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e36 BMW m3, mostly stock LS1.
Single 16" spal 2450cfm fan.
I'm looking for some help/ideas on solving my track day cooling issue in the most efficient manner.
With no fan shroud I had overheating issues while stopped. I built a fan shroud that has worked perfectly for street driving. I now have no issues with heat in any type of daily driving. I've even sat in stop go traffic for 40 minutes on a 90* day and didn't have an issue.
However, when I run on track the extended full throttle has me hitting 235* water temp in just a few laps. My radiator should have equal cooling efficiency to a stock f-body radiator. It's only about 1" shorter and ~1.5" more narrow, but easily double as wide. I have ducting to the radiator as well. I'm beginning to wonder if my fan shroud is actually trapping the hot air in on track days. Should I make holes in my shroud to let some air escape?
Should I look at upgrading the radiator to something even better as the next step? It's also possible that I really need to cut holes in the hood just to let some air escape. I'd like to avoid that if at all possible though.
some shrouds have flaps built in to them that open up at higher speeds to allow more flow thru. I am not sure what they are made of, but they stay closed at low speeds so that the fan is pulling thru radiator and then flex open at higher speeds. I thought of trying some heavy rubber or leather maybe to make the flaps.
If you don't have an air dam I would try adding one. These create hi/low pressure zones to help pull air through the radiator core along with some overall aero perks.
What have you done to help evacuate hot air from the engine bay?
Heat wrapped or ceramic coated headers?
My ducting to the radiator is basically an air dam in the front. I have nothing to pull heat from the engine bay. Only way to do this in this car would be hood vents. I'm desperate not to cut holes in my hood, but will if I absolutely need to.
Headers are ceramic coated, heat reflective tape for days all over the engine bay.
Yeah at speed you shouldn't need the fan. It should cool just from forward motion. I would cut some holes in that shroud.
I realize space is tight but having that shroud tight against the radiator like that means you have effectively cut the radiator down to the size of the fan. It is only going to cool via the surface area that has air flowing over it.
Maybe ditch the shroud then get some weather strip and try to seal the fan right to the radiator.
The belly pan is a good idea. Helped tremendously on my Datsun.
Positive no air pockets, already have a 160* tstat in as well.
Space is insanely tight but I managed to make about 1/2" gap between the fan and the back of the radiator. Mounting the fan directly to the back of the radiator (with no shroud) makes the car overheat when stopped in traffic.
When you say belly pan, do you mean something to direct air from the front of the bumper/grill opening to the radiator? Because I have that already as well .
Appreciate the suggestions fellas! I may try cutting some holes in the shroud and seeing how that goes. If that fails, I may "upgrade" to another radiator, but I am doubtful that will actually make a difference. The last thing I wanted was to spend more money on an 'upgrade' that won't solve the issue.
Can't simply cut holes or you'll be back to the same issues as before. Cut holes and then pop rivet flaps that are slightly larger than the holes to the outside of the shroud. At idle with the fan going the flap will prevent air from being sucked through the holes and bypassing the core, at speed they will open and alliow air to pass.
Material for testing need not endure forever, rubber style placemats for the dinner table, thin mat meant to protect flooring, thick neoprene, anything with a little rigidity should work. You could maybe even hinge aluminum pieces but they need to be larger than the hole and lay flat. SPAL apparently even makes some!
A single fan might be enough for daily but for track use you probably need something that moves more air. I have the Dodge Intrepid two speed dual fans on my s10 swap and it never goes on high and keeps the temps in the 190 degree range. I made 3 back to back passes on a mustang dyno over the weekend and the temp stayed rock solid. Another tip it to not hot lap your car and pop the hood between passes to let the engine bay temps cool off.
1. use distilled water (not coolant) probably a track rule anyways
2. Wrap the exhaust, and then blanket over that. Keep all temp inside the tubes.
3. spray methanol/water to bring down EGT if it goes high
4. Make sure you have enough ignition timing (dialed in on a dyno w/ EGT sensor is good). Reduced/retarded timing leads to high EGT and high coolant temps.
I'm running 20% antifreeze and 80% water (distilled only), with some MoCool in the system as well. With this mix I don't have to worry about water freezing as the car sits in the garage for the winter.
When I say on track, I'm talking road course, not drag strip. Hood is always opened when the car is stopped. If I sit and let the car idle with the fan on it drops the temps right back down to the 185* range. Windowing my shroud will be the next step, and possibly change the radiator.
Some people need to keep in mind he is running a stock LS1 with no turbo etc and a aftermarket radiator (better than the stock LS1 radiator). These meth suggestions/timing/wrapping the exhaust is not needed...
IMO it's an airflow problem. OP like you said, get some windows with rubber flaps installed and see what happens. You confirmed that around town you have no issues (fan doing all the work). But when road racing, it gets hot (single fan can not keep up AND you do not have the benefit of proper airflow).
Do you have an AC condenser??? If so, is it in front of the radiator and DIRTY?? That will hinder airflow as well.
Looking forward to what you do and if it helps.
I have not road raced my car, but I don't suspect I would have an issue:
A belly or chin pan is one that goes underneath the car from the front to a foot or so behind the radiator. Cuts down on turbulence underneath the vehicle which can impeed airflow through the radiator
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Cooling issues on Track - HELP! with pics 
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