Cough and misfire and boost spikes

[cc-rider]

I've got a Kenne Bell boosted Camaro. And I have been fighting what I thought was boost spikes. When I'd do hard shifts, it would sometimes cough and then pull a ton of timing. I could literally hear the engine do something that sounded like a cough (for lack of a better term). On my logs, I would see a very very short but large boost spike that lasted a millisecond.

So I tried something odd. I had kept pulling timing in this area thinking that it was the culprit. I put back in the original timing curve that Kenne Bell had for their canned tune which was about 3-5 degrees higher in this area of my spark chart depending on the area. Took it out and beat the snot out of it. And I'll be damned...it fixed the problem. I couldn't believe it.

Any of the tuning experts know what this anomaly is? Was the fuel transient shot combined with too low of timing causing a misfire that belched back up into the manifold and registered the boost spike or something? Does the higher timing help the flame to get going and not cause the misfire?

[GHuggins]

There's been post about this in the past, but basically the misfire causes a couple of things - engine pause due to the non firing cylinder so I guess boost has a split second to "back up" and there's no heat going out during the exhaust stroke resulting in a lack of scavenging to help pull that air mix in during the next intake stroke. You'll always pretty much see these little quick boost spikes with misfires... You might even want to try adding another degree or two if it took 5 to clear It out...

[10_SS]

I've had "backfires" on engines with severely retarded timing under load or heavy transition (like when your messing with the distributor) it could be the same thing here just more sensitive.

[07GTS]

ive had a mis and due to the cam it reverbed back into the intake causing a spike in boost as well as increased IAT at the same event, it also coated my injector tips with unburnt crap fuel on the problem cylinders and they needed a clean, was found to be lean as i entered boost from failing pump

[cc-rider]

There's been post about this in the past, but basically the misfire causes a couple of things - engine pause due to the non firing cylinder so I guess boost has a split second to "back up" and there's no heat going out during the exhaust stroke resulting in a lack of scavenging to help pull that air mix in during the next intake stroke. You'll always pretty much see these little quick boost spikes with misfires... You might even want to try adding another degree or two if it took 5 to clear It out...

It's running about 17 degrees of timing on the big end now. So I'm a bit hesitant to add even more back. But I'm going to monitor my KR for a bit. So far, not getting much. So maybe I can add another degree in.