i did a search, but couldnt find the reason the greddy exhaust makes the popping sound when shifting or letting off the gas from high rpm...any ideas>

 

This is normal and other exhausts do this, In fact I like it.

https://www.rx8club.com/rx-8-discussion-3/popping-31011/

 

so its because the engine is running too rich/lean, and the stock muffler can hide it? thats pretty much the answer i found in that thread.
there was also a response that all high strung engines do it, but no answer as to why

 

it's called backfire

the stock muffler does a very good job muffling it :D

as a matter of fact, all rotaries do it, the Greddy exhaust just amplifies it more :D

 

oh, and if you do it hard enough, your car will shoot flames!!!

 

I believe it's related too reduced back flow, and of course, as others said above, reduced noise muffling.

 

I like the sound of it too. I imagain flames coming out of my muffler. just wondering how high you gotta rev to shoot flame? how can you see it? only with a camera or naked eye?I even like the rotary sound it makes around 3k rpm. just keep the car runing at that range you car hear the echo from the curb.

 

you pretty much have to run straight-pipe to get some fire-shooting action, the catalytic converter basically eliminates fire-shooting on this car :o

oh and yes you will see it when it happens, not from driver's seat, but from the rear view mirror, when cars behind you back off in fear of the flamethrowing tailpipe :D

 

When i had my bike, I used to coast in gear, turn the engine off, give it WOT and restart it, it was hard on the bike, but it made for a huge Ba-Boom and a 55 gal drum size mushroom cloud of bright orange/yellow flame, it seriously looked like my bike exploded. I would only do it every once in a while, but it was hella bad! lol

a backfire is the sound of unburnt fuel igniting/exploding in the exhaust system, lots of high-strung cars will do it, cause of large ammount of advanced timing and the tune on the engine causing some of the unburn fuel to enter the exhaust system, then ignite. Same with shooting flames out the tailpipe, its just combustable left overs from the motor finaly getting a chance to burn.

When you go HIGH rpm (in almost any motor) the A/F ratio get RICHER, meaning more fuel is present, some of that fuel isnt burnt in the combustion chamber, so it exits the motor and travels thru the exhaust system, most cars now have very good catalytic converters, so the fuel is 'removed' from the exhaust, somewhat eliminating the backfire. Though highflow cats and 'test-pipes' allow this fuel to make it out the exhaust system, and if the conditions are right, it can ignite, causing a loud pop and sometimes flames, anything from a pale blue flash, to an all out yellow/orange fire ball.

The reason it usualy happens when you go 'off/trailing throtle' at high rpm is due to the following :

At high RPM the motor is injecting more fuel that at any other point in the power band, so this extra fuel leaves the motor unburnt, this fuel is atomized (tiny, tiny droplets) in the exhaust gas, the fuel is already super heated and in a near vapor form (very combustable) so its begging to burn/explode, although, there is very little oxygen in exhaust gas, so it lacks all the material to combust. When you let off the gas, the motor acts like a pump, letting clear air/oxygen move thru the motor and into the exhaust, once this happens you now have almost everything you need to make fire (air and fuel) all your missing is the spark or other ignition device, sometimes the super heated nature of the exhaust gas is enough to cause 'spontaneous combustion' other times when you go back on throtle it will be enough to cause ignition, also things like hot spots in the exhaust system can cause ignition.

That was the way I always understood a back fire, Its nothing to be afraid of, unless its happening IN-FRONT of your motor, ie at your carb. inlet...then watch out. lol

I personaly love the faint pop that the stock motor makes when revving, and cant wait till i get a differnt exhaust on that will let that true pop/burble out.

If you want to hear crazy back fire, go to an F1 race (or similar high strung engines) and listen when they go off-throtle entering a corner, pa pop pa pa pa pop pa pop!

 

I can hear mine pop with stock exhaust only when i am reving the engine, and rpm's drop fast, but thats it the window is open and i really listen hard in neutral. From the outside, you can hear the pop much more, but once again, thats in neutral if reving.

 

The factory exhaust will actually shoot flames when it's hot enough. But it's nothing like when it's opened up. I personally find the popping to be intoxicating.

 

I noticed the same thing, and was wondering about it myself. Thanks for the explanations.

 

I've got a B&B Midpipe (no catalytic converter) with my stock muffler. It's considerably louder than stock, similar to adding a cat-back. It'll shoot pretty good flames (12-24 inches) if I rev the he11 out of it and keep backing in and out of the throttle, almost at redline.

This weekend, I had the car at BeaveRun and people were telling me that they were enjoying the show from behind me

 

when flames shoot out or when backfire occurs, is it bad for the muffler itself?

 

no not really, but be prepared to change mufflers frequently :D

 

I would say no, although it does depend on the make-up of the muffler. Most mufflers use non-flamable material as sound dampning inside a muffler, so it really doesnt make much differnce if its just hot exhaust gas or fire. Also keep in mind that the flames and are moving in a stream of super heated exhaust gas, so they dont 'burn' in one section, the move through pretty quick.

If your asking if it will hurt your (or any) muffler, forget about it, just enjoy it. :D

Ive been thinking about the whole exhaust setup. I think I am going to weld up my own straight pipe (no cat) in place of my cat, and keep the stock muffler add a resonator before the muffler and change the tips on the muffler.

This will give me a better look from the back end of the car, a better sound (from no cat) and the stock muffler with additional resonator will help tone the noise down, but ill still get a nice backfire! also could be done pretty cheap.