toddk911

Interesting.

"I’m sure some of you have heard of anti-lag systems or sometimes known as misfiring systems, thanks to anime like Initial D. You might have noticed that most of the cars have flames coming out of their exhaust when they shift gears. If you’ve watched Top Gear’s review on the Prodrive P2, you will see that the P2 has it too. That’s a misfiring system in action. Let’s just call it anti-lag from now on. So what does anti-lag do?

First of all, we have to have a quick re-cap on how turbocharging works. Essentially, exhaust gas is used to spin a turbine which compresses intake air. But what happens when you shift gears? You have to lift your foot off the throttle. Exhaust gas velocity drops, and the turbine blades slow down. Intake boost pressure drops. For the next gear, you have to wait until the turbine spins up again for the boost to kick in. This is what you call turbo lag. However, turbo lag should not be confused with boost threshold, which is the minimum engine RPM which is required for the turbine to physically supply boost.


A typical antilag system works when the throttle is closed, which is what happens when you take your foot off the accelerator pedal. An antilag system introduces some unburnt petrol into the exhaust manifold. The heat of the manifold causes the unburnt petrol to combust, and the exhaust gas produced by this combustion keeps the turbine spinning, preventing the blades from slowing down - effectively reducing or eliminating turbo lag.

There are two ways to go about this. An aftermarket anti-lag system like those that come with aftermarket ECUs like MoTeC will adjust ignition timing during closed throttle situations to a point where the exhaust stream becomes really rich with unburnt petrol. This is done by retarding the timing to about 40 degrees after top dead center. Top dead center is the point where the piston is furthest from the crankshaft. Rally cars use a different way of introducing petrol into the exhaust manifold. There are separate injectors that introduce fuel directly into the exhaust manifold. Some of this mixture will continue burning in the turbine and down the exhaust system, resulting in the flames and explosions you hear coming out of the exhaust muffler.

The use of anti-lag greatly reduces the life of a turbocharger and engine because of the extreme heat from the combustion in the exhaust manifolds. This is why it is normally only used in races and rallies and not suitable for street use, as the lifespans will become too impractical. It also increases emmissions and is generally too loud for street use, making it illegal on the road."

Synth

Nice write up and info, thanks. I had never even heard of it until Initial D and was wondering if it was made up lol!

toddk911

Yea, seems cool, but I guess not really for street usage.

Although a diverter valve on our cars seems to do the same thing with less issue.

What part of Southern MD? I grew up in St. Mary's county.

J1NX3D

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tedesco

Since a bit more than one week I have a similar system installed on my car. It is very simple and works fine. It uses a soft cut rev limiter, than cuts spark randomly to keep engine rpm below the threshold. Additionaly to the explenation written above, it is not enough to just inject fuel into the exhaust or retard idgnitioin you also need oxygen supply. What you do is to floor the throttle pedal so that the engine is running into the rev limit and ingnition is cut off randomly. As this is done with wide open throttle, enough air is pumped through the engine and the unburned mixture of the cylinders that had ingition cuts ignites in the header and keep the turbo spinning. So there are two effects:
1. more air is pumped through the engine because the throttle is open which keeps the turbo spinning even without backfires and fuel beeing burned in the header just due to the fakt that the engine serves as a bib pump. I could achive about 0.25bar without any hard backfires
2. if you want more boost the rev limit needs to be raised to let more unburned air pass into the header. This goes along with massive backfires and you feel like in the 2nd world war but it allows you to set almost any bosst pressure you like. On my car I set the rev limit to 5100/min which generates about 0.75bar bost with the car standing still.
One thing I have to say is that you better do not try this on your stock car. I would strongly reccomend not to have a cat or any restriction in the exhaust. I think ball bearing turbos would also be a bad choice for such a set-up.
Allthough it is (unfortunatly!) quite spectacular, it should not be too hard on header and turbo in respect of stress due to high temperatures. With a system like the above, most of the fuel will burn in the headers but the maximum temperatures will occure in the exhaust behind the turbo. The systems that use ignition retard start the burn in the cylinders which results in very high manifold and turbine temperatures. Allthough they opperate a lot quiter the termal stress on important components would be higher.

My system is activated by a clutch pedal switch. Once you push the clutch the soft rev limit is active till you engage again, so you can do full throttle shifts. There is no need to change anything for all day driving. Porsche already prepared the car for this . Both, the break pedal as the clutch pedal already have some brackets to mount such a swith. On the brake pedal it is used to activate the brake lights, on the clutch pedal it is normaly not used...

toddk911

So you have been running this system for a while and no problems?

How much sooner do you see full boost?

tedesco

as written I have it installed now for about one week but weather did not allow too much testing. It is raining all day, no grip at all. You also really need to be brave to activate it as it sounds like someone is starting a war. In any case boost is instantaniouse. Fear a bit about by (stock) drive shafts. If weather allows I will do some more testing on the weekend. It is more a toy thing for me to play around with. I am interested in it from the technical perspective. I do not bother that it makes no sense...

eospeed

ST has this on his car.

Kit_Chris

Tedesco, PLEASE keep us updated. Who produces the components? Which other mods do you have?

Regards,
Chris

toddk911

yes, a breakdown of parts or accessories you used would be great.

Unless you plan on packing it to resell

HIGHBOOST

This is very interesting, I'd like to know how it performs as soon as it ets dry for you!

tedesco

There is no secret about it. What you need is a rev limiter and a switch, that is all. No other hardware required, but once again: You have to have a straight through exhaust. The backfires are quite violent!

Don´t have a video cam but will try to do a movie with my camera on the weekend.

My car is quite modified. Running 1.4bar boost and doing 100-160km/h in 4.3 to 4.5 sec according to data log.

toddk911

So how often are the backfires?

Ian Carr

google: bang bang anti lag system and you will find lots of info.

its a pretty cool system but for street use with stock exhaust you will either burn out gaskets or you can eventually burn out the turbo. One problem they have always had was with all the extra heat, it does burn out the seals in the turbo.

Synth

I grew up in St. Mary's County too, went to Leonardtown High, graduated in 97. What about you?