Aft,

Looking for some advice on this one.
I'm having a Simtek ECU fitted to my rallycross impreza, but as it is only a pure race car, and due to the nature of the sport will be running a very agressive antilag statergy.

However, this leave's me with a major problem that the brake servo won't have any vacuum in the inlet manifold as it will alway be in possitive pressure. And with nearly 500bhp on tap, i want some good brakes!

The second part of the problem is i'm running a reversed inlet manifold, so i'm a little bit short of space. I have been told about a corsa diesel alternator with a vac pump on the back, but i don't know if i have enought space and secondly if it will have enough suck.

I have thought about an elecy vac pump, but again not sure what would be suitable and if it would be upto the job.

Fitting a peddle box isn't any option at this point in time, so we need to work a solution out. Someone out there running a ALS must have come across this issue before..

Any advice

Si

 

i think the als on the simtek works slightly differently so you dont loose the vacuum for the servo, i havent noticed it on mine.

Give Martyn a ring at Alan Jeffery - Engine Tuner

 

You can either fit an electric ( or mechanical ) vacuum pump, as per most diesel cars.

Or you could fit a vacuum reservoir ( and non-return valve of course ) to the servo line.

One example.

Crane Vacuum Reserve Systems - summitracing.com

This a search for vacuum pumps...no doubt there are others.

Brake Systems - summitracing.com

Some diesel cars use a pump built into the alternator.....some are driven mechanically off the engine, and others are belt driven.

Or if you wanted to adapt a Sierra's electric pump and use it for power assistance instead of the Subaru servo.

 

Is there any reason why you can't remove the guts inside the servo, weld it back up and fit a solid rod directly from the brake pedal? thus doing away with the need for servo assistance. It would give you a better pedal feel on the limit as well.
I bought a rod for the rally car (which ran a MoTeC anti Lag system) from TEG for about £40.00.
Blank off the vacuum pipes from the inlet manifold an dmaster cylinder and redrill the brake pedal approx 12mm higher than the existing hole.


HTH
Rob

 

Thats the important bit. Seeing as servo assitance is lost. Unless you change the leverage available at the pedal, the brakes will almost become useless.

In changing the leverage, you may sort pedal effort required, but your foot will need to move more, to create that same braking effort, due to the change in leverage.

 

The answer from groupngc8 has sort of missed the point, i'm acturally trying to keep the servo assist, not remove it.

The vacuum reservoir idea is good, but how long will it last as it won't be recharged during the race (whilst als active). I need to do approx 6 laps, but i assume the more you use the brakes, the poorer they will become as the vacuum leeks away over the laps as they are used? or have i got the wrong idea on this principal?

si

 

cough cough

 

Correct.

A vacuum pump will offer a permanent solution. Whether electric, or mechanical.

 

fair enough!
but why do you want to keep the servo assistance?

 

To avoid hacking up the current set-up ?

IMHO

DunxC

 

And servo brakes work perfectly !!

 

I think Si want's properly useful ALS, not the sort of ALS setup on most road cars that gives lots of noise and a very minor effect. On the road you might get away with it anyway as you're not always on boost. However in competition you will soon use up the vacuum and not allow any more to be generated. The other solution is to use EGR based ALS which doesn't rely on filling the inlet plenum with air to feed the ALS, instead it's fed directly into the exhasut stream, while the fuel goes through the engine with enough air to allow ignition as it exits.