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I am getting parts for my brake set up . I have just bought an 8pot D2 BBK for my GC8 and I have seen that DBA makes a rear disk with a 312disk which I am thinking of using . I have a set of Brembo 4pot Junior kit (can fit up to 300mm) which I am thinking to use . Will those 4pots work in the rear as I had bought them years ago but never had the chance to use them .
The car is mixed use of daily/hill racing and soon hoping to hit the tracks .
Any opinions would be welcomed .
Have you done the math? By that I mean used one of the spreadsheets that calculates Front / Rear brake pressures and axle torque for a given caliper / pad size and brake disc size? I have used a spreadsheet provided by the engineers at PFC, but I'm sure Brembo probably has similar.
My experience with GC8's on road and track is that they do not need a lot of rear brake, and it is very easy to overbrake the rear on them. I run an Alcon 4 pot caliper on the front with a 330mm rotor, and the STi twin piston rears on a standard rotor. This combination (with twice the brake line pressure to the front brakes) will lock the front brakes just before the rears, if I put more rear bias in I'll lock the rears before the fronts.
A "daily" driven machine normally requires pads that work from cold, but the "hill racing" may be a problem? Exactly what you you mean by that - hill-climb races, fast drives through the hills? If the latter are they relatively steep with hard baking on the down-hills which ill put a lot of heat into the brakes, or fast and flowing?
I can't make specific comments on the caliper/disc selection, other than to suggest giving careful though to the relative piston diameters available - it isn't uncommon for the same basic caliper to be available in 2,3 or even 4 configurations - the greater the caliper bore the greater the clamping force and/or lower the line pressures required.
If you're using an aftermarket pedal box with bias bar and two master cylinders, you can use a smaller master cylinder to increase line pressure, or a larger one to reduce it.
All things being equal, a larger diameter disc will have a greater braking torque, as the mean radius will be larger, so you won't only get better potential cooling, but braking. The trade-of is usually greater rotational inertia and, especially, unsprung mass - but not always, as alloy bells can actually reduce the total mass.
There is one very important factor to consider, that's sometimes overlooked, and that's the affect the initial co-efficient of friction of the pads, and their thermal curves, will have on the brakes. Higher/lower co-efficient pads can be used to bias the brakes as required, but how they change as they heat is important, as it's possible to make drastic changes in balance as their characteristics change.
Thank you everyone fro the inputs . I have not done any math calculation at all . I bought the calipers of a mate that will be selling his car they are literally brand new and he gave me a sweet deal that I couldn't resist as even with better disks and pads the oem dimensions (WRX not STi) where not up the task . In the rear I currently have single piston vented disk not the twin pots and I thought the 4pots might help with balancing braking .
The thing is if I use the twin piston rear caliper of the STi I will have to get the whole rear hub as the brake shoes are bigger , hence why I am discussing the dba 312mm disks which will allow me to keep my current brake shoe dimensions . But I could always just use the 2piston calipers of the sti with the dba disks .