Backfire

[d_dan]

so guys....

we all know what back fire is,

but how actually is it caused?

I know what help make it happen?
eg. decat and intake and exhaust mods so im thinking

is it the car running rich and when going hard the heat of the exhaust causing it to ignite?

i know my car usually only backfires coming into mivec

[Kace]

so guys....

we all know what back fire is,

but how actually is it caused?

I know what help make it happen?
eg. decat and intake and exhaust mods so im thinking

is it the car running rich and when going hard the heat of the exhaust causing it to ignite?

i know my car usually only backfires coming into mivec

Hey that sounds kind of cool - let us know when you work out how it is caused

[optical illusion]

My car usually backfires coz it's f**ked

[Dragonheart]

Never had this happen me, but Drew has an intruder and she used backfire all the time cause the gaskets were gone on the exhaust, doubt its the same in the cars though, once the heat built up she'd let fly! That was sitting in idle, then he got it fixed cause the neighbours complained. Boooriiiiiing.......

[Bernard]

Have you noticed any black smoke Dan?

[Myfeckin FTO]

.............
is it the car running rich and when going hard the heat of the exhaust causing it to ignite?

i know my car usually only backfires coming into mivec

Backfire is caused by unburnt fuel in the exhaust (as you already know) so its possible that its running a bit rich. Has this happened recently since you added a mod or two (fuel pump, FRP, ECU etc??). Course it might just be the odd pop on the overrun (full throttle then back off suddenly) which is nothing to worry about - my Zed does it all the time and sounds really mean.

[d_dan]

@ bernard no none at all.

@ my feckin yea this is propper backfire from power not cos the cars fuc*ed.

its happening since i get a new filter for the HKS mushroom
dont know if she popping flames but defenitely banging!

really notice if i go hard in 2nd and let off for third

[steelroe]

Anything to do with the butterfly valve you installed in the exhaust.

[d_dan]

no its been backfiring fron then!

the butterfly is always open unless i close it myself!
must say though if ya set it right.
(closed about 40% when your taking off) you get a gain on power from the extra back pressure that ya loose from fitting the larger exhausts

[Myfeckin FTO]

no its been backfiring fron then!

the butterfly is always open unless i close it myself!
must say though if ya set it right.
(closed about 40% when your taking off) you get a gain on power from the extra back pressure that ya loose from fitting the larger exhausts

I think that the whole science of "flow characteristics of an exhaust" and "backpressure" get quite muddled on modified forums.

If you think you are getting more power from closing an exhaust butterfly then its possible the flow of your breathing mods aren't good. Backpressure will have little or no effect on the bhp of a NA engine. Exhaust gas flow will have a much greater effect - for example a very large diameter exhaust bore or a badly designed exhaust and/or ill fitting manifold to downpipe to Cat to centre section etc on an NA engine may cause the exhaust gas to cool too quickly before exiting and hamper performance - this should not be confused with backpressure.

What may also be happening is that with all the mods to free-up gas flow that you have moved your peak power and torque up the rev range and by reducing the flow of gas you are altering particularly the peak torque to lower down the rev range and it feels quicker in mid-range.

Its a tricky science - so passing it off as simply "backpressure" is quite misleading.

[d_dan]

its not excessive... dont actually thing theres any sort of problem with it!

i was putting it down to the decat etc.

[Myfeckin FTO]

its not excessive... dont actually thing theres any sort of problem with it!

i was putting it down to the decat etc.

Yip - Like I said earlier - its most likely just a freeflowing exhaust that pops and crackles on the overrun - same as my Zed. Where fuel would normally have been burnt up much earlier on the OE exhaust its now getting as far as the backbox and igniting on the freer flowing exhaust.
- Possibly combined with a slight bit of overfueling but still nothing to worry about.

[d_dan]

looking forward will there be any difference now later after i have the neo mapped!

pop more? maybe not at all

[Myfeckin FTO]

BTW - is that exhaust butterfly valve helping to reduce the sound much?

[d_dan]

i havnt got a chance to stand behind it and someone rev the car for me!

but i do notich while driving you can put the boot firmly to the floor and it sounds like any normal car plodding along!#


then release the valve and hell breaks loose.

also another thing i found is if you open it and close it once that it seems to change the airflow a bit and the sound of the car changes....
takes a bit of the rap off the sound

[mcgon1979]

Unlike turbo cars that backfire when you let off the gas (the unburnt fuel gets flushed through the hot exhaust and pops and bangs as it ignites) the MIVEC does the odd pop and bang coming into the mivec range. Happens to me too man. I can only assume its some unburnt fuel getting through when your wide open throttle and poppping in the exhaust. I am decatted also and never noticed before that.

[d_dan]

ahh sure... na its just somethign nice!
iv a friend with a 200bhp 1.6 and that will pop and bacnk and put out flames whenever he wants. but i dont really car would be cool but not pushed either ya know!

[Wildhound]

I have a decat and I get something like this when I shift between about 7/8000rpm.

I don't know if it's an actual backfire but it makes a pretty sweet, sharp noise that it never made with the cat in there. Sounds cool.

[CJ]

If you're planning on getting it mapped, I suggest the mapper uses a wide-band lambda to alter the AF ratio, it sounds like you're overfuelling quite a bit - NA cars shouldn't pop and bang often.

When I first got the RX7, it used to pop / bang / flame all the time on sudden deceleration. I had an Apexi Power FC installed and mapped (and at the same time installed filters, a straight thru mid pipe in lieu of the cat and a 3" exhuast) - pops and bangs only occured occasionaly afterwards. I subsequently had leaned out the fuel mix about a month later which pretty much stopped unburnt fuel ending up in the exhaust.

CJ

[d_dan]

just got the car back, he reduced the fuel in up high as it was running quite rich.

[Dragonheart]

Ah man I cant get mine to do this at all! Disgusted!