Helped my dad load the LS7 block into his car yesterday so it'll go to the shop this week. I don't think they're too busy these days so hopefully it'll come back quickly.
I'm ready to spill the beans on the brake setup. Got far enough along on this now that I think it is actually going to happen lol. Have made a bunch of progress recently.
Fall last year I thought I'd get creative and put some Porsche calipers on the front with CX9 rotors and buy the SBG setup for the rear and move the stock caliper out to keep things in balance. Well, the massive caliper didn't fit under the 17" Enkeis, and got super busy with life, so the stuff has just been sitting. Then magically, a set of 18" wheels showed up and I have brake clearance haha.
This was originally intended to be a budget setup just to throw some bigger brakes up front wiht a CX9 rotor, but my dad (rightfully so) gave me a ton of shit about unsprung weight, rotating mass...etc etc.
The pad is comically large compared to the ~credit card sized front pad from the stock rx7.
The front only cheap and cheerful project has now become a four wheel big brake project with 2 piece rotors that will be punching up at $7000-8000 Brembo/AP Racing territory for hopefully ~$3500 out of pocket. More than half of that will be the custom rotors which would be much cheaper if the hats already existed.
The calipers are from a 2017+ Cayman S up front, and an '06 - '12 Cayman S in the rear. Porsche is a parts bin company so I don't know the full list of models, but tons of 911's have used them too.
Rotor rings will be a 350x34 front and a 325x24 rear specific for the Porsche calipers. Hats will be designed to my spec to fit the RX7. For those keeping track, that is an increase of 2.2" front and 1.22" rear, and thickness increase of almost 1/2" front.
Before ordering custom rotors, they wanted me to verify fitment. Actually putting my engineering degree to use for once lol I fired up my Solidworks from college and started drawing parts.
The front bracket and the rear rotor template are printing right now. Should verify fitment on the front and get working on the rear fit-up next weekend.
So, how is it all going to work -
Doing some math on the brake torque output, there will be a rearward shift of mechanical/hydraulic brake bias by about 2.7%. My goal will be to get away with still running the factory prop valve, but an adjustable one is an easy addition if this doesn't work out. The factory bias is definitely heavily front biased, but 2.7% is a pretty big change. Another thing I could try which is commonly done is to stagger pad compounds - slightly less friction in the rear would work as well.
Stock Balance Ratios = 67%/33%
New Balance Ratios = 64.3%/35.7%
Percentage of original Torque at equal pressure = 134.2%/151.2%
Doing some more math, with the increase in piston volume pedal travel is going to increase by ~19% vs where I'm at now. At most I think the difference will be about 3/4". When I built the car ages ago I put the 929 master cylinder in the car which I haven't hated, but it definitely takes some leg and I would say without question it is oversized for the stock brakes with a very short pedal. The 1" master cylinder bore of the 929 MC pushes ~15% more fluid than stock. It is also right in the same range as the stock Porsche MC with these brakes, so I should gain some travel back in the pedal but not so much that it feels long. If it doesn't feel how I want, I can move my pedal ratio to fine tune it, but I'm thinking it should feel natural. There is very little flex in the brakes currently with the pedal travel only going to taking up the pad air gap and then it feels solid.
The primary goal is an improvement in brake life, and thermal performance so they can actually be track worthy. EBC Yellows are the best pad I've found for my use on the street that don't fade and have good bite, but they're dusted in 3000 miles up front and 5000 miles rear with no track time.
The stock brakes aren't inadequate stopping power wise, but definitely are not up to the performance of the rest of the car. I will say, with the new power, and the new tires...I have felt from both the driver seat and the passenger seat the need for a more aggressive application of the brakes from 120-130 mph. It isn't that the power isn't there, its that it takes unnaturally high force application. You really need to stomp on them now which can definitely lead to under-using the brakes at high speed. I doubt I'll be able to do any stop tests or anything, but I think there's room for improvement in stopping distance, and also driver confidence without being so touchy that they lock up right away.
Pretty excited to see how all this works out.
