9 replies to this topic

[Lenhamracer]

Dear members

 

I am rebuilding my hillclimb clubman into a racer. As the final drive was very short for hillclimbing I want to change for a longer one. What would you recommend. The engine is a cooper S on split webers and so on, it produces more than 120hp, gearbox 4 speed straight cut, 10" wheels. Would you go for 3.76, 3.9 or 4.0?

Thank you very much

 

Thomas

[rally1380]

Hi Thomas, and welcome.

 

I'm not a racer, but the perfect final drive ratio may well alter from circuit to circuit.....some might be tight and twisty with short straights, some may have long straights with fast corners.  I know this isn't answering the question, but certainly food for thought.

[nicklouse]

What was your ratio that you were not happy with?

What ratio drop gears.

What are you looking to change?

[fwdracer]

Mini Miglia run similar horsepower-+10bhp  (on 10" wheels) and diff is (regulation) 3.9 on 1:1 drops - 8K rev ceiling.

 

What are peak power revs on your unit?

[Guess-Works.com]

The 3.9 and 4.1's are a popular choice for those running track day cars and sprints..

 

But as above, it really depends upon the track and any regulations which are to be adhered to.

[nicklouse]

And 4.1 and 4.3 were popular UK hill ratios, up north.

[Cooperman]

Depending on the circuit a 3.9:1 or 4.1:1 were the popular ratios with proper 'S' engines with EN40B cranks capable of pulling strongly tight up to 8000+ rpm in top.

Then SC drop gears were used to give the small variations in maximum length of straights to enable absolute max. revs to be pulled jus before braking at the end of the longest straight. A SC gear set can be changed much easier than a crown-wheel & pinion.

A 4.1:1 FDR will give c.13 mph per 1000 rpm in top, so 8000 rpm is 104 mph, whilst those revs with a 3.9:1 will be about 115 mph.

I use a 3.9:1 in my rally 'S' and I use up to just over 7000 rpm, which is sufficient for rallying.

[Ivor Badger]

A 4.1 will be high enough for anywhere, especially with a clubman front. Could go for 1.04 drop gears, then you can drop it if necessary with a 1.08 primary gear.

[wzd345]

Below is the setup I used a few years ago and it was most effective for circuits, hillclimbs and sprints, you might find the info helpful.  The low FD was selected because my most frequently used circuit had a relatively short main straight.

 

Quaife dog gear set, LSD, race straightcut drop gears - 1.0416, centre oil pickup, race output shafts & bearings, semi helical final drive. Ratios: 2.309, 1.49, 1.197, 1.00, final drive 4.07. Primary gear 24 tooth, effective final drive 4.239. KAD Quickshift.

 

Engine: Full race 1425cc

Carburation: Weber 45DCOE tipo 152 on Maniflow 7in steel inlet, MED integrated filter/induction box with revised carb trumpets.

Ignition: Aldon Automotive race distributor & ignitor pack, Luminition blue silicone 8mm race leads, Aldon epoxy solid state coil.

Exhaust: Maniflow big bore race LCB with matching Maniflow exhaust system, single box silencer, centre exit.

Power plot at ambient 14c, barometric 1000mb.

Max torque 107.10 ft lbs @ 5312 rpm
Max power 119.7 RPM @ 6991 rpm
Power loss, trans/tyres 19.4 bhp
Power at wheels 100.3 bhp
Max road speed in test 98.00 mph
Max engine speed in test 7655 rpm

 

 

Just remember: torque wins races, BHP sells cars - Enzo Ferrari

[fastcarl]

I once used  4.9   FD on my hill climb mini  101 mph   at 9000rpm.

 

carl