marksboy7

iTrader: (6)

Ok I'm getting a hard pedal on the brakes on my car and I'm thinking it's because of my cam. I'm getting about 70-74kPa at idle. Now this is my manifold pressure right? What is that in terms of vacuum and is that what's causing my brake issues? Thought I might need a vacuum canister.

soundengineer

iTrader: (16)

vacuum is opposite of manifold pressure
70 kpa pressure is 30 kpa vacuum(almost 9 inHg of vacuum)

considering stock is around 30kpa pressure at idle...70 kpa of vacuum(20-21 ish inHg of vacuum)

way to get a manual vacuum pump, and connect to your brake booster... then pump the vaccum out till you see when your pedal gets feeling good again, then suppliment the system with a separate vacuum pump, mechanical, electrical...your choice.


or just deal with the pedal feeling like it does, or switch to a manual brake system with the right valves and plunger to get the feel you desire.

Blackbird-WS6

iTrader: (15)

first question... what cam?

soundengineer

iTrader: (16)

that doesnt really matter....
pretty much any cam that has 4* overlap or larger will have very little Idle Vacuum(meaning it idles higher up in the manifold pressure values.)

cam overlap kills your vacuum
even a 224 cam has some vacuum issues

Blackbird-WS6

iTrader: (15)

i had a cam that had 25 or 29*(cant remember offhand, its one of the 2) of overlap and didnt have no brake problems

Ferocity02

iTrader: (60)

If it's the cam in his sig, then the overlap is -3 deg. I would say that he should have more vacuum than 9 inHg at idle.

What is the idle speed?
What are you measuring the vacuum with?

bww3588

iTrader: (49)

AGreed. However, with my ms4, I had 9 inches at idle and my brakes worked fine. No difference between pedal with the stock cam.

marksboy7

iTrader: (6)

I won't give out the cam specs but it has 27 degrees of overlap. Right now it's idling about 1200 rpms. It hasn't been tuned yet, could that be part of the problem?

soundengineer

iTrader: (16)

27* of overlap means you arent going to have very good vacuum...which means you probably wont have very good feeling brakes.

get a tune that has a proper amount of spark at idle may help a little, but its not going to be enough to get you back in the same kpa range as stock to have decent vacuum.

marksboy7

iTrader: (6)

Do you think a vacuum canister will help any or will I just have to get a vacuum pump to get a feel back in the brakes?

marksboy7

iTrader: (6)

Anyone think that'll help? ^