25 replies to this topic

[minisilverbullet]

I am trying to work out some gear box options. 

 

I am torn between a helical (Single groove) Gearset with Straight Cut Drop Gears or a SCCR box. 

 

​I am not sure which benefits my application. The box will be used with a k1100 1380 with a 3.44 final drive. 

 

​I am not sure i need the close ratio due to the head but ardent the straight cut gears stronger?

 

​The car will be used on the road. 

 

​sorry many questions - originally I intended to ask if people can live with then, both in terms of  the long 1st gear and the noise. 

[Cooperman]

Straight cut drop gears are so noisy they can easily spoil the pleasure of driving.

SC CR gears are no stronger than helical - well, less strong in fact, but cheaper & easier to machine for low-volume production runs.

If you have a cam which has a narrow torque & power band you have to have a SC CR gear set or the engine will be 'off the cam' whenever you change gear. The big downsize is that with the high 1st gear you need a low FDR in order to get good acceleration when pulling away from rest and to prevent high clutch wear.

SC drop gears are for racing to enable the overall gear ratio to be altered slightly to enable best lap times on different tracks without having to take the engine out for different circuits. I regret fitting them to my full rally Cooper 'S' and will be reverting to helical drops the next time the engine comes out as I am fed up with having to wear ear plugs when driving on the roads. It's OK when wearing a crash helmet.

It's all a question of matching the engine characteristics to the required gear ratios.

[minisilverbullet]

I see!

 

So it is actually the straight cut drop gears that are noisy? so even my first choice of  helical (Single groove) Gearset with Straight Cut Drop Gears will be noisy?

 

​I think the torque curve of the engine will be similar to this: 

 

[nicklouse]

All straight cut are noisy. But the drops create more noise than the box.

Have a think on how many cog to cog connections there are for the drops and the box.

Drops 2 box 1.

[Cooperman]

That is a very flat torque & power curve. A SC CR gearbox would be entirely unsuitable and drop gears unnecessary as you won't be changing from 1:1 to 1.1:1 or 0.9:1 drop ratios for different circuits.

Use a standard helical gearbox with a X-pin diff and around 3.1:1 FDR, or 3.44:1 if you want better acceleration and are prepared for higher revs at a given cruising speed.

[nicklouse]

Craig you are Malmo way? Good driving roads? 3.44 diff. Just don't get on the motorway up to GB as it would be a killer.

But a thought. Have a chat with GuessWorks about 5 speed boxes. Most have the same 1:1 top gear but have a better spread that would allow a taller diff for better cruising but keep the gears for spirited driving.

[minisilverbullet]

Yip NE of Malmö. 

 

I have a 10 minute blast up the motorway to work each day, but nothing much more than that. 

 

Currently I have a 3.21 FD, probably that would be perfect to keep that. But the FD needs to be changed in order to have the car registered as modified, no matter how weird that sounds. 

 

Specialist components (where the head kit comes from) advocate a 3.44 FD. Guess works has some really useful tools on his page, I will play around with them. 

[nicklouse]

Nothing surprises me about Sweden.

[MRA]

Having driven loads of minis over the years on the roads with SCCR and drops, I will list the facts as they are..

 

1) SCCR gear kits will produce little noise in 4th as that is direct and as such all the torque is going through the shaft from input gear to final drive with little load on the actual gears.

 

2) Drops are certainly noisier than helical drops, however like all things it is a personal preference, I haven't had a helical box in any of Minis since 1984, well I have but only to drive it home to change it. 

 

3) Straight cut gears are only stronger if the material is better, ie comparable helical and SC gears same material the helical will be a lot stronger.  however because Rover liked to do everything on the cheap, you got cheap gear materials too.

 

4)  The old 3 synchro are a completely different ball game the noise from those was horrendous, unless the tops had been cut back and then they would run a fair bit quieter.

 

5) There are in fact more gears in contact within the gearbox than with your drops...  1st motion gear to laygear cluster = 2, laygear cluster back to mainshaft ie 1st, 2nd & 3rd gears = 2 total = 4.

 

6) In nearly every gear set I have seen or made the noise is to do with 2 things, one oil shear as the teeth mesh the oil gets pumped out at supersonic speeds, and also the quality of the tooth flank surface finish, some are very poor others are pretty good.

 

With a decent 1330 SPi running a 3.1:1 and 12" wheels and tyres with a SCCR kit you can still get off the line easily, with my 1380 turbo I aim for 60mph in 1st at 7500 rpm.  works well for me and in the wet it is still drivable even with 16psi boost.

 

SCCR & drops are really a personal preference, my advice is to find somebody that already has one and take it for a spin to see what you think...  my 16 year old daughter wants SCCR in her Mini...

[MRA]

To add to that... a SC final drive sounds awesome from the road side but they are a lot loader than your SC gear kit or drops.

[nicklouse]

Point 5 I agree but they are not all transferring the driving force. And the noise from ears just meshing rather than transferring list is different.

And I do find the helical gears in my box quite strong. Not the best ratios for hat I needed but not too bad. Just miss first for some starts.

Does anyone still run SC FDs?

Again the greater noise comes from the drops than the box. Everyone thought I was running full SC when I never had.

I know most things come down to personal impressions and like the above mine comes from driving both. Not on the road but hillclimbing. And the odd big black track.

And in this case I would buy some ear plugs or defenders with built in radio.

[MRA]

Point 5 seems to be causing a question or two.... can you confirm what you mean by the following

 

QUOTE

Have a think on how many cog to cog connections there are for the drops and the box.

Drops 2 box 1.

UNQUOTE

 

The only 5 speed boxes that I know of that have 1:1 in top is KAD's 5 speed dog box and my own sequential dog box.

 

Most FD's are either standard or semi helical, as semi helical runs a little quieter (the SC FD's drown out everything else in the whole world)  yeah they are that noisy

Edited by MRA, 26 February 2016 - 12:45 AM.

[nicklouse]

Which of these Minis/mini derivatives have SC boxes?



Or to put it a different way. Can you hear the more noise from the cars with the SC boxes.

Mmmm sequential dog box? When was this? If the late 90s I blame you for me going to Uni.


Thanks.

[MRA]

Well the rossi / GTM / kit car and the metro had SC gears, but I couldn't hear well enough to tell if they where just the drops or drops and gear kit, however up to the MK2 escort none had SC FD's....  and on to the second half

[MRA]

oh what was that escort doing ???

Edited by MRA, 26 February 2016 - 02:32 AM.