I've searched, but can't find an answer to this yet:
I'm reading about on here about detonation, but I'd like to know what that means and what the symptoms would be. How would I know there's detonation occurring?

My car makes a "pop" when shifting at high rpms (above 5k), but I figured this was was a normal pressure variance in the exhaust. I'm not hearing a "bang" like a gunshot, more like a single "pop" from the exhaust, not unlike what a Harley does every .5 seconds. It doesn't sound excessively loud from in the cab; perhaps it does if you're behind me. Please tell me this is normal.

Appreciate it. (Please don't flame me; its an innocent question.)

My car:
'93 Rx7 base, Pettit ported 13b, Pettit blueprinted ceramic coated turbos, Pettit downpipe + center pipe + Greddy exhaust (no cats), Pettit intake, Pettit pulley upgrade, stock ECU.

 

detonation is when gas inside the combustion chamber "ignites" out of timing. It has been described as sounding like marbles and in a rotary the main symptom is a blown engine Seriously rotaries can't handle detonation that's why tuning is so crucial with us.

During severe detonation you will feel instant power loss (blown engine). In mild cases during WOT you would hear "like marbles" banging around the engine. It's not overly loud but its obvious enough sound that it should not be present. If ignored it WILL be followed by loss of power (again blown engine)

It's normal on a modified rotary to hear a pop or pops and even shoot flames (cars that don't have cats) between shifts. What is going on is that during WOT runs and in between shifts, UNBURNT fuel passes through your engine and gets ignited in your exhaust path. It's perfectly safe and normal.

FYI- Rotaries run rich to prevent detonation, on top of that exhaust temperatures on a rotary are much higher than its piston counter part. Given that combination it makes perfect sense that the fuel ignites in your exhaust...

 

You'll also hear it referred to as pre-ignition. The air/fuel mixture pre-ignites out of timing, before TDC on the compression phase. Because of the position of the eccentric at that point, the energy produced has no where to go. The weakest spot is usually apex seals but I've seen pictures of dented rotor faces.

 

Detonation and pre-ignition are two different things, Jim.

-J

 

Good reads....

http://www.factorypipe.com/t_deto.php

http://en.wikipedia.org/wiki/Water_injection_(engines)

 

I've always regarded them as synonomous. I'm not proud, well OK maybe just a little embarassed.....what's the difference?
EDIT: just read the link above.

 

On a stock car the catalytic converter, air pump, ACV, and ISC valve all work together to eliminate backfiring as the throttle closes.