Need a lil help. Sbf 302 twin turbo on e85 blowthru carburetor. Camshaft f cam. My car backfires on deceleration when ya hit hard. It never did this until cam swap. Is there something I'm doing wrong? I have a bov to atmosphere. Just need some schooling

 

My car does an unwanted explosion if I hard decel. But mines stick so I have a clutch and I don’t allow that to happen. What you just said sounds pretty normal to me.

 

There are a couple things that will cause it:

Exhaust leak will cause it, oxygen mixes with unburnt fuel in the hot exhaust and allows it to ignite.

Not enough ignition timing on decel, the little bit of fuel and air that is slipping in will burn late and it is still burning when the exhaust valve opens. If you don't have vac advance hooked up that will often cause it. I am not sure how you are controlling your ignition system, post details if you want ideas on fixing it.

Less likely is the timing chain is off a tooth (cam install), but it would run bad.

 

Timing locked 34 degrees. Car runs great cruising normal driving. The pop comes in when I run her hard and let off pedal. Could a bov cause it?

 

I had one that would do this. Timing was locked. Thought it was 28. Used the wrong line on damper so it was really 18. Corrected it and it didnt do it again.

 

I'll bump the timing and see how it goes. Thanks for your time

 

Your blow-off valve (BOV) setup and carb tuning need a second look. Check if your BOV is releasing enough pressure on deceleration to prevent backfires. Also, double-check your carburetor tuning; the cam swap might require a richer mixture to compensate for the increased airflow. It sounds like a bit of fine-tuning is needed to get everything working smoothly together again.

 

My afr is looking good not showing lean if anything a lil rich. The bov not sure about I can't see if it's opening all the way.

 

Fuel vapor in the hotside will cause backfires on hard decel.

 

Just to add one more thing, your cam didn't swap the firing order at all did it? I had a cam do that and the store I purchased it from didnt say anything about it and it took a while to chase down, in the end I swapped 2 plug wires on the dizzy and it was good to go.