Hi, Just finished re-installing the Brembo brake calipers after sanding off the Porsche imprint and repainting them and thought I'd share a few pictures. Don't look at the mess too much. It's a work in progress. 1) Control knob for turning brake bias cable that connects to master cylinders. 2) Left side view of Tilton tandem brake master cylinder set-up connected to 308 pedal box. 3) Right view of tandem set-up. 4) Right front wheel and caliper. 5) Right front caliper. 6) Right rear caliper. Wil Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Nice job, how is pedal pressure/feel compared to standard? I have the Tilton adjuster, but use AP master cylinders, which have been changed a couple of times to get the right basic front/rear bias.
Wil, What size are the Tiltons (got part #'s)? Looks like you had to custom fab the frame around them. And yes, how does it feel/how far does the pedal need to go and pressure involved. i hate that stock brake MC with Brembo front the pedal goes deep, THEN i have about an inch of 'feel.' It is very manageable due to using VERY aggressive rear pads to balance it, but would love to have shorter pedal movement. MANY MANY MANY THANKS!!!!
Thank you. I haven't bled the system yet (one of the new brake hoses was incorrect) so I can't answer your question but the pedal should feel rock hard. The stock 308 master is a Bonaldi type (Benditalia) which tend to have a squishy feel to them. The Tiltons are much firmer due to the design of the piston seals. I'm also replacing the rubber brake hoses with stainless braided. I came up with the master cylinder sizes with some calculations but I'm sure I'll be doing some swapping with smaller and larger units. Most projects like this require some tinkering. One thing helps, the Tilton Masters are cheap and easy to swap. Wil
Steve, I think the master cylinder sizes are 5/8" (16mm) rear and 13/16" (20mm) front but like I told StephenS, I expect to have to change that and it also depends on the number and sizes of the caliper pistons which will probably be different on your car. The upper and lower mounting plates are cut out of rolled aluminum plate (not extruded) 6061 T6, 1/4" for the bottom plate and 1/8" for the top plate. The bottom plate is sandwiched between the pedal box and the body of the car. I had to make some modifications to the pedal box too but nothing real difficult. The whole set-up is a slightly refined version of what Paul Delatush has on his 308. I'll let you know how it works but I have great confidence in it. Wil
Hi Wil I hope that you have a typo and reversed the master cylinder sizes for your car. a 16mm rear master cyl. will produce more pressure than the 20mm front with the same input force and stroke. I doubt you want a higher pressure to the rear calipers. Assuming a 6:1 pedal ratio, and 25lbs force at the pedal: 16mm = 481 psi 20mm = 291 psi Dual setups generally are reversed, with a larger MC for the rear circuit. I believe you have the same piston sizes at all 4 wheels (if I am not mistaken), so you will want to be careful with your initial MC sizing to get the f/r balance in the ballpark. Should only be fine tuning for load and tire with the prop valve. Parts look great! Eric
Eric, Thanks for the in-put. I said up front that I fully expect to have to change master cylinders but I needed to start some place. And I could have it totally wrong. Redesigning brake systems is definitely not a daily thing with me. Actually the front and rear calipers are not the same. The fronts have more than double the piston area. A 5/8" master cylinder has a piston area of .3068" and a 13/16" master has a piston area of .5185". Roughly speaking, the 13/16" master would have a 4 to 1 mechanical advantage on the front caliper pistons and a 5/8" master would have a 3 to 1 advantage on the rear caliper pistons. If the car does a 360 the first time I stomp on the brake pedal I'll know I need to re-think this but if you see a fundamental mistake in my thinking I'm happy to listen. Wil
I'm no expert, but have AP 6 pots front, Brembo 4 pot rears and havew ended up with a 0.7" front and 3/4" rear.
Hi Wil, your force calcs of the master cylinders is a bit off. There are 2 considerations for mc's, force output desired for a pedal pressure, and volume output requirements. With the known caliper piston size difference for your calipers f/r, you can generate a brake torque for each axle and try to determine how much less force you want to the rear. Remeber, set up the difference f/r for a hard braking event, (meaning front weight transfer and unloaded rear). Quick formula for master cylinder psi output: Pressure in psi = force input (pressure on pedal x pedal lever ratio) / Area of the master cylinder piston (pi x radius squared) Ex: 150 lbs (25 lbs on pedal x pedal ratio of 6) / .63" mc (5/8") area = 0.32 =469 psi output from MC. Its always more complicated than first glance (isnt everything?) You have to consider how firm you want your pedal, and with what travel amount. To set up racing cars I calculate deceleration requirements and use formulas that include the tire grip front and rear, the weight transfer amount based on chassis specs and CG height, and known corner weights. This way I always know how much weight will be on each tire during deceleration , and I set up the pressure to the f/r calipers accordingly. (also knowing the pad friction and braking torque generated at a given pressure for the front and rear calipers) I hope I am helping and not just yapping techno crap. There will always be some trial and error You should be able to get the f/r cylinders close for your car initially. Eric
Thanks. Yeah, a lot depends on total piston area at the front and back but that's just one factor. Whatever works! Wil
Greg, I originally cut up the old calipers untill all that was left was the parking brake function but when I was done they still weighed a ton so I shelved that. For now I'm just forgoing the parking brake so I can get the car on the road. Next winter I'll put some more though into it. If I can't find anything commercially available by then that will fit the bill, so to speak, and also not cost a fortune, I'm cosidering making my own. Wil
Eric[/QUOTE] Eric, I just walked into the house after being on the road since Monday night so I'm not exactly in the mood right now to disect what you're saying but I will take a closer look later. I should tell you though that while I'm not an engineer, a fair bit of math went into my MC selection. Also, I'm a Former SCCA national competitor so I'm not totally unfamiliar with factors such as pedal arm ratios, tire compounds, friction pad materials, weight transfer (wet and dry), etc. Like you and I have both said: In the end it will still take some trial and eror testing. Thanks for the info though. I WILL study it. Wil
Wil, Eric, and all, PLEASE keep this thread 'alive' and post your finding Wil. Eric, how shall i say this, REALLY KNOWS HIS stuff. There is not much info out there for guys like me to follow if/when the time comes for me to dump the stock MC for dual setup and balance bar. ALL help/posts/info from you, Eric, etc is VERY VERY VERY MUCH appreciated!!! For now, the Brembo front, awesome Girodisc rear rotor, and stock Brembo front and DS3000 rear pads with many spare parts due to wear/tear/track is all my wallet dictates The current 'problem' is the darn pedal goes in too deep. Heck, if i could just reduce by 50% or so of how deep the pedal needs to go i'd be a happy camper. Anyone know if there is a way to do that with the stock MC??? Change the ratio of the pedal???? ALL help is ALWAYS appreciated and my apologies if this seems like parachuting your thread Wil.
Thanks for the kind words Steven, but in the end Im probably as full of **** as the next guy. I have also found that all the clever engineering and math can add up to nothing in the real world. So in the end it will be trial and error to find the combo that suits car and driver best. Wil, it is plain that you are no stranger to building performance cars correctly, and I now believe you can drive them as well. I certainly dont mean to preach to the choir. Just hoping to help out on the frontside. I am stuck here in Japan for a while and I wont get to play with a project of my own for a bit, so I meddle around with other guys projects to feel better! haha. Eric
VElocity engineer, It would be so cool if you gave us a technical primer on brake systems. Could you start with a 1000lb race car and take us through the math of designing a system including disc size, factoring in disc cooling, mastercylinder size using the universal Tilton style tandem master, and show us what happens when we change caliper piston area and tire sizes? It would be a really cool thread that I am sure would have huge readership.
Hi Fatbillybob, sorry for the late reply, I will see what I ccan do. I can go through the process for changing road car parts or designing a racing system.The problem is all the tools I use for this design are math spreadsheets and some special programs. I cant show that here. Let me consider the best way to do this, and Ill see what I can post. Cant give away all my secrets, I get paid to do this! Eric
We don't want you to give away secrets. I was more interested in understanding brake systems in a "primer" sort of way, factoring in things like a brake rotor scrubs energy by having a speciifc heat capacity and using a smaller rotor may work if you can cool it and how you make such trade offs or generic calculations etc... It would be great to understand such compromises and or compromises I have not even thought of. It is all pretty interesting to me and would help me and others to understand why one aftermarket system may meet compromises better than others for specific purposes and uses.
Eric, Well, it took me a few days to have some spare quiet time to sit down and go through your formulas and all my figures and you are right. I did get the front and rear master cylinders mixed up! I think I may even want to go larger on the rear MC. I'll have to check through my spares to see what I've got. Thanks for the in-put eventhough it is a little humilating but better that than waste a lot of time trying to figure out what I did wrong after throwing the car into a spin with the brake pedal. Just in case you or anyone else are interested, the pedal ratio on the 308 is 4.5 to 1 (it's going to be a very hard pedal) and your area calculation for a 5/8" piston is off slightly but probably not enough to have too much affect in the final results. Regards, Wil
Hi Wil, Glad to help in any way. Your system is going to be very nice in the end. It is obvious that you have put a lot of thought and time into the car. For your amusement and fatbillybob's too, I am including a spreadsheet of calculated data (of which there are several more pages), that gives some information and direct comparison of the OE system and the Girodisc as well as the brembo. Please note: # 9 is the pad material friction, # 10 is the piston area for each system, #12 is the static (un proprtioned) balance by brake torque at identical pressures, # 14 is the actual balance at the wheels-with 50 bar MC output. Note that the brembo with OE rear pads gets too much front brake. something that Steven Rochlin has worked out with some higher coef. pads in the rear, just as we sell in the Girodisc kit. The Girodisc is engineered to stay very close to the OE balance, but raise the braking torque (and heat capacity) at each axle. anyway, hope it makes some sense, and maybe helps you with your system.feel free to fire off any questions. Eric Image Unavailable, Please Login
As another point of reference, with Eric's and Martin's help I adjusted my 308's bias which has the same setup (Brembo front, stock calipers rear with Girodisc floating hat rotors) with Porterfield R4S pads for the fronts, and EBC Greenstuff pads in the rear. FYI for onlookers, the Brembo calipers use the same size/configuration pads as the Ferrari 360, so there are lots of choices there. I should also mention that the Girodisc front kit wasn't available at the time I upgraded, and I consider it to be a better choice now for folks considering a similar upgrade because proper bias is built into the design of the total package.
There you go giving away all the secrets again.... this will come up in your annual performance review Eric. And to think some people wonder if he knows his stuff! That is just one page of what we go through to design a system. You should see some of the esoteric dribble he makes me look at, pressure/torque curves, efficiency curves, heat cycle simulations etc etc. In the end it seems to work just like he said it would. Well done.
Oops the boss is watching...good thing I didnt mention what I put in the coffee. I will take another moment to give some detail about the Girodisc 308 kit. Here are the important points: 1.It is designed to be as close as possible to the brake balance that Ferrari designed into the car. The pedal feel will not become overly soft as can happen when oversized calipers are used. No need to change your master cylinder or booster. It also fits in your OE 16" wheel! 2.The entire system is 22 lbs lighter than OE parts, while the front rotors are 36mm larger in diameter, and the front brake torque increases by 30%. heat capacity, cooling rate, and fade resistance are vastly improved. Rotational inertia and unsprung weight are reduced. The rear brake will have plenty of braking capacity for hard driving, track days, and autocrosses, and you keep the parking brake. 3.The rear rotors are 3 lbs each lighter than the OE rotors, and have better cooling vane design. the rear pads are chosen specifically to match the front pads and keep the brake torque correct for chassis balance. 4.The Girodisc system is $2900 for the 4 WHEEL KIT, and in comparison the Brembo FRONT ONLY system retails for $2595, and leaves you to deal with improving the rear on your own. There is not a better deal available for improving the 308 with bolt on parts. But I am not Ron Poppiel, or Jay the juice man...I am not a great salseman. The logic for this kit is there, and it makes sense. We designed the kit to appeal to the broadest range of 308 owners looking for improved brakes and not just flash. If you still want the biggest baddest mega piston, ceramic rotored brakes ever on your 308, call us. We can make that happen too, just have your amex ready. Now buy the kit and keep my boss happy! I am already in enough trouble! Eric Image Unavailable, Please Login Image Unavailable, Please Login
Can anyone tell me if a twin master cylinder set up would work well with the standard original calipers, if race pads and stainless hoses were also fitted, or would it be pointless and money wasted, I was interested in having the versatility of brake bias. I have removed a lot of weight, especially at the front of the car and was wondering if it might be too light at the front and cause brake issues with the possible inbalance of the car, or would this not be a factor.