So I've seen all kind of different backfires from Rx7s. Everything from a little pop too a large fireball. Why is that? Does turbo or non-turbo make a difference? I know what causes our cars to backfire, just wondering why there are differences.

 

peripheral exhaust port rotaries don't burn all of the fuel, and it just gets tossed out of the exhaust.

 

Basicly it is just different amounts of unburnt fuel igniting in the exhaust, so the sound will be somewhat different every time.

 

Moderatly stock cars will shoot giant flame ***** if you take out the cat's and run a free flowing exhaust. My FB shoots bowling ball flames out the back. and 90 percent of the time it sounds like a t shirt cannon. thump. My T2 will shoot flames soon.

 

It has to do with port size, design and location.

 

besides the cat, there is an anti afterburn valve which directs smog pump air to the primary runners of the intake manifold during deceleration. If you remove the air pump and/or ACV it will no longer function and you may get a backfire. The FD's use their idle speed control valve for anti afterburn instead of the air pump/ACV.

Also problems with sensors can cause rich conditions on deceleration that cause backfire. Open vented blowoff valves on turbo cars can cause backfiring as well. That extra air gets measured by the airflow meter and the ECU injects extra fuel which then causes a backfire.

 

Is there anyway an N/A (stock port) wouldn't shoot ridiculous flames?

 

^ Yes. They don't shoot flames from the factory, do they? Make sure the air pump, ACV, main catalytic converter, and TPS are working correctly.

 

No I know that the cats need to be removed in order to backfire. But I was wondering if I keep all of the other emissions crap will it decrease the size?

 

Well I Idk what you could do for secound gens but I know when I had a stock ignition on my FB that it was like a machine gun every shift and on decell. steady flames. It was awesome, but caused way too much attention. I put on a secound gen leading coil and the waisted spark solved 99% of back fires. It will still do it if I let the secoundarys run for more than a few secounds and then decell. and every now and then it just does it. but rare. thats with no acv, no smog pump, 2.5" underaxle to strait through muffler. But secound gens already have a secound gen ignition. but I'd say if you upgraded your ignition to burn more completly it sould lessen the back fires.