It's here...

I think the target rwhp I used for the RX-7 is accepted by most as an accurate number. It's not the highest one I've heard discussed. The powertrain loss was a conservative assumption. Even if you use a less conservative assumption, the min weight for the E36 with the SIR comes out of the equation lower than where it is today. That leaves us with the adders and subtractors. The BMW has some benefits over the RX-7, but the RX-7 has some benefits over the BMW too. I'd like to understand how the subjective part of the weight spec was made.

Fred
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Fred,

Great to see you on the forums. Can't wait to see you out on track again next year.

The spec weight was set before any of the current 'process' was in place. Frankly, without throwing any previous committees under the bus, I have no idea how the weight got set at 2850. Without restriction, it is just too light. And spec weight has little to do with curb weight other than a sanity check as to if it could actually get to spec weight...it is not part of any process.

We can let the debate begin on the following:

The RX-7 and the BMW will put out close to the same hp with the new 2006 rules
The RX-7 has a lower CG
The RX-7 has better aero
The RX-7 is lighter by 180lbs
The BMW has a huge torque advantage
The BMW has a much wider powerband
The BMW has bigger brakes

That is how I see the pro's and con's on the cars. Add or subtract if I screwed the pooch. Do people see this as equal? Advantage to one or the other? Let's hash it out.

AB
 
Now this is the basis for a good discussion.

I agree that the two cars "look" fairly matched at this point, but I don't think you can give enough of weight to the torque advantage. That is what puts the BMWs up front in my view, and makes even an average prepped car go fast. The torque curves I have seen on an ITS 2.5 are flatter and higher than those on my 3.5L V8.

In any event, I'm not sure you can argue with Andy's post. On paper, the cars look pretty close with the SIR.
 
I think that discussion is ideally done if you compare the two cars, at race prep levels, but at the same weight. For the sake of discussion, just assume 2700, to keep the comparision relevant.

Now how do they stack up?

Which one is better in-

Aero?
Power curve? ( grunt out of corners, and legs, and driveability)
braking?
Handling? (transitional, predictability and outrigth G forces?)


Further, each category needs to asigned a percentage of value, vs the other categories. Aero, for example, is a very small portion of the picture compared to the power curve.

Once you determine the answers to those questions I think you have the basis for very valid comparisions.
 
I think the target rwhp I used for the RX-7 is accepted by most as an accurate number. It's not the highest one I've heard discussed. The powertrain loss was a conservative assumption. Even if you use a less conservative assumption, the min weight for the E36 with the SIR comes out of the equation lower than where it is today. That leaves us with the adders and subtractors. The BMW has some benefits over the RX-7, but the RX-7 has some benefits over the BMW too. I'd like to understand how the subjective part of the weight spec was made.

Fred
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16 to 18% loss is a good average for a 5spd RWD package.
 
I see that HP numbers are used alot...what about torque...how is that put into the equasion? The BMW has LOTS and I have seen how they come off the corners...a good balanced chassis with big brakes and good torque=good laptimes. An RX7 seems to have to absolutely hit every corner just right to get the run off the corner to avoid dipping into a lackluster torque curve (same goes for the puny 1.8 Integra GSR and 99 Miata, Prelude, 240SX etc). That seems to be the advantage. If an SIR simply limits HP and not torque, we will be in the same boat as before (if the car can produce 195 WHP and same torque). I am interested to see torque info on classification.
 
I see that HP numbers are used alot...what about torque...how is that put into the equasion? The BMW has LOTS and I have seen how they come off the corners...a good balanced chassis with big brakes and good torque=good laptimes. An RX7 seems to have to absolutely hit every corner just right to get the run off the corner to avoid dipping into a lackluster torque curve (same goes for the puny 1.8 Integra GSR and 99 Miata, Prelude, 240SX etc). That seems to be the advantage. If an SIR simply limits HP and not torque, we will be in the same boat as before (if the car can produce 195 WHP and same torque). I am interested to see torque info on classification.
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Evan, we can't take all the strong points away from the E36. What happens now is a good handling E36 and a good handling 240z or RX7 are all close to equal in the turns. I would say advantage goes to the lighter cars. The Z with a good exit can run out of the turn with a Bimmer for the first couple hundred feet. Once the Bimmer gets its legs it runs away down the straight. Capping the top end should limit how far it can get away. I don't believe anyone can create a perfect world this just gets it closer. The other point is weight once it is rolling will have less effect up top than the SIR will.

think everyone should understand that it not about turning E36's or any other car instant loosers, If it was I personally would be writing letters and screaming my head off. It is about bringing a good car and maybe other cars in the future into a performance window that will make for good competition. Once inside that window it will still be up to the teams.shops and drivers to get the job done as far as building a winner.
 
I see that HP numbers are used alot...what about torque...how is that put into the equasion? The BMW has LOTS and I have seen how they come off the corners...a good balanced chassis with big brakes and good torque=good laptimes. An RX7 seems to have to absolutely hit every corner just right to get the run off the corner to avoid dipping into a lackluster torque curve (same goes for the puny 1.8 Integra GSR and 99 Miata, Prelude, 240SX etc). That seems to be the advantage. If an SIR simply limits HP and not torque, we will be in the same boat as before (if the car can produce 195 WHP and same torque). I am interested to see torque info on classification.
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Torque is not a factor in the 'formula' part of the 'process'. It is a subjective piece we call adders. Typically, torque/displacement is an adder should it be warranted.
 
If we may, the GSR has been pretty highly debated and although the HP number may now be in line with the RX7 and BMW's, how does NO torque and small brakes make this car equal to the previous two cars. Is it more aerodynamic? Am I missing something?
 
If we may, the GSR has been pretty highly debated and although the HP number may now be in line with the RX7 and BMW's, how does NO torque and small brakes make this car equal to the previous two cars. Is it more aerodynamic? Am I missing something?
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Vtec/and good gear ratio's?
 
Jeff and Ron

I still have my 94 325 and directly from the BMW owners manual it has curb weight of 3021 lbs ( 3086 A/T) and list 189 hp @5900 and 181 ftlbs @ 4000. My co workers RX7 (1991) list curb weight 2787 with 160 hp @ 6000 and 140 tq @4000. Maybe the BMW is listed light but for IT specs it is not at all unreasonable to loose 170 lbs, The Mazda only get to loose 107, maybe it should be listed at 2600 lbs. My VR6 GTI SSB car has a listed curb weight of 2830 but runs ITS at 2680 or 150 lbs less... Did anybody explore lowering the Mazda weight ? I think it is reasonable to think that any IT car should weigh 150 lbs ( w/driver ) less than its curb with all the stuff you can junk....
 
Vtec/and good gear ratio's?
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What does VTEC have to do with anything? OK so you can rev the car to 8,200 RPM. How many RPM's does the RX7 rev to? VTEC enables more HP to come from small displacement engines by having two cam lobes. One for cruising speed and one for full throttle acceleration.

I would argue that the gear ratios are not that good since 5th gear is quite tall and with no tq you are dead on corners that are in between 4th and 5th.
 
If we may, the GSR has been pretty highly debated and although the HP number may now be in line with the RX7 and BMW's, how does NO torque and small brakes make this car equal to the previous two cars. Is it more aerodynamic? Am I missing something? [/b]
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What does a full prep GSR put to the ground for torque?
 
Jeff and Ron

I still have my 94 325 and directly from the BMW owners manual it has curb weight of 3021 lbs ( 3086 A/T) and list 189 hp @5900 and 181 ftlbs @ 4000. My co workers RX7 (1991) list curb weight 2787 with 160 hp @ 6000 and 140 tq @4000. Maybe the BMW is listed light but for IT specs it is not at all unreasonable to loose 170 lbs, The Mazda only get to loose 107, maybe it should be listed at 2600 lbs. My VR6 GTI SSB car has a listed curb weight of 2830 but runs ITS at 2680 or 150 lbs less... Did anybody explore lowering the Mazda weight ? I think it is reasonable to think that any IT car should weigh 150 lbs ( w/driver ) less than its curb with all the stuff you can junk....
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The Integra GSR and Prelude VTEC's are so heavy that I will need 150lbs of lead, spare tire, and a lot of cage to get it to the min weight.
 
Fred, thank you. That is helpful. Perhaps the real solution was to add 100 lbs to the BMW and take 100 off the Z, the RX7, and others. I could lose 100 lbs on my car easily. Can the others? Steve E., can 100 come off an RX7?
 
The Integra GSR and Prelude VTEC's are so heavy that I will need 150lbs of lead, spare tire, and a lot of cage to get it to the min weight.
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Lets see what does Vtec have to do with it? How about the best of both worlds. With prper programming you have the best of both cam curves. You can maximize the torque and yet you still can bring in the extra lift when the HP is needed. Torque is great but some cars are designed to be driven flat out. Just like the RX7 i don't buy the whole lack of torque aregument there either. With the correct final drive and the excellent gear ratios Mazda offers you are in to power curve or those motors most of the time.


Jeff the 240z cannot not loose 100lbs in most all cases. Why offer it a weight it can't make?
 
Hey Jeff...

This was suggested several times in old threads and summarily shot down.

Not many BMW people seemed to have a problem with giving "breaks" to other models...we asked that you leave our car alone and give "help" to the others that "need" it...but...the vocal few continued with their scream for big lead and/or restriction...and so it is.

Fred, thank you. That is helpful. Perhaps the real solution was to add 100 lbs to the BMW and take 100 off the Z, the RX7, and others. I could lose 100 lbs on my car easily. Can the others? Steve E., can 100 come off an RX7?
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Fred, thank you. That is helpful. Perhaps the real solution was to add 100 lbs to the BMW and take 100 off the Z, the RX7, and others. I could lose 100 lbs on my car easily. Can the others? Steve E., can 100 come off an RX7? [/b]
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Jeff,

Couple points. Why are you hung up on curb weights? Different cars will be able to take out different amounts of weight - so using any kind of standard is not possible. I was thinking half-heartedly about an ITA Fiero. How much weight do you think you could really pull out of that car? Weight has to be based on power and dynamic factors.

With regard to your potential solution based on Fred's post. You are effectly suggesting moving the whole performance envleope 'down' so that one car doesn't have to go too far up. That to me is not a great idea on a couple fronts. 1st, we would have to move everyone down to that new 'target'. Knowing if all the cars can get there is impossible as a first hurdle, then the probability that everyone could lose 100lbs has to be zero.

You effectively want to re-engineer the entire process so that one car doesn't have to fit? I don't see that as a solution.
 
Lets see what does Vtec have to do with it? How about the best of both worlds. With prper programming you have the best of both cam curves. You can maximize the torque and yet you still can bring in the extra lift when the HP is needed. Torque is great but some cars are designed to be driven flat out. Just like the RX7 i don't buy the whole lack of torque aregument there either. With the correct final drive and the excellent gear ratios Mazda offers you are in to power curve or those motors most of the time.
Jeff the 240z cannot not loose 100lbs in most all cases. Why offer it a weight it can't make?
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when you run vtec, If you fall off the curve, the cruising cam lobes do little to help get power to the ground...they are to make the car pass emissions and get good mileage. you have basically the same torque as a ls motor (not much sometimes less) but more cam on top...so coming off the corners or binding up in tight turns these cars really hurt. thats why you dont see them at the front when the big togs are there. there is a well prepped one here in the SE Scott Seck...he is relatively competitive, but the rx7's and BMW's usually dominate anyways and he is a really good driver.
 
What does VTEC have to do with anything? OK so you can rev the car to 8,200 RPM. How many RPM's does the RX7 rev to? VTEC enables more HP to come from small displacement engines by having two cam lobes. One for cruising speed and one for full throttle acceleration.

I would argue that the gear ratios are not that good since 5th gear is quite tall and with no tq you are dead on corners that are in between 4th and 5th.
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I might misunderstand something here but it isn't that it allows it to rev to 9k it is that it makes reving to 9k worthwhile. HP is a function of torque and rpm. Turn VTEC off you could still physically be able to rev to 9k but wouldn't be worthwhile because torque would cease to exist making the rpm useless. Isn't that the point of Honda's techniques is while using lower peak cylinder pressures (less torque) but stretching the torque out into the rpm range they get the HP through revs? VTEC brings the torque to much broader rpm ranges.
 
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