What makes valvers pop?

[cliokiz]

My valver has been de-catted and is straight through to the back box, with a K-TEC s/s system (de)cat back.

It pops rediculously loud sometimes just by tapping the accelerator, but the thing i like most is when the engine is cold, and you just hold your foot slightly on the accelerator as you come down through the revs, it burbles and splutters and it sounds f**king lovely!

Unfortunately, when it warms up it doesn't burble/splutter as much, but instead lets out rediculously loud pops that sound like fireworks exploding.

Now i love both, i think it sounds 'rally' stylee, and my car has a bit of a rally style look about it, but i just wondered what makes it happen?

I'm guessing when the car is cold, it's just unburnt fuel igniting in the manifold, and the same when it pops really loud, however after 'popping' for a while, it tends to stink of burning oil, and the oil temperature raises quite high, could it be burning oil?

What can i do to make my valver sound even more 'rally' style (if anything)?

Cheers

 

[G_F]

Its the decat that making it pop and bang.

 

[cliokiz]

Well obviously it helps, but the source of what makes it pop must come from the engine surely?

Even when i had my cat on it still popped and spluttered just very quietly

 

[BenR]

its caused by extreem lean fueling mixtures on overrun, not rich like everybody believes.

 

[cliokiz]

I'm guessing this is normal? Is it not burning my oil then? Smells oily...

 

[Lam7r]

The smell could be due to having no cat mate. Mine stinks sometimes but its not really an oily smell like you describe its more a fuel smell

 

[ChrisE]

I had the same with mine mate...

maybe the piston rings gone...! cos i think it was burning oil!!

 

[BenR]

its normal, dont worry.

 

[mr_merc]

its caused by extreem lean fueling mixtures on overrun, not rich like everybody believes.

Ben, can you explain this to me then?

It's obviously my ignorance but as I understood it:

1. Exhaust gets hot
2. Exhaust has no real restriction in it
3. 3rd gear (usually) coming off the throttle in the mid range and a gentle touch on the throttle
4. The gentle touch on the throttle sends fuel into the engine, but doesn't spark it properly
5. Unburnt fuel vapour runs into the exhaust and explodes when mixed with "oxygen" and hot exhaust

Now I feel like a muppet... go on please?

 

[BenR]

unless your exhaust is glowing red hot then it isnt hot enough to ignite any neat fuel.

When you touch the throttle you allow the ECU to read a small decrease in manifold vaccum along with a small change in TPS value and it will inject a teeny weeny portion of fuel, typically leading to a lean mixture.

The ignition system is always sparking so it will be ignited, but a lean mixture burns slower and is still burning once your exhaust valves open, hence the little pops and burbles.

For you to get popping from an unburnt mixture it needs to be extreemly rich, have a source of ignition (antilag systems use a red hot turbo or you would melt exhuast valves with later ignition) and the average cars exhuast system just isnt hot enough. And if you did burn a rich mixture you would get flames, not pops.

 

[cliokiz]

Another question - can it cause damage to the engine?

Obvioiusly the little burbles you get won't do any harm, but my valver has a straight through system to the B/Box and if the engine is REALLY hot (ie lots of driving around the 4/5k range in a low gear), and i tap the accelerator at or below the 4krpm range, it'll let out the biggest pop you've ever heard in your life! Sounds like a gunshot, makes me jump sometimes when i don't expect it it's that loud!

The previous owner said once it popped so loud an old lady dropped her shopping in shock!

So my question is, is this dangerous? It's done it for a while now, and obviously i encourage it by plenty of accelerator tappage as i love it, shoots flames out and all that when you have a complete and utter c**k driving up your anus, but just wondered if i should try not to!

Cheers!

 

[cliokiz]

if you did burn a rich mixture you would get flames, not pops.

I get both at the same time? Pops extremely loud and kicks flames out.. ?

 

[BenR]

no damage, mines been doing that for 140,000 miles and every valver owner does the trialing throttle popping and burble thing lol.

 

[Waitey]

I used to flames with my old valver. So a assume this was from it running lean and the combustion cycle happened down the full length of the exhaust?

 

[Martin]

I'm wondering why my car does'nt do this at all....all my other clios have.

I've got a full exhaust with de-cat but no popping and flames..

 

[Waitey]

Mine did it for 150k and lived

 

[mr_merc]

unless your exhaust is glowing red hot then it isnt hot enough to ignite any neat fuel.

When you touch the throttle you allow the ECU to read a small decrease in manifold vaccum along with a small change in TPS value and it will inject a teeny weeny portion of fuel, typically leading to a lean mixture.

The ignition system is always sparking so it will be ignited, but a lean mixture burns slower and is still burning once your exhaust valves open, hence the little pops and burbles.

For you to get popping from an unburnt mixture it needs to be extreemly rich, have a source of ignition (antilag systems use a red hot turbo or you would melt exhuast valves with later ignition) and the average cars exhuast system just isnt hot enough. And if you did burn a rich mixture you would get flames, not pops.

Thanks Ben, that makes perfect sense when put like that.

That said, I have been informed by followers that I get the odd flame in 3rd on a trailing throttle so that baffles me a bit if this is the result of a lean burn?

 

[BenR]

yea, but most peoples ideas of a flame is a a blue pop as opposed to a full bore trailing flame lasting a second or so.

 

[little_grey_devil]

its awsome mine does it sounds like a gun shot if you get a gooden mine tends to spit little flames out so my mates told me wen hes follwed a few times

 

[Greeny.]

This is a flame:

Nothing as amazing as turbos can do but passed the time in my chavvy stages growning up with my 1.0 Fiesta mk3 with choke on full and a staight through system


Im no way as cool now tho