BOOOM fire in my exhaust

hgallegos915 · Post by **hgallegos915** » February 22nd, 2005, 2:03 am

hmm ok this is strange..in other cars that I had the kat removed.. this never happened...on my mx while getting near to redline from 1st to second..then shifting... BANG i see this HUGE wite flash in my rear view mirror... i figured its normal because of the high rpms? then again on another test run BOOOOOM HUGE ball of fire... wth is this normal when your car has no kat? ugh im starting to hate my mx3.. altough one step closer to a klze or klde. can it be bad timing?

IanL · Post by **IanL** » February 22nd, 2005, 3:14 am

You have described "backfiring". I think it's unburnt fuel igniting because of the hot exhaust, when it cames into contact with oxygen at the end of the pipe. You can't do anything about the heat of the exhaust, so you need to wonder why the unburnt fuel is in the exhaust gas.

It may be unavoidable with your setup - maybe a pulse of unburnt fuel always happens with gearchanges at redline, but the cat helps to cool things down at the rear.

Try changing 500 rpm before redline - apart from 1st to 2nd, you will get better acceleration anyway.

drftking · Post by **drftking** » February 22nd, 2005, 3:16 am

its because of you dont have a cat. My friends cobra is the same way. when he was running no cat he would bet flames to shoot out when shifting up to 3rd gear.

RaverChankoMX3 · Post by **RaverChankoMX3** » February 22nd, 2005, 8:59 am

First of all, shooting fireballs is cool. Secondly, it is because you removed your cat and are shifting hard. If you shift normally (yea, i have that problem too, taking classes) you won't have that *problem*.

jschrauwen · Post by **jschrauwen** » February 22nd, 2005, 9:17 am

You must be aware that although you may be impressed by this fireball show, there are probably ramifications or consequences of this. As with your unsuccessfull bid with the law with your lighting you may also draw unwanted attention to yourself with this fascination. I seem to remember years ago when friends of mine would run open headers all the way back and they too would get this incredible backfire. Imagine the sound and bang generated by your exhaust. That's the part your hearing leaving the end of the exhaust. This mini-explosion in your exhaust is also going to travel in as many directions as possible - one being back up your exhaust to the manifold and exhaust valves. I believe that if left in this manner you run the strong likelihood of doing serious damage to your exhaust valves. You've already had a negative effect in your lighting situation, hate to see you experience another judicial run-in or even worse - cooked exhaust valves. Remember our cars or for that matter all cars require a certain amount of backpressure. When a "freeflow sytem" is installed, it was never intended to remove the cat. You may be unknowingly robbing your car of potential power. Don't want to rain on your parade BUT, you may want to reconsider. IMHO.

93SOHC · Post by **93SOHC** » February 22nd, 2005, 12:33 pm

so, say you instead of putting the cat back on put some kind of resonator in its place, that should somewhat equal out the back pressure right? (its been 5 years since I took my test for exhaust and emmisions for ASE) Since Florida has no smog laws, i'm going to remove my cat when I do my BP swap down there in about 4 months. But with a shiny new bp, I don't want to harm it. Maybe a highflow cat would work better than just throwin a resonator on there

Neil · Post by **Neil** » February 22nd, 2005, 12:43 pm

I just bought a High Flow Cat for when i do my ZE/Exhaust late June this year. I figured having the cat was just as easy as not having one, and i want the car to run good so even though i had a few people telling me to go without, i went with it anyway.

jschrauwen · Post by **jschrauwen** » February 22nd, 2005, 3:52 pm

Didlin wrote:I just bought a High Flow Cat for when i do my ZE/Exhaust late June this year. I figured having the cat was just as easy as not having one, and i want the car to run good so even though i had a few people telling me to go without, i went with it anyway.

Smart move.

mazdubber · Post by **mazdubber** » February 22nd, 2005, 5:11 pm

I'm having flanges put on my cat so I can remove it and put in a test pipe easily.

snellgrove · Post by **snellgrove** » February 22nd, 2005, 5:41 pm

yeah, having no cat will result in flames.

as far as im aware.. when you come off the throttle quickly (for a gear change) the lack of air makes the engine run rich, the sensors in the exhaust detect this, and the ECU responds by putting in less fuel to make it run correctly again, but its got a bit of a delay on it.. so theres a small amount of time where you've effectively pumped a load of fuel down the exhaust..

the Cat is there to burn this safely away, but seeing as you dont have one... you get to witness the wonderful effects

I wouldn't worry about this, i'd positively enjoy it..

now can anyone tell me why, if I rev my car in neutral from idle speed, to say 5k... its perfectly smooth revving, they fly up and down back to idle..... but on the way down, you hear lots of miniture backfires in the exhaust..

I do have a cat, (as far as im aware! only got the car last week) I do like the sound of it, but I dunno if my car is running 100.00% correctly!

-there is a tiny air-leak on the air-intake piping though...(well, its split.. actually!

) it has to be said.. bit of tape wrapped round it.. lol

jschrauwen · Post by **jschrauwen** » February 22nd, 2005, 6:35 pm

snellgrove wrote: but on the way down, you hear lots of miniture backfires in the exhaust..
I dunno if my car is running 100.00% correctly!
-there is a tiny air-leak on the air-intake piping though...(well, its split.. actually! ) it has to be said.. bit of tape wrapped round it.. lol

Especially when you take your rpm's up to 5k there's going to be engine flex/twist. That twist will play upon the intake tube creating a vaccum leak. But I don't think that is related to your backfires. Again, that's an exhaust issue. I suspect that you have a compromised exhaust system - leak - somewhere. Confirm the integrity, including cat, resonator and muffler.

hgallegos915 · Post by **hgallegos915** » February 23rd, 2005, 1:58 am

I did this as a temporary splution to my slow car problem... yes yes it does seem a bit faster but it will still struggle the hell out of itself after 80 mph... ugh!! im starting to hate my mx3...altough about the burn valves... hehe would be an EXELLENT excuse to get a klde...but still i hate this..cant go over 80 arghhhhh well now its around 83.. the ecu has no codes...im starting to think my ecu is bad... :/

RaverChankoMX3 · Post by **RaverChankoMX3** » February 23rd, 2005, 11:59 am

jschrauwen wrote:You must be aware that although you may be impressed by this fireball show, there are probably ramifications or consequences of this. As with your unsuccessfull bid with the law with your lighting you may also draw unwanted attention to yourself with this fascination. I seem to remember years ago when friends of mine would run open headers all the way back and they too would get this incredible backfire. Imagine the sound and bang generated by your exhaust. That's the part your hearing leaving the end of the exhaust. This mini-explosion in your exhaust is also going to travel in as many directions as possible - one being back up your exhaust to the manifold and exhaust valves. I believe that if left in this manner you run the strong likelihood of doing serious damage to your exhaust valves. You've already had a negative effect in your lighting situation, hate to see you experience another judicial run-in or even worse - cooked exhaust valves. Remember our cars or for that matter all cars require a certain amount of backpressure. When a "freeflow sytem" is installed, it was never intended to remove the cat. You may be unknowingly robbing your car of potential power. Don't want to rain on your parade BUT, you may want to reconsider. IMHO.

Sorry to rain on your parade but there are plenty of professional racecars like JGTC, Rally, LeMans that shoot flames all day long. Secondly, YOU DON'T NEED BACKPRESSURE!

Backpressure is restriction. Restriction is a BAD THING. Exhaust velocity flow is a GOOD THING. If you'd like to read more about The Back Pressure Myth: http://www.club240.com/forums/showthrea ... eadid=1406

Enjoi!

Mnemonic · Post by **Mnemonic** » February 23rd, 2005, 12:02 pm

well not all backpressure is bad

snellgrove · Post by **snellgrove** » February 23rd, 2005, 3:52 pm

afaik, its only turbocharged cars that really hate backpressure.. I believe normally aspirated cars don't mind so much, and in some cases actually run better with a certain amount of it present.. this of course varies from model of car, to model of car.