BMW M4 Track Day Issues

[remmoto]

hi all

first time posting here as I'm at a bit of a loss. I've tracked my car around COTA multiple times with no problems, but recently it seems that if I push in the slightest the car overheats, im down on power, and brakes feel mushy

Im running a 2015 bmw m4 DCT w/ girodiscs and pagids, stainless steel brakelines, castrol srf and a basic bilstein suspension and stock power, 275/35/18 square tires range between hankook rs4's, pirelli's, and michelin ps4s. i added a brake cooling kit w/ some ducting which seemed to help but im still down on power and brakes still get mushy.

i can tell im down on power as i usually can hit 155mph on the backstraight of cota but recently it struggles to hit 145mph. its not necessarily weather related, as it cools here in texas im still having this problem.

the top mount intercooler definitely works and i plan on flushing my coolant and replacing the brake fluid but i feel like im a loss of why im down on power, why the car gets very hot after a couple laps of pushing, and why the brakes get mushy.

i would love advice on what to do next time i go out to track, either things i should look for, replace on my car, or measure.

thanks in advance.

[melanthius]

Originally Posted by remmoto

hi all

first time posting here as I'm at a bit of a loss. I've tracked my car around COTA multiple times with no problems, but recently it seems that if I push in the slightest the car overheats, im down on power, and brakes feel mushy

Im running a 2015 bmw m4 DCT w/ girodiscs and pagids, stainless steel brakelines, castrol srf and a basic bilstein suspension and stock power, 275/35/18 square tires range between hankook rs4's, pirelli's, and michelin ps4s. i added a brake cooling kit w/ some ducting which seemed to help but im still down on power and brakes still get mushy.

i can tell im down on power as i usually can hit 155mph on the backstraight of cota but recently it struggles to hit 145mph. its not necessarily weather related, as it cools here in texas im still having this problem.

the top mount intercooler definitely works and i plan on flushing my coolant and replacing the brake fluid but i feel like im a loss of why im down on power, why the car gets very hot after a couple laps of pushing, and why the brakes get mushy.

i would love advice on what to do next time i go out to track, either things i should look for, replace on my car, or measure.

thanks in advance.

No drivetrain warnings? Where are you on the engine coolant temp gauge?

Seems like some radiator cleaning is the easy thing to try, check engine air filters and perform MAF cleaning.

Then engine coolant flush might be next.

Next I'd say fresh spark plugs, you can run one step colder NGK's which my car really seems
to like even though I'm on stock power levels. While you're at it, might want to consider preventative maintenance on ignition coils (replace). Mine failed and they took the spark plugs with them, that was a bad day driving to the track and suddenly getting drivetrain malfunction and limp mode.

For mushy brakes I had this issue too despite countless bleeding sessions.

next time out I'll be on a new bbk, but I've seen a lot of recommendations to perform DSC ABS bleeding using ISTA, along with pedal calibration on ISTA

Mine is a 2015 DCT also, so I think these issues might just occur more likely with older cars

[remmoto]

Hey, thanks for posting. No drivetrain warnings. My temp usually hit 250 and would go into limp mode, however, with the brake cooling kit I added it seemed to stick around 245 which is still pretty high.

Those are good suggestions, I'll do those along with a coolant flush and see how it performs after. I do plan on a BBK with Alcon's. The GT4 and GTMore both use much better brakes I'm guessing they know it's one of the weak points of the platform. It is a little hard to hand over $10k-$11k, especially since you'll need a solid suspension setup.

Good callout on the coils and spark plugs, I did replace those recently as I did have one fail to cause me to go into limp mode while out on track, around the carousel of all places at COTA. It was tricky to diagnose as it only happened when I pushed the car, would never have known around the street!

[OG Shark]

remmoto it is still pretty warm around here - definitely at the point where it can create heating issues in the car. To me it sounds like your IATs are getting high enough to where the car is pulling power. We are still a bit away from seeing friendly weather here & COTA is extremely hard on temps.

What pace do you typically run out there? Any video as well? Also your trap speeds on the back straight - when you hit 155 what is the ambient vs when you hit 145? 155 would definitely be on the high side for a stock S55 - guessing that is in very good ambient conditions? Pace & video can give me a pretty good idea of what to expect from temps at COTA - been able to log quite a few laps out there.

Also for reference - when we were setting the stock benchmark for my M2C it was mid 80's when I clocked my fastest lap. I trapped 144.6 on the back straight. Yes the M2C is down a little bit in power over a '15 - but this was on a good jump out of 11 and threshold braking into 12 (I was running AP Racing BBK on all four corners at the time - I will not track COTA on the stock brakes in any manner as I can fade them even with good track pads & fluid on a stock F8x). It took me tuned, flex fuel, & Wagner TMIC to get approach 155. Now with the Full Race Turbos I hit 164 in ~ 80* ambient and expect that to be ~170 in good weather.

Another thing to consider - as you go out there more maybe realizing an improvement in pace and how hard you can push the car? Being able to push harder & in higher ambients could definitely be a cause.

One last thing - do you run with either DSC or MDM on?

[remmoto]

Originally Posted by OG Shark

remmoto it is still pretty warm around here - definitely at the point where it can create heating issues in the car. To me it sounds like your IATs are getting high enough to where the car is pulling power. We are still a bit away from seeing friendly weather here & COTA is extremely hard on temps.

What pace do you typically run out there? Any video as well? Also your trap speeds on the back straight - when you hit 155 what is the ambient vs when you hit 145? 155 would definitely be on the high side for a stock S55 - guessing that is in very good ambient conditions? Pace & video can give me a pretty good idea of what to expect from temps at COTA - been able to log quite a few laps out there.

Also for reference - when we were setting the stock benchmark for my M2C it was mid 80's when I clocked my fastest lap. I trapped 144.6 on the back straight. Yes the M2C is down a little bit in power over a '15 - but this was on a good jump out of 11 and threshold braking into 12 (I was running AP Racing BBK on all four corners at the time - I will not track COTA on the stock brakes in any manner as I can fade them even with good track pads & fluid on a stock F8x). It took me tuned, flex fuel, & Wagner TMIC to get approach 155. Now with the Full Race Turbos I hit 164 in ~ 80* ambient and expect that to be ~170 in good weather.

Another thing to consider - as you go out there more maybe realizing an improvement in pace and how hard you can push the car? Being able to push harder & in higher ambients could definitely be a cause.

One last thing - do you run with either DSC or MDM on?

Howdy, I can typically hit 150-155 on the back straight even when its 95+ out with RS4's and solid exit on T11 and I don't hit 155 until right at braking at 135 meters to 140 meters, it wasn't until recently that it struggles to get to 140-145 after the first couple laps.

No nannies on, everything fully off unless its wet then I run MDM until I get a feel for the track.

Do you or anyone happen to know the threshold of the IAT taking power?

Edit: Forgot to mention footage/data, I do some have footage it's just a visor cam and my visor obstructs most of it which is my fault for poor placement. I'd be happy to share it privately.

[NYG]

Something has to be up. I've ran my M4CS at 100+ degree weather at Lime Rock Park and barely went over 200 on oil and water. I don't know exactly what it could be but I think there's an issue.

The brakes are understandable - you aren't going to dodge that until you upgrade on brake cooling and BBK.

[D_SheerDrivingPleasure]

COTA seems like it's very hard on the brakes so a BBK might be inevitable, but before dropping $10k on one you might want to try the following. Sorry if this was covered above my.

1. quality two piece brake rotors, girodisc is a good option.

2. Remove the splash sheilds to increase airflow.

3. Racing brake calliper rebuild. Their kit includes stainless steel piston which resist heat better than OE aluminum ones. The kit also includes high temp seals and boots

4. Ti backing plates to resist heat transfer.

5. fresh brake pads. The pad material helps prevent heat transfer.

[Suds]

OP, for power when we’re your spark plugs changed last?
You said you are not tuned, but tracking a car will take some life out of them.

Also are you measuring speed from your speedometer or a GPS unit.

[jmg]

What tires were you using when hitting 155 vs 145? Same rolling diameter? Pressures?

[remmoto]

Originally Posted by Suds

OP, for power when we’re your spark plugs changed last?
You said you are not tuned, but tracking a car will take some life out of them.

Also are you measuring speed from your speedometer or a GPS unit.

Replaced maybe.. 6 months ago? I haven't tracked as much since then, maybe a few sessions since. Measuring speed from my speedometer.

[remmoto]

Originally Posted by jmg

What tires were you using when hitting 155 vs 145? Same rolling diameter? Pressures?

Same tires, 275x35x18 Hankook RS4's and MPS4S.

Im not swapping tires, it's first couple laps I hit 150-155, after that brakes get mushy and I'm down on power, doing 140-145 on back straight.

PSI is fine, I typically go 25-28 PSI cold, roughly 35 PSI hot, give or take a few depending on the lap and weather.

[remmoto]

Originally Posted by NYG

Something has to be up. I've ran my M4CS at 100+ degree weather at Lime Rock Park and barely went over 200 on oil and water. I don't know exactly what it could be but I think there's an issue.

The brakes are understandable - you aren't going to dodge that until you upgrade on brake cooling and BBK.

Exactly my frustration, I can't seem to find the answer at the moment or how to find the answer. I assume 220 is fine on a hard track like COTA, but 240+? It will hit 250+ and go into limp mode if I don't back off after a few laps.

I did check the top mount intercooler and see adequate coolant, it felt like room temp when I came off track.

[uncle ben]

It seems to be your heat exchangers aren’t working as they once did. Maybe a good cleaning and straightening bent fins may fix the issue.

You may want to look at upgrades. Not sure how else to help cooling dramatically. Vented gts hood?

[LuvMyE92]

I don't know COTA, but I've done a lot of track driving in the past. In my experience, brakes need the following to work properly, not particularly in order:

- proper racing pads that can handle the heat
- proper brake fluid - which must be fresh! - to handle the heat
- depending on the car, brake cooling ducts

For instance, the OP mentions Pagid, but there are several different compounds from OE up to (I presume) full-on race pads. The latter will dust like crazy, destroy your rotors and not work at all when cold. But they'll stop you when the car is super hot and you're on that last lap trying to get that last extra 1/10 of a second.

Also, of course, there is technique, as someone who doesn't use the brakes properly can get them to overheat much quicker. But we shall assume that you know how to do that...

[Suds]

How many miles are on your car and how hot has it been mid day in Austin.
I always use GPS for true speed on the track.
I track with Chin and Schnell Fest at COTA. Are you running with these groups? If so I would like to say hi and will be there Nov. 18-20 for Schnell Fest.

Originally Posted by remmoto

Same tires, 275x35x18 Hankook RS4's and MPS4S.

Im not swapping tires, it's first couple laps I hit 150-155, after that brakes get mushy and I'm down on power, doing 140-145 on back straight.

PSI is fine, I typically go 25-28 PSI cold, roughly 35 PSI hot, give or take a few depending on the lap and weather.

[remmoto]

Originally Posted by Suds

How many miles are on your car and how hot has it been mid day in Austin.
I always use GPS for true speed on the track.
I track with Chin and Schnell Fest at COTA. Are you running with these groups? If so I would like to say hi and will be there Nov. 18-20 for Schnell Fest.

23k miles, ~4k are track miles pretty much. Typically high 80's mid 90's. I'll use my solo2 and get GPS for true speed on track next time.

I used to run with Chin, not so much anymore, if I do its usually in my F4 though.