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That Popping sound
- Thread starter Jon172
- Start date
Anti lag means that a turbo that would usually spool at 3,500rpm for arguments sake would spool at 1,500rpm for example.
It does this by sending loads of mixture through the cylinders, but retarding the ignition so that not much of it burns. The unburnt fuel ignites on the exhaust manifold (as it is so hot) and generates exhaust gas. This in turn spins the turbo and makes boost whilst keeping engine revs low.
Obviously there is a lot more to it than this - but this is just an overview.
Thats right, Anti lag basically keeps the turbo on boost all the time, practically from idle, can apparently be activated on some turbo car ECUs (Integrale for one). Not a good idea on a standard car though, as Frosty says the unburnt fuel ignites on the exhaust, this raises the temps considerably and would destroy a standard exhaust in very few miles! Sounds awesome though and is one of the reasons I love turbo cars! The group B rally casr of old were amazing (Delta S4, Metro 6R4 etc.) brutal!
After much discussion with a college heres what happens,
The engine acts like a power pump when you push the accelerator fuel is squirted into the engine to make the revs go up - when you take your foot off the gas the engine is still rotating at the same speed and sucks petrol through the engine without igniting it and spits it out through the hot back end where it boils/burns/explodes and makes a noise.
Standard escort and fiesta turbos do it on overrun with just a mongoose exhaust....
My Fiesta Turbo pops and burles like a goodun on overrun, with standard exhaust you get none of it, fit a magnex and you get a little popping, but i have straight through mongoose S/S system, 2.5" from turbo to back box, 4" tail pipe, and it burbles and pops nicely.
My car used to make light cracking noises in higher gears if I backed off the throttle and then opened it again very slightly (cams, head etc with cat). But I fitted a de-cat a few weeks ago and now it makes a big bang if I floor it to high revs and then do the same slight throttle opening. I also get flames and its just as well the Mongoose tailpipe sticks out a long way from the bumper.
popping is unburnt fuel, which as I learnt from BenR can be from overfuelling OR underfuelling, lean or rich mixtures. The less restriction there is in your exhaust system, the more likely you are to hear popping.
Anti lag keeps the turbo spinning by letting fuel and air through the cylinders even off throttle but not firing the mixture with a spark. Therefore it reaches the hot manifold and ignites there, spinning the turbo up. The effect is that in between gear changes, the revs will not drop with anti lag engaged.
i have experimented with the pop facination on my carbed XR2....its got a race 2 box system and i can play with idle/overrun fueling.
Basically.......if i set it perfect, itll idle smooth and wont pop very much, maybe a slight huma nd burble occasionally.
If i run it lean, on overrun, the fuel passes though unburnt and jsut creates a layer of light fuel on packing etc etc. Lots and lots of continuous lgihts pops and crakles....which i like..
Run rich, you get fuel dumping, and big bangs and pufs of big black smoke, not to mention bore wash and high amounts of carbon buildup.
Exhaust system must be HOT though, mine only does it when hot.....otherwise itll just hummmm....
It was probably running a ALS (anti-lag system) assuming it was a turbod car. This system when off-throttle still pumps fuel into the cylinders and retards the sparks so it doesnt ignite in there. Then when the unburnt fuel is exhausted it meets the hot manifold explodes, keeps the turbo spinning and spits flames out the back end.
Simple really, just a way of keeping the turbo spinning so when the next on throttle moment arrives it is all ready and waiting.
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