NJTurbo]

I am not sure what DP you are running, make sure it is not hitting anywhere. Heat it expands, could be false knock. Also i would try to run a tank of decent fuel through it. What chip you got

 

[zachsgn]

Thrasher 92 chip with stock DP.

 

[NJTurbo]

I like a scanmaster, that is me. Little lights do nothing for me. Is this something that just started. A little bit of knock on pump gas is acceptable. A little bit.......make sure nothing is hitting the DP or the DP hitting the ac box. Make sure motor mounts are good as well, when hot.... things heat up and move around more, I had a bad motor mount and when I nailed it the DP was hitting the bottom of AC box giving me false knock

 

[bruce]

Originally posted by zachsgn
Lately I have been getting knock (2 yellow lights on knock gauge) after the engine has reached operating temp at WOT. No knock at WOT when the engine is cool/cold. Any ideas why?

Just as a FWIW:

In an ignition based engine, the combustion processes are well underway, BEFORE the spark plug ignites. Just the act of compressing the Air Fuel Mixture puts heat into it. So the spark actually just cascades, a reaction that's already started.

Raise the coolant temp., or the incoming air's temp., or the fuel's temp, and the combustion process is all the further along, BEFORE the spark occurs. So Detonation, and preignition start in.

While the coolant temp might read an AVERAGE of say 165dF, there's areas on the cylinder that can get over 500dF. The warmer the engine is, the easier it is for those temps to be reached.

Real long story made real short.