final drive ratio

#1

This may sound like a dumb question since it seems pretty clear in the rules…

Is there’s any concievable way that you can legally change the final drive ratio?

Jens

#2

jensscott wrote:

[quote]This may sound like a dumb question since it seems pretty clear in the rules…

Is there’s any concievable way that you can legally change the final drive ratio?

Jens[/quote]Nope

#3

jensscott wrote:

[quote]This may sound like a dumb question since it seems pretty clear in the rules…

Is there’s any concievable way that you can legally change the final drive ratio?

Jens[/quote]

Someone check his/Skip’s car at the next event.

:woohoo:

#4

nasaregistrar wrote:

[quote]jensscott wrote:

[quote]This may sound like a dumb question since it seems pretty clear in the rules…

Is there’s any concievable way that you can legally change the final drive ratio?

Jens[/quote]Nope[/quote]

Actually, I’m not sure that that’s entirely correct. The rules state that either 205/55/14 or 205/50/15 ra-1’s are to be used. The 14" tires are 0.1" less in diameter vs. the 15", which equates to an additional 38 revolutions / mile (955 vs. 917) based on toyo spec sheets. This equates to a 4.1% increase in the gearing with 205/55/14 tires, I believe, which would effectively turn a 3.73 into a 3.88. Someone tell me if I’m wrong (what am I saying - this is the internet, OF COURSE someone will tell me if I’m wrong!), but I believe this is how it works…

#5

be my guest Jon

#6

That’s a very interesting concept which I didn’t consider.

The difference in tire diameter does not actually effect the ratio, but as you say it gives a similar effect as a higher ratio. I believe your math is correct.

#7

jensscott wrote:

easy killer it was a joke hence the stupid face.

#8

Sorry, I misunderstood.

#9

I was wondering if carter, carlton, or chris could weigh in on the question so it would be sort-of official.

#10

You guy will have to plug in the correct ratios and tire sizes but this makes it nice n’ easy for ya.

http://bimmerworld.com/techtips/GearingCalculator.xlsB

Carter can you change the rules so I get a 4.45 diff?? I’ll take your silence as a yes! :woohoo:

#11

jensscott wrote:

[quote]I was wondering if carter, carlton, or chris could weigh in on the question so it would be sort-of official.[/quote] This has come up before but the rule says:

9.3.11. Differential
9.3.11.1. The final drive ratio for each eligible car is specified in Appendix A.
9.3.11.2. Factory limited slip differentials are permitted.
9.3.11.3. Welding to create a "locked" differential is permitted.
9.3.11.4. Finned, larger capacity differential covers may be used.
9.3.11.5. Differential lubricant may be substituted.

and the Appendix shows:

325i E30 1987 1988 168 2850 2750 16.37 SO 3.73
325i E30 1990 1991 168 2811 2750 16.37 SO 3.73
325i E30 1989 1989 168 2895 2750 16.37 SO 3.73
325i Conv E30 1987 1990 168 3015 2750 16.37 SO 3.73
325i Conv E30 1991 1992 168 2988 2750 16.37 SO 3.73
325is E30 1987 1988 168 2815 2750 16.37 SO 3.73
325is E30 1989 1991 168 2865 2750 16.37 SO 3.73

#12

In a word…no.

This is not a "tinkerer" series. The class was designed to make it easy for drivers to build a simple car and go racing, at a reasonable cost.

Carter

#13

I believe that Jens is very gently, very deftly trying to point out a potential loophole.

I’ll be a little more blunt because I’d like to see it closed – it’s specifically in the wording of the engine swap section:

[quote]9.3.2. Engine Swapping
9.3.2.1. Cars that do not have an original type engine, (e.g. the engine was not available in the model, chassis and year of the car), shall be classed based upon the vehicle for which the engine was original.
9.3.2.2. The car shall meet the weight minimum of the chassis, model and year for which the engine was originally available in the chassis of a US model, (e.g. it will assume the characteristics of the donor car).
9.3.2.2.1. Location and maximum ballast weight allowed is specified in 9.3.13.
9.3.2.3. Swapping or mixing of engine components between different engine types is not permitted, (e.g. mating the head from a M40 engine with the block from a M10). [/quote]

I don’t necessarily think that the hole’s there, given a combination of 9.3.2.1 and Appendix A, but with a slanted reading between the lines, the argument could be made.

#14

the differential matches the engine choice - a 1.8i gets a 4.10 diff and the 2.5i gets a 3.73 (the other models are moot now). I must not be seeing the issue.
bruce

#15

It looks like that’s one thing that we’ll make perfectly clear for the 2007 Rules.

Something like "All drivetrain components that came with a specific engine must stay with that engine."

Carter

#16

Carter wrote:

[quote]It looks like that’s one thing that we’ll make perfectly clear for the 2007 Rules.

Something like "All drivetrain components that came with a specific engine must stay with that engine."

Carter[/quote]

That would be good.

#17

sharkd wrote:

[quote]I believe that Jens is very gently, very deftly trying to point out a potential loophole.

I’ll be a little more blunt because I’d like to see it closed – it’s specifically in the wording of the engine swap section:

[quote]9.3.2. Engine Swapping
9.3.2.1. Cars that do not have an original type engine, (e.g. the engine was not available in the model, chassis and year of the car), shall be classed based upon the vehicle for which the engine was original.
9.3.2.2. The car shall meet the weight minimum of the chassis, model and year for which the engine was originally available in the chassis of a US model, (e.g. it will assume the characteristics of the donor car).
9.3.2.2.1. Location and maximum ballast weight allowed is specified in 9.3.13.
9.3.2.3. Swapping or mixing of engine components between different engine types is not permitted, (e.g. mating the head from a M40 engine with the block from a M10). [/quote]

I don’t necessarily think that the hole’s there, given a combination of 9.3.2.1 and Appendix A, but with a slanted reading between the lines, the argument could be made.[/quote]

9.3.2.1 talks about changing the class… so if something was SU… it would become SO.

9.3.2.2 talks about changing the weight minimum. The "e.g" statemenet means "for example". Becuase the "e.g" is referring to te previous statement which only refers to weight, not diferential ration, only the weight minimum transferrs.

9.3.11.1 links the diferential ratio to the model. If you put a 325 engine in a 318… it’s still a 318 and thus it would maintain it’s 4.10
Additionally, becuase it doesn’t specify changing ratios when swapping engins, rule 1.3 prohibits changing the ratio.

Things are also made complicated by rule 9.3.1.7.1.1 and 9.4.12.1.1 which spacifically talk about what to do when you swap an engine. Where as the differential section 9.3.11 doesn’t have an engine swapping clause.

So…in short, I think you can put a 325 engine in a 318 and keep the 4.0 rear which would be against the spirit of the rules, but not the letter. So lets get that hole plugged because I don’t want to get whooped by some frankin car.

I would like some more thought in making a 318 competitive with a 325 by noodling with the minimum weight rules.

#18

sharkd wrote:

[quote]I believe that Jens is very gently, very deftly trying to point out a potential loophole.

I’ll be a little more blunt because I’d like to see it closed – it’s specifically in the wording of the engine swap section:

[quote]9.3.2. Engine Swapping
9.3.2.1. Cars that do not have an original type engine, (e.g. the engine was not available in the model, chassis and year of the car), shall be classed based upon the vehicle for which the engine was original.
9.3.2.2. The car shall meet the weight minimum of the chassis, model and year for which the engine was originally available in the chassis of a US model, (e.g. it will assume the characteristics of the donor car).
9.3.2.2.1. Location and maximum ballast weight allowed is specified in 9.3.13.
9.3.2.3. Swapping or mixing of engine components between different engine types is not permitted, (e.g. mating the head from a M40 engine with the block from a M10). [/quote]

I don’t necessarily think that the hole’s there, given a combination of 9.3.2.1 and Appendix A, but with a slanted reading between the lines, the argument could be made.[/quote]

9.3.2.1 talks about changing the class… so if something was SU… it would become SO.

9.3.2.2 talks about changing the weight minimum. The "e.g" statemenet means "for example". Becuase the "e.g" is referring to te previous statement which only refers to weight, not diferential ration, only the weight minimum transferrs.

9.3.11.1 links the diferential ratio to the model. If you put a 325 engine in a 318… it’s still a 318 and thus it would maintain it’s 4.10
Additionally, becuase it doesn’t specify changing ratios when swapping engins, rule 1.3 prohibits changing the ratio.

Things are also made complicated by rule 9.3.1.7.1.1 and 9.4.12.1.1 which spacifically talk about what to do when you swap an engine. Where as the differential section 9.3.11 doesn’t have an engine swapping clause.

So…in short, I think you can put a 325 engine in a 318 and keep the 4.0 rear which would be against the spirit of the rules, but not the letter. So lets get that hole plugged because I don’t want to get whooped by some frankin car.

I would like some more thought in making a 318 competitive with a 325 by noodling with the minimum weight rules.