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#14 -- Power Brakes & Camshafts

7/18/2023

When running power brakes there are always concerns about the cam selection; will it provide enough vaccum to operate my power brakes? There is not a simple yes or no answer. It is a matter of degrees. The power brakes power assist is provided by engine vaccum. The more vaccum the more boost. That seems simple, but many think it is a cut and dried, black or white situation - it is not! It is a matter of degrees. As the cam gets larger (degrees of duration @0.050") the vaccum (espescially around idle) will be reduced. But on the other hand as the engine displacement increases the vaccum will rise (that means increases to chevy guys). So we get to how much vaccum do you need. Now we get to my favorite word "trade-offs". As the cam gets larger (duration) you can make more power (torque/hp) but you will need to push the brake pedal harder. Keep in mind this will only have a big effect near idle. As the rpms increase the vaccum (boost) increases. For example: if you are cruising above idle rpm and you have to suddenly stop what is the first thing you do? (After you swear at the idiot who ran his pedal bike into your lane) You quickly take your foot off of the accelerator, the engine drops rpm, and the vaccum rises instantly and you have maximum boost to your brakes (and the idiot lives to do it again). So what's your problem? The problem is when you are driving or cruising very slowly (like in a funeral procession for a pedal biker or in a parade) your vaccum will be very low and your boost is very low. It may take two (or more) feet on your brake pedal to stop. How do we get around this? drive faster is one way. Another way is to drive with two feet, one on the brake and one on the accelerator and shift your transmission into neutral. This will allow the vaccum to increase as the rpm increases and give you more boost. As the drive you must decide how much power brake boost you can live with, or without There are other ways to increase the vaccum.  Increase the spark advance at idle. If you can tolerate 14°/16° initial spark timing that will do wonders for your idle and low end vaccu, Use a vaccum cannister. Use a vaccum pump. If you have a hydraulic flat tappet cam we have lifters available that bleed down at lower rpm to increase the vaccum. P/N 5003.