Next up on the car was to get the brakes on. This is one of those areas. A great deal can and has been said about what brakes and brake parts you need for racing.
What I am doing on the Sierra as a start, might raise lots of question marks, but here it is.
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At the front, stock standard 3l brakes. Discs, calipers, pads from Midas, rubber hoses. The discs I am using here had been grooved.
At the back, I took off the drums and replaced with the solid discs and calipers off a Sapphire (the hub carriers must be replaced to get the caliper mountings. These carriers was among the parts I swapped Wanegofast for the seat). STD rubber hoses.
For biase control, the std pressure reducer. In this car's case I used the one that was on there, but reversed it. For the drum brakes, it acts as a step-up, but for the discs you need a step down. So it went in backwards. They are not all identical in sizes, so I will see how this works, maybe change it for another later on.
STD brake booster and master also for the moment. No fancy brake fluid, just cleaned the system and replaced it all with Ferodo's DOT 5.1 fluid. This set-up has and is being used on several Sapphires and Sierras racing at K. It does run a bit hot and pads don't last very long, but as long as you have the 5.1 fluid in, it seems to work. So I am going to at least try it before changing it.
On the Sapphire I never even tried the OEM set-up, probably bought into the hype of big brakes and multi-pot calipers. There I went straight to big discs (330mm) on the front and also cross drilled them. On them were the calipers off a BMW 330i. At the back was also vented front discs off a 320i BMW along with its calipers. It was overkill and also I got my maths wrong on the biase, could never get the back to not lock up when you really stand on the brakes. They were eventually replaced with a 4-cylinder Sierra discs with a Ford Bantam's calipers. That along with the FORD pressure reducer AND a Wilwood biase controller got the set-up balanced. That worked very well, pads also lasted very long. But then racing against the other Sapphires with the std brakes, there was no advantage under braking, they could brake as late and although they had to change pads more often, my modified and bigger brakes came to nothing, no gain.
I say all that because while there is no denying that spending your money on a well sized Wilwood set-up of discs, calipers and braided hoses, along with the R1000/liter full synth racing brake fluid will yield very good results, that should not necessarily be your starting point. Such a set-up is quite expensive, so if you don't need it, spend that money elsewhere. Also, by simply looking at a higher performance or bigger/heavier production car, you can put pretty decent brakes on without breaking the bank. It just takes some thought and planning. In years gone by (quite a few by now!), even Wesbank modified racers used production car brakes, just with harder pads.
Some braking principals (it is a huge and very much specialist field, so I type out high level stuff of basics).
Perhaps the first thing to say is that braking performance is not about how many pistons you can fit in there or even how big the pistons are. Brakes are simple hydraulic systems and of more importance is getting the ratio of caliper size from front to back right and then also matched to the master. If you just wanted more clamping force, then simply fit a smaller master cylinder or bigger booster. Simpler and cheaper than 8-pot calipers.
Heat is the killer and normal production car brakes cannot work at the very high temps. You can fit improved pads (harder), but will still end up with discs that will warp and crack, and if they don't, the hard pads will eat them for breakfast. But hard pads, the expensive fluid and probably braided hoses can get you out of a hole.
Better option is to fit bigger discs and bigger calipers. What you are looking for is a big pad, not a big piston so much. Too big a piston and your brake pedal will be long anyway. Along with a big pad will eventually go more than one piston, because the pad can only go that wide before it needs to get longer to get extra size. Then you end up where the biggest piston that can fit in there will not be able to produce an even force over the full length of the pad. There is where more pistons are used.
This bigger pad will run cooler than a small one, even on the very same disc. It is because for the same force exerted, it is spread over a bigger area. I am struggling a bit to find the right words to explain this, but imagine dragging your hand with palm down across a carpet. And put about 10kg weight on it. Your hand might get warm if you drag it far enough. Now do the same, but support all of it just on the tip of one finger. You might actually blister your finger, so much hotter it will get. And yet, the same force as a applied and the same amount of drag was generated. The surface pressure is hugely different.
The bigger disc in itself present more surface area to the surrounding air, so will get rid of heat quicker. If they are cross drilled, then even more area is exposed. The vent holes and also the grooves you see on some serves the purpose of venting gas from between the brake pad and disc surface at the high temps.
Don't neglect the rear brakes. You hear if often that the rear brakes do almost nothing. It is not true. It is almost true for the guys who race shopping trolleys (FWD hatchbacks), but on real cars the rear brakes does a lot. Nominal brake distribution is around 80:20 front to back. To get that you need caliper piston diameter ratio of around 60:40 front to back. Discs size front to back does not need to be identical, but same order of magnitude makes it easier. And vented if possible.