backfiring

[Christos Adam]

Ok so after fixing the sparkplug issue I went for a test drive to see if the car can hold boost (previously it was crapping out at full boost). For that purpose I had (poor) Lucy at the passenger seat constantly looking at the stand alone's boost pressure.
The results were good showing that the car was boosting up nicely up to 17 psi (as it was tuned at the dyno).
What I didn't like though was that high up there at the point I was hitting the rev limiter (7500 rpm) there was a lot of backfire.
I lowered the rev limiter to more sane (for non built engine with 130K miles) levels ~6500 rpm but the backfire was stil there. Just to understand the "testing procedure", I was accelerating on 2nd gear on a high hill, the engine was hitting the rev limiter and after that there was a periodic backfire every second or so.

The car has a very short 3" exhaust and no cat so at this point I'm wondering if it is "normal" to backfire?

The interesting thing is that I never realized how annoying and destructive (to my attention) it can be...when I was watching other cars backfiring I always though that is "cool" (I guess be careful what to wish for).

Anyway I'll try to put my full length exhaust and see if it still does that.

[Christine Grice]

What mechanism is your car using for it's rev limiter? Fuel cut? ignition cut? a mixture of the 2?

If you are cutting ignition and there ends up being a bunch of extra fuel in the cylinders, that can result in some impressive backfires.

[Christos Adam]

Thank you Christine.
I found out that:
the ECU kills any boost increase that the ECU may be providing when you're within 300 rpm of the limit, and from that point upwards it retards ignition progressively. When you reach the limit it kills the fuel completely (but not the ignition)