Brake Boosting...how to pull this trick off?

[dmention7]

To quote myself from an almost identical thread: (http://www.mazdas247.com/forum/showthread.php?t=123725788)

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.

I think people should take a few seconds to actually understand what brake boosting is before posting a bunch of scary misinformation about how it's going to destroy your entire car....


It's not dangerous and unintelligent, it's not going to blow up your motor or grenade your transmission. All it's going to do is eliminate a few 10ths of a second of spool time at the expense of the amount brake rotor/pad material you'd spend applying the brakes for a few seconds.


EDIT: unless you're talking about trying to do it from a dig... which does seem silly. Generally the term brake boosting is associated with something you do from a roll. From a dig, it's just as effective to learn how to launch properly. The MS3 has more than ample torque to smoke the tires in 1st with a simple low-rpm launch.


EDIT#2: Sport6 has it right. Just feather the brake with your left foot, while using your right foot to press the accelerator until you've built full boost. It does take a bit of practice to hold a constant speed while building boost, if you're not used to left-foot braking.

 

[HOBDisease]

There's a difference between braking boosting and "riding them for a few seconds at whatever speed you happen to be traveling"...when you're riding the brakes for a little bit the engine is decelerating...the only "force" the brakes are acting against is the spinning motion of the rotor... but when you're brake boosting you're applying the brakes to slow down the rotor while you're at WOT with the engine attempting to spin the rotor with everything its got. Brake boosting is not going to grenade your entire car but it does put more-than-normal strains on the engine and the drivetrain, and doing it for a prolonged time WILL **** your brakes without lubrication...if you're just running something that's "slow" or about evenly matched then don't even bother...but if you're desperate...go right on ahead.

 

[mattj3636]

your not WOT? you use the acelerator just enough to build your boost, and you counter use the brake to maintain a steady speed...

 

[HOBDisease]

Either case the amount of throttle it takes to build boost is near WOT, correct me if I'm wrong.

 

[Wagonbacker9]

throttle and boost are directly related...

 

[mattj3636]

okay then correction, your using the acelerator to spool up the turbo, you can give it slight throttle and your turbo will still spool and build boost.

its primarily used just to get rid of turbo lag, you dont have to be WOT. i do it on the highway often.

 

[HOBDisease]

Throttle and boost are NOT directly related.

 

[Wagonbacker9]

Throttle and boost are NOT directly related.

that is quite possibly the STUPIDEST thing I've ever read. Directly related simply means that as one rises, so does the other. if you give the car more throttle, you will get more boost. "Direct" doesn't imply a 1:1 relationship, obviously thats not true, what scale would you use to assign such a thing.. and there are obviously other factors at play like load and RPM...

 

[AWDthis]

^ Thats true...i think he was thinking you said directly proportional.

 

[HOBDisease]

Excuse me, misunderstanding on my part, all I'm saying is in order to brake boost (full boost) will require close to full throttle to achieve.

 

[mattj3636]

okay but the point of brake boosting is to get aruond turbo lag when racing from a roll, even if you use partial throttle, half throttle for example, you'll still have instant boost when you let go of the brake and then go WOT, you'll have boost built up already, not necessarily full 15.6 psi or whatever our cars run, but even having 7-8 already built up will get rid of the lag

 

[Wagonbacker9]

Excuse me, misunderstanding on my part, all I'm saying is in order to brake boost (full boost) will require close to full throttle to achieve.

supporting the spirit of your point... the truth of this would depend on RPM... the load would be provided by the brakes, but there are still other factors to consider.

 

[HOBDisease]

One more thought I would like to get out there...when you say throttle is directly related to boost, I'm assuming you're saying the amount of pressure inside the manifold, right? Okay now picture this...as you increase throttle at a set rate, does the engine not increase vacuum (negative pressure) before it builds "boost"? So if you plotted pressure (positive or negative) and throttle together, will you still call the two as being directly related? Correct me if I've mistaken.

 

[Wagonbacker9]

One more thought I would like to get out there...when you say throttle is directly related to boost, I'm assuming you're saying the amount of pressure inside the manifold, right? Okay now picture this...as you increase throttle at a set rate, does the engine not increase vacuum (negative pressure) before it builds "boost"? So if you plotted pressure (positive or negative) and throttle together, will you still call the two as being directly related? Correct me if I've mistaken.

your car builds the most vacuume with the throttle completely closed... the throttle body will ALWAYS cause more restriction than a turbo.

There may be the slightest moments where this is not true if you go from heavy vacuume and low turbo speed to WOT, and variable geometry turbos may or may not be an exception as well.

The only real (longer than a few milliseconds) exception I can think of to a direct relationship between throttle and boost is a drive by wire system, where even with your foot to the floor the TB doesn't open proportionally... in this case I would amend my intended statement to mean throttle position as measured at the throttle body, not the pedal.

to directly address your question, NO. If what you described was accurate.. if you were rolling on the throttle in say 3rd gear at 60... what you described would be starting at 20lbs or so of vac (for me)... and then as I rolled on the throttle, I would generate MORE vacuum. This is not the case. The amount of vacuum would decrease and I would build boost as soon as the amount of restriction by the throttle plate (and subsiquent actions by the ECU) allowed the turbo to do so.

 

[HOBDisease]

Correct me if I'm wrong but I believe a spark ignition engine produces the most vacuum with no load @ a cruising rpm say 1500-2500

 

[Wagonbacker9]

I'll take a look at that... honestly I don't know if I've ever looked at my boost gauge under those conditions... really only care what the vac reading is at idle, and what full boost is.

 

[HOBDisease]

Alright man, pretty good discussion though

 

[Wagonbacker9]

lol lil off topic.. sorta.

 

[mattj3636]

my vac is around 24 at idle.. normal?

 

[PCspeed3]

mmmmmmm not worth it