Want to win nationals in autox, need help with gearing
 

Guys I plan on racing in either AP or BP next year and need some advice on weather to run 4.3 or 4.77. If you autox you know what I am trying to do. Will 4.3 put me up in rpm's to allow me to stay in 2nd then 3rd, or do I need the 4.77's.

If you have run either please let me know where you are in the rpm scale.

My goal is to win the nationals in one of the above class. In AP it would involve beating a 69 corvette. In BP it would involve beating a 2nd gen.

Thanks for your help

since the rules states that the solo2 circuits should be designed under 70mph... you should keep that in mind...
extra shifting will cost time. but falling out of power range will cost more time.

Sounds like a pretty tall order, but good luck. Actually, in AP it would involve beating a Sunbeam Tiger. (2) 2nd gens in the top 5 at Nat'ls in BP. Woohoo! The best advice I was ever given (as far as autocrossing): Keep practicing and be smooth!

Good luck,

Mike Frazer
'90 GXL, "slightly" modified

Your sig indicates you have a 3rd gen car. I don't think you can run "B".

Rob

3rd Gen Class
 

Tecnically the 3rd gen is in SS, then moves to ASP, then to BP. However I could run AP according to Howard Duncan.

Think about SM2 also (is it nationally recognized yet?). Just bring your checkbook!

oh yeah, 4.77s sound like a good idea. Something in beween that and 4.3 would work well also.

Just some calculated numbers to help you decide.

2nd Gear
25" Tire Dia

4.33 Rear Gear
60 mph = 7042 RPM
20 mph = 2347 RPM

4.77 Rear Gear
60mph = 7757 RPM
20mph = 2586 RPM

Rob

26X12 size
 

Rob, thanks for the numbers.

Can you please do a comparison for me. Currently I run stock gears and 275/40/17. What would it be with 26/12. That is the slick size I will be able to run in Prepared class.

Thanks for the numbers.

Allan

will run 16x12 not 26x12
 

Will be running the goodyear slicks. Not sure of the size I think the the 26, that may be where I got the number from.

Sorry for the mix up.

Get a custom 4.5 made up. :)

Custom 4.5
 

Do you run that now? If so tell me about your RPM's.
Where did you have it made, how much did you pay for it?

Thanks

Allan

Allan,

Can't get a 4.5, but you may be able to get a 4.44 made up.. Check with speedsourceinc.com.

PaulC

Gears
 

Went ahead and ordered 4.77 from RX7.com. Only question now is how big the injectors should be.

Re: 26X12 size
 

Allan,

Just do the following:
Stock tire diameter in. (24.9)/new tire diameter in.(26) * ratio (4.1)

This is equivalent to a 3.92 ratio.

A 275-40-17 is 25.7" diameter which would equal 3.97.

The way to calculate tire diameter (unless it's a slick which usually has diameter listed) is (wheel size, inches *25.4)+(2*aspect height))/25.4

where

aspect height (e.g., 275) = tire width mm * aspect mm * 0.01. So a 275-40 would be 275*40*0.01= 110

If you go with 4.77 and a 26 inch slick= 24.9/26*4.77=
4.57 ratio.

Gene