Lightweight- stripped M4 track car

[ZGM3]

I have been toying with the idea (mostly for fun) of just how lightweight we could get our new M3/4 if someone decided that they did not want it as a daily driver and wanted to turn it into a track car (2 options: street legal and non street legal).

I know that the car is heavy to begin with and it is not the most ideal tack car for the money but we can all dream can't we!!

How much weight reduction do you think is possible for street legal and how much more for a track only? Whats your guess on the new weight distribution front to rear?

What are your best guesses? and what would it entail removing and adding?

REMOVING (assuming option less car): carpeting, soundproofing, stereo, AC/Heat, ceiling/door/rear deck panels, font & rear seats, tools and flat kit, airbags, all unnecessary interior trim, headlights (track only).
What else would you remove?

ADDITION: of lightweight racing seats, roll bar & harness, fuel cell, carbon brakes, lightweight wheels,
what else would you add?

So how much would our new M3/4 weigh?

[tooch]

do it

[mkoesel]

Originally Posted by ZGM3

So how much would our new M3/4 weigh?

2700 lbs. or so. I think the E92 M3 GT2 weighed about that much.

[ZGM3]

Maybe I wasn't clear, this was just for fun and wanted to get an idea of how lite we could get a new M4, I'm not stripping my car, but there might be a bunch of stripped F80/F82's in about 7-12 years.

[mkoesel]

Originally Posted by ZGM3

Maybe I wasn't clear, this was just for fun and wanted to get an idea of how lite we could get a new M4...

I found your post to be very clear, actually, FWIW.

[JoeFromPA]

This is really hard to say because there are so many potential avenues to go that involve spending money. However, let's assume you want to spend less than $2500. (and that is mostly spent on a pair of used manuaully adjustable seats and a straight line or heavily gutted exhaust)

My guess is you could drop 400-500 pounds before it would start becoming a true exercise in frustration.

[saxonb]

Wouldn't you just go stripped M2?

Cheaper, lighter and faster presumably.

Wish they sold these:

https://www.press.bmwgroup.com/globa...item=node__809

[mastek]

Originally Posted by mkoesel

2700 lbs. or so. I think the E92 M3 GT2 weighed about that much.

The e92m3 GT2 is not an e92 chassis....it's a tube frame race chassis = not a single part is shared with the e92.

All you need to stay street legal is working headlights, taillights, seatbelts, all 4 turn signals and noise levels at 92db.
If you strip this f82m4 to your specs and add the aftermarket parts you will be at around 3,100 lbs. But I suggest a race cage for safety which will add 100 lbs.

[mkoesel]

Originally Posted by mastek

The e92m3 GT2 is not an e92 chassis....it's a tube frame race chassis = not a single part is shared with the e92.

No, I'm quite certain that is not the case:

http://www.racecar-engineering.com/cars/bmw-m3-gt2/

You are perhaps thinking of the Turner Motorsport Rolex GT cars:

http://www.turnermotorsport.com/t-tu..._for_sale.aspx

I'll stand by my 2700 lbs. estimate for a stripped, race ready M4.

[mastek]

Originally Posted by mkoesel

No, I'm quite certain that is not the case:

http://www.racecar-engineering.com/cars/bmw-m3-gt2/

You are perhaps thinking of the Turner Motorsport Rolex GT cars:

http://www.turnermotorsport.com/t-tu..._for_sale.aspx

I'll stand by my 2700 lbs. estimate for a stripped, race ready M4.

The e92m3 GT2 is considered a tube chassis race car due to it not using the OE tub's frame rails for suspension and axle pickup points. DTM also has a tub that then has a tube frame chassis attached to it.

Quote from the race car article you linked:

"The BMW M3 GT2 racecars are built using pressed steel bodyshells taken from the M3 production line at Regensburg, which has been used for production of sporting versions of the manufacturer’s road car models since the first iteration of the M3 in 1986. Installation of the CAD drawn and FEA tested BMW Motorsport rollcage / chassis frame is carried out by a subcontractor, which also modifies the floorpan to accommodate a transaxle rear end and a racing exhaust system"

The e92m3 tub taken from Regensburg is all that is e92 about this car...and it's only the cockpit structure while the front and rear frame rails are cut off and replaced with a tube frame. The transmission is in the rear of the car attached to the rear axle....you think that would be possible with a production body shell? All this is to achieve a lower center of gravity with a completely different suspension system and mounting points and to save weight to 2600 lbs.

A good example of a street car turned into a pro race car is the Continental Challenge series...where an e92m3 fully stripped and with the lightest racing components reaches 3300 lbs. So with all things being equal and the f82m4 being 200 lbs. lighter then the e92m3 in OE form ...you will never see a 2700 lbs. number. That's tube frame territory.

[FTS]

Originally Posted by mkoesel

No, I'm quite certain that is not the case:

http://www.racecar-engineering.com/cars/bmw-m3-gt2/

From the same article:

"The BMW M3 GT2 racecars are built using pressed steel bodyshells taken from the M3 production line at Regensburg"

"Installation of the CAD drawn and FEA tested BMW Motorsport rollcage / chassis frame is carried out by a subcontractor, which also modifies the floorpan to accommodate a transaxle rear end and a racing exhaust system"

"As a result, the engine location in the racecar is lower and further rearward than in the production car, to the benefit of weight distribution, handling and traction. "

Unfortunately, it has been, like most cars, sillouhette racing. As far as I know the only non-tubeframe chassis cars true to production form are the Porsche 911 Cup/RSR and Ferrari 430 Scuderia/458 Specialle.

[mkoesel]

Originally Posted by mastek

The e92m3 GT2 is considered a tube chassis race car due to it not using the OE tub's frame rails for suspension and axle pickup points. DTM also has a tub that then has a tube frame chassis attached to it.

Except that you just said:

The e92m3 GT2 is not an e92 chassis....it's a tube frame race chassis = not a single part is shared with the e92.

So you're new definition contradicts your earlier statement. And in fact your incorrect claim is why I pointed you to that article in the first place. The part you cited in your post clearly states that the car absolutely does share parts with the production M3.

But let's move on. I'm very skeptical that a stripped F8x won't be able to shed more than 400 lbs off the 3300 lbs. production car's weight. So sub-3k should be very doable, even with a cage. I will acknowledge, though, that 2700 lbs. was probably aggressive. The GT2 has CF body panels after all (though it also has massive rubber and some ballast too). But The GS class cars you cite are built to regulations, not for minimum weight.

[mkoesel]

Originally Posted by FTS

As far as I know the only non-tubeframe chassis cars true to production form are the Porsche 911 Cup/RSR and Ferrari 430 Scuderia/458 Specialle.

The only ones anywhere, or the only ones in a specific class?

[FTS]

Conti and Tudor series cars. I am not sure of the Aston though, hmm, I should looked that up.

[mkoesel]

Originally Posted by FTS

Conti and Tudor series cars. I am not sure of the Aston though, hmm, I should looked that up.

Well, I'm still not sure exactly to what you are restricting this to, but the entire field in the GS and ST Continental classes are fully production-based cars.

[FTS]

You are right about Conti series, that is production based, thank you for correcting me. I should have more accurately put it as old ALMS and GrandAm series and now Tudor series. Any of their classes didn't/doesn't have production-based cars, with the exceptions I mentioned. Too many allowances and exceptions are being made.

Conti series is glorified club racing IMO, performance adjustments are ridiculous for pro racing, but there is so much interest in it I am amazed at the type and number of cars entering each race; I am definitely missing the point in that one

[mastek]

Originally Posted by mkoesel

Except that you just said:

The e92m3 GT2 is not an e92 chassis....it's a tube frame race chassis = not a single part is shared with the e92.

So you're new definition contradicts your earlier statement. And in fact your incorrect claim is why I pointed you to that article in the first place. The part you cited in your post clearly states that the car absolutely does share parts with the production M3.

But let's move on. I'm very skeptical that a stripped F8x won't be able to shed more than 400 lbs off the 3300 lbs. production car's weight. So sub-3k should be very doable, even with a cage. I will acknowledge, though, that 2700 lbs. was probably aggressive. The GT2 has CF body panels after all (though it also has massive rubber and some ballast too). But The GS class cars you cite are built to regulations, not for minimum weight.

That part is an e92 body shell that is modified beyond recognition and outside anything usable on the street car. That makes the e92m3 GT2 stand as sharing not a single part with its street counterpart.

The Continental Series is the "only" pro racing series in the world that uses common street e92m3 cars modified to racing spec. And they are building to a minimum weight as most racing series do. 3,300 lbs. is the least weight they can get. Conti penalizes certain cars (like the Camaro) with ballast weight to even the field out.

The point here is ....what weight can you get the F82m4 down to in full race trim?
Having built 3 BMW M race cars myself....I can tell you that 2700 lbs. is tube frame territory.
But have it your way as you seem convinced. To the OP, realistically you are looking at 3,100 lbs. and that will not be easy to achieve. Good news is the lower center of gravity and gobs of torque should make the f82m4 a great club series racer if the cooling can be figured out for the engine.

[mastek]

Originally Posted by FTS

You are right about Conti series, that is production based, thank you for correcting me. I should have more accurately put it as old ALMS and GrandAm series and now Tudor series. Any of their classes didn't/doesn't have production-based cars, with the exceptions I mentioned. Too many allowances and exceptions are being made.

Conti series is glorified club racing IMO, performance adjustments are ridiculous for pro racing, but there is so much interest in it I am amazed at the type and number of cars entering each race; I am definitely missing the point in that one

Try to see the Laguna Seca race from weeks ago and you'll definitely catch the point.
It's the best professional production car w2w racing in this country right now.
And the fact that some of us mere mortals can join and race makes it accessible too....unlike the entry and running fees for P. Cup and F. Challenge racing.

[mkoesel]

Originally Posted by mastek

That part is an e92 body shell that is modified beyond recognition and outside anything usable on the street car. That makes the e92m3 GT2 stand as sharing not a single part with its street counterpart.

Well no point in going in circles further. We obviously have different interpretations of the word "nothing". The Turner GT car has been my goto reference example for tubular chassis E92 M3 and will remain that (though it does use some production body panels to my knowledge).

The Continental Series is the "only" pro racing series in the world that uses common street e92m3 cars modified to racing spec. And they are building to a minimum weight as most racing series do. 3,300 lbs.

Again we 'll have to agree to disagree. As we've both mentioned, the field is balanced using ballast to normalize the competition.

The point here is ....what weight can you get the F82m4 down to in full race trim? Having built 3 BMW M race cars myself....I can tell you that 2700 lbs. is tube frame territory.

I don't know where the weight will come from but neither one of us has parts break-down with numbers here so neither do you. Perhaps we can start by asking what makes the GT2 600 lbs lighter than the GS car. Yeah, yeah, we know - it's in the frame and subframes, etc. But there is a lot of detail there.

OP isn't building a car, by the way; did you miss that? The question is theoretical. You want to say a 2xxx lb. F8x is impossible for, theoretically, limitless money. That's not a bet I am willing to take. People accomplish what others deem impossible on finite budgets all the time.

So I think the guys who build GT cars good get their heads together with the guys that build GS cars, toss out the rule book, and end up with the car you think can't be built if they so desired. I may not convince you - ok, I can appreciate that, I respect your skepticism. My gut tells me it can be done.

Regarding 2700 lbs. agree - I already said above I probably went too aggressive with that number.

[mkoesel]

Originally Posted by FTS

I should have more accurately put it as old ALMS and GrandAm series and now Tudor series. Any of their classes didn't/doesn't have production-based cars, with the exceptions I mentioned. Too many allowances and exceptions are being made.

I hear you, and understand you now.

So assuming what you said earlier about the underpinnings of specific cars is true, about this 911 RSR (for example), I have to wonder then just how much less a 911 shell weighs than a stock E92 unit body that they can compete at the same or similar weight without the "tube chassis" as mastek is describing it, supposedly sitting under the M3 GT2.

Oh sure, the ℗-car is a purpose built sports car - that gives it a huge advantage from the get go. Same case with the other examples you cited. No doubt about that. Pretty staggering though, the apparent massive weight penalty of the E9x.

[FTS]

Good question mkoesel, I certainly do not have comparable numbers. But, as you know, because they still balance performance with weight across the range, I don't think weight eventually determines ultimate performance in these 'pro' series. One area in which probably weight makes the ultimate difference is if a platform is under the minimum weight and they have been imposed weight penalty, that platform has the chance to distribute that weight to their advantage within the car without upsetting the balance. I may be wrong on this.

I think the more determining factors are weight distribution of the chassis, suspension pickup points and configuration, engine internals, transmission internals, chassis width and track width, etc.

So, for example, most tube-frame chassis have double wishbone front suspension structure that is not used on the representative street cars, but in the case of 911 Cup and RSR they still use MacPherson struts configuration, which is a disadvantage of course. In the case of the 458, it uses double wishbone on the street car which transfers into the race car.

[Arcoril]

Originally Posted by FTS

Unfortunately, it has been, like most cars, sillouhette racing. As far as I know the only non-tubeframe chassis cars true to production form are the Porsche 911 Cup/RSR and Ferrari 430 Scuderia/458 Specialle.

From what I understand, the new C7.R's chassis is also surprisingly similar to the chassis in the standard C7/Z06.