Hydroboost guidance

[scott_fx]

Hey Guys,

I'm working on the final mechanical modifications to my 66 chevelle. I am having a hell of a time getting good brake performance. I have an ls378 with low vacuum so I added an electric pump. The brakes are c5 brakes and you’d think the brakes would bite but it feels like I’m driving a car with drum brakes. I’ve swapped out master cylinders, pads, proportioning valves, bled and rebled the lines. Nothing is helping much. Pressure at the calipers was about 1,100-1,200 psi iirc.

I bit the bullet and got some 6 piston willwoods with 13” rotors up front and 4 piston 13” rotors in the back. I want to do this one last time so I’m thinking of going with a hydroboost setup. The hydra boost system is nice but damn... that’s gonna stretch the pockets. I was looking at the CPP show prep but the pressure seems low on that unit.

Do you guys have any suggestions for my setup? I’d like to stay at or bellow $1,000 for everything (hydroboost, MC & proportioning valve if possible.

thanks in advance

[c4racer2]

Not sure how good those vacuum pumps are.

If you design a system for manual it will bite just fine and have reasonable pedal pressure but it takes a lot of work to do the math and get it right. Boost can cover up a lot of things on brake system design.

People run them, but I don’t think C5/6 or Most off the shelf wildwood setups have big enough pistons to work properly as manual brakes. They are all designed for power applications.

So you have two options - design it all correctly for manual operation including piston area front and rear, rotor size, master bore, pedal ratio and pad friction. Or take a system designed to work on power and run a hydro boost.

I like the first approach personally. But it takes some getting used to. The pedal has longer travel to get into the area where it bites hard. It shouldn’t require any more pedal pressure than a well designed power setup if you design it properly. But the feel is different. I was able to adapt to it so far - we’ll see how it works for me at the track.

[stab6902]

The C5/C6 style wheel brakes are designed to work with a 1"' master cylinder with a dual 9" vacuum booster. Is this what you're running? How many inches of vacuum is your booster seeing?

There's a chance the Wilwood brake calipers you bought won't perform any better than what you have on the car right now - it's not the piston count that matters, it's the piston area.

[scott_fx]

The C5/C6 style wheel brakes are designed to work with a 1"' master cylinder with a dual 9" vacuum booster. Is this what you're running? How many inches of vacuum is your booster seeing?

There's a chance the Wilwood brake calipers you bought won't perform any better than what you have on the car right now - it's not the piston count that matters, it's the piston area.

I had a 1” with a dual 9” and I believe I had about 20” inches of vacuum with the electric pump.

I purchased the c5 calipers off of eBay. So I wanted to make sure I started with all new stuff

[stab6902]

Hmm, all that sounds fine. What's your pedal ratio? It should be around 3.5 (the bottom "power brake" hole on a stock brake pedal). Your pedal isn't bottoming out on the floorboard, is it? Your pressure seems low... you should be seeing 1500+ psi before booster runout with that much vacuum.