Type 9 gearbox ratio

[pilotprice]

Just a quick question

I have a sigma 150 with a 5 speed type 9. When I got the car, it didn't feel that quick compared to a mates 1600 k series. After a bit of digging I noticed the diff crown wheel was 3.64. I swapped the diff for a 3.92 and acceleration improved slightly.

Now the previous owner was a little odd, I'm not sure why he would of fit a 3.62 none lsd diff to a 5 speed. Now I'm thinking that he may of swapped the gearbox ratios? This is a total guess but it seems to be missing a bit of zing on acceleration. Is there anyway to calculate the gear ratios and if found to be none standard, would this even affect things?

Car has been RR at 149hp btw but is neck and neck with the k series 1600 down the straights on track (think the k series is supposed to be 115hp)

[Aeroscreens]

Download gearcalc from here and enter your relevant details and this will give you among other things the MPH per 1000 revs in each gear,

The standard ratios for the type 9 were 1st 3.36, 2nd, 1.81, 3rd 1.225, 4th 1.0, 5th 0.82

You'll then be able to see if your 7 matches the figures in gearcalc.

[pilotprice]

Cheers, will get recording and comparing

Ps would a 4.1 diff improve acceleration?

[tight fart]

Mine after a rebuild are
2.66
1.75
1.26
1.00
0.89

5th could do with being a bit longer.

[HustleRussell]

pilotprice said:

Just a quick question

I have a sigma 150 with a 5 speed type 9. When I got the car, it didn't feel that quick compared to a mates 1600 k series. After a bit of digging I noticed the diff crown wheel was 3.64. I swapped the diff for a 3.92 and acceleration improved slightly.

Now the previous owner was a little odd, I'm not sure why he would of fit a 3.62 none lsd diff to a 5 speed. Now I'm thinking that he may of swapped the gearbox ratios? This is a total guess but it seems to be missing a bit of zing on acceleration. Is there anyway to calculate the gear ratios and if found to be none standard, would this even affect things?

Car has been RR at 149hp btw but is neck and neck with the k series 1600 down the straights on track (think the k series is supposed to be 115hp)

A standard 1600k makes more like 130bhp. Don't think it's likely the previous owner fitted longer gears- easily confirmed though. The 1:3.92 diff is a good move.

I've had standard 1600 k-series cars catching me on the start / finish straight in my slip stream and mine's a '140'

[pilotprice]

Ahh, that's reassuring to hear (in an odd way)
The K just felt like it wanted to get off and go at 3k+
I found the 150 engine needing to rev to get going. The cams obviously just shift the powerband up higher. The RR graph is linear that I have.

Has anyone got a k1600 rr graph to compare?

[HustleRussell]

By the way I'm not aware of any T9 gearset where 4th gear isn't direct 1.00:1 ratio so... drag race from 30mph in 4th?

[pilotprice]

I've posted to see if anyone local has a sigma engine car to me

[pilotprice]

Swapping my 3.6 to a 3.9 definitely aided acceleration.
It was a nightmare to swap though. Lots of tears that day

[HustleRussell]

3.9:1 is definitely the right ratio if you've got an overdrive gearbox. 3.6:1 is probably just the ticket if you've got a 6-speed. I'm surprised Caterham are supplying the longer diff and 5-speed gearbox together in kits.