Brake boosting... your experiences?

L

lestat13

Member
I was in the 2008.5 vs 2009 thread and everyone is talking about throttle position.... a question I had a long time ago came back to me for some reason. Brake boosting (as it was explained to me) is when you apply enough brake and throttle simultaneously so that the car maintains speed yet builds boost. That way you can take off from a roll at full boost.

I tried this a few times with just intake, intake/downpipe, and intake/downpipe/tmic. The car seemed to launch even slower and bog. Well maybe not bog, but it definitely didn't get up and go like it normally does.

Any thoughts, experiences, or can anyone enlighten me on brake boosting?
 
if you have an intake you should be able to hear your turbo spool while your brake boosting. i only brake boost when im going from a 30+ mph roll.
 
i do it on my car sometimes. when done properly the car definitly shoots forward,
 
brake boosting is much more popular in the Evo world where you are running turbo's that have a huge spool up time. If you want to learn alot about it head over to Evolutionm.net and rumuge through their threads. It might help on the speed3 some, but u will notice a much bigger difference on a large turbo as the speed3's spool time is fairly quick.
 
Well...essentially when you do this your working against the clutch...and everything else in the drive train. Brake boosting is rolling along and stepping on the brake while gently feeding the accelerator in correct? So your revs are rising but your not going any faster. Therefore something has to be slipping somewhere, its probably going to be the clutch. Plus your kind of binding everything up. Thats why it shoots forward, its kind of like an elastic band effect. Your putting extra twist into the driveshafts and the transmission they WANT to spin faster but cant so all the transmission teeth are being FORCED into one another and your clutch is being ground down. Its pretty small but still very binding, and I would say pretty hard on everything (we do have strong trannies though and the SRT-4 drivers used to do this A LOT)

For instance in my shifter kart once your in motion you don't need the clutch. Its a straight sequential box, pull to upshift push to downshift but if you dont let up off the gas a smidge to unbind the gears when upshifting you will NEVER get it into gear.There is a certain amount of lash or slack in drivetrains they are designed that way to allow for when you get off the gas and such. A racecar runs much tighter clearances in the gearing, and like when you get OFF the gas the engine braking is intense and instant. If you let off the gas in our cars it happens slower. Trust me, its because of the slack in the gearbox. So when you brake and get on the gas you take that slack or lash out of the drivetrain...the extra push you feel is also because there is no time for the gears to engage i.e. take up the slack as they are already puching on one another.

The Ferrari's that have sequential boxes can flat shift on upshifts with no clutch because:

1.) They have straight cut gears (We have helical)
2.) The Magnetti Marelli Box cuts ignition as soon as it feels the lever being pulled. (Same as letting off the gas a smidge in the shifter kart) This unbinds the gears and there is NO explosion pushing the piston on its downstroke due to NO spark. The really smart LMP2 cars and F1 cars with hydraulic valves can keep both intake and exhaust valves closed to control engine braking...

Dammit I got sidetracked...

Trust me its hard on the car... :)
 
brakeboosting isnt as bad as you make it out to be, you're simply applying load to the turbo so it will build positive pressure. If your clutch is slipping you need a new damn clutch. Also BBing in 5th gear at low rpms will not build much pressure as you have to be in a efficient rpm range for the turbo to get enough air.
 
If the clutch doesnt slip explain to me how you go no faster yet build revs while in the same gear?

I am pretty sure the ONLY thing that can really slip in a drivetrain is the clutch, unless you have some sheared gears...
 
I think maybe you're misunderstanding a bit of the mechanics of brake boosting. The only components being unnecessarily stressed are the brakes--and even then, you're almost never brake boosting for more than a few seconds at a time, so it's no harder on the brakes than riding them for a few seconds at whatever speed you happen to be travelling.

From the drivetrain's perspective, there is no more stress than if you got on it hard under any other circumstances. In fact, from the point of view of your drivetrain (everything from the brake rotors inward), the situation is 100% mechanically identical to driving up a hill just steep enough to keep you from accelerating at WOT.

The engine doesn't speed up, nothing speeds up except for the turbo.
 
when applying both the brake and gas during BBing the rpm's do not climb, just a thought..
 
dmention7 said:
I think maybe you're misunderstanding a bit of the mechanics of brake boosting. The only components being unnecessarily stressed are the brakes--and even then, you're almost never brake boosting for more than a few seconds at a time, so it's no harder on the brakes than riding them for a few seconds at whatever speed you happen to be travelling.

From the drivetrain's perspective, there is no more stress than if you got on it hard under any other circumstances. In fact, from the point of view of your drivetrain (everything from the brake rotors inward), the situation is 100% mechanically identical to driving up a hill just steep enough to keep you from accelerating at WOT.
Click to expand...

that makes perfect sense
 
pretty sure the revs do not go up while you are brake boosting... the post above this one describes it well by saying its like going up a hill
 
954_ms3 said:
when applying both the brake and gas during BBing the rpm's do not climb, just a thought..
Click to expand...

Usually no, the rpms do not climb. You're keeping the car from accelerating by using the brake. If the rpms climb your clutch is either slipping or youre not giving it enough brake. The only thing you are doing is adding LOAD to the turbo and the brakes.
 
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