Anti Lag (another technical question)

[Rani]

Just returned from Jordan yesterday (had a great time btw, gotta love this peace thing), and (as always) I have a question that's been bothering me.
Why is there such a difference between the anti lag in PWRC and WRC cars?
The WRC's seem to have a healthy popping sound while the PWRC cars sound like they are about to shoot the pistons out through the hood\bonnet.
Any thoughts?

[Zico]

Maybe the PWRC cars only have a mere dump valve?

ALS is a complex system, this is how it works.

Firstly, boost is controlled very acurately by using 2 fuel injectors as air valves, these feed the boost/atmospheric pressure to the waiste gate actuator, allowing minute and very fast acting boost control.
Secondly, the normal method of controlling engine iddle via an idle control valve, that bypasses the throtle butterfly is dispensed with, the static idle is set in the old fashioned way by a locked off bypass screw.
Thirdly, where the idle control valve used to be, a new valve is fitted that has a solenoid controlled valve (looks like an engine inlet valve internally) that can open/close the throttle buterfly bypass orifice very qickly.
Forthly, a miram turbo shaft is used to withstand the massive increase in turbo temperature generated by ALS.
Fifth, there is no dump valve used on an ALS equipped engine, the whole point of ALS is to keep boosting the engine, even on closed throttle.
The way it works is that when you come off the throttle, for example braking hard into a corner, the throttle butterfly closes as per normal, once the boost drops to a certain level, the ECU starts to pulse the Throttle butterfly bypass valve, this has the same effect as you constantly stabbing the throttle on and off very quickly, this means that the engine is being driven by the ECU as though it wants to accelerate again, however this occilation of the throttle bypass valve is happening so fast, it has the effect of allowing the turbo to stay spinning yet produces no additional torque to drive the car forward. The ignition timing is also controlled during this off throttle period to again reduce torque yet maintain boost presure.
The effect of all this is that massive heat is generated in the turbo exhaust side, which ignites all the excess fuel, there is no deliberate overfuelling going on to explode the turbo impellar area.
The most modern of ALS systems on the current world rally cars are far more efficient than a couple of years ago, which is why the ALS banging was less aparent this year on the WRC rallies.
The turbo used in ALS equipped rally cars is smaller than you would see on a race car for two reasons. the first is that the FIA has a mandatory 34mm turbo inlet restrictor that limits air flow into the turbo, this means that it is pointless useing a large inlet turbine unit as the inlet could not flow any more air, secondly the lag would increase due to the inertia of the larger impeller.

I hope that helps a little.

[dimviii]

very good answer!! bravo Zico! ;)

[OldF]

Zico. You seem to have good knowledge of turbos.

Do you, or someone else, know how much turbo boosts is used on group N and WRC cars?
Do you have any idea at which revs the 34 mm restrictor starts to choke?

It would be nice to see a compressor map of for example a Garret TR30R turbo but as far as I know they sell these turbos only to racing teams.

[Mirek]

In one old WRC I saw the absolute pressure of 3,2 Bar...

[Zico]

Modern WRC cars use aprox 4-5 BAR ! according to http://www.wrc.com/jsp/index.jsp?lnk=221&featureid=87&desc=The%20cars and Re- 34mm restrictor airflow choke point Ive read several figures between 4k and 5k rpm. (Dont ask me where tho) So keep this as an estimated figure.

I dont have a figures for the Grp N cars 32mm restrictor, nor any WRC turbo maps I can share, Id imagine this info to be fairly confidential. Maybe Garrett themselves might be able to give you ballpark figures?


Sry, I cant be of much help..

[dimviii]

at several gr. N mitsubishis i ve seen from 1,7-1,9 bar

[Mirek]

I think Fabia Evo 1 had airflow choke at 5500 rpm. But it is 5 years old car...

[dimviii]

a photo from a tr30r ex focus wrc 2001 from net
http://i12.photobucket.com/albums/a244/v8polo/IMGP0150.jpg

[zerodegreec]

Has exhaust recirculation been used rather than this method lately?

Why not implement some type of high pressure boost from a cylinder of compressed air to offset the lag and eliminate the ALS system all together? I am sure some rule would prevent it but I am sure you could get something to work for short bursts over a limited duration.

[Zico]

Has exhaust recirculation been used rather than this method lately?

Why not implement some type of high pressure boost from a cylinder of compressed air to offset the lag and eliminate the ALS system all together? I am sure some rule would prevent it but I am sure you could get something to work for short bursts over a limited duration.

The very system you describe was used briefly by Ford and I think it was Subaru?... a year or 2 back.. The FIA quickly banned it.

[Daniel]

The very system you describe was used briefly by Ford and I think it was Subaru?... a year or 2 back.. The FIA quickly banned it.

Was used by Ford in the Escort WRC back in the 90's. The FIA didn't actually ban it for a few rallies as it was technically legal as all the air going into the engine passed through the restrictor.

Interesting "cheats" thread. Some are badly disguised, some well disguised and some like the pressure tank in the Fords are brilliant in their simplicity and legality!

http://forums.autosport.com/showthread.php?threadid=90222

[grugsticles]

at several gr. N mitsubishis i ve seen from 1,7-1,9 bar
I can attest to that.
I cant speak for all Gp N cars, but the few that ive seen all ran about 20 to 25 pound of boost.
Full boost was usually achieved about the 3500rpm mark.
with a 32mm restrictor, I think that about 6000rpm is the max for a WRC car before power is significantly resticed, and about 5500rpm in a Gp N car.

[grugsticles]

Seeing as I cant edit :(

Just found this article:
About Audi Quatro which in North America ran a 40mm restrictor, 22 psi and made 380 BHP. Unrestriced it would produce at least 400BHP @ 25 psi although Id personally guess more towards the 500bhp mark.

[Viking]

Seeing as I cant edit :(

Just found this article:
About Audi Quatro which in North America ran a 40mm restrictor, 22 psi and made 380 BHP. Unrestriced it would produce at least 400BHP @ 25 psi although Id personally guess more towards the 500bhp mark.


Norwegian unrestriced 2050ccm 4cyl Audi, 750hp@7100rpm

http://www.tsracing.no/A3.htm