E89 Z4 Track-ready Sleeper Build

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Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
More fluid flow only helps if the system is capable of the heat leaving due to air flow, or you get heat soaked. I know you went bigger radiator (caused other issues). Did you ever look at the higher wattage fans from the 1 series? I know some guys trim the plastic in front of the intercoolers thinking no big deal, but it's a high pressure area, but that only works when the car is moving. Sealing up any openings allowing air to leak around the radiator will help, but probably have that covered already. That's the extent of my CFD knowledge....

Getting to that point of needing hood vents.....
Didn't look into fans because they wouldn't run on track anyhow, and I don't have any problems with water temps when power output is low.

I got the idea for a helper pump from the M2 N55 where it also runs through an oil to water exchanger.

As for hood vents, on the Z4 I am thinking the most 'sleeper' option would be outlets near the side indicators.
 

Bnks334

Sergeant
Dec 1, 2016
352
New York
So it seems the car survived the injector stunt. All index 12s are now back in with new compressed seals.

Alright, I have now confirmed that EBC orange stuff is a much better 1hr endurance pad than PB race pads. They feel absolutely fantastic as soon as you get enough heat into them. They dont work on street though.

I have a reoccuring problem where chargepipe clamps keeps getting loose as soon as I am near a track. I have decided to try out the revshift motor mounts, but not sure what the lead-time is. I have also ordered poly rtabs to replace my current M rtabs with limiters. This because the rear end feels a bit wobbly on braking and hard acceleration, and the rtabs are the only big rubber bushings left on the car.

As for other next steps, I still have a major cooling bottleneck. As pointed out by @Bnks334 I need better ducting to the coolers. I would also like to try and run a helper coolant pump. I would then switch this on together with the DCT and oil pan oil pumps whenever I enter a track. On the road I would then keep it off in order to avoid the problem where my AC stops working because the condensor behind the first radiator doesnt get enough cooling. I have bought a 3600L/h pump with 38mm aluminum in/outlets. I have also bought another 25row cooler that I intend to install in front of the oil cooler for the semi-dry oil sump.

Here's my idea on how to run the system. When the helper pump is off, water wont pass through it. If the OEM pump is off and the helper pump is on, the water will just run through a closed loop.

Do you see any issues with this setup?

View attachment 27379
Hard to tell from that pic but I do not think that setup would be as effective as anticipated. The 3rd cooler you plan to install would probably see little flow. It all depends on how much restriction the fittings and elbows present. Parallel cooling only works when both coolers have the exact same flow characteristics. If one cooler has shorter feed lines with less elbows/connections then it will get significantly more flow. You would need to put a venturi t-fitting in place to ensure fluid flows through the "bypass" 3rd cooler.

It look like your current system is set up in series? Can you post pictures of exactly how it's plumbed into the main coolant loop?

Heat exchange is a 3-part equation. Improving the rate of coolant flow only helps improve one part of that equation. With that being said, it's pretty much understood that more flow will never reduce cooling. But, it's kind of throwing parts at the problem and seeing if it helps kind of approach. I was under the impression our water pumps had pretty high rates of flow but maybe no so much when you put it within the context of a 1 hour race.
 
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Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
Hard to tell from that pic but I do not think that setup would be as effective as anticipated. The 3rd cooler you plan to install would probably see little flow. It all depends on how much restriction the fittings and elbows present. Parallel cooling only works when both coolers have the exact same flow characteristics. If one cooler has shorter feed lines with less elbows/connections then it will get significantly more flow. You would need to put a venturi t-fitting in place to ensure fluid flows through the "bypass" 3rd cooler.

It look like your current system is set up in series? Can you post pictures of exactly how it's plumbed into the main coolant loop?
Does the oem aux radiator run with a venturi T fitting?

The reason I want them in parallel is because the smaller aux radiator would run 10mm lines as opposed to 38 for the main aux radiator.
 

Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
Heat exchange is a 3-part equation. Improving the rate of coolant flow only helps improve one part of that equation. With that being said, it's pretty much understood that more flow will never reduce cooling. But, it's kind of throwing parts at the problem and seeing if it helps kind of approach. I was under the impression our water pumps had pretty high rates of flow but maybe no so much when you put it within the context of a 1 hour race.
Flow is still limited by the oem pump in the proposed setup. I think it is 4000l/h or so (edit: wrong see post below)? So the helper pump would just act as a switch to open and close the additional coolers, and make it so that the flow speed through the main rear radiator would be only 10% of the two aux radiators. I guess the helper pump would also reduce the pressure drop otherwise present in parallel system? Whatever the benefit of that would be...

Honestly not sure if this setup makes sense.
 
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Bnks334

Sergeant
Dec 1, 2016
352
New York
Does the oem aux radiator run with a venturi T fitting?

The reason I want them in parallel is because the smaller aux radiator would run 10mm lines as opposed to 38 for the main aux radiator.
I can't speak to it as I've never held it in my hands.

https://www.ecstuning.com/b-genuine-bmw-parts/secondary-radiator-kit/17117602241kt/

Look at the pictures of the kit and realoem, it looks to me like the return line of the aux radiator t's into the radiator to thermostat return line. The feed for the aux radiator is found in the "heating/cooling" section of realoem so that infers that it is somehow cooling the fluid that is already being diverted to the heater core. Again I can't tell exactly how the aux rad feed is plumbed into the system but it's not diverting any flow from the main radiator that it would need fluid forced through it. It looks to be cooling fluid that is already tee'd off the radiator inlet/outlet.

Edit: I found an install guide for the PPk radiator. I looks like it does indeed plumb into the heater core line. I does kind of look like a venturi fitting is used but you would need to cut the steel bands off to get a better look at how the aux radiator ensure it gets fed flow:

https://www.1addicts.com/forums/showthread.php?p=17571606
attachment.jpg
 
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Bnks334

Sergeant
Dec 1, 2016
352
New York
I guess the helper pump would also reduce the pressure drop otherwise present in parallel system? Whatever the benefit of that would be...

Honestly not sure if this setup makes sense.
I believe it's the opposite. When plumbing in series, heat exchange becomes less and less effective. in series, the flow has no choice but to run through all cores. The final cooler in the series will see less pressure and it will be fed cooler fluid which reduces the efficiency of the cooler. More strain is place on the water-pump to draw coolant through the series of coolers. This isn't all that important in a car though because we don't care about evenly dispersing the heat like trying to heat a home.

My initial reply was more implying that maybe having the two cores in series like you do is causing more coolant to bypass the radiator altogether. The cooling system is more complicated than just a simple inlet/outlet.

There is also the problem with them being stacked in front of one another. The OE cooler might not be exchanging much heat at all since it's only seeing 200f+ super heated air. I know they say it should be OK so long as you leave a 1" gap or so but I don't know how much of an affect there really is in practice.
 

Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
I believe it's the opposite. When plumbing in series, heat exchange becomes less and less effective. in series, the flow has no choice but to run through all cores. The final cooler in the series will see less pressure and it will be fed cooler fluid which reduces the efficiency of the cooler. More strain is place on the water-pump to draw coolant through the series of coolers. This isn't all that important in a car though because we don't care about evenly dispersing the heat like trying to heat a home.

My initial reply was more implying that maybe having the two cores in series like you do is causing more coolant to bypass the radiator altogether. The cooling system is more complicated than just a simple inlet/outlet.

There is also the problem with them being stacked in front of one another. The OE cooler might not be exchanging much heat at all since it's only seeing 200f+ super heated air. I know they say it should be OK so long as you leave a 1" gap or so but I don't know how much of an affect there really is in practice.
There's no doubt that stacking coolers (increasing thickness) isn't as effective as increasing area. But I mean, it is the only option, so I just want to get the best out of it. What I liked about the series setup was the cross flow principle.

But basically you believe that the proposed future setup, with all coolers in parallel is perfect as long as the right T couplers are used? Then the remaining question is whether I should put the helper pump in parallel with the stock pump instead to increase total flow, or keep it on the aux loop to help with reducing pressure drop. Whatever that means.
 

Bnks334

Sergeant
Dec 1, 2016
352
New York
There's no doubt that stacking coolers (increasing thickness) isn't as effective as increasing area. But I mean, it is the only option, so I just want to get the best out of it. What I liked about the series setup was the cross flow principle.

But basically you believe that the proposed future setup, with all coolers in parallel is perfect as long as the right T couplers are used? Then the remaining question is whether I should put the helper pump in parallel with the stock pump instead to increase total flow, or keep it on the aux loop to help with reducing pressure drop. Whatever that means.
I'd leave the aux coolant pump as serving to pump coolant through the 2nd and third coolers.

I would propose you simplify the proposed system though by putting the smaller 3rd cooler in-series with one of the two larger cores. Otherwise, I don't think you'll get much flow through it. Even a venturi fitting doesn't guarantee fluid dynamics will force fluid through the smaller core. The venturi fitting would have to present more restriction in the line then the sum of all the head loss of the 3rd core, lines, and return fittings (every bend adds restriction). I don't know of too many use cases in automotive coolant lines. A simple T will not work is all I know lol.
 
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Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
I tried to research a bit on BMWs different radiator setups, and here is an overview:

S55 notes
- Mechanical water pump (flow rate unknown)
- Separate 20W - 800 l/h electric water pump for turbo chargers (allowing for cooling while engine is off)
- Separate electric water pump for cabin heater, placed before heat exchanger (info here)
- 13.9L coolant capacity

S55-cooling.jpg BMW-S55-720x500.jpg


Notes on N55 M2
- Oil-to-water exchanger in series after aux radiator
- 50W electric water pump placed between aux radiator and oil-to-water exchanger. My sketch below:
I believe @Hydra Performance did something similar?

M2N55.jpg M2N55a.jpg


Notes on 1M
- Aux radiator installed in parallel with main radiator.
- 8.4L coolant capacity

1M.jpg


Notes on B58
- Mechanical water pump
- Coolant from turbo by-passes engine (unlike N55, N54 and S55)
- 10.5L coolant capacity

B58-cooling.jpg


Common for all
- Aux radiators always installed in parallel with main radiator
- All T connections used are either 90 or 45deg. Main engine-to-radiator flow uses the straight path, whereas aux flow goes through a 45 or 90deg bend assisted by gravity by downwards fitting orientation. Aux lines always use smaller diameter than main radiator lines.

Notes on water pump flow
According to this, a 450bhp car should have a 9000l/h water pump. The N54 has a 400 Watts 9000 l/h water pump operating at 0.8bar. If the differential pressure goes up, flow goes down and vice versa. I have 120.000km on my OE water pump, not sure if performance degrades with time? Apparently the pump is self-diagnosing. Anyhow, I guess the benefit of running a helper pump is that the additional aux radiators do not influence the pressure or lower the OE flow rate.

Sketch of @Bnks334 proposal (my interpretation)
Blue = DCT oil cooler (80-100C, 176F-212F)
Brown = Engine oil cooler (110-140C, 230F-284F)
Orange = Coolant lines (90-110C, 194F-230F)
Aux coolant pump is 100W - 3600l/h (40% of the main pump)
OE radiator is 32mm with cross flow for DCT heating
Large aux radiator is 40mm single pass
Small aux radiator is 50mm single pass (same as both oil coolers)

Sketchtotal.png
 

Bnks334

Sergeant
Dec 1, 2016
352
New York
We got a bit side-tracked with the factory aux radiator lol. It's was only important to the extent of understanding how BMW is ensuring coolant flow through the additional coolers that they install (to get ideas). I think the answer to that is that BMW is tapping off of the heater core hose which has flow directed to it already. That and many cars like the Z4 even have a small pump to boost flow through the heater core.

In the proposed sketch you had the 3rd cooler in parallel. The main point was that since it is not the exact same size, and not plumbed exactly the same, as the 2nd core it runs in parallel with then you would not be utilizing one or the other to its full effectiveness due to fluid dynamics dictating flow to the path of least resistance. In a closed loop cooling system, gravity is not playing any role in how the coolant flows. The fittings, diameters, length of lines, etc. are important for determining the resistance in each circuit. Running the 3rd cooler in series with the 2nd means you don't have to worry about any of the complexities of getting flow right in a parallel system. The fact that the 2nd and 3rd cooler are "in-parallel" to the 1st OE cooler doesn't matter much since you have an aux pump in place. The only concern there is that both pumps are matched close enough.

The new sketch looks better. The aux water pump will push fluid through both additional cores on command of your switch. I don't think push/pull really matters all that much. I am guessing you sketched it pre-cooling because there is better fitment on that side of the car for the aux pump to mount? I would maybe recommend installing the aux pump post coolers though so that it sees cooler fluid. As we already know, heat kills electronics lol.
 
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Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
We got a bit side-tracked with the factory aux radiator lol. It's was only important to the extent of understanding how BMW is ensuring coolant flow through the additional coolers that they install (to get ideas). I think the answer to that is that BMW is tapping off of the heater core hose which has flow directed to it already. That and many cars like the Z4 even have a small pump to boost flow through the heater core.

In the proposed sketch you had the 3rd cooler in parallel. The main point was that since it is not the exact same size, and not plumbed exactly the same, as the 2nd core it runs in parallel with then you would not be utilizing one or the other to its full effectiveness due to fluid dynamics dictating flow to the path of least resistance. In a closed loop cooling system, gravity is not playing any role in how the coolant flows. The fittings, diameters, length of lines, etc. are important for determining the resistance in each circuit. Running the 3rd cooler in series with the 2nd means you don't have to worry about any of the complexities of getting flow right in a parallel system. The fact that the 2nd and 3rd cooler are "in-parallel" to the 1st OE cooler doesn't matter much since you have an aux pump in place. The only concern there is that both pumps are matched close enough.

The new sketch looks better. The aux water pump will push fluid through both additional cores on command of your switch. I don't think push/pull really matters all that much. I am guessing you sketched it pre-cooling because there is better fitment on that side of the car for the aux pump to mount? I would maybe recommend installing the aux pump post coolers though so that it sees cooler fluid. As we already know, heat kills electronics lol.
Great point on the pump, and yes, the coolers running different IDs is still a concern. After studying the OEM pictures, I now like the idea of welding two 10AN connectors to the end tanks of the large aux radiator, and just connecting the smaller aux radiator via those.

Previously I tested both series and parallel configurations of the large aux radiator, and didn't notice any difference in cooling performance. If anything, the series config was performing a tiny bit worse.

No matter what, I believe the performance of the helper pump (100W 3600l/h) is a fairly good match for the 400W 9000l/h OE pump. If they both run at these flow rates, 40% of the coolant passes through the two aux radiators. This sounds fairly balanced to me. The benefit of the helper pump then being that what the OE pump sees in terms of flow resistance from the main radiator, would be less than stock.

And yes, basically I would connect all pumps marked in green with the existing cabin switch, and turn them on when entering tracks. When they are off the AC should work more or less as normal, and cooling performance is back to OEM.

It is either this, or the series setup you like more.

final.png
 
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Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
So had four of these custom made

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1098127615.jpg


With these we now have the option to run either a parallel or straight series setup with the two aux radiators. The T-coupler is complete with BNKS internals:

bnks-gate.jpg


Pretty excited about how those turned out.

I also ordered a 200psi pump and some fittings. My friend has some meth injection nozzles, and my idea is to try and see if we can produce a medium-pressure water mist to cool the air in front of the main radiator and fmic. The idea was originally offered by @jts1981 and the benefit of running medium pressure rather than low-pressure water spray is to achieve much less water consumption and dry cooling. I do not want the front of the car dripping with water given the track application. The cooling benefit of such a system might be negligible, but desperate times it is...

Finally I ordered this set of $120 cast wheels to store at local tracks with used slicks. They are 18x9 et30 so I can run 250-650-18 slicks in a square setup. Less expensive tire brands such as Rydanz (Medium) and Zestino (Soft) are locally produced and typically come in those sizes for slicks. I actually wanted 9.5J ET35 in forged Z4 OEM design (style 293) but that would have tripled the price, and I wont be running these on the street anyway...

925717941.jpg
 
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Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
The booster pump is in, and here's the first picture. We are about 50% done, and should be able to finish up everything by the end of tomorrow.

1035569680.jpg


As it turns out the pump needs 24V to pump 3600L/h. At 13.7V it only pumps 2500L/h consuming 70W. This is still 20W more than the M2 N55 booster pump which runs a small aux radiator and an oil-to-coolant heat exchanger. Unfortunately the M2 is also prone to overheating in +100F weather.

421884899.jpg


I have decided to run three auxiliary radiators in series with this pump. The pump is placed between aux radiator number 1 and 2, so it is seeing cooled coolant as recommended by @Bnks334. Aux radiator 1 is a 25row unit placed in front of the "low flow" 25row oil cooler/reservoir for the semi-dry oil sump. This was the only option given the limited space on that side. Keep in mind that this side now houses two pumps, two coolers and the horns. Aux radiator number 2 is the well-known full sized radiator placed in front of the A/C condenser and main radiator. The A/C should work better on the road as this radiator won't see the same flow as previously when the booster pump is off. As can be seen above we also moved the DCT cooler away from the direct air-flow entering through the kidneys. The location is now more similar to typical bmw oem locations of transmission coolers. The 3rd and smallest aux radiator (13row) is configured in a V together with the OEM location "high flow" oil cooler to increase the total cooler surface area within the space available.

Besides the flow boost, the new setup offers a 34% increase in radiator "free flow" surface area. The total radiator core volume has increased +20% compared to the previous setup and is almost three times the size of a stock Z4 35i radiator. Oil cooling surface area suffers with this setup, but overall the balance of cooling surface area for coolant, oil and dct is now much closer to that of the S55.

IMG_20190611_100420.jpg
 
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Bnks334

Sergeant
Dec 1, 2016
352
New York
time consuming but necessary. I am definitely looking forward to seeing if you notice any difference in temps with the ducting in place.

Go down the door and window isle of your local home improvement store. You should be able to find some rubber trim to put on the edges of the duct so that it will "seal" to the bumper etc. They also sell all sorts of foam strips (like for sealing air conditioners in your window) that can be used to seal small gaps.

Don't forget to paint the ducts black before you bolt everything back together (if you want to) lol. Made that mistake too and didn't like all the aluminum you could see. Black looks much cleaner now.
 
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Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
Go down the door and window isle of your local home improvement store. You should be able to find some rubber trim to put on the edges of the duct so that it will "seal" to the bumper etc. They also sell all sorts of foam strips (like for sealing air conditioners in your window) that can be used to seal small gaps.

Don't forget to paint the ducts black before you bolt everything back together (if you want to) lol. Made that mistake too and didn't like all the aluminum you could see. Black looks much cleaner now.
Sealing and "paint" added as you recommended. Paint being black duct tape on the driver's side duct. The passenger side duct is much darker due to the duct angle and only the mounting bracket had to be "painted". The same duct tape and some automotive "foam" was used to try and seal up the air scoops around the FMIC and main radiators.

805784511.jpg


2144379479.jpg
1738937635.jpg


1798126775.jpg


There's almost no space left on this car. We even had to remove the horn from the driver's side wheel duct.

1602631847.jpg
498726987.jpg
768090148.jpg



So I believe this is the first Z4 in the world with 9 coolers and 3 auxiliary pumps. Here's how the she looks assembled:

643353953.jpg


1224073005.jpg



Heat shielding

Below is how we wrapped the aluminum tubing that carries coolant to the block, and mounted a heat shield between the downpipe cat and the oil pan. At this point everything counts haha.

648340067.jpg
1148248688.jpg



Track tires

We also test mounted the new track wheels. A square 18x9J ET30 with 255/35R18 Hankook RS3 tires is a perfect fit with -2.7deg front camber and does not require spacers. See pictures below. There is only a very small amount of rubbing on the inside fender with full lock.

If anyone wants to run 265/35R18 square, it is most likely possible with ET35 wheels, lots of camber and a small spacer up front. There will be rubbing on full steering lock though...

2080189298.jpg
819628757.jpg


After confirming what size is possible, I selected these used Pirelli DM slicks, 245-645-18. Essentially the same size as Michelin Pilot Sport 4S 255/35R18. I will still be running the forged OEM replicas with 265/235 on the street and for most of my track driving. The slicks are only needed for qualifying and time attack competitions with free tire choice.

1220639205.jpg
 

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Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
So here's the result from today's test at the track. It looks like coolant temps are doing much better, although it was extremely hot again today.


Log notes:
36C 96F according to weather app
43C 110F indicated in cluster
48%rh Low altitude
DSC=off
New aux radiators
New booster pump
New dct cooler location
New ducting for all coolers
Custom vrsf 7.5 HD (upper stepped part removed)

Results:
Fastest lap: 1m36s (no cool down before starting lap)
StartEndDifferenceStartEndDifferenceComments
Coolant212F230F18F100C110C10CLooks like an improvement
Oil264F277F13F129C136C7C
DCT207F214F7F97C101C4CPeaked at 225F during the following lap, new record
IAT158F199F41F70C93C13CProbably not a useful datapoint. See log instead.


Compared to last setup, similar 100F weather
1m38s lap w/traffic (cool down before starting lap)
StartEndDifferenceStartEndDifferenceComments
Coolant196F226F30F91C108C17COld setup with two radiators configured in series
IAT127F172F45F53C78C25CSame FMIC, worse ducting


Compared to old CSF only setup, similar 100F weather, but less humid
1m30 of hot lapping around different track
StartEndDifferenceStartEndDifferenceComments
Coolant219F243F34F104C117C13COnly CSF
Oil262F277F15F128C136C8CSmaller coolers
DCT201F207F6F94C97C3CBetter location
IAT124158F34F51C70C19CLarger FMIC
 

Asbjorn

Sergeant
Mar 10, 2018
432
Europe, based in China
Went through the data again, this time comparing to a test day with much cooler weather. Logs used:

Colder weather (two radiators in series, two large oil coolers, nonHD 7in FMIC, poor ducting and insulation from radiator, 100% coolant):
Log from three days ago:

CurrentPrevious (two radiators in series only)
Session 1Session 2
110F ambient, 1:36-ish laps84F ambient (cluster), 1:40-ish laps84F ambient (cluster), 1:40-ish laps
iat min 115F (46C),
peak oil 280F (138C), 170F over ambient
time to -10F oil from peak: 100s, coasting
time from 208F to 232F (+24F) coolant: 109s
peak iat 212F (102F over ambient)
iat min 93F (34C),
peak oil 268F (131C), 184F over ambient
time to -10F oil from peak: 100s, coasting
time from 187F to 223F (+36F) coolant:104s
peak iat 165F (81F over ambient)
iat min 95F (35C),
peak oil 273F (134C), 189F over ambient
time to -10F oil: 110s, coasting
time from 205F to 228F (+23F) coolant: 104s
peak iat 162F (78F over ambient)

So my conclusions here are
1) With the 7.5in HD custom FMIC, better ducting and insulation from radiators, iats do in fact get closer to ambient when coasting.
2) Peak iats over ambient were higher. I take this as evidence that I was pushing harder. This is supported by the lap times. BTW I also note that third gear pulls are pretty useless at evaluating actual FMIC performance on track, see *) below
3) Although the oil pan oil cooler is now covered by an aux radiator, peak oil over ambient doesn't seem to suffer. The rate at which the oil cools also doesn't seem to suffer. This was my biggest concern with the new setup.
4) Although pushing harder, and doing so in much hotter weather, the rate of temperature increase for coolant was actually slightly better.
5) Coolant increasing from 208F to 232F (+24F) in 109s is still unacceptable for any type of endurance competition, but it has to be compared to when I was running CSF only: From 219F to 248F (+29F) in 106s (100F ambient). Even the previous setup would take twice as long to "achieve" that.


*) When FMIC cold, iat doesn't increase from start to end of a 3rd gear pull:

When FMIC is a bit heat soaked, iat actually decreases during a 3rd gear pull:

None of this means that iats can't go as high as 212F later. In fact it did within the very same log. The above pulls were done before and after the track "session" while still on track:


Next steps
I'm convinced coolant cooling is still where efforts need to be placed. I am also convinced that the combination of aux radiators with booster pump is effective on this car. The fact that the N55 M2 uses a booster pump and the M2C + new S58 with larger radiators don't, tells me that the N5x electric coolant pump was found to be a weak link after adding an aux radiator.

I have ordered the 120W (3600l/h) version of the booster pump I installed as a first easy upgrade. Lets see if that makes a difference.

I am also considering making some air pressure measurements with and without the under tray. Perhaps it would be beneficial to make a custom under tray in aluminum with large outlets behind the fmic/fan and aux coolers. But it is my general belief that since no major air flow changes were made between the M2 and M2C, that this is not really where time needs to be invested. However it needs to be noted that the M2C does indeed have an outlet for its oil cooler behind the bumper.

img10012466310.jpeg

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20951668571_eac17bc1f6_b.jpg
 

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