Boost Breaking Brake Booster Benefits?

 

I was chatting with a colleague of mine about turbos and he asked ".. so if you have a turbo, doesn't boost prevent the brakes from working?"

I was like.. what?

The thought was:
Brakes use engine vacuum to assist the driver in pushing the brake pedal down (vacuum servo). With turbo boost you create positive manifold pressure (i.e. boost) and now the brake booster does not have a vacuum to work with to assist with braking!

No this is not the case.

Here are some reasons:

1. The Brake Booster contains a one-way valve so it only stores vacuum. Positive manifold pressure does not affect the brake booster system.
2. Boost only happens during acceleration, so if you're just coasting, chances are, you'll be in vacuum anyway.
3. If you are braking during acceleration, you would lift your foot off the accelerator, causing the engine to run into vacuum, before you press the brakes.
4. If you are left-foot braking during acceleration, there will be sufficient vacuum inside the brake booster system to assist with braking (usually up to two or three full brakes). Even if you do the full brakes under acceleration, reducing the engine speed would reduce exhaust gases and hence drop your manifold pressure into vacuum again.

Boost doesn't break the braking system. It may only affect the vacuum servo if you somehow use up all the stored vacuum. Remember, even without the vacuum servo, you can still use the brake pedal, it'll just require much much more foot power. It's a brake "booster" after all.

The only event that could potentially make you lose brake booster vacuum is if your engine is stuck on full throttle. It's called 'Unintended Acceleration'. In this situation, the engine is no longer in vacuum and after depressing the brake numerous times, you could run out of brake booster vacuum.

But this is an unlikely scenario. Apart from the numerous mechanisms preventing an engine from being stuck in full throttle, with a screaming engine, the driver would notice it..

Some things to help prevent a disaster:

• Disengaging the powertrain (via the clutch) will stop the car from accelerating and you'll then hope that your rev limiter on your computer prevent the motor from going nuts.
• Turning off the ignition to in an effort to stop the engine (but you'll definitely lose vacuum and brake booster as well as power steering). But note that there should be enough stored vacuum inside the brake booster system to allow the car to stop.
• Don't forget there's the e-brake. Once you've disengaged the motor from the gearbox, slowly engage the handbrake. Pull it slowly or you'll drift sideways.

So relax. If you have a turbo you're not gonna break your brake booster system.. And you will be able to brake normally in normal operating conditions!