DIY Anti-Lag/ no load Boost?

[gwagensteve]

This is a bit dense, but stay with me on this. I've been kicking this around and drawing some ideas together, and think I might be on to something here. Here's the background.

A) I've done some reading about anti-lag used to provide no load boost for launching drag cars. This is how it works:

When anti lag is enabled, without having your foot on the accelerator at all, the following things happen - Ignition timing is massively retarded, Idle air control is opened up to let air into the motor, and the car is richened up. The result is lots of unburnt fuel in the exhaust, which burns in the manifold and spools the turbo. apparently, effectively full boost is available when the car is at idle. Motec, for one, can run this function.

B)Stock EFI cars drop fuel out of the car to rev limit them. With fuel pulled, revs and boost fall the engine simply runs out of power and cycles. BwaaaaBwaaaaBwaaaa style.

C) Most of the fastest Japanese drag cars eliminate the fuel cut rev limiter and replace it with an ignition cut rev limiter. I thought this was to to raise the stock limiter. They don't use nitrous to get boost into the cars off the line (very common here in Australia) they just run them up to the limiter all banging and farting and spitting flames, and launch. More on that in a minute.

D) The other day, for some reason, fuel pressure on my aftermarket fuel pressure regulator spiked up to nearly twice correct pressure - about 60PSI. The car ran like poo, but made lots of boost with no load (10PSI on the gauge while free revving with it popping and banging)

E) Reading about the Jaycar shift light kit I have, it drives an ignition cut rev limiter, and warns that if the car is driven on the limiter, very high exhaust temperatures will result (due to the excess fuel not being ignited until it gets into the manifold.

drawing this stuff together, I've had a bit of an idea.

Let's say I fit the Jaycar rev limiter, but set it at about the engines boost threshold, so I free rev the engine to, lets say, 3000rpm. At this point, the limiter starts pulling sparks out of the engine. The throttle is fully open, so there's lots of air in the motor, and boost was coming on when the limiter kicked in. However, There's lots of fuel not getting burnt, and this should be going through to the exhaust. This should be burning in the exhaust and spooling the turbo, but the revs can't rise- The car is being fuelled for 3000rpm, it's making full boost (or thereabouts.)

If you haven't read between the lines already, the idea is that if I can , say, throw an arming switch and then activate the system (activated by having the clutch pressed) I might be able to get full boost at sensible revs, and therefore launch the car with maximum torque at the wheels, instantly. It's not going to be all that useful, but It might really improve performance in mud and on greasy hills. With a working handbrake, it might make, say, 3rd low assaults on nasty wet hills a piece of cake - handbrake on, switch on, clutch in, foot to the floor, 3000rpm, 10PSI boost, clutch out - bang! - instant, full torque at the wheels, in a tall gear, so lots of wheelspeed.

It might also break everything, and melt the turbo, or not work at all but what do people think? Does it sound feasible?

I do plan running an EGT gauge to prevent melting the turbo/exhaust, and know it won't be able to be run often/for long, but it might be useful in hard terrain.

Steve.

[cj!]

From what Iittle I know the early anti lag systems (ALS) were pretty hard on the engines and turbos due to high heat and loads. You might want to add a coolant temp sensor that cuts off the ALS when it reaches a certain temp. The later ALS bypass air directly to the exhaust manifold with a bypass valve and work well but you would want a new ECM and a turbo speed sensor so that you can map the throttle position and control the open amount of the bypass valve, etc. In fact thinking about it you might want a turbo speed sensor in any ALS system as the turbo speeds must be getting pretty high which could kill the turbo. From what I have heard they can work very well and produce heaps of torque at low rpm due to the high boost now available which would be .

It would be an interesting project but if it goes wrong it won't be pretty. I look forward to Ross's input on this one.

[mightymouse]

If you can justify the risk to your turbo then perhaps its worth going down this path - if not then leave well alone, but you already know that......

As you indicated a pyro will be an essential tool - but if you look around there are units used with diesel engines that also have programmable contacts that could be used to provide a degree of turbine overheat protection. The question however is how to protect - if you override the system then revs will suddenly go sky high and if you cut the engine then that could be a PITA as well. A buzzer might be the answer to bring the situation to your attention...

As I dont know what the exhaust wheel material is, its hard to predict its failure point. These AL systems are used on vehicles where overhaul intervals are short and so exhaust wheel issues really dont worry them too much.

OE's don't go down this path - largely because of emissions so there's no durability information available. We tend to use technologies like electric superchargers to deal with low end boost issues

However I also think that your heading down the path to an aftermarket injection system pretty quickly - all these "extras" are not going to be great for reliability and integration IMO and perhaps nows the time to get some real flexibility. for spark and fuel management.

And ..... given your turbo situation then perhaps its time to supercharge the sucker and get it over with.... Of course a torque converter would also allow you to load the engine up ( you didn't want to hear that.... ) Turbo automatics are very easy to get on boost from standstill - especally if you play with the converter stall.

The small Daihatsu 4WD tray we had here was supercharged and produced impressive bottom end torque with just two cylinders.

So - its a risky but technically possible. I'm concerned that your geting into areas that you don't really have the equipment to really set up properly and by the time you get equipped you could have used more "traditional" approaches to getting off idle boost.

Find a appropriate auto.....