Driv200

iTrader: (1)

First Road Race debut was a success! Took 1st in NASA TT1 and set a new personal best lap time of 1:21.2 at Hallett. After a 6 month rebuild and new everything....this is very rewarding for my builder and I as we are still sorting the car. There were a couple faster cars including an EVO X with full aero on A7's! As long as it's in the EVO family..

Need vacuum assist help. Has anyone added an electric vacuum pump? Where/How/Pics?

I am loosing 2 seconds per lap having to lift early on long straights and coast prior to using my brakes. On long straights at 100% boost, I can't do threshold braking or late braking immediately off boost. I have zero brake effect unless I coast. The pedal is ROCK HARD with zero effect. I am getting killed in braking zones against cars at my level. I can't ever trust brakes will be there. I can't tuck up behind anyone in braking zone or set up for pass after apex.

Previous threads have offered two solutions:
* go to manual brakes
* add vacuum pump - I prefer this one.

My stats: EVO IX RS, 32lbs boost, ABS, AP racing brakes.

Balrok

iTrader: (15)

I've dealt with it by feel for years. But yes the brake booster pulls on engine vac and that takes a second to bleed so maybe moving the booster line to an electric pump "could" solve it.

kyoo

iTrader: (29)

whaaat? this is the first I've ever heard of this?

Ayoustin

iTrader: (2)

Sounds more like you have a bad check valve on your vacuum booster. All cars made in the past 25 years have check valves going to the vacuum booster so the brakes can be pumped 2-4 times even after the car has been shut off. The only way I can think you could end up without any assist in the booster (and not have a bad check valve) is if you were brake boosting through every corner on the track. The only cars I know of using vacuum pumps are drag cars and that's because they don't create enough vacuum at idle due to large overlap cams.

kyoo

iTrader: (29)

yea I'm really hoping for more info on this, as it seems very bizarre - if this is an actual issue with the car, why is it an issue because of boost? and if it's because of boost, why is it not an issue with all turbo cars?

I will note one thing - I asked my tuner to tune to let the revs fall more quickly after I let off the throttle, as I believed it impacted engine braking a tad. If anything, I feel the opposite on the track, where the pedal is soft initially and goes down at first before firming and biting.

kaj

iTrader: (60)

Positive pressure from boost keeps the brakes from creating vacuum assist. I agree with above that a check valve should keep this from happening, though that's just using common sense and I don't completely understand how it all works from an engineering point of few.
Revs should come down as the car is decelerating and not be affected by idle, I'd think...? Rev hang usually only affects RPM between shifts. You should have plenty of vacuum when braking for a turn. The only way I could see it being an issue is if someone were braking in neutral or with the clutch in.
Maybe you have dealing with pad knock back? I know, at one time, I had to tap my brake pedal once or twice before braking to take up the slack. I felt like Keiichi Tsuchiya in one of those Option videos LOL

kyoo

iTrader: (29)

I don't want to derail too much, but engine braking does impact braking a good deal. we busted a friend's axle and it felt like we lost a lot of braking on that side of the car. I was dealing with the brakes not braking as hard as I wanted to (unrelated my soft brakes saga) at the time, and it gave me a mind to consider that, if I let go of a throttle in a shift and the revs hang, what's to say that it's not "trying" to do the same when I'm off throttle but staying in gear?

but agree, something sounds not right here, I've never experienced hard brakes immediately after the throttle, on track or autox. wonder if this happens at autox too? but I also don't run anywhere near 32psi.

kaj

iTrader: (60)

Because we have the clutch out, so engine is doing the braking, giving us lots of vacuum. With clutch in or in neutral after revving the car, is when it hangs.

Same here: only 25psi... but never had a problem with brakes. It sounds like it may be a thing, since Balrok also mentions it. Maybe high boost is affecting the check valve or other systems in the car, causing a delay in vacuum. I'm very curious.

Driv200

iTrader: (1)

Ayoustin

iTrader: (2)

How much is high boost? Are you sure you aren't at a higher pressure than what the check valve is rated for?

kaj

iTrader: (60)

My longest straight puts me decently into 5th gear on a 6spd. That's coming out of 2nd and 3rd gear corners ("Sunset" at Buttonwillow and Turn 11 at Laguna Seca). I'm running GSC S1 cams at 25psi.
At some point I may be making more power/boost/etc so all this definitely interests me.

kyoo

iTrader: (29)

his original post says 32psi, though not sure on what turbo that is.

Ayoustin

iTrader: (2)

Easy test would be to throw a vacuum gauge in the line behind the check valve and see if there's vacuum there.

kyoo

iTrader: (29)

even if it only happens immediately after WOT? genuinely asking, I'm not 100% sure how the system works

kaj

iTrader: (60)

It's possible. Test the check valve to 32psi and see if it holds. If not, then it could be failing and, basically, pressurizing the brake booster. In which case, that could explain why his car has to be in decel for a bit for vacuum to be restored and brakes work (if that's what's actually happening).
Unless there's something else at play that I'm unaware of (really, really possible )