Best Final Drive ration for the Speed Championship

[Mike Desmond]

I have a 1600cc K series engined Superlught prodicing about 140 bhp with a 6 speed gearbox and 3.62 final drive with LSD. I have competed in a number of events over the last few years (not very quickly!) and have carried out a number of mods to help me go faster. My next project is whether to change the final drive ratio for to a 3.92. I have spoken to various people about this and there seems to be a view that it depends on the circuit etc etc. Having listened to what everyone has said, I thought I would try to find out whether there was a concerted view of what was best. I await developments with interest.

 

Regards

Mike

[robmar]

I think in general it is better to go the 3.92 option, there are not that many places you will run out of revs (maybe goodwood and aintree) in that spec of car in 6th gear, plus you get the advantage of lower gearing for all the other venues

 

However IMO unless you are chasing those last few tenths then maybe not worth it especially if you use your car a lot ont he road as you will be running higher revs to reach the same speed IYSWIM

 

Rob

[Mike Desmond]

Rob

 

Thanks for your response. I don't use the car on the road; I use it mainly for competition and the odd track day. I am warming towards a 3.92 at the moment. I may be persuaded by what other views I receive.

 

Regards

Mike

[Richard Price]

Mike,

I originally had a 3.6 diff with my lightly modified (class 2/3 legal ) 1600 / 6 speed.

I swapped from the 3.6 to a 3.9 in the quest for slightly better times.

Whilst, on the whole, it looks to work OK, its not all positive.

At Curborough, on a double lapper, with the 3.6 diff, I'd have eight gear changes. But with the 3.9 diff, I now need to make 15 gear changes!

Whilst I'm quicker over the finish line with the 3.9 diff, my times are little different.

Curborough is tricky enough with less gearchanges!!

 

I don't run out of revs at Aintree (113mph last year), and on my first visit to Goodwood this year, I guess I was pulling just over 7k rpm in the quickst places.

 

I've been running 195/45 tyres this year gives a theoretical 126mph @ 7600 limiter.

With the 215/50-13's that I'll be running next year, I should get a slightly lower 124mph @ 7600 limiter.

 

 

[Richard Price]

Mike,

Just another thought!

I've been running a video camera in the car for the last two seasons.

By reviewing my video after each run, I think I've found more time than most of the physical changes to the car.

Quite big changes to the car often only make a few tenths of a second to sprint/hillclimb times.

Knowing how to drive the courses, and driving with confidence will find whole seconds!

 

There is no substitute for practice!

 

 

[Adrian Williams]

Mike

 

3.92 diff is better just about everywhere IMHO, Goodwood is the fastest place we go and you wont run out of revs there with 140 bhp. As Richard has said there are a set of circumstances such as Curborouigh where the extra gear changes loose the time you've gained but generally the shorter diff will be better particularly on the hills.

 

Adrian