IT Class Philosophy

[lateapex911]

And is rev limit also a consideration??

I understand that the RX7 in general is low on torque. However, it can run up to some ungodly rev limit.

So instead of making torque, you put a really crazy diff in it (something like a 5.1 for the 2nd gens) and get awful close to the torque being put out at the wheels with a car that can only push a 7000 RPM redline and therefore only a 4.3 or so gearset, but has torque.

Just asking...

Joe Mac [/b]

Torque, is, essentially, tq.

The tq I mentioned, (101 -105) was measured after the diff... Yes, the engine can rev to about 8K, but peak hp occurs earlier. Your car is known to be a strong tq AND hp engine. IIRC, you car can put over 150 HP down and tq is very close, but you don't rev as high.

Net net is I need to maintain a minimum of 4500 rpm and shift between 7 and 8K, while you can run a lower rev range. But, grunt and pull are much greater for you, at nearly any part of the curves.

And while gear multiplication helps acceleration, when taken to extremes, top speed could become very limited if the gearing gets too high in an attempt to keep up with the "Jones" acceleration.....sure, it might match you to 40 MPH, but then it might run out of revs in 5th at 80mph.

 

[steve b]

First, it's not just a formula, it's a process. And it started out as an attempt to add objectivity into the classification procedure, and to create a method for fixing classification errors.

As much, it was decided to incorporate major items that affect a racing cars lap times. All along, it's been accepted that no formula or process can create perfect parity, at least considering the practical limitations of the club we operate in.

So, there are certain cars that are just not treated well by the process, and others that actually do well by it. My car, the fist gen RX-7 falls outside the process goals because of it's severe lack of tq. Would I like to change that? Sure! But it is what it is. But, and this is important, the root cause must be identified.

I have been reluctant to move cars like it down a class, because if it isn't competitive in it's current class at it's process weight, then it won't be in any other class at process weight, all things being equal.

(In the RX-7s case, if we were to add a level of fine tuning to the process that accounted for it's abnormally low torque, we would first have to solve for the current class, then, if it couldn't fit it would be solved for the next lower class)

I suspect that the original process was seen by many as a starting point, and that depending on the success and failures of the process, tweaks could be implemented along the way. To me, tq is something that i feel should be a standard consideration in the adderss and subtracters part of the process.
[/b]

I agree (in the case of the MR2) that using the same process and moving the car down to B will just produce a heavy back of the pack B car. But it would be a good first step. It is my understanding that the weight of the MR2 was reduced from 2370 to 2270.

Did the process change that caused that? Or was that a non-existent competition adjustment? Whatever it was, it didn't work because the cars are still back markers. The fastest ones are still 3 seconds off the pace at SP.

But I say move the car to B, make it heavier if you have to, run the 6" rims and let the chips fall where they may. Then maybe the car can get a 100 pound adjustment in B (later) like it did in A and then maybe you start to see competitive MR2s

 

[gran racing]

For cars that people are not able to (even if that's means simply do not have the means to get it to min. weight), adjusting the class using the same process would make a difference. That would be the primary advantage of making the change.

 

[JamesB]

--><div class='quotetop'>QUOTE(steve b @ Sep 7 2007, 11:39 AM) [snapback]122726[/snapback]</div><div class='quotemain'>
I agree (in the case of the MR2) that using the same process and moving the car down to B will just produce a heavy back of the pack B car. But it would be a good first step. It is my understanding that the weight of the MR2 was reduced from 2370 to 2270.

Did the process change that caused that? Or was that a non-existent competition adjustment? Whatever it was, it didn't work because the cars are still back markers. The fastest ones are still 3 seconds off the pace at SP.

But I say move the car to B, make it heavier if you have to, run the 6" rims and let the chips fall where they may. Then maybe the car can get a 100 pound adjustment in B (later) like it did in A and then maybe you start to see competitive MR2s
[/quote]


Steve just to clarify, none of the MARRS MR2's are 10/10th builds. And one is having no issue raising hell in the top 10 along with some other non 10/10th built cars fighting for position. So until a 10/10th build is made I cannot pass judgement comparing to the caliber of cars running the pointy end of the MARRS ITA field.

Can it run in B, I think so with the right weight and a 10/10ths build might have the chance of catching that pesky volvo and gaggle of 2002's once a proper motor is built.

 

[77ITA]

All this talk of torque and RX-7s being too slow for ITA, I'm curious... how many of you are running the Mazda Comp 5.125 ring and pinion (P/N:M068-27-110A)? I know it's spendy, but it should do quite a bit for the car. Remember, torque multiplication. If anyone is running it, what is your gear limited top speed? Surely it's not 80mph like estimated above.

 

[Rabbit07]

All this talk of torque and RX-7s being too slow for ITA, I'm curious... how many of you are running the Mazda Comp 5:125 ring and pinion (P/N:M068-27-110A)? I know it's spendy, but it should do quite a bit for the car. Remember, torque multiplication.
[/b]

See Post #61

 

[77ITA]

See Post #61
[/b]

I did read his post, but I am interested in hearing what people are actually using in their ITA cars and the "80mph top speed" sounds more like a an estimate than product of mathmatical equation or testing with the 5.125

My math skills are on par with a child (if not worse), so I won't try working it out myself

 

[dickita15]

Yes I run the 5:12 and it helps. Most of my friends run the 4:88 or 4:40. The gearing does not change the torque number; it does help the transmission gear spacing and makes it a little easier to keep it above 6500 rpm. On the other hand my friends shift less.

Also while the rotary has a reputation for high revving the 390 CFM nikki carb severely limits the power as you approach 8000 rpm.

on edit i estimate top speed with 5:12 and 45 series tires at 120 mph. I was at about 7700 rpm in 5th at Mid Ohio at the end of the straight.

 

[Andy Bettencourt]

--><div class='quotetop'>QUOTE(steve b @ Sep 7 2007, 11:39 AM) [snapback]122726[/snapback]

<div class='quotemain'>

I agree (in the case of the MR2) that using the same process and moving the car down to B will just produce a heavy back of the pack B car. But it would be a good first step. It is my understanding that the weight of the MR2 was reduced from 2370 to 2270.

Did the process change that caused that? Or was that a non-existent competition adjustment? Whatever it was, it didn't work because the cars are still back markers. The fastest ones are still 3 seconds off the pace at SP.

But I say move the car to B, make it heavier if you have to, run the 6" rims and let the chips fall where they may. Then maybe the car can get a 100 pound adjustment in B (later) like it did in A and then maybe you start to see competitive MR2s [/b][/quote]

Well I can tell you that won't happen. If the MR2 is moved to ITB - at ITB process weight - and it is still a backmarker, then it's a backmarker. The weight reduction wasn't done to try and garner some more competition potential. Just like the cars that gained weight didn't gain it to try and reign them in. It happened by running cars that hadn't been through the classification process - and resetting their weight if it was 'off' by 100 or more lbs - up or down.

Each car is what it is. R, S, A, B or C. In theory, the MR2 would be just as competitive in B as it is in A - but as some have pointed out, it could at least nail minimum weight.

****************

And on the 5.12...most RX-7's are running the 4.88 or the 5.12. 12A's and 13B's. It's the ONLY way to make them go. You have a 4.10, you are a sitting duck. I wouldn't race our BEST ITS RX-7 in ITA with a 4.10.

 

[tnord]

the prep level that the one dude went through to get his rx7 to weight is how you HAVE to class the cars. i have to admit giving a little chuckle when people say their car is at 100% prep, because it's usually VERY easy to see that it's not.

 

[steve b]

the prep level that the one dude went through to get his rx7 to weight is how you HAVE to class the cars. i have to admit giving a little chuckle when people say their car is at 100% prep, because it's usually VERY easy to see that it's not.
[/b]

But are we to assume that all of the cars running away from them are 100% prepared?

I'm going to back down and finish getting my license and learn a few things before I beat this horse any more. I only added my .02 because I've been told that I purchased one of the best prepared MR2s (by several sources) and therefore felt obligated to related my experiences and feelings on the topic.

Believe me, if there is one car on the track running the same lap times as me(regardless of position), I'll be able to have fun out there.

 

[lateapex911]

I did read his post, but I am interested in hearing what people are actually using in their ITA cars and the "80mph top speed" sounds more like a an estimate than product of mathmatical equation or testing with the 5.125

My math skills are on par with a child (if not worse), so I won't try working it out myself [/b]

Reread the words..

when taken to extremes, top speed could become very limited if the gearing gets too high in an attempt to keep up with the "Jones" acceleration.....sure, it might match you to 40 MPH, but then it might run out of revs in 5th at 80mph.[/b]

Extremes, like above 5.12.... in other words, you can't magically "fix" a lack of torque, without incurring penalties. Yes, you can make the car acclerate faster, but you will run out of top end. So, they go by at the end of the straight when the motor is spinning 8400 and breathing thru a straw.

Of course 80 MPH isn't an estimate, never said it was...just an illustration of a concept, taken to extremes to help make the point more obvious....

Dickita (cha cha cha...had to) runs a 5:12, I run a 4.88. He tends to run at NHIS and Lime Rock, with occasional forays to Watkins glen and Mid Ohio, whereas I tentd to love the longer tracks like the Glen and Mid O, and Atlanta and (this year) VIR...so I use the 4.88 for a better top end, and less shifting.

It's all a compromise. But lack of tq is lack of tq. And tq wins races.

 

[tnord]

But are we to assume that all of the cars running away from them are 100% prepared?

I'm going to back down and finish getting my license and learn a few things before I beat this horse any more. I only added my .02 because I've been told that I purchased one of the best prepared MR2s (by several sources) and therefore felt obligated to related my experiences and feelings on the topic.

Believe me, if there is one car on the track running the same lap times as me(regardless of position), I'll be able to have fun out there.
[/b]

no. you are to assume that both their car and their driver are better prepared.

 

[spnkzss]

Steve just to clarify, none of the MARRS MR2's are 10/10th builds. And one is having no issue raising hell in the top 10 along with some other non 10/10th built cars fighting for position. So until a 10/10th build is made I cannot pass judgement comparing to the caliber of cars running the pointy end of the MARRS ITA field.

[/b]

But that kind of statement can be taken the wrong way also. In MARRS ITA, there is a pretty good gap between top 5 and 5-10. If the MR2 was able to run top 5 in MARRS ITA then there is nothing more to talk about. If I remember correctly that MR2 is running low 31s which is pretty far off of the mid 28s.

Not trying to add to the debate, just don't want statements like that to be too generalized.

 

[gran racing]

If the MR2 is moved to ITB - at ITB process weight - and it is still a backmarker, then it's a backmarker.[/b]

That would be completely fair, and expected.

the prep level that the one dude went through to get his rx7 to weight is how you HAVE to class the cars.[/b]

If it could fit into a class where the weight was easier to attain, why does it "HAVE" to be at the more challenging (money, safety, significant hours) weight?

I've been told that I purchased one of the best prepared MR2s (by several sources).[/b]

And you have. If it happened to be a different car (Miata, 240SX, Integra, CRX) and prepared to the same extent, it would be one hell of a car for the class. Then again, it wouldn't have been sold to you as cheaply.

 

[JamesB]

Absolutely, he is running in the 31's with a well prepared chasis and a junkyard motor with a heck of a well tuned header/exhaust. i have no idea what the potential could be if he had a balenced, .040 motor with a .5 compression bump and port matching with a well tuned fuel map. Could he make 3 seconds off just that, I dont think so. Can he work on himself as the driver and give a 10/10ths effort and make it up there? I think so. I dont run by lap times because dick has a well pepared car but hes in the 40's, Meanwhile AJ is in the mid 30's and doug is in the low 30's. I look at how is car is down the straight, and hes not really loosing steam to the other cars out there where it matters.

 

[tnord]

That would be completely fair, and expected.
[/b]

maybe for the first year. but i bet 3 years later and it'd be the same old sob story.

If it could fit into a class where the weight was easier to attain, why does it "HAVE" to be at the more challenging (money, safety, significant hours) weight?
[/b]

well, for one you have to look at max performance potential, not *something less.* max performance is reached by removing every bit of weight you can and relocating it where ever you want.

it has nothing to do with money, and everything to do with max potential.

 

[gran racing]

max performance is reached by removing every bit of weight you can and relocating it where ever you want. [/b]

Exactly. In many cases people can't get to the point of the relocation (again, for whatever reason) and just struggle with getting it down to spec weight to begin with. Why make things more difficult for people to achieve weight if there's an option to make it easier?

 

[Andy Bettencourt]

Exactly. In many cases people can't get to the point of the relocation (again, for whatever reason) and just struggle with getting it down to spec weight to begin with. Why make things more difficult for people to achieve weight if there's an option to make it easier?

[/b]

While I agree with you in principle Dave, how do you define 'difficult'? In hours? In dollars? How many hours? How much money?

We could all be classed 'one class down' and not even have had to remove our stock interiors. I think we all understand what you are saying but try and define it for us so that you can explain to one guy his car is classed fine where it is and tell another he was right, even though it's possible, it costs too much and/or takes too much time.

 

[jamsilvia]

Reread the words..
Extremes, like above 5.12.... in other words, you can't magically "fix" a lack of torque, without incurring penalties. Yes, you can make the car acclerate faster, but you will run out of top end. So, they go by at the end of the straight when the motor is spinning 8400 and breathing thru a straw.
[/b]

Sorry - didn't mean to pick on any one car here, but for an example.

When I originally asked, I was actually comparing the 2nd gen RX7 and the ITS 240SX. Graphing out the torque from the 5.12 vs the 240 with a 4.3, the tq at the wheels is similar. Both have a 0.76 top gear ratio.
240 @ 7000 RPM in 5th, 4.363 = 149mph
rx7 @ 8200 RPM in 5th, 5.12 = 149mph

(both with 225x15x50 tires, calculated from http://www.catherineandken.co.uk/sti/tyres.html

It's all a compromise. But lack of tq is lack of tq. And tq wins races.
[/b]

I think I could argue that HP wins races...if only start/finish was closer to the exit of a turn instead of in the middle of a straight!! (typically anyway!)

In your 1st gen's defense, I'd say that the torque differences with the ITA RX7 vs the ITA 240SX are far greater than what I had in mind when I wrote originally. Heck, I think the ITA 240's put out more torque than the ITS 240's at some points in the powerband.

joe