AP Racing brake systems in development

[der_rainman]

Arnie - nice find! I'm curious to see the backside of that kit. I'm hoping its compatible with the usual hose diameter that most people use with their ducting. Respectively I hope Essex's kit works with that type of hose and isn't a one-off custom bit.

[JRitt]

Thanks for the link Arnie...that looks cool indeed. I'd also love to see the backside, as there's not much room to work in there.

Arnie - nice find! I'm curious to see the backside of that kit. I'm hoping its compatible with the usual hose diameter that most people use with their ducting. Respectively I hope Essex's kit works with that type of hose and isn't a one-off custom bit.

On the FB page, APR wrote 'This will fit a 3" high temp. brake hose to feed air-flow to your hot brakes on the track."

Three inch hose is a generally accepted standard size, what we currently use in racing, and what we will be using in our application.

[Arnie_1]

Cheers Jeff! Very cool they are using the 3" standard hose size. Maybe you can contact them directly to get some insider info. And since they are still in the developmental stage maybe, as a brake manufacturer, you can add your input before things are finalized.

[000 Racing]

Hi Jeff, due to my race category rules I have to run no bigger than the standard diameter 294mm I believe.. can I use the comp calipers on a standard disc or one of yours about the same.. I am sure I could fudge it to 300mm ??
If not I need to keep looking..
Thanks
Chris

[Arnie_1]

I imagine, technically speaking, the piston size of that caliper is matched specifically to that diameter to maintain proper brake bias. So even if you were to get the bracket machined so the caliper could fit the smaller rotor it might not be ideal. I guess the question is would those few mm's be within reason for a decent brake bias, or would even that amount of change throw things off significantly?

[JRitt]

Hi Jeff, due to my race category rules I have to run no bigger than the standard diameter 294mm I believe.. can I use the comp calipers on a standard disc or one of yours about the same.. I am sure I could fudge it to 300mm ??
If not I need to keep looking..
Thanks
Chris

Hi Chris,
I obviously haven't seen the rules for your class/series, but if you are limited to the "OEM-sized" discs, you'll likely run into issues with disc width as well. The USDM stockers are only 24-25mm wide I believe, while our Competition Systems are using a 32mm wide disc. The sanctioning body will likely not go for that much added thermal capacity...but it just depends on how the rules are worded, etc.

That said, I can special order different variants of the CP8350 that are narrower. To address Arnie's point on brake bias, the narrower CP8350's also have a range of piston sizes available that would mate up to the smaller diameter discs to ensure appropriate bias. We would just have to do the math to determine the appropriate size, so no problems there.

Also, AP Racing has a range of brake discs in the 290mm-295mm range that would match the narrower version of the CP8350 caliper. You'd be on your own for fabricating the appropriate caliper mounting brackets and disc hats to get the parts on the car though. Shoot me an email and I can present some more detailed options to you. Thanks.

[Arnie_1]

Or, if he really wants a 4-pot while remaining with that rotor diameter, he could just use the OEM Subaru 4 pot and some 2 piece standard rotors like DBA's. Or the fancier AP Racing Group N 4 pot. Woot!

[Matt Andrews]

Originally Posted by JRitt

Thanks for the link Arnie...that looks cool indeed. I'd also love to see the backside, as there's not much room to work in there.

On the FB page, APR wrote 'This will fit a 3" high temp. brake hose to feed air-flow to your hot brakes on the track."

Three inch hose is a generally accepted standard size, what we currently use in racing, and what we will be using in our application.

I figured this was the case. I honestly was thinking that a smaller size would be sufficient and easier to route. I know the guys at APR well. If we need more info, let me know, but this seems really straight forward.

[ICantAffordAnLFA]

Is there an eta on these?

I've 3 dates at Silverstone coming up.

[JRitt]

I can't give any firm dates yet, but we are supposed to do field testing next week on both Competition Systems. If all goes well, they will go into production immediately thereafter.

[Captain Snooze]

@JRitt
About 30 years ago I was friends with a guy who was into hill climbing in a big way. We were discussing brakes and he said brake ducting on road cars was a bad idea. The story went something like this: if you were using hard pads on a street car they would never get up to temperature and when you used them on a track thermal shock was much greater (i.e. a much faster heating and cooling cycle). He said this wasn't a problem with race cars because the discs were replaced often but if you didn't replace them they were more prone to cracking.
Your thoughts please.

[JRitt]

@JRitt
About 30 years ago I was friends with a guy who was into hill climbing in a big way. We were discussing brakes and he said brake ducting on road cars was a bad idea. The story went something like this: if you were using hard pads on a street car they would never get up to temperature and when you used them on a track thermal shock was much greater (i.e. a much faster heating and cooling cycle). He said this wasn't a problem with race cars because the discs were replaced often but if you didn't replace them they were more prone to cracking.
Your thoughts please.

Brake ducts on a road car are not a bad idea, you just have to know how to manage them. When a disc is run on the track, the iron expands quite a bit due to heat. When it cools off, it shrinks. The constant heating and cooling, growing and contracting, is what stresses the metal and causes it to crack. Since cooling ducts provide greater airflow and cooling to the discs, they increase the rate of cooling.

Ideally, your discs and pads would maintain a nice steady temperature on the track, without any violent swings upward or downward in temperature. In that situation, the consistency of the brakes would be very good...pads and discs stay at the same temp, and maintain a consistent mu (coefficient of friction). The discs aren't oscillating up and down in temperature, so they aren't as prone to cracking.

Race teams keep a close watch on brake temperatures, and they shoot to eliminate wild swings in temperature. They have a target temperature range based on the pads and overall brake setup they are running for a given track. They can adjust how much cooling air is allowed into the brake ducts, by blocking the duct inlets on the front of the car. If you watch a race at certain tracks, you'll see brake ducts that are partially (or even fully) blocked off.

On a track that is really tough on brakes, you may need as much cooling air as possible, just to keep the brakes in a temperature range where they aren't fading. On a different track however, you may have one very high speed, hard stop, followed by long straights and some low speed stops. In such a case, the brakes would have plenty of time to cool down, even without ducting. If the ducts are wide open, they could introduce so much cool air that the pads don't work as well by the time the car gets back to the hard stop (most race pads don't work great cold...mu varies by temperature), and the discs will get quite a shock going from rather cool (several hundred degrees F) to very hot (possibly 1200F+) during the short time span of that stop. In that case, it would make sense to not use the ducts, in order to keep some heat in the pads and discs during the cooler running portion of the track. That way the upward temp swing isn't as great when you get back to the hard stop, and the pads are already closer to their ideal operating temp.

Also keep in mind that pro race cars have different setups for different tracks. In NASCAR for example, they run heavy duty equipment on a road course like Watkins Glen, whereas on a super speedway that isn't so tough on brakes, they'll run the lightest equipment possible...different calipers, discs, and pads.

For most of the enthusiast, track day, club race guys like us, we don't have the luxury of multiple brake setups. We have one setup, and we have to make it work the best we can. We can use disc paint, which shows the max temp. the discs have reached. Caliper temperature stickers are also available, and you can have a friend check temps with a pyrometer in the hot pits. That is all valuable info to get an understanding of how your brakes are working and the temps they are reaching. Real-time temperature collection is more difficult and expensive.

Then you have to interpret that data based on the tracks you're running and the demands you are placing on the brakes. Are you having any pad fade, are you exceeding the max temps. recommended for the pads you're running, is your pedal getting mushy (fluid fade)??? Then you can decide if you need more or less cooling air, size of duct opening, etc. It's something that takes time and experimentation until you can really dial it in, but every car setup, track, and driver is different. What works for one person in a certain situation, may not be ideal for the next.

[Matt Andrews]

Only reason I could see brake ducts being bad on the street would be if your pad selection was such that they never got into their effective temp range on the street. This could eat rotors and not stop effectively. But with the proper pad selection this wouldn't be an issue. It goes without saying though, that brake ducts on the street would be boarderline pointless if you never put the car on the track.

[track_warrior]

Originally Posted by Matt Andrews

Only reason I could see brake ducts being bad on the street would be if your pad selection was such that they never got into their effective temp range on the street. This could eat rotors and not stop effectively. But with the proper pad selection this wouldn't be an issue. It goes without saying though, that brake ducts on the street would be boarderline pointless if you never put the car on the track.

Well unless you do very spirited driving on canyons and use the brakes a lot. Twisted sisters pass around my area has you using the brakes a lot during the downhill which is 12 miles long, but there are only so many few high speed sections that the ducts will get enough air to cool the brakes. So i agree in a part that for street driving they might be pointless but for the track i see them as a necessity specially if you live in a place where you track the car with temps over 100F. Cant wait for an oil cooler for this car as well.