Re-classing E46 M3 - TTB -> TT4?

[int2str]

So, since it'll be TTB no more, but E46 M3 needs to find a new home.

 

Since I'm new to the modification factor scheme and power/weight classing, is this correct:

 

2004 BMW M3 (E46) Coupe; base class is "ST" (from PT rules)

3385lbs ~ 285hp (unconfirmed) = 11.9

 

Modification factors:

+0.1 Vehicle weight >3300lbs

+0.3 Tire size 255

+0.4 OEM Aero

= 11.9 + 0.1 + 0.3 + 0.4 = 12.7 = ST4

 

In TTB, I was pretty tight on points on my still street driven car and could not consider Aero.

However, assuming that the ST rules will be the same/similar for TT, it seems like I would basically NEED Aero to be competitive with the car to get me closer to the 12.0 (aero would get me to 12.3 then).

 

So if my calculation and assumptions are correct, I'll need to throw money at the car to remain competitive.

TTC does not seem to be an option for an E46 M3 with decent tires.

 

Correct?

Also, any news on TT rules for 2017?

[flier129]

I don't have a good answer for you, but I've come to tell you it's average hp for the ratio and not your peak hp

 

Max hp + 3 highest hp data points 500rpm apart, divide by 4 = Avg hp

[int2str]

Yes, understood.

So that will make it even worse....

 

My power/weight ratio will be so high that I would have to seriously throw money at the problem to try to make the car faster. Loose 300lbs somehow? Add 50hp? Big brakes, Aero, Lexan windows, carbon everything?

 

Remember, this car is still street driven and had a great home in TTB.

TTC is not an option (car's base class is "ST"). So, where do I go from here?

[djqd36]

Sounds like your options are lose weight or adopt the aero.

 

Another idea is to reduce your tire size to 245, and run A7's.

Can you really not loose any weight at all? Even 50-75lbs will help. Do you have a passenger seat?

Do you have any way of adding power reasonably?

 

TT rules and ST rules are the same.

[int2str]

Loosing weight would be hard, given the fact the car is still street driven. Yes, it has a passenger seat and I'd like to keep it. But of course, as I said, carbon everything (hood, roof, trunk, fenders etc.), Lexan windows, wire harness reduction etc. would help, but most would be $$$. 50 lbs sounds tough if you ask me at this point.

 

Would love Aero on track, but again, front splitter will be annoying getting to/from the track. But it would seem it's a must have if there's really no option outside of TT4 for the E46 M3 (which doesn't seem like there is).

 

For power, no, a naturally aspirated engine, California Carb legal means that coming by 50 HP would be $$$ as well.

 

*sigh* the more I think about it, the more I think I'm screwed for 2017...

If cost saving was the motivation for the rule changes, it really doesn't seem to apply.

[Fair]

Also, any news on TT rules for 2017?

As others have said, the ST4/TT4 rules are the same and they have been out for a month now.

 

I'd get your car dyno'd before you look any further at classing. Once you know that (average power) number you can look at weights and see where your car fits best.

 

I suspect your E46 M3 might be better off in TT3 with OEM aero and a 275mm tire. I don't see how an E46 M3 stays in TT4 unless they add a lot of ballast or cut avg power. I could be wrong.

 

 

Going to TT-Number class aero limits is a big jump in costs and loses a lot of steetability. I'm juggling that decision now with my TTD E46 330Ci above.

 

 

But even as a shop owner that does this sort of zero work, it's expensive and time consuming to take a car to the limits of the aero rules for TT# classes. I've done it and it took 2 seasons of changes, testing, and work to get the aero bits dialed in right.

[daytonars4]

TT3 is for the well built E46 M3's in my region if you want to remain competitive. TT4 is an easy fit and should have you near the front of the class if you work everything out well. You can pretty easily get another 10-20whp if your setup peak is only around 285whp now. From what I understand, the base is 12. If you are running 255-275 you get to gain .3 which brings you to 11.7. Add another .5 for OEM aero and weight and that gets you to 11.2. You would need to get to an avg whp of about 302 which means a peak I would guess around 315-320 at 3385lbs. With just a better tune alone you should be close. I doubt a non-aero e46 M3 would regularly podium in my region in TT4 (Midatlantic), but there's variance across the country.

 

E46 M3 frankly is one of the easiest cars to get into TT4. All the stock e36 M3's that use to make up TTB are screwed bc the mods take power levels to a point that just aren't attainable. I have an e36 with an S54 I'll do a few events with. But with half of last years TTB cars now too low on power for TT4, I doubt we hit contingency often.

[int2str]

I added Aero to my car. Haven't dynoed the car yet.

So still going with the guessed peak figure of 285, here's where it stands:

 

3385lbs ~ 285hp (unconfirmed) = 11.9

+0.1 Vehicle weight >3300lbs

+0.3 Tire size 255

= 11.9 + 0.1 + 0.3 = 12.3

 

Also the weight will have gone up now actually.

Will have to try to make it up somehow

 

I really think I will not be able to be competitive in TT4.

Oh well.....

 

I miss TTB alread :'(

[427R]

I really think I will not be able to be competitive in TT4.

Oh well.....I miss TTB alread :'(

You'll probably end up doing better than you think. I moved into TT3 at the beginning of this season, believing I wouldn't be as competitive as I would need to be. I set goals throughout the season and did much better than expected. Being in TT3, raised my level of competitiveness and that made all the difference...plus some changes to the car. All in all, we had a very successful and fun year and feel we're very competitive in TT3. May try our hand at ST3 someday.

[int2str]

Alright, time to update this thread.

I was actually quite wrong on the horsepower.

Car is much closer to 12:1 than I thought.

 

Here's where it's at now:

 

Weight: 3406 (estimate currently; car was 3386 at last check on scale - before AERO + trailer hitch)

Average HP: 294 (304 peak!)

 

3406 / 294 = 11.58

+0.2 Vehicle weight >3400lbs (has to be >3400 now.... )

+0.3 Tire size 255

=

12.08

 

So that will actually clamp cost for me a little bit. That means no exhaust or other mods. Though I'll probably do brakes at some point.

And no more weight loss. I'm fine with that.

[JCathers]

its my understanding that it is actually -0.3 on the <275mm tire rule.. the verbiage used in the rules seems to be the exact opposite of what makes sense - it would be a higher weight-to-power ratio for running narrower tires if you read it the way its written, I'm not really sure what is going on there but I have to assume its the opposite of what they're saying. Everyone in TT4 is going to have an initial base of 11.7:1 because we're not allowed to run larger than 275's, so we all get the -0.3 break... which also seems asinine to me, but what can you do.

[int2str]

Why?

 

From the rules:

Tire Size: Size 245 or smaller (DOT-approved) = +0.7
Size 275 to 250 (DOT- approved) = +0.3

 

This makes sense. That doesn't look the wrong way around at all?

[JCathers]

Why?

 

From the rules:

Tire Size: Size 245 or smaller (DOT-approved) = +0.7
Size 275 to 250 (DOT- approved) = +0.3

 

This makes sense. That doesn't look the wrong way around at all?

 

 

So you're at 11.58:1 right now - if you run 275's you add +0.3 so you now have to be at 11.88:1 weight/power (ignoring the weight points for simplicity).. but if you run a narrower tire you have to add 0.7, bringing your weight/power ratio to 12.28:1 right? How does that make sense? Being penalized and forced to run a higher weight/power ratio for running a narrower tire. Unless I'm missing something glaring, I feel like I'm living on Bizarro.

 

Also, you don't start with your cars power to weight ratio before adding modification factors - you start with the base class ratio of 12:1 then add/subtract the modification factors - once you figure out that ratio, you have to get your car at or above it. It's been discussed and confirmed that everyone is starting at 11.7:1 in TT4 because we're all getting the 0.3 break for running 275 or smaller, since tires larger than 275 are banned.

 

They used to have a TT1-3 class calculator in the form of an excel spreadsheet posted on the NASA site but I can't find it now :/

[Clavette]

Why?

 

From the rules:

Tire Size: Size 245 or smaller (DOT-approved) = +0.7
Size 275 to 250 (DOT- approved) = +0.3

 

This makes sense. That doesn't look the wrong way around at all?

 

 

So you're at 11.58:1 right now - if you run 275's you add +0.3 so you now have to be at 11.88:1 weight/power (ignoring the weight points for simplicity).. but if you run a narrower tire you have to add 0.7, bringing your weight/power ratio to 12.28:1 right? How does that make sense? Being penalized and forced to run a higher weight/power ratio for running a narrower tire. Unless I'm missing something glaring, I feel like I'm living on Bizarro.

 

Also, you don't start with your cars power to weight ratio before adding modification factors - you start with the base class ratio of 12:1 then add/subtract the modification factors - once you figure out that ratio, you have to get your car at or above it. It's been discussed and confirmed that everyone is starting at 11.7:1 in TT4 because we're all getting the 0.3 break for running 275 or smaller, since tires larger than 275 are banned.

 

They used to have a TT1-3 class calculator in the form of an excel spreadsheet posted on the NASA site but I can't find it now :/

 

I think you're misunderstanding how to do factors.

 

To run in TT4, your final adjusted wt/hp has to be above 12:1.

 

So let's just take tires as only modification that your car has for simplicity.

 

First you start with your unadjusted wt/hp. Average hp divided by actual wt. Before all adjustments/modifiers.

 

If your unadjusted wt/hp is 11.31, then you would have to run 245's DOT or skinnier (+0.7) to have a final adjusted wt/hp of 12:01.

 

If your unadjusted wt/hp is 11.71, then you would have to run 275's DOT (+0.3) to have a final adjusted wt/hp of 12:01.

 

So, basically running narrower tires allow you to run a lower unadjusted wt/hp which basically means either more starting power or less starting weight.

 

I'm in TT3. My average hp is 338. My weight is 3145. This gives me an unadjusted wt/hp of 9.305. I run 245 Hoosiers (+0.7) and non-OEM aero (+0.0) which puts me at 10.005 final adjusted wt/hp. If I tried to run 275's, I would be at 9.605 and would have to either add weight, cut power, or move to TT2.

 

Hopefully this explanation helps.

 

Denis

Edited January 1, 2017 by Guest

[int2str]

Yes, Denis has explained it well.

 

I'll repeat the calculation for my car as well here:

 

3406 lbs / 294 avg.hp. = 11.58 : 1

+0.2 Vehicle weight >3400lbs

+0.3 Tire size 255

=

12.08 : 1 = TT4

[JCathers]

Why?

 

From the rules:

Tire Size: Size 245 or smaller (DOT-approved) = +0.7
Size 275 to 250 (DOT- approved) = +0.3

 

This makes sense. That doesn't look the wrong way around at all?

 

 

So you're at 11.58:1 right now - if you run 275's you add +0.3 so you now have to be at 11.88:1 weight/power (ignoring the weight points for simplicity).. but if you run a narrower tire you have to add 0.7, bringing your weight/power ratio to 12.28:1 right? How does that make sense? Being penalized and forced to run a higher weight/power ratio for running a narrower tire. Unless I'm missing something glaring, I feel like I'm living on Bizarro.

 

Also, you don't start with your cars power to weight ratio before adding modification factors - you start with the base class ratio of 12:1 then add/subtract the modification factors - once you figure out that ratio, you have to get your car at or above it. It's been discussed and confirmed that everyone is starting at 11.7:1 in TT4 because we're all getting the 0.3 break for running 275 or smaller, since tires larger than 275 are banned.

 

They used to have a TT1-3 class calculator in the form of an excel spreadsheet posted on the NASA site but I can't find it now :/

 

I think you're misunderstanding how to do factors.

 

To run in TT4, you're final adjusted wt/hp has to be above 12:1.

 

So let's just take tires as only modification that your car has for simplicity.

 

First you start with your unadjusted wt/hp. Average hp divided by actual wt. Before all adjustments/modifiers.

 

If your unadjusted wt/hp is 11.31, then you would have to run 245's DOT or skinnier (+0.7) to have a final adjusted wt/hp of 12:01.

 

If your unadjusted wt/hp is 11.71, then you would have to run 275's DOT (+0.3) to have a final adjusted wt/hp of 12:01.

 

So, basically running narrower tires allow you to run a lower unadjusted wt/hp which basically means either more starting power or less starting weight.

 

I'm in TT3. My average hp is 338. My weight is 3145. This gives me an unadjusted wt/hp of 9.305. I run 245 Hoosiers (+0.7) and non-OEM aero (+0.0) which puts me at 10.005 final adjusted wt/hp. If I tried to run 275's, I would be at 9.605 and would have to either add weight, cut power, or move to TT2.

 

Hopefully this explanation helps.

 

Denis

 

That makes sense, I guess I've been looking at it from the flip side since I'm well above 12:1 in B trim so I've been working toward getting it to the actual 11.8:1 I'll be at with the "+0.3" I'll get for <275's and the "-0.1" for being <3000lbs - I misunderstood the OP and thought he was under the impression that he had ballast/detune up to 12.08:1

[Clavette]

Yes, Denis has explained it well.

 

I'll repeat the calculation for my car as well here:

 

3406 lbs / 294 avg.hp. = 11.58 : 1

+0.2 Vehicle weight >3400lbs

+0.3 Tire size 255

=

12.08 : 1 = TT4

 

If I were you, I'd drop weight back as low as you can and switch to 245's. Hoosier 245's are plenty wide.

[int2str]

Leaving the horsepower where it currently is, I would be able to drop weight to 3292.8 lbs. Or, about 100lbs less than it is currently. Then the million $$$ question becomes whether that makes a big enough difference to make up for the downsides.

 

Loosing 100lbs at this point would be massively reducing streetability and the car is already not that great to drive on the road

 

If I ever decide to trailer it, then of course, all bets are off...

[427R]

Then the million $$$ question becomes whether that makes a big enough difference to make up for the downsides.

Yes, weight loss will help.