16 replies to this topic

[whistler]

Looking for a final drive choice for my new build 1098.

It has straight cuts and going to be using 10" wheels. Normally I would use a 3.4 FD to make a comfortable start on my 1275's but this engine is hopefully going to have similar torque from low down and it has been suggested that a 3.1FD would be OK with the S/C high first gear. Anyone tried a 3.1 with my combination?

[mini13]

I'd say the 3.1 will be a bit tall in 1st, 

[r.tec]

Straight cut gear set plus 3.1 fd won't make much fun. At least 3.44 would be better but then 1st gear is nearly as high as 2nd on normal helical gears.

 

You can try it out on Guessworks gear diagram maker. There you can play around with different gear kits and final drives.

Edited by r.tec, 05 March 2020 - 12:59 PM.

[imack]

1098 producing low down torque and a sccr gear set doesn't sound like a good combination.

[Spider]

It seems an odd gearset choice, if the engines going to make reasonable torque down low and being a 1098 engine, it sounds like it would have a power band from roughly 1500 to 6500 + RPM ??

I'd run a stock gearset and a 3.44 final drive in that.  Maybe an 'S' gearset if I wanted something a bit closer.

[whistler]

I'm running a Piper BP255 which has a torque range of 1500 to 6000. The S/C gear set is because I have these in our 2 other cars and I prefer the close ratios purely from a driving point of view. I was just hoping somebody had experience of a longer diff. As that doesn't appear to the case then I'll stick with the 3.4:1.

[nicklouse]

Ok what gear set? And what are the gear ratios? As not all straight cut gear sets are the same.

[robert.hedges]

I've gone all through this myself with my 1098 build. To my mind a 3.44 all day long with a low reving small bore. My 998 had the 2.95 FD and whilst it was ok on motorways there was no go from a standstill whatsoever. I'll happily take the extra 500 rpm, loss of mpg and extra noise from the 3.44 at 70 on the motorway and gain the power low down power. Personal choice.

Edited by robert.hedges, 05 March 2020 - 07:08 PM.

[timmy850]

My 1098 (+080, 266 cam, big valve 202 head) is running standard ratio gears and a 3.44 diff. In hindsight I reckon the 3.1 would have been a better choice as it rips through the gears now, and will pull from low rpm easily

If only you could swap them easily while the engine is in like most cars..

[Cooperman]

I had a Cooper 'S' into which I fitted a 3.44:1 when I fitted a SCCR gear set.

Even the 3.44 was too high really and I had to slip the clutch quite a lot in order to get a good 'off the line' acceleration.

The SCCR gear set is really for full-on competition use where a well prepared engine will rev to around 7000 rpm amd a low FDR can be used for best acceleration.

I have to say tjhat I would never use a SCCR gear set on any sort of road car in which I want to cruise on main roads. 

The 1098 engine will give good torque, but inevitably less than a 1275, so a 3.76:1 might be a sensible compromise with the SCCR gears.

On a 1275 Cooper which I have, it has the original Cooper 'S' gear ratios and I run a 3.44:1 which seems about ideal.

[nicklouse]

just to take this the other way from Uncle, i had a standard box with a 4:3 FD (or 4:1 i forget and have not counted) using first was useless just used second. now a race gearset is going in so i can have a first gear that is usable.

[whistler]

Ok what gear set? And what are the gear ratios? As not all straight cut gear sets are the same.

Clubman set C-STN39 with 2.583 first gear.

[whistler]

I had a Cooper 'S' into which I fitted a 3.44:1 when I fitted a SCCR gear set.

Even the 3.44 was too high really and I had to slip the clutch quite a lot in order to get a good 'off the line' acceleration.

The SCCR gear set is really for full-on competition use where a well prepared engine will rev to around 7000 rpm amd a low FDR can be used for best acceleration.

I have to say tjhat I would never use a SCCR gear set on any sort of road car in which I want to cruise on main roads. 

The 1098 engine will give good torque, but inevitably less than a 1275, so a 3.76:1 might be a sensible compromise with the SCCR gears.

On a 1275 Cooper which I have, it has the original Cooper 'S' gear ratios and I run a 3.44:1 which seems about ideal.

To take your points one at a time.

It's a road car so no need for a good 'off the line acceleration'. We don't do traffic light grand prix anymore.

As I said earlier, we like the close ratios even for a road car. In the past I've driven quite a few HGV's with close ratio gearboxes and prefer them to wide spaced ones.

A SCCR gearset makes no difference when cruising as the gear noise is not heard, only in 1st to 3rd. Modern SCCR gears do not scream or whine like to old ST gearsets of the past. We don't use SC drop gears, never had, never would.

This 1098 (+0.100") plus good head and cam will likely output about 75ftlb., which is quite comparable with a lot of 1275's. Both our 1275's push out a respectable 80ftlbs.

[whistler]

My 1098 (+080, 266 cam, big valve 202 head) is running standard ratio gears and a 3.44 diff. In hindsight I reckon the 3.1 would have been a better choice as it rips through the gears now, and will pull from low rpm easily

If only you could swap them easily while the engine is in like most cars..

Thanks for your answer. You've hit the nail on the head. 

[sonscar]

Different car but same engine,my healey sprite had a woeful 4.2 diff which I changed to a 3.7.Cruising is good but it has a "crash" first gear which makes you use second more than you probably should and it is just too high.Hill starts require more clutch slip than I am comfortable with too.Just my experience with a warm 1098.Steve..