posted on May 04, 2010 17:11
|The silver machined aluminum things are the inlet restrictors. The ID is 29.4mm, or smaller than the inside of your typical Honda Civic cold air intake! They are placed in a high pressure zone in the front of the car to try and squeeze every bit of air possible past them. Check out all of the lightweight dry carbon ducting.
The engine is forced to breathe through two tiny 29.4mm restrictors by homologation rules. This is the main reason for the low sounding power numbers. Since the airflow to the engine is limited, the engine is redlined at a relatively low 8,600 rpm as there is simply not enough breathing to efficiently rev higher. The engine maintains the dual VANOS variable cam phasing of the intake and exhaust cams and the cams are more aggressive than stock. The heads intake ports are actually smaller than the stock M3's to improve flow velocity and give a broader powerband. Due to the inlet restrictors, the larger stock ports would simply have stagnant flow, lack of bottom end power and throttle response. This is all the information that BMW was willing to share about the engine and we were not allowed close enough to deduce anything else. We assume that this engine probably has a very high compression ratio as this is a common trick for other forms of restricted inlet racing. We also assume that there are some interesting tricks going on with cam design, the variable cam timing and engine mapping to give more pumping induced pull against the restrictor--another common restricted inlet engine set of tricks.
|The engine compartment air management is amazing. Everything is done to increase downforce and minimize drag. The air from the lower part of the grill opening is fed by streamlined ducts through the engine coolant heat exchangers then out the top of the hood. The curved ducts supply air to the rear mounted heat exchangers for the engine oil, transaxle and air conditioning systems. The center grill ducts feed the engine and are designed to develop positive pressure before the inlet restrictors. Everything is dry carbon, even the wheelhouse liners!
Lubrication is handled by a dry sump system. This allows a low profile oil pan and the engine is set lower and more rearward in the chassis for better weight distribution. The rules allow engine relocation as long as the engine isn’t set back farther than the stock firewall. Engine control is handled by BMW's Power 400 motorsports engine management system. The ECU uses production car like CANBUS multiplexing protocol and smart sensors for engine control, one way telemetry and datalogging. The Power 400 controls the production drive by wire throttle body with driver selectable engine mapping and multi-mode traction control.
|The exhaust system is double-walled and recessed into the floor for aerodynamic reasons. With a sealed cockpit and a 32C max temperature dictated by the rules, thermal management of the exhaust is very important. The outer jacket of the exhaust is vented to the carbon fiber chimney which vents the air to a low pressure zone outside the car. This device has significantly reduced the system air conditioning load!
The engine's exhaust exits into 4-1 headers with a crossover pipe just past the down tubes. The exhaust is sunk into the floor for better aerodynamics and fits into a double wall oval section directly under the car. A unique feature is the double wall exhaust and heat chimney. Air is vented from under the car through the exhaust's outer wall and exits up a carbon fiber chimney built into the cars A Pillar. This feature really cuts down cabin temperature, important because ALMS rules prohibit a cabin temperature of more than 32C or 90 degrees F.
|Swirl pot gives a high bleeding point for the cooling system and help deaerate the coolant. All track cars need these.
Wednesday, May 05, 2010 4:57 AM
Cool stuff. I didn't see a picture of the rear of the car. I'm curious what the rear diffuser looks like now that you've mentioned the restrictions on them.
Wednesday, May 05, 2010 7:32 AM
As always, a totally badass look into a real race car. Any chance of getting under the hood of one of the LMP Acuras?
Wednesday, May 05, 2010 8:14 AM
motoIQ bringing the Euro racing flare...nice, I'm liking it...
Wednesday, May 05, 2010 8:15 AM
We were not allowed to take pictures of the rear underneath of the car or the underneath in general.
Wednesday, May 05, 2010 8:58 AM
Very impressive stuff! This article really helps me to get a feel for how complicated even the production based GT cars are in the ALMS.
Wednesday, May 05, 2010 10:26 AM
When I see racing coverage in other magazines I usually pass it up. Mike you always seem to make this stuff interesting for racing novices like myself.
Some of the big print mags are trying to copy this format which I think is good for the industry. Car and Driver's Csaba Csere titled and article in the June 2010 issue "Suck Squeese Bang Blow" or something close to that. Hrm, I wonder where that idea came from. Regardless of the title it was an interesting read. Since our electronic format offers unlimited room we'll be able to go into more detail.
Wednesday, May 05, 2010 10:29 AM
I suppose I should clarify I have the upmost respect for Car and Driver as a whole especially Mr. Csere. But as the saying goes "imitation is a form of flattery."
Wednesday, May 05, 2010 1:48 PM
I like how everyting on the car is so trick and well executed....EXCEPT for the hole for the linear pot. What the hell did they use to cut that hole? Butter knife? Looks like a hole I would cut. ;)
Wednesday, May 05, 2010 2:15 PM
I love that car.
Wednesday, May 05, 2010 3:17 PM
Wonderful car, great article and great pictures; cheers to you guys. This should really help increase the traffic problem here.
jeff- theres a couple pictures of the 09 underbody with all the panels on at http://speedhunters.com/archive/2009/09/09/car-feature-gt-gt-ultimate-bimmer-the-m3-gt2.aspx As mike already mentioned there isn't much they can do with the rear diffuser because of the regulations. From what i can tell it just angles up and meets with the rear bumper. The real thing that would be interesting is to see, is all the ducting and routing between the underbody and the actual chassis, which apparently is what their really trying to hide...
eric- how does that work w/ the branding of the products? Since they use a "BMW Power 400" is that manufactured by you guys, specificly for them, and they just slap their "BMW Power 400" on it?
Wednesday, May 05, 2010 3:31 PM
What's the purpose of the bar that's bolted on near the front of the engine bay going the full width of the car and turning down toward the ground?
Wednesday, May 05, 2010 3:45 PM
for string alignment...
Wednesday, May 05, 2010 9:03 PM
Eric, thats interesting becasue we were told that the electronics were all in-house BWM developed that had a lot in common with the OEM ECU. They told us the electronics were not third party unless they misunderstood my questions.
They were not cofortable with us looking to closely at the engine and the underneath of the car. The diffuser is just a turn up as no vertical parts are allowed. Probably seome of the reason why there are so many details to generate side vortexes.
Wednesday, May 05, 2010 10:00 PM
I'm sorry but I just have to say it, I'm in LOVE with that shift knob! it looks so... functional. I also like the idea of the removable roof and seat for emergency access, I could see it really come in handy if the car ends up on its side and it's suspected the driver compressed their spine. Great article!
Thursday, May 06, 2010 1:21 AM
My bad for the misinformation. That was the previous generation factory built V8 race cars that had the Pectel and Pi electronics. BMW Motorsport did develop their own ecu for the current generation cars. This car is still using a Pi Omega dash still however. It has the same dash as the Sierra Evo.
Thursday, May 06, 2010 5:48 PM
Very cool about the emergency crash access. They probably learned something after this nasty crash Joey Hand took a few years ago:
Friday, May 07, 2010 1:51 AM
Cool M3. Imagine what it could do without the 29.4 restrictors?
Tuesday, May 11, 2010 2:01 PM
Is that common in racecars to use a digital protractor on the steeringwheel for steering angle?
Wednesday, May 12, 2010 8:45 PM
You know with all the development NASCAR did on the COT, I'm surprised that they don't also have the removable roof. Guess they're too busy fixing races to care.
Thursday, May 13, 2010 6:37 AM
Correct on the old cars.
Correct on the dash.
PR says everything is BMW.
Some things are so small they can be hidden anywhere...
Also, you know where's Waldo. Play where's the LJB with the pictishttp://photos.motoiq.com/MotoIQ/Features/Rahal-Letterman-ALMS-BMW-M3/JEF6172/844127506_9939h-L.jpg
Tuesday, February 15, 2011 6:27 PM
The BMW "Kidney grille" feeds the engine via the restrictors as well as the long tubes that travel over the engine and through the firewall which supply the AC system and driver cooling duct.
The large side NACA ducts located above the smaller rear brake ducts, supply the rear heat exchanger. The article said the front ducts travel the length of the car from the grille to the rear diffuser while the side ducts feed the AC which is backwards.