Rotary Diff ratio?
Does anyone have any idea what would be a good diff ratio for an RX-2 at Bathurst running a carbied 12A BP with a 4 speed and 205/60/13s?
David Paterson,
Qld Improved Production Series Commentator
rdmdog Registered User
Posts: 1075
(3/13/06 5:04 pm) Reply
Re: Rotary Diff ratio?
Dave, Ill e-mail you an exel spread sheet I use, you should be able to use it backwards!!
Somebody posted the web address for one a while ago, but I cant find it.
diff
Not sure if it has any relation, but i used to use a 4.4 in my Appendix J Cortina up there, and that was pulling 8,000 down conrod, using the same size tyres.
I'm thinking either 4.4 or 4.8, depending on how hard it revs??
gmontrack Registered User
Posts: 109
(3/14/06 8:06 pm) Reply
Re: diff
The thing you need to remember is first you have to get up the hill before you come down conrod straight. If you go to low a ratio it will be to slow up which is not good. I would think that a 4.4 would be the pick on 13"s tyres. You could try 4.1 but that maybe just a bit slow upthrough the cutting etc.
best of luck
Capella69 Registered User
Posts: 1
(3/19/06 9:10 pm) Reply
Re: diff
Hi Dave.I ran a 12a bridgeport with weber in IP races at Bathurst in 1999,it had 205/60/14s ,121 5speed and 4.4 diff. I was changing to 5th at 8500 about 100m after hump on Conrod and getting 7700 in 5th(std 121 overdrive) just before the chase.Hope this helps.
MACMECH Registered User
Posts: 233
(3/20/06 1:18 pm) Reply
DIFF RATIO??
Hi Dave,
suggestion, find out the MAX rev's you want to use down the straight. work on the top speed being 235km/h at those rev's and work your ratio back from there.
i took an educated guess when i was there with the 13b (carby) and while not game enough to look at the tacho through the chase 240-245km/h rings a bell.
my little advise, is to not over rev down the straight and use the gearbox for going up the mountain. 4.11 or 3.9 ratio my guess.
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