Cylinder Wash on cars with Burble / Pops and Bangs?

[Dominic-Toretto]

Hey everyone,

I have a question regarding cars that come from the factory with the exhaust burble / crackles . IE: Some BMW's, Porsches and Jaguars.

How is it that Cylinder wash does not occur, given that the cars are dumping extra fuel in to the cylinders which passes all the way through to the exhaust where it then ignites. Have the coatings of cylinder walls been enhanced in recent years, or is it more a case of the amount of excess fuel being added is so tiny that it will not affect the coating on the cylinder walls?

All input appreciated

Thanks guys!

 

[red eye]

It’s all about when the exhaust valve opens, open them early will let more still expanding gasses out. If they let more fuel in they’ll create a world shortage of metals found in cats

 

[Dis86]

Curious one. I'd assume some will but more than likely those crap aftermarket modified vehicles that will suffer from it.

 

[NoNameNoNumber]

During the overlap when the injector fires, the vacuum in the exhaust will pull that straight through, never even touching the bores. Also The exhaust valve will likely be closed by 20º or so after TDC so very little of the bore would ever see this mist.

 

[Nasher]

It will be the exhaust manifold and cat which is more likely to be an issue. But that can also lead on to other problems I guess.

The aftermarket ones which do it excessively will break something eventually though.

 

[red eye]

During the overlap when the injector fires, the vacuum in the exhaust will pull that straight through, never even touching the bores. Also The exhaust valve will likely be closed by 20º or so after TDC so very little of the bore would ever see this mist.

Only a little amount of fuel goes though during overlap not all, it wouldn’t idle if it did. The pulse from detonation creates a vacuum behind it sucking all the exhaust gas that the piston couldn’t push out and help the fresh charge into the cylinder (scavaging)tying to get 100% of the cylinder with 14:7. The piston can’t get all the gas out and it cannot completely fill the cylinder with fresh charge, it needs scavaging the goal is 100% volumetric efficiency in reality not many n/a engines can achieve 100% ve, race engines and turbos can iirc e32 m3 did and that made 100bhp per liter.

 

[Finglonga]

I would be more concerned about the amount of fuel going into the Cat' as it can destroy them.

 

[red eye]

I would be more concerned about the amount of fuel going into the Cat' as it can destroy them.

A small amount is ok as it will ignite in the exhaust, but these amg’s And m cars do it but they don’t kill cats if they did there would be massive warranty claimes.

An old skool way was to wind the mixture screw on the carbs so they over fuel, but then came injection and the way to make them pop and bang was ignition cut that dump a load of fuel into the exhaust it would still be burning out of the tail pipe, not the nice blue flame but cigarette lighter turned all the way up flames

 

[Nasher]

The factory setup will have been well tested. But it will probably kill it quicker than it would.

 

[sideways14a]

Most old school cars wont have cats anymore if they are at the pops n bangs stage.
Heck just removing the kittys can give some limited exhaust hilarity, a bit of fiddling with the fuel/timing and off you go - bang city.

I remember one of my mates cars nearly burning the foot off one of the lads while a load of us were trying to hold it down on the dyno one day, sitting in the boot was not the best idea when it was blowing 3 foot stonkers out the pipes.

 

[Frozennova]

I can't comment for all of them but the BMWs during "burble" command Lambda 1. I haven't dug into the strategy as a whole to far but I expect they're also using very early injection to fire the raw fuel straight out of an open exhaust valve.

It's excessively rich combined with high EGTs that kill the cats. OEM strategies monitor EGT and won't activate burble if EGTs are high