It would be interesting to hear from you who have experience running 1/4 mile (or similar) on a Sierra RS Cossie, what diff ratio would be the best to use?
I have now the std 3,62:1, but want to replace it with another diff,:3,9:1 or 4,1:1 ratio. I have them both but not sure which one to choose.
Thanks.

 

The 3.9 made a HUGE improvement on my mates track car, I'd say go with that one if you already have it.

 

Thanks Jonny, very interesting to learn about this.

Anyone else have experience with this? Especially on a 1/4 mile track?
Is the 4,1:1 to much? Will I then start in 2nd gear?

 

What size wheels and tyres are you running?

 

When racing I have now started to use Toyo R888 205x50x15 for much better tracktion, but normal I am using 215x40x17.
I did try 235x40x17 but the traction was not good, my 60 feet was slow or 2,3 sec. best.

 

Hi Sigurjon

Without knowing your power or terminal speed this is based on just looking at a gear calculator.

Running on 205.50.15 with the 4.1 diff ratio you will only be able to do 117mph in 4th gear (assuming 7000rpm limit) and the last thing you want to do it change into 5th as more gear changes obviously means slower time.

A 3.9 diff ratio will allow 123mph in 4th gear which i would personally recomend unless you are running over 500bhp

I personally ran my car with 225.55.15 tyres but on standard gear and diff ratio's and was crossing the line in 4th gear at about 6000rpm at 120mph so think that i had it close however a 3.9 ratio would have been better.

Also im not a fan of the Toyo 888 tyres for drag racing as it does not really matter what pressure you run in them they do not get any better traction due to the side walls being too strong.

 

Thank you mate for sharing your experience.
I was also aiming for the 3,9:1, so that will be the choice
I am also running appr. 6000 rev in 4th but I can not get as high as 120 mph I did best only 111 mph, what power ratio are you running? And what time did you get at this speed?
I have also tried bigger tire, but my biggest problem have been the start, far too much wheelspin and the 60 feet time just about 2,3 sec.best.
There are many discussions on whether to warm the Toyo R888 before run or not, have you any experience on that?

 

I have not used Toyo R888 myself but have friends that have used them so can only report what they have found.

I always warm the tyres before the run however my outing was on BFGoodridge Drag Radial tyres.

That occasion was my first go at 1/4mile for 6 years and i was running approximatly 450bhp and the time was 12.4 seconds but broke the gearbox early on in the day and had problems selecting 3rd gear.