anti-lag system

[Bernd Felsche]

dennis writes:

>Has anyone on this list tried to make, or used, an anti-lag system? 

Two options come to mind immediately .... read on.

>For those not familiar with this term, some of the rally cars and
>other cars in big dollar classes that use a larger and more
>difficult to spool turbo use these systems to decrease lag. 

>This system allows a car to come out of a corner on a track already
>in boost after lifting and breaking, without left foot breaking it
>and shortening pad/rotor life. Or to launch at the dragstrip with a
>manual transmission, and have boost built up already.

>Some say they can get substantial amounts of boost at idle with
>these systems. 

Fuel consumption isn't a big problem under race conditions. :-)

>Once activated, it is a system where when the throttle is closed,
>ignition timing is retarded and additional fuel is added to the
>engine. When the throttle is opened again, everything returns to
>normal. I think it requires a slighly greater amount of airflow
>too. This could be accomplished with the idle speed motor. There
>may be more to this than what I've gathered.   If anyone knows
>more, let me know it too. 

That causes the fuel to burn in the exhaust manifold as combustion
cannot be completed - the expanding gases in the exhaust manifold
cause the turbine to spool up.

Note that your CO and HC emissions go through the roof when you do
this. A catalytic convertor is likely to melt under prolonged
exposure due to those conditions.

The HC emissions get so high that the unburnt fuel will
spontaneously ignite near the exit of the exhaust system.

>Some aftermarket programmable engine management systems, like Motec
>for example, offer this as part of their programming. I would
>imagine that you could build a stand-alone system that does this
>cheaply using an additional injector, some means of easily
>retarding timing(MSD?), a switch that comes on when the throttle is
>released, and an activation switch. You wouldn't want it on all of
>the time, just when racing(or maybe when being tailgated).   I also
>think you might be able to feed the map sensor signal wire some
>votage(on a 2bar system), say just above 2.5 where it would think
>it's in boost, while tricking the 02 so it doesn't freak out, to

The O2 won't just freak... it'll die under those conditions.
OK if you have the ability to change sensors every couple of races,
not so good on the road.

Also, drivability suffers - the very rich mix can make the engine
die - you can flood an engine after starting. Especially when you
change the AFR from around 18:1 to about 3:1.

>get the ECM to do this for you. That way the computer would think
>you're making boost and respond, hopefully, with increased injector
>pulsewidth and retarded timing. And since the car would be running
>rough, the idle speed would automatically increase to keep it
>running. 

It's a mistake IMHO to put too much fuel into the cylinder in the
first place. That leads to a high-maintenance engine.

>Has anyone got a reason this MAP/O2 trick wouldn't work?

It might work; for a while.

Two options - as I said before...

1. Electric air pump to add air into the exhaust manifold - a simple
   check-valve ensures that you don't get any blow-back when you
   open the throttle and the valve sets the pressure you want in the
   exhaust manifold.  [This idea is adapted from the now common
   practice of pumping air into a cat to optimise the conversion
   under less-than-ideal conditions (i.e. quite often).]

   By sensing the position of the check-valve (either directly or
   through a pressure switch/sensor), you can run an injector to add
   fuel to the additional air.  The ECU should check that the engine
   is hot before injecting the fuel though - just to be sure that
   it'll ignite spontaneously. 
   
   What's also important is how and where you inject. You definitely
   want to avoid a back-fire through the auxiliary air system!

   Use the existing O2 sensor to ensure correct mixture when
   off-boost. You probably don't need the pre-boost spool after being
   off-boost for more than say 3 seconds, and certainly not at idle.
   That allows you to stabilise the idle mixture and saves some fuel.

   The driver can always blip the throttle to activate the pre-boost
   spool.

2. Get a different turbocharger - Garret make one with integral
   electric drive to keep it spinning when off-boost. The electric
   drive can also be used yto re-charge your battery - so it saves
   on a big alternator (a small one is advisable as a fail-safe).

-- 
Real Name: Bernd Felsche
    Email: nospam.bernie at perth.DIALix.com.au
	http://www.perth.dialix.com.au/~bernie - Private HP
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