I like the standard 3rd & 4th. I want to make first and second taller for more flexibility in motorkahanas, hillclimbs etc. But I still need to get the car off the line for drag races.

The budget only extends to an off the shelf gear set not a custom jobby.

I'm considering the 2.82/1.66 set which is vastly different to the 3.78/2.06 in the standard box.

A few things which will help pull these gears are the 4.375 ring and pinion, small tyres 595mm and the fact the car is reasonably light 750 kgs.

However making it harder is the engine isn't a torquey stroker it's a revvy 100 RW HP 1916 with engle 130.

Thoughs & suggestions appreciated thanks.

CYA CT

I would try that particular combo myself, but your clutch will be the key.

Too much clutch and you will struggle to get off the line.

I know that Adam in SA uses a 3.1 with 4.125 diff, but he is using a 2.5lt type 4.

If you are worried, then Albins does make a 3.0/2.0 combo as well as a 3.333/2.08 combo.
Both will be better than stock, with the taller first ratio.

I keep coming back to your combo being more of a 'screamer' than a 'grunter',
but as I said, if it were me, that is the ratio I would try.

Even if I had to alter the engine a little to make it work.
IE advance tha cam, heavier FW, smaller durationcam.

I think that Alex Holzl has currently got a 2.76(2.67?) first gear with 3.875 diff, and ran some low 13 just recently withhis 2332cc(yeah, bigger engine).

in my old hillclimb car i had the 3.0, 2.0 combo with a 4.125 and a 205 60 x15 tyre the engine was only a 1916 that was a preety revy thing, i just made sure i spun the tyres a tad to get off the line fast, it worked great because i had a usable first gear on tight corners instead of bogging in second
adam

Thanks for the replies and the U2U. By the sounds of things that 2.82 will be too tall to get the thing off the line.

Here's how the gear ratios are looking:

1st 3.0 = 61kms @ 7000 rpm
2nd 2.0 = 93kms @ 7000 or 106kms @ 8000 rpm
3rd 1.58 = 118kms @ 7000
4th 1.04 = 178kms @ 7000

The way it's playing out in my head is that 1st & 2nd are the hillclimb/motokahana gears and 3rd & 4th are the supersprint gears. All 4 should probably work together prety well for drag racing.

CYA CT

It sounds like either way is a compromise for either circuits or drags. Is it legal/allowed to just use different size wheels for drags and get the best box you can for circuit racing (or the other way around, depending on your priority)? Just thinking out loud...

What R&P CT?
2nd to third is very close
That third to 4th step is quite large....1.48 or 1.44 may be better.

The gearbox is a late 1300 swing axel converted to IRS mainly for those particular 3rd & 4th gears. It's a 4375 R & P.

Stock ratios for this box are 3.78 / 2.06 / 1.58 / 1.04.

Tyre wise I don't have many choices on the race track. I need something narrow so it will heat up quickly. It needs to get to 60 degrees and the hightest I've measured is in the 50's. Mind you the set up is getting better and I can drive the car harder now which heats up the tyres more giving more grip. The tyre size I use is 195/55R15 (595mm OD) and the tyre is a Yokohama A032R.

On the street I use 16 inch rims with a 195/50R16 610mm OD. I could go to a 205/55R15 for drag racing which, from memory, is around 630mm ID.

1.58 and 1.04 are aftermarket gear ratios.

Stock gears for that tranny is fine tooth 1.26 and .93.

I did some sums and a 1.44 or 1.40 3rd would best suit the other ratios that you have chosen(1.40 is best)

Ultimately you want reduced percentage of rev-drop in the higher gear shifts.

Hi Dave,

You must be right about the 0.93 4th.

I cranked up the gear ratio calculator and it said that with that gear and my R & P and tyre size 100 kmph is 3600 rpm.

I remember the engine was pulling 3600rpm up the New England highway on the long journey to the VW Warwick Weekend.

It was a 100 km speed limit on a double or nothing points weekend so I'm sure that's what we were sticking to.

Now the gearbox would be
3.0 / 2.0 / 1.26 /0.93

CYA CT

[ Edited on 2-2-2007 by fullnoise ]

[ Edited on 2-2-2007 by fullnoise ]