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Race brakes, no booster?

260DET
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260DET Experienced

260DET

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Dedicated race car, the choice is between the standard type master cylinder, a booster and a proportioning valve, and, a non boosted system with one or two master cylinders. My main concern is that the non boosted system will require too much pedal pressure which will deaden brake feel, the boosted system on a similar car works well for me and is easy to modulate. I know that no booster is cool and offers more scope for balance with two cylinders but I don't want a heavy pedal. Experiences?

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GTSBoy Grand Master

GTSBoy

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I'm in our US office this week.  A day after saying unkind things about Porsches there has been a GT$ parked outside my window all day and I've had to pretend to ignore it.  Lovely looking thing from behind.

Back to the point at hand though.....Balance bar and 2 masters.  Do it right.  Pedal feel will be umpty bazzillion times better.  There is no reason to expect the pedal effort to be too high if you get the pedal ratio and master/caliper piston sizes matched properly.  This might take more than a guess to get right though.

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Dale FZ1 Veteran

Dale FZ1

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8 hours ago, GTSBoy said:

Balance bar and 2 masters.  Do it right.  Pedal feel will be umpty bazzillion times better.  

get the pedal ratio and master/caliper piston sizes matched properly.  This might take more than a guess to get right though.

The difference is night and day for feel.

Initial setup prep for M/C sizing is by maths to get the basic proportions in the correct ballpark.  And it's quite possible that you will need to trial one or two combinations.  You may not know that you've hit the best combination until you experience one that's not as "right".

My first go, the pedal wasn't terribly heavy, had excellent feel, but the travel was way too l-o-n-g.  Not a good feeling during a heavy decel event from 175 to 60 and that tyre wall seems very close.

Second go with different M/C sizes, the pedal length was where I felt it needed to be, but seemed WAY heavy.  After the first couple of applications, the driver becomes acclimatised to what's required, and you become aware that pedal feel is still sensational.

A few events later and I had a run in Mafia's 34 GTR (lovely car, 400awkW so pretty strong).  Boosted brakes were sensationally strong but devoid of feel and progression.

If you've got the time, budget, and a bit of perseverance, a proper balance bar setup that's actually set up is streets ahead and you don't notice pedal weight.

Some people will disagree and run with modern ABS setups and rely on the technology to do the stopping.  Each to their own.

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260DET Experienced

260DET

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Have spent a couple of hours googling for a simple formula based on master cylinder sizes to total caliper piston sizes with no luck, that would be handy for both options. For the boosted option I do have some info on a MC size that should work, for the manual option nothing. Cost is not relevant, a new booster and MC is probably more expensive.

Dale FZ1 Veteran

Dale FZ1

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www.motorsportbrakes.com.au/

Consult with Marty, brakes is his day job and he knows this stuff inside out.  Far easier to get it right, and he offers great support.  It's not just about selling product for him.

You're going to need the piston sizes of your calipers to get any calculations done.

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