Exhaust popping........

[swansea v6]

I have just helped a mate fit a sports exhaust to his mark 1 mx-5 and it now sounds very, very good!! After fitting it the exhaust now pops and bangs on the over run, very cool noise but made me wonder.
I think the exhaust pops and bangs due to un-burnt fuel igniting on the hot exhaust and is caused by the car over fuelling. So why should a new sports exhaust cause the it to over fuel???

Or I have totally misunderstood it all......

[NiceCupOfTea]

What exhaust was it?

[soad]

Hmm, i'm all too

[TheEnd]

It can do that if there is an airleak, which sucks some air into the exhaust

[Dan67]

Well I guess its because engines need some back pressure to work. The exhuast back pressure stops some unburnt fuel/exhuast gases leaving the combustion chamber. Less back pressure means more unburnt fuel entering the exhuast systems. Also if you have removed/changed the cat as well this can mean more unburnt fuel in the exhaust as the CAT catches the hydrocarbons in the exhaust.
All this excess fuel must be igniting on the hot exhast pipes giving you your pops.

Edited by Dan67 on Monday 3rd May 15:51

[focusboy]

Or if there is a very small blow near the front of the exhaust, it will give pops and bangs on deacceleration. (as said above)

[swansea v6]

Exhaust was dual exit stainless stell one he picked up from ebay, I will find out exact make when I see him, we also did remove the cat, which increased noise dramatically!!!!

[_Batty_]

sounds like an MX5parts one

[The Wookie]

Dan67 said:

Well I guess its because engines need some back pressure to work. The exhuast back pressure stops some unburnt fuel/exhuast gases leaving the combustion chamber. Less back pressure means more unburnt fuel entering the exhuast systems.

This is a common misconception, cylinder scavenging is defined almost entirely by cam profile and manifold length/diameter/design. Virtually any restriction is undesirable and 4 stroke engines don't need backpressure to work.

[snotrag]

Most likely the MXparts exhaust.

I have a Posh S/S manifold, a Decat pipe, and the MX5parts single exit on mine and its pretty rude - it pops and burbles nicely and you get a nice 'rifle crack' when you change up at speed when its hot.


Whats actually happened is - those pops and bangs were always happening, but your old exhaust was muffling and silencing them.

Your just hearing them more now.

[RossB_eg4]

You'll probably find that the exhaust fitted is more free flowing than the previous one.

Normally any unburnt fuel would be slow in getting through the exhaust and would probably evaporate somewhere amongst the cat and the centre silencer; where as with a higher flowing exhaust there will be far less back pressure and the unburnt fuel will be expelled a lor quicker, often contributing to the pop/crackle.

My old civic is pretty good at popping and flaming at full throttle changes.

[jon-]

MR2 Turbo + Decat + massive exhaust = http://www.postworkout.com/jon/public/mr2/flame.jp...

[callyman]

The Wookie said:

Dan67 said:

Well I guess its because engines need some back pressure to work. The exhuast back pressure stops some unburnt fuel/exhuast gases leaving the combustion chamber. Less back pressure means more unburnt fuel entering the exhuast systems.

This is a common misconception, cylinder scavenging is defined almost entirely by cam profile and manifold length/diameter/design. Virtually any restriction is undesirable and 4 stroke engines don't need backpressure to work.

Agreed, most twin cam engines have some overlap so on run down un burnt fuel 'can' get down the exhaust. Having a new clean SS exhaust has made it louder and therefore more noticable.
My engine pops and bangs (until full temp is reached) when i let off from a squirt up the rev range.
Nothing to worry about.

[y2blade]

snotrag said:

Whats actually happened is - those pops and bangs were always happening, but your old exhaust was muffling and silencing them.

Your just hearing them more now.

+1

[V88Dicky]

DFCO.....Decceleration Fuel Cut Off. Thats what causes the pops and bangs on my car. And I like it

[MrMoonyMan]

One of the best things in life.