Tony Ryan

Just wondering what Ratios the top runners use for best overall times ? Do you change a diff for these events or just go with std diffs etc.. ?
Regards
Tony

www.touringcarspares.com

Disabled Account

Tony, I would say a 3.9 diff would be ideal - especially with 17" or 18" wheels.

The 3.9 is also a good compromise for road use/track day cars as it sharpens up the acceleration (in all gears) but you would still have a respectable top speed of 144-148 MPH

Tony Ryan

Doug ,
I agree a 3.9 is an advantage on track but wonders whether a very short Diff would encourage greater acceleration upto the max you need on a short run . If you estimate your power to give a particular terminal speed then wouldn't a shorter diff get you there quicker ?
Just trying to understand the Dynamics of this really !

Disabled Account

Well yes, as a 1/4 mile ONLY car I would guess that a 4.2 or even 4.4 diff would actually be better than a 3.9........The only disadvantage being the time you would loose on the extra gear change(s) with such "short" gearing.

markk

iTrader: (2)

ive never actually done a recorded 1/4 mile time but , from my experiance in gearing a car for accelleration only then the higher diff has always been better for me, i run an ultra close ratio gear kit and a high ratio diff, some people will say that a turbo car has a wider power band when on boost so close ratio is not needed , but as always 9 out of the 10 that say that have never used a close ratio box, and changing the diff up in the ratios only goes to bring the gears togther even more, i run a 4.27:1 generally all the time as its the best all rounder for me and a fifth of 1:1

the actual sprint from stood still to flat out at 120mph is a very short time indeed

Tony Ryan

markk ,
that was really what i was getting at a close ratio box and a short diff seems like the way to get to terminal speed quickly , there must be other variables especially when you add loads of horsepower but in theory it seems right , mind you ive only ever done Brighton Speed trials in my old Race sapphire on the hardest slicks and stiffest suspension so i really wouldnt know . I guess the purpose is really to know where im going with ratios , ive a 4.8 which im not using which may suit 1/4mile racers better than a spare for circuit use .
Regards
Tony

www.touringcarspares.com

markk

iTrader: (2)

4.8 is a high diff but coupled with a T5 fifth gear would give a max speed of around 150 mph at 7500ish on 17's if iirc , i used to run a 5.3 but that was in a normally aspirated cossie and revved to 9k so that made it alot differant,

i find that the std road boxes i.e the T5 that 1st gear ia way too low , so youve got your track goers who come to a hairpin shall we say and they have to select 1st gear from second and the differance in soeed really upsets the cars balance and sends the revs way too high for the travelled speed - this is good for us as we can just nip down the inside while there fookin about

Tony Ryan

Thats the difference in set up . I'd never consider selecting 2nd gear for just that reason , but 1st !!!! Druids at Brands and top bend at Lydden are about as close as i get to a Hairpin and they are flat out in 3rd all guns blazing .
Talking of that ive got to Boast about the classiest move ive made in a long time , Yesterday at brands , 2nd race , new tyres and a race long battle with a BTC 306 and a quick driver , took 6 laps to line up but overtook on the OUTSIDE OF PADDOCK HILL BEND in 4th gear at full chat , fook me that focused the attention !!!
Regards
Tony

www.touringcarspares.com

markk

iTrader: (2)

"rubbin's racin' "

Tony Ryan

I put it down to my new 9x 17" race wheels ( available from me at competitive prices ) Not the best pic but you get the idea.

markk

iTrader: (2)

im after some 8 x 17's at ridiculously low prices pref with a very low ET ,

tight northerner !