394mm/390 CCM Brakes!
07-03-2016, 12:08 AM
#61
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So for those who think about these things...
I’ve calculated out the front/rear brake bias based on rotor size and caliper piston dia. The 993 turbo has an unusually high front bias with small 28mm pistons in the rear (cf na 993/993rs/963 – 993 rs uses 30/36mm pistons). Some people advocate using the 993RS calipers on our cars to increase rear bias. The other variable is the pressure limiting valve. The 993 turbo has a 55 bar rear pressure limiting valve (vs 993/993rs 40 bar, 964 45 bar, 964 rs 55bar). The effective rotor sizes are also different. Having a LSD would also make a difference.
Any hoo calculating out the front/rear brake torque ratios including all variable above (not including pad surface area/lsd). I get a front/rear ratio (at 70 bar line pressures) of 3 for 993, 2.6 for 993rs, 3.2 for 964 rs and 3.7 for 993 turbo.
Some people feel the 993rs calipers are too much (without a pressure limiting valve when matched with 993turbo fronts – ie rears lock up).
Calculating/estimating the front back torque ratios for the RB set up, knowing the piston sizes and essentially similar sized rotors (front/back), I get 2.5 ish at 70 bar pressures with the rear pressure limiting valve, and 1.4 ish without pressure limiting valve (I still have the stock valve). So this set up increases the rear bias from 3.7 to 2.5 (at 70 bar with pressure limiting valve).
I’ll see how this changes things on the track (next Sat) but so far, these RB brakes feel great. No hint of rear lock up, if anything probably still leaving more brake potential in the rear.
(all calculations available upon request!).
I’ve calculated out the front/rear brake bias based on rotor size and caliper piston dia. The 993 turbo has an unusually high front bias with small 28mm pistons in the rear (cf na 993/993rs/963 – 993 rs uses 30/36mm pistons). Some people advocate using the 993RS calipers on our cars to increase rear bias. The other variable is the pressure limiting valve. The 993 turbo has a 55 bar rear pressure limiting valve (vs 993/993rs 40 bar, 964 45 bar, 964 rs 55bar). The effective rotor sizes are also different. Having a LSD would also make a difference.
Any hoo calculating out the front/rear brake torque ratios including all variable above (not including pad surface area/lsd). I get a front/rear ratio (at 70 bar line pressures) of 3 for 993, 2.6 for 993rs, 3.2 for 964 rs and 3.7 for 993 turbo.
Some people feel the 993rs calipers are too much (without a pressure limiting valve when matched with 993turbo fronts – ie rears lock up).
Calculating/estimating the front back torque ratios for the RB set up, knowing the piston sizes and essentially similar sized rotors (front/back), I get 2.5 ish at 70 bar pressures with the rear pressure limiting valve, and 1.4 ish without pressure limiting valve (I still have the stock valve). So this set up increases the rear bias from 3.7 to 2.5 (at 70 bar with pressure limiting valve).
I’ll see how this changes things on the track (next Sat) but so far, these RB brakes feel great. No hint of rear lock up, if anything probably still leaving more brake potential in the rear.
(all calculations available upon request!).
If so, wow.
07-03-2016, 03:13 AM
#62
Rennlist Member
Thread Starter
^ yup
regular brake line pressures run 800 psi under 'normalish' conditions to '2000' psi for max effort.
ie. say 100 lb pedal pressure if stomping on the brakes, pedal ratio say 1:8 (usually 1:4 to 1:10 - I don't know what our pedal ratio is, I'll go take some measurements!), = 800 lbs, if your master cylinder is 1" (turns out 993/993 turbo master cylinder size is around 25mm) - that's 800 psi...
regular brake line pressures run 800 psi under 'normalish' conditions to '2000' psi for max effort.
ie. say 100 lb pedal pressure if stomping on the brakes, pedal ratio say 1:8 (usually 1:4 to 1:10 - I don't know what our pedal ratio is, I'll go take some measurements!), = 800 lbs, if your master cylinder is 1" (turns out 993/993 turbo master cylinder size is around 25mm) - that's 800 psi...
07-03-2016, 04:09 AM
#63
Rennlist Member
Thread Starter
actually 100b pedal pressure is not that much, I think most pressures at the pedal run 125-175 lbs. How much do you weigh? stand on one foot and compare what your weight is and what pressure you are pushing the brakes when you have to scrub off speed before ?turn 11 at MRLS!
07-03-2016, 08:28 PM
#64
Rennlist Member
Thread Starter
Just made some measurements, pedal ratio is about 1:5.
master cylinder is 25.4mm = 1 inch. dia => area 3.14x 0.5x0.5= 0.785 sq inch
so for 1000psi => X (pedal pressure) x 5 / 0.785 , so X = 157lb pedal pressure to create 1000 psi (without power assist).
I wonder if I can log brake pressures through the obd2 on my data logger or the durametric, will have to check if I can.
master cylinder is 25.4mm = 1 inch. dia => area 3.14x 0.5x0.5= 0.785 sq inch
so for 1000psi => X (pedal pressure) x 5 / 0.785 , so X = 157lb pedal pressure to create 1000 psi (without power assist).
I wonder if I can log brake pressures through the obd2 on my data logger or the durametric, will have to check if I can.
07-05-2016, 05:42 PM
#65
Former Vendor
The pad size has nothing to do with the braking force, however for transmitting the same amount of work, a larger (area) brake pad can keep the braking temperature lower, therefore extend the overall brake life.
07-10-2016, 03:00 AM
#67
Rennlist Member
Thread Starter
very wet track day today.
Got some reasonable sessions in the morning but afternoon was not much fun (too wet).
Brakes work nice! Slightly more pedal movement before brakes start to work. Need much less pedal pressures. Car slows down so quickly that it took all morning before I could start to figure out when and where to brake. I tend to brake early and do quite a bit of trail braking (to be easy on the brakes) and the car would slow down so much faster that I was scrubbing too much speed off. Just need more time to get used to it. ABS seems to work ok. There is some dust but not bad at all. The discs look barely broken in. The front/rear bias seems fine. I think eventually I should be able to brake quite a bit later.
The 19" wheels/tires work fine, slightly more harsh of a ride cf 18" as expected, not a problem at the track but more noticeable on the drive down over rough roads, running few psi lower pressures seem to help, not a big difference though. Was getting some understeer on the track, not sure if it was just because it was slick (wet/cold) or the wheels/tires/pressures. I had things figured out pretty well with the 18's, it's going to take a bit til I'm happy with these wheels.
Will get the car on the lift to inspect everything tomorrow.
Got some reasonable sessions in the morning but afternoon was not much fun (too wet).
Brakes work nice! Slightly more pedal movement before brakes start to work. Need much less pedal pressures. Car slows down so quickly that it took all morning before I could start to figure out when and where to brake. I tend to brake early and do quite a bit of trail braking (to be easy on the brakes) and the car would slow down so much faster that I was scrubbing too much speed off. Just need more time to get used to it. ABS seems to work ok. There is some dust but not bad at all. The discs look barely broken in. The front/rear bias seems fine. I think eventually I should be able to brake quite a bit later.
The 19" wheels/tires work fine, slightly more harsh of a ride cf 18" as expected, not a problem at the track but more noticeable on the drive down over rough roads, running few psi lower pressures seem to help, not a big difference though. Was getting some understeer on the track, not sure if it was just because it was slick (wet/cold) or the wheels/tires/pressures. I had things figured out pretty well with the 18's, it's going to take a bit til I'm happy with these wheels.
Will get the car on the lift to inspect everything tomorrow.
07-24-2016, 09:00 PM
#70
Rennlist Member
Thread Starter
My friend Tim ^ mentioned to me at the track the other day my brake light was coming on less than 50% of the time, in areas he knew I must be braking (although he said it made me look like a better driver than I am as I didn't look like I was braking..). Had my daughter stand behind the car today, and my brake light was not coming on (including 3rd light). Fuses okay. I suspected the switch in the pedal cluster might be bad. Well, switch is fine, with these brakes, pedal travel is less before they start to work. I had to adjust the switch so that they work with less pedal movement. Didn't take any pics, pretty straightforward, just need to loosen and turn a couple of times until the lights come on with less pedal movement.
some pics from cars and coffee bbq in Langley today. Old girl got some attention. (oh yeah new plastidip colour scheme)
some pics from cars and coffee bbq in Langley today. Old girl got some attention. (oh yeah new plastidip colour scheme)
09-03-2016, 12:52 PM
#73
Rennlist Member
Thread Starter
update after more seat time.
So far am pretty happy with the brakes. I'm using RB's street/track pads (I believe it is a GM part) they are in between their street and sintered full track pad. Very user friendly for the street with min/no noise and min dust. Absolutely no complaints at all for the street.
On the track they have been great with no noticeable fade. Modulation is not a problem but the pedal feel is different with little braking with the first few mm of pedal movement and then once it starts to bite, there is little force and pedal movement before the car slows down quickly. Pedal force is 1/2 what it used to be and overall the pedal is higher to get the same amount of braking cf big reds (with giros). Gas pedal now further away for heal toeing. Ceramic type brakes are supposed to get hotter (for similar sized rotors vs steel) but on my car temps are much cooler vs giros, although I'm not using the new brakes to their potential yet and I was much closer to the limit with the giros/big reds.
FWIW temp readings in degrees celcius (measured in paddock after cool down lap) with temp gun - front:
Big reds/Giros: caliper 125, rotor 240
RB: caliper 109, rotor 130, pad 150
no noticeable wear.
My car unfortunately is done for the season, this was the last regular track day weekend up here in the Northwest for me and the weekend was cut short as I have blown my clutch and had to have my car flat decked back the 4 hours from Shelton to Vancouver last night...
Will post a different thread when I figure out what mischief I've done to it, but it seems bad.
So far am pretty happy with the brakes. I'm using RB's street/track pads (I believe it is a GM part) they are in between their street and sintered full track pad. Very user friendly for the street with min/no noise and min dust. Absolutely no complaints at all for the street.
On the track they have been great with no noticeable fade. Modulation is not a problem but the pedal feel is different with little braking with the first few mm of pedal movement and then once it starts to bite, there is little force and pedal movement before the car slows down quickly. Pedal force is 1/2 what it used to be and overall the pedal is higher to get the same amount of braking cf big reds (with giros). Gas pedal now further away for heal toeing. Ceramic type brakes are supposed to get hotter (for similar sized rotors vs steel) but on my car temps are much cooler vs giros, although I'm not using the new brakes to their potential yet and I was much closer to the limit with the giros/big reds.
FWIW temp readings in degrees celcius (measured in paddock after cool down lap) with temp gun - front:
Big reds/Giros: caliper 125, rotor 240
RB: caliper 109, rotor 130, pad 150
no noticeable wear.
My car unfortunately is done for the season, this was the last regular track day weekend up here in the Northwest for me and the weekend was cut short as I have blown my clutch and had to have my car flat decked back the 4 hours from Shelton to Vancouver last night...
Will post a different thread when I figure out what mischief I've done to it, but it seems bad.
09-03-2016, 02:10 PM
#74
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Wow Ryojo, sorry you had to deal with that. But it was fun till that happened, right? :-)
What clutch are ya using, or should I say "were" you using? I have the 764PP, and 4.0 disc. Was hoping this would handle more than enough torque. Stock clutch was torched, or I should say the PP/Flywheel was.
What clutch are ya using, or should I say "were" you using? I have the 764PP, and 4.0 disc. Was hoping this would handle more than enough torque. Stock clutch was torched, or I should say the PP/Flywheel was.
09-03-2016, 04:14 PM
#75
Rennlist Member
Thread Starter
Richard - Yup fun til it happened... (saw your brother in-law again!)
factory CUP style flywheel, Sachs Disc, Sachs Motorsport 999 PP triple strap uprated (designed for 775 hp/tq, 3850lbs afaik - but it was used/came with engine) didn't think I could break that though...
factory CUP style flywheel, Sachs Disc, Sachs Motorsport 999 PP triple strap uprated (designed for 775 hp/tq, 3850lbs afaik - but it was used/came with engine) didn't think I could break that though...