I have a very basic understanding of one anti lag system on some models of Toyota Celica. I am interested if anyone knows the various types of Anti-lag Systems that exist in the real world and/or racing. Can someone explain the details of ALS?

2 Answers 2


A couple anti lag systems I am familiar with...

VNT/VGT - The exhaust turbine fins move based on the wastegate. This allows it to spool faster, then open up to be less restrictive at high RPM. The 1989 Shelby CSX-VNT used the VNT turbo. Porsche used a VGT turbo in recent years.

Not sure if this one has an official name, but I've always heard it referred to as a D-Valve or a dump valve. It is basically a 1 way check valve installed on the upper intercooler hose. This way there are 2 paths. When you are not in boost, you pull through an air filter on the 1 way check valve. Once you have sufficient boost in the intercooler hose, it closes the check valve. You get better unboosted power since you don't have to pull through the intercooler and turbo.

Twin turbos will spool faster than 1 large turbo since you have smaller exhaust housings. There are also sequential turbos where you have 1 small turbo for quick spool, and one larger turbo for higher boost. You can use a supercharger / turbocharger setup.

Ball bearing turbos spool a lot faster than traditional turbos.


In racing applications, often fuel is simply dumped into the exhaust manifold. It burns/explodes and raises the pressure in the manifold, which keeps the turbo spinning. I also read about an experiment where there was a valve in the exhaust manifold to relieve the back pressure when the throttle was closed (which would slow the turbo), but I don't recall hearing whether it was effective or not. In street applications, I know that both BMW and Audi are experimenting with electric "turbos" that rely more on an electric motor than on exhaust gasses.

The earliest anti-lag system I know about is the twin-turbo set-up on the Porsche 959, which simply had two sequential turbos. The first one was smaller and provided boost at lower RPMs, while the second was larger and contributed more boost at higher RPMs.

  • yes, read about the Porche, nice deep track there. That was amazing thing in the 80's put that on street car. In formula 1 there are pre-spinning the turbo with an electric motor with a ceiling of 125,000 RPM to reduce turbo lag. Commented Dec 8, 2015 at 13:10
  • I was not aware of a valve in the exhaust to relieve backpressure when the throttle is closed. There shouldn't be significant backpressure on the exhaust side when the throttle is closed. However on the intake side, backpressure will build up quick if your boosting and close the throttle. This device is a called a blow off valve. Helps extend the life of the turbo also. Very common on modern turbo engines. You can even have it release back before the turbo to help keep it spooled.
    – rpmerf
    Commented Dec 9, 2015 at 20:00
  • @rpmerf: My A4 has what's called a "diverter valve" that routes the overboost to the upstream side of the turbo. That seems to be standard on the VW/Audi engines, but blowoff valves are more common on Porsches.
    – TMN
    Commented Dec 9, 2015 at 21:28

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