Hi, been a while since visiting (too long actually). Finally fitted the primary ratio I made for the 99 rally car and WOW, what a difference! Thought i had a 31:30 fitted but found it was a 31:26. I made ( with Dennis's help) a 30:31 and changed the ratio from .84 to 1.15. The car is a different animal now with no more sluggish acceleration and supper long 1st gear. Don't get me wrong, it was fast once you got into the top end of 2nd but this didn't suit most events. Very pleased with the outcome. The only modification needed was adding one link to the chains.

That's good to hear! Any more details on what you did?

The process is taking a top 31 tooth cog and machining the centre out and a lower 27 tooth and machining the teeth off. press the 27 inner into the 31 outer, tig them together and you now have a 31 tooth lower gear. Fit a standard 30 top gear and then add one link to each chain. You can cut down engine timing chains to do this as they are the same chain just longer. The machining is a slow process as the gears are certainly hard but with the right lathe tool and a bit of patientce it's achievable. Finding the gears to start is the tricky bit.

Oh, I have gears.
Thanks for the awesome recipe! I'll let you know how it turns out.

I'm interested to see how it goes with a standard gearbox, should have great acceleration. I think it will be way too short if you are running a turbo.

rsp57 wrote:Hi, been a while since visiting (too long actually). Finally fitted the primary ratio I made for the 99 rally car and WOW, what a difference! Thought i had a 31:30 fitted but found it was a 31:26. I made ( with Dennis's help) a 30:31.

Glad to help, great you got it fitted. A bit more of a process that just bolting it on. Got a picture with the cover off? It would be interesting to compare with the road cars going taller gears.

What are you running for the main gear set? 4spd, 5spd, Sport & Rally or similar?

Sorry Dennis no photo, I don’t realise until the job is finished that there are others that would be interested in seeing what’s been done. I’m going to make a 30/30 for a friend in Sweden so will take pics of that one. Geoff, the gear kit is an FLD straight cut 4sp dog change and 6:31 ring and pinion.

That's a great setup!
So did you build a 31:27 (1.15) or a 31:30 (1.03)?

In RallyHo's 900 we run a S&R gearset (pretty similar ratios to FLD), S&R 6:31, and I think a 30:30. We talked a little about what a shorter primary would be like but I think we decided the car was geared OK (on one event last year we pretty much ran out of gear in 4th on one stage!)

I used to run a 5spd with 30:31 (0.97) primary and the ratios in 2nd and 3rd were pretty close to your old setup in 1st and 2nd. I tried launching in 2nd a few times and it wasn't much fun!

Hi Geoff, I made a 31:30 (1.03). I think with the 4sp it will run out of legs on the longer events. It used to max at 180kph. Haven't driven it in competition yet as there have been no events due to rain and flooding since last November here. Yeah, launching even in first was a big time loss with lots of clutch action and with a paddle clutch not easy.

With your new primary ratio you'll probably max out around 145kph. I don't know about Australian roads but I know a lot of 'well prepped' cars here top out around the same speed. But we do get some long straights, we had a stage last year where we had the 900 up to 150kph.

Interesting anecdote: we used to have a tarmac event that had wide-open roads with long straights. One year there were two Evos that were broken down right next to each other on a stage. Both had blown engines due to bouncing off the rev limiter in top gear for a few miles.