boost or no boost

[ks71z28]

I calculated my system brake torque from my old set up, 12" fronts 2.75" caliper bore, 11" rear with 2.5" bore. 1.125" master, power brakes 9" dual diaphram

New
12.75" front rotor, (2)1.69" pistons bore, rear 12" rotor, 1.75" bore, 7/8" master, manual brakes. (for better brake feel)

I cannot stop the car. Old brakes had poor feel, but would lock up and stop on a dime if needed. New system no way here is what my calculations revealed

Old total system torque- 2040 ft lbs
Pressure to calipers with booster 1080psi

New system total torque- 1077 ft lbs
pressure to calipers no booster- 938 psi

Conclusion, those big GM single piston calipers grab! If I change to a smaller bore master 13/16" i can gain 13%, and 3/4" I can gain 36%, but still off the old system.

Keep this in mind when upgrading to "big brake kits"

[David Pozzi]

Are you using the corvette calipers?

The single diaphragm booster has a better feel in my opinion.

Our Baer kit on Mary's 73 has the early 90's vette calipers, which are 38mm or so, I think the later calipers are slightly larger. I tried manual on that all the way down to a 13/16" bore. I could lock the brakes if I stood on the pedal but Mary could not. I couldn't see braking at that level for 1/2 hour on a race track, so we put the booster back on with a 15/16" bore master. I would have liked to try a 3/4" on it.
Early 70's ford master cyls work if you file the bolt holes wider, they have manual versions with deep pushrod holes, the ports are on the engine side though, but it works fine.

[ks71z28]

Are you using the corvette calipers?

The single diaphragm booster has a better feel in my opinion.

Our Baer kit on Mary's 73 has the early 90's vette calipers, which are 38mm or so, I think the later calipers are slightly larger. I tried manual on that all the way down to a 13/16" bore. I could lock the brakes if I stood on the pedal but Mary could not. I couldn't see braking at that level for 1/2 hour on a race track, so we put the booster back on with a 15/16" bore master. I would have liked to try a 3/4" on it.
Early 70's ford master cyls work if you file the bolt holes wider, they have manual versions with deep pushrod holes, the ports are on the engine side though, but it works fine.
Dave,

I have the LS1 calipers with a 43 MM bore, which is bigger than the C5 caliper. With EBC Yellow stuff pads, I cannot lock the brakes, I want to try a 3/4 master, but fear that will take too much pedal travel. I like to left foot brake the car, and with a booster it is tough. I agree the dual booster has very poor feel. thanks for your insite

Keith

[Apogee]

Keith, I know that you've been fighting this for a while...do you think it could be the pads? I haven't personally run the EBC Yellowstuffs, but we've got customers running setups similar to yours except for the pads on 1000# plus heavier cars with excellent results. Achieving lockup isn't an issue for them.

We recently had a similar situation though with a customer running the lifetime replacement Performance Friction pads sold through Autozone. He was running a hydroboost and generating excessive pressures at the calipers and could barely get the thing to stop. Swapped out the pads after fighting with it for days with the cheapest NAO pads Autozone had to offer and it was night and day difference. Could've been a bad batch of pads or something. Just food for thought.

Tobin
KORE3

[ks71z28]

Anyone have pads they want to loan me to try??? I need C5 fronts and LS1 rears????