18 replies to this topic

[whistler]

While I have the engine out for the pickup pipe replacement I've been contemplating going back to helical standard gear set with a 3.1 FD instead of the current set of S/C gears and 3.44.
Can't run a 3-1 FD with S/Cuts as 1st is too high.
Anyone with a 1098 using a 3.1 FD? Would be useful have another opinion.

[Cooperman]

It's more a case of the state of tune of your engine and where the torque band is.

If you have a 'hot' cam which really doesn't give strong torque below around 3000 rpm, then a 3.1:1 FDR might be a bit too high. However, a 1098 normally gives good bottom-end torque and will happily pull a 3.1 FDR with a standard ratio gearbox.

The SCCR gear ratios are really for competition use and need a low FDR to keep the engine 'on the cam'. 

[Spider]

Where's the power band on your engine ?

 

<Edit: Cooperman beat me to it ! >

Edited by Spider, 02 June 2025 - 07:33 PM.

[IronmanG]

It's more a case of the state of tune of your engine and where the torque band is.
If you have a 'hot' cam which really doesn't give strong torque below around 3000 rpm, then a 3.1:1 FDR might be a bit too high. However, a 1098 normally gives good bottom-end torque and will happily pull a 3.1 FDR with a standard ratio gearbox.
The SCCR gear ratios are really for competition use and need a low FDR to keep the engine 'on the cam'.

I had the 998 City e back in the day with a 2.9 fd with 12 inch wheels. It did 80 in third and 85 in 4th. It wouldn't pull past about 4000 ish revs in fourth.
When you say the engine needs enough torque to pull the desired fd how much is that. For example my 1310 has the rs+ cam which is a high 270 ish cam.
But I bet it still has more torque than my old 998 running the factory cam from 1200rpm and up so why can't I run a 2.9 on my 1310?
I know it wouldn't be ideal but it would be better than the old engine?

[whistler]

Where's the power band on your engine ?

 

<Edit: Cooperman beat me to it ! >

Piper 255 cam. Hope you can read it OK.

Attached Files

•  RustyRR.jpg   22.62K   12 downloads

Edited by whistler, 03 June 2025 - 09:20 AM.

[whistler]

It's more a case of the state of tune of your engine and where the torque band is.

If you have a 'hot' cam which really doesn't give strong torque below around 3000 rpm, then a 3.1:1 FDR might be a bit too high. However, a 1098 normally gives good bottom-end torque and will happily pull a 3.1 FDR with a standard ratio gearbox.

The SCCR gear ratios are really for competition use and need a low FDR to keep the engine 'on the cam'. 

I've posted the RR report on Spider's post. I would be changing back to helical gearset if I went to 3.1 FD.

[stoneface]

I was running SCCR gears with a 3.2 diff in a car producing 112lbft and it was horrible.

 

I just changed to a standard gearset and kept the 3.2 diff to hopefully make it more driveable. 

 

I've only driven it up and down the drive and it is noticeably better, with less clutch slip needed to pull away. Not taken it on the road yet to give it my full accessment.

[KTS]

a little difficult to read, but peak torque delivery between 2.8K and 5K ?

 

in standard helical form there's a 4 (5?) different gear sets available (plus 4 drop gear combinations) which combined with a the FD ratios provides plenty of options to find a combination which will suit the way you want to drive the car (motorway cruiser, backroad blasts, race etc) with the power delivery from the engine

 

interestingly;  i got similar drag power readings on the rolling road with a full helical setup compared to your S/C setup so potentially gearbox losses aren't that different between helicals and S/C (at first glance - other factors to be considered of course)

Edited by KTS, 03 June 2025 - 10:23 AM.

[Spider]

 

Where's the power band on your engine ?

 

<Edit: Cooperman beat me to it ! >

Piper 255 cam. Hope you can read it OK.

 

 

If I am reading that graph right, for a 255 I would expect the power band to be from 1000 / 1200 RPM up to about 6000-ish, depending on head and carbs, however,looking at your graph and also going off KTS's post, it looks like the band is between 2.8-ish and 5-ish.

Without getting bogged down on that, just working on the numbers you have, I'd suggest a Cooper S Helical Close Ratio gearset and a 3.44 or 3.65  final drive. If you do change your final drive, remember to change the speedo drive gears too !

[Shooter63]

Where's the power band on your engine ?
 
<Edit: Cooperman beat me to it ! >

Piper 255 cam. Hope you can read it OK.

 
If I am reading that graph right, for a 255 I would expect the power band to be from 1000 / 1200 RPM up to about 6000-ish, depending on head and carbs, however,looking at your graph and also going off KTS's post, it looks like the band is between 2.8-ish and 5-ish.

Without getting bogged down on that, just working on the numbers you have, I'd suggest a Cooper S Helical Close Ratio gearset and a 3.44 or 3.65  final drive. If you do change your final drive, remember to change the speedo drive gears too !

I think the problem is that a lot of people believe the 255 cam is called that because that's the cam duration, its not, its more close to 270 degrees hence pushing the torque curve.

Shooter

[Spider]

I think the problem is that a lot of people believe the 255 cam is called that because that's the cam duration, its not, its more close to 270 degrees hence pushing the torque curve.

Shooter

 

Cheers Shooter - I thought the same when I saw the Graph and I looked it up before I posted to be sure, it's a '270 / 252⁰' low over-lap Cam;-

 

 

Having a low over-lap, should bring it in to the power band sooner.

 

Comparing to factory grinds, it's somewhat 'similar-ish' to a 731;-

 

[Lplus]

I have a1098 at +20, BP255, flat top pistons, stock 295 head, twin 1.25s, mg metro distributor with no vac advance, 3.2 diff, 10 in wheels, standard gearset.  As is it's not a struggle to get underway but the torque isn't huge below 3000, rather as whistler's torque curve shows.  It goes well above 3000 though. A 3.1 might be fine with a standard first but I'm not convinced it could cope with a close ratio first.

[Aridgerunner]

I have watched this topic with interest as I have also changed to a 3.2 final drive. The engine is a Metro engine bored +.060" with 10.3 compression offset dish pistons and Minispares Evo 002 camshaft. Also 12" wheels. From what I'm reading I think it will be fine.

But....I have searched for new speedometer drive gears and can only find the drive spindle. Does anyone know where I can a complete set?

[whistler]

 

 

Where's the power band on your engine ?

 

<Edit: Cooperman beat me to it ! >

Piper 255 cam. Hope you can read it OK.

 

 

If I am reading that graph right, for a 255 I would expect the power band to be from 1000 / 1200 RPM up to about 6000-ish, depending on head and carbs, however,looking at your graph and also going off KTS's post, it looks like the band is between 2.8-ish and 5-ish.

Without getting bogged down on that, just working on the numbers you have, I'd suggest a Cooper S Helical Close Ratio gearset and a 3.44 or 3.65  final drive. If you do change your final drive, remember to change the speedo drive gears too !

 

The torque band is 2.8-ish to 5-ish. Power band is the one below. It pulls well from low down, which is what I wanted. From what I can find the Cooper S Helical set (Minispares) has the same first gear ratio as the Clubman set already installed so no good for 3.1 FD. At the moment I'm fighting the 1st motion shaft end nut (11/8"). Already snapped my go to socket. Waiting for a new one today sometime. If I can't remove the nut then I'll be sticking with the Clubman S/Cuts and 3.44 FD.

Edited by whistler, Yesterday, 10:49 AM.

[whistler]

Here's a better image.

Attached Files

•  RustyRRmod.jpg   32.46K   1 downloads