Brake help

[67CamaroLSX]

Working on a 67 Camaro. Here's my set up. Wilwood SLC 56 4 piston C5 calipers up front. Rotor 12.85", Piston area is 4.12, bore is 1.62. Rear Wilwood dynalite 4 piston. 12.19" rotors, 3.00 piston area, bore is 1.38. Pads are Wilwood BP-10 Master cylinder currently is 1 1/8. Wilwood proportioning valve. Booster is a 9". Pedal is around 4.1, but I have to do some better measuring. Car has around 10-11" vacuum at idle. With pedal in upper hole the car stops decent but pedal is squishy. Pedal in lower hole, its stiff and not much braking. I know it doesn't quite have enough vacuum for the booster to work properly. Should I drop down a size or two in master cylinder and increase pedal ratio? What direction would you recommend going to get the proper braking force I need? Thanks for any help.

[67CamaroLSX]

So after getting home a pulling pedal to get a better measurement, it looks like pedal ratio is at about 3.57. Should i try and get it to 5.1 or less?

[67CamaroLSX]

I was hoping to get a couple replies for some guidance. Wasnt sure what to do...so i ordered a 1" master cylinder and will increase the pedal ratio and see where i'm at.

[Rod]

I'm not a brake guy, but I'm watching to see what comes about.......

[stab6902]

A 1-1/8" master cylinder has a piston area of 0.99 square inches, and a 1" master cylinder has a piston area of 0.79 square inches. This means by going to the 1" master, you will pick up 0.99/0.79=1.25 meaning 25% more pressure at the expense of 25% more pedal travel.

You state that using the power brake hole on the pedal (with a pedal ratio of ~3.5) results in a hard pedal, but using the manual brake hole (with a pedal ratio of ~6) results in a "squishy," meaning long, pedal. Using the 1" master cylinder and the power brake hole will act like 1-1/8" master cylinder with a pedal ratio of 3.5*1.25=4.375, which might be a "happy medium" for you.

If you didn't want to go through the expense/effort of changing the master cylinder, you could drill a new hole in your brake pedal arm (roughly half way between the two existing holes) to get the same result.

[67CamaroLSX]

Thanks. I was thinking about drilling a new hole in the pedal to try and bump it up to about 4.5 pedal ratio. I have a wilwood 1" master cylinder also to try. Also though about an hydroboost setup if this doesn't work.

[RobNoLimit]

$.02 I agree with Stab's comments. But I notice that you have 10-11 in vac. to work with. That's pretty low. And, therefore, not much assist for a booster. I would add in a vacuum can and/or remote vacuum pump. (can first as a try, then pump if needed) The down side is, if the can works, it will fail you on a tight autocross when there is no time to store vacuum between stops. Even the pump may not keep up. One of the reasons racers move away from assisted brakes. As to the Hydro-boost, It's a 50/50. They work amazingly well. Tons of brakes. BUT, the plumbing gets expensive and it's 'cluttery'. Also, it holds heat, AND, doesn't allow the driver to modulate the brakes much. this is why you don't see a lot of hydro set-ups on race cars. ABS brake makes an electric/hydro unit that is really strong, and is better to modulate than a standard hydro, but, they are $$. - but not really when compared to the plumbing and a cooler added. I would move towards a 4.5 to 1 ratio and a vacuum can and see where that takes you. BTW, please give us some feedback as you go. Thanks, hope this is helpful.

[67CamaroLSX]

Thanks RobNoLimit for the advice. I had a 1" master cylinder on the way. I drilled a new hole in the pedal to give me a 4.5- 1 pedal ratio. Should be able to get it on this weekend. Thought about hydro boost but not sure if my power steering pump only puts out i believe 2.1gpm. I'm running cts v accessories. Started looking at the cans there cheap so i'll probably go that route next.