Top End Noise, comdustion or mechinical?

[James & Son]

Top End Noise, combustion or mechanical?

I brought this over from the lub. thread. I am constantly listening to my engine since I want to hear anything different. Since I live in a wide range of temperatures I think it gives me one added advantage to determining what causes top end noise, combustion or mechanical.

Originally Posted by James & Son
I don't know how many miles you have on your car or when you changed the thermostat last or your timing belt. Two things effect the top end sound of your motor. A change in injection timing and how close to tdc the injection timing is at. The other is a thermostat that is running at 180F degrees instead of the 197F as measured at the head. A cold thermostat will put your 40 wt oil closer to a 50 wt.

Take your pick I bet when everything is to specifications it will sound normal. Are your cam and followers original. Whether they have been changed or not you should check the injection rocker adjust setting. This affects the injection timing as well. Mine was way to tight (unbelievably only 1/8 of a turn from bottoming).

I want to add one more thing about top end engine sound. I am pretty certain fuel temperature has a major effect. I notice that my engine runs much quieter when the temp. is above 0C and especially after 30 minute or more drives. The fuel temperature normalizes with the coolant temperature and the combustion at idle is such that it must be not only reduced but injection timing is moved away from top dead center and it becomes much more quiet. The fuel temperature sensor is an important contributor to the combustion noise at idle, and the injection quantity and timing is adjusted accordingly.

I guess I still have not come to a complete conclusion here. Anybody else want to add their opinions to see what the general consensus is.