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I installed a Tilton 3-pedal box in my 944. My brake booster had to go due to v8 engine conversion so I did manual masters on a pedal box with an aluminum plate bolted to the floor. The pedal box is bolted to the 3/8" plate with tapped holes. The plate is through-bolted to the floor and door sill. Makes for a nicely solid platform and great pedal feel. The cable throttle works via Tilton's rotating assembly. The dual brake masters drive M030 calipers and the clutch master the Chevy slave cylinder. It's all rather heavy and leg intensive but matches a manual steering rack well for track driving.
The biggest issue with all of this is the shape of the firewall. For master cylinder clearance, the pedals ended up about 4" rearward from original. This worked well for me as I'm 5' 7" and wanted to move my seat rearward anyway for helmet clearance to the halo of my roll cage. Anyone over 6' can't really drive my car anymore, though, as the seat reaches is rearmost position before they have adequate leg room.
I've driven Formula SAE racers that had manual brakes but still had excellent stopping power and pedal feel thanks to weighing a good bit less than half a ton.
What do manual brakes feel like on the 944, which is obviously much heavier? My S keeps getting lighter and lighter but it's probably never going to weigh much less than 2500lb or so. Are manual brakes viable for street use?
This comment is not 944 specific but we built Chevy Monza'so in the mid 1970'September with 500+ HP and manual applied brakes, no brake booster, no ABS, no Traction Control. The race car had a top speed of 140 at Watkins Glen. I raced the car. The weight of the car was about 2200 lb.
You design the brake pedal mechanical advantage to compensate for no brake booster assist. The applied driver brake force was similar to vacuum booster assist brakes on a street car
...You design the brake pedal mechanical advantage to compensate for no brake booster assist. The applied driver brake force was similar to vacuum booster assist brakes on a street car
Interesting.
By this do you mean that you moved the position of the attachment pin on the pedal that attaches to the master cylinder to create more leverage for the same pedal applied presure?
and...
Do you have any thoughts on how this could be achieved on the factory 944 brake pedal?
Why do you want manual brakes? Is it only for the adjustable bias? Why do you need adjustable bias. Not being mean, its just a lot of work to convert.
When you do a V8 swap, the second bank of cylinders is in the way of the brake booster. There are conversion brackets to use the stock master cylinder without the booster, but, in my opinion, that would make the pedal effort too great to make a 2-hour stint very fun. There are ways to put on a hydroboost system running off of the power steering pump, which gives you power brakes, but doesn't have a great pedal feel, in terms of sensitivity.
So, the manual, dual master cylinder, tilton pedal box seems like a solution that will let us play with different master cylinder bore sizes to find the amount of pedal effort we like and give us the best brake pedal feel. Additionally, because of the non-stock brake size on the front, the adjustable bias will help us fine-tune the front-rear balance of the braking (master cylinder size will also help with this).
Putting in the pedals will be a bit more work, as you mention, but I think it'll make the car perform "better" and it will also reduce the complexity of the system (which might improve reliability).
It'll still be a few months out... But I'll let you know how it turns out!
Originally Posted by FrenchToast
Didn't it have F40 brakes or something?
Yes! Good memory! (But we might be switching it to GT3 brakes because of the lower cost and greater availability of parts.)
By this do you mean that you moved the position of the attachment pin on the pedal that attaches to the master cylinder to create more leverage for the same pedal applied presure?
and...
Do you have any thoughts on how this could be achieved on the factory 944 brake pedal?
It's all about ratios. There is one ratio which is the master cylinder bore area to the front calipers' total piston area (for turbo calipers, just calculate the area of the pistons on one side of the caliper).
And then you have the ratio of the lever (pedal). Add these together, and you come up with a final ratio - something like 70:1, meaning 1 unit of force on the brake pedal will equal 70 units of force at the caliper. Now, that might be our value for the system with the brake booster, and we might want a ratio of 120:1 for a manual brake system. We can change the bore sizes of the masters and order pedals with different fulcrum points to achieve that.
There are some people with V8 conversions that drill a new hole on the pedal to move the master cylinder linkage bar up half or 3/4 of an inch, and that helps, but now the linkage bar isn't pushing straight, and you should weld up the old hole in the pedal for strength.
FrenchToast: "Why do you want manual brakes? Is it only for the adjustable bias? Why do you need adjustable bias. Not being mean, its just a lot of work to convert."
Noah: "I don't want manual brakes... just intrigued with the possibilities of what people are doing. I HATE the left side engine bay rear of the upper strut. The booster & mater cyl gets in the way for wrenching & attaching stiffening tubes from firewall to upper strut.
I posted this to learn how people are using the aftermarket peddles & what mods and gains or losses they experience."
Hi Van, did you get this pedal box installed? if so, id be very grateful if you would share some pictures? Im hoping to use the same pedal box and wondered how it fitted around the steering column etc?
Here's a rather novel solution that has proven to be awesome over the past couple of years. I wanted to stay with power assisted brakes on the LS racecar, but hydroboost was out of the question, since there is no power steering. I felt it was just too complicated to add a power steering pump just for the power assist brakes. Here is my solution. Super for a race car, not so practical for a street car. It has raced TRAC GT3 for 2 years now without a problem. It's a light car with standard turbo / S2 brakes, and they just work! Outside of the box solution!
02-28-2017, 03:51 PM
There is one ratio which is the master cylinder bore area to the front calipers' total piston area (for turbo calipers, just calculate the area of the pistons on one side of the caliper).
