my car backfires!
 

Ok my car is 2003 US spec
Recently I installed Vortech S/C with Vortech recommaned spark plugs.
For exhaust, I am running Amuse Dual, Stock header/CAT.

Between fast shift at 9000rpm, my friend behind me, saw small flame INSIDE of the both of rear mufflers.
The flame is so small so that it burns inside of muffler and only can be seen at night.
He said it happends everytime I shift at 9000rpm.
It was during long hard driving on high speed.
From what I know, this can seriously damage my CAT right?

What could be the problem? S/C belt slipping?
I think it is too rich but I'm not getting any CEL or unusal things.
also I'm running min 93 octan.

btw, where the F.I. forum go?

if you do not have catalyst is normal.
When i change the complete exhaust line in my ex mazda Rx-7 when i acelerate to 8.000 rpm ever see a backfire

Excuse my broken English

I do have my stock catalyst on...
This is why it really worries me :(

You could be running a bit rich but you won't know this till you check it on a dyno or with an a/f gauge (wide band).

The Forced Induction forum got placed in the "Special Interest" section. Moving this now.

Technically, that's not a backfire. If fuel was burning in the intake manifold, it would be a backfire.

Sounds to me like a the packing in the muffler is getting superheated, maybe from just a bit excess fuel and burning.