28 replies to this topic

[minilee94]

What will standard 1275 spi helical gears withstand power wise

[mini13]

about 140 turbo horses,

[minilee94]

Okay sweet as thank you just has a quote for

X pin diff
Rebuild kit for gear box and sccr gears

£701

Ahhhh

[MIGLIACARS]

not totally on the topic but

 

which are stronger

 

pre A plus 24 tooth gears

 

or A plus 29 tooth gears

[minilee94]

Is that aimed at me if soo I have no clue lol

Are sccr gears really worth it

On a well speced 1380 stage 4

Edited by minilee94, 16 August 2013 - 08:22 PM.

[mini13]

I think the Pre A+ are stronger, but I dont really have any evidence

[MIGLIACARS]

ok here we are.

 

ive used all kinds of s/c drop gears. 

mini spares

jkd

and med the latest ones.

ive always used these as thats what people in motorsport do.

i know run a 1293 supercharged engine.

 

but now due to all these fancy expensive dogboxes and drop gears breaking so easily im now going to try 24 tooth drop gears helical, and im now trying a c/r syncro box. helical. 

 

im hoping ill get more than 3 races from them as thats all i got from the s/c drops and dogboxes i used in this engine.

 

ill keep you informed as to how/if they last.

 

ps  When i first started in motorsport I used green and white mini spares as my engine and car builder.

Ian there is a very knowledgeable man, and use to say that standard stuff was good and difficult to break, and was never one for all this fancy stuff. I never really understood this but 10 years on I m thinking that maybe he is right.

 

 

Ive been racing now for ten years and every year all this new better stuff keeps on emerging or so they say.

 

Race engine are no faster now or reliable as they were 10 years ago.

 

 

there is no faster mini than green and whites 8 port rally crosser.   and unless they have drasticly changed it it doesnt run all the latest mini products. 

[oltonlad]

the pre A+ gear sets have better ratio's than the A+ gear sets, as far as straight cut gears go they aren't any stronger than a helical set but they are close ratio and because they are straight cut they don't sap as much power from the engine so that you get more of the engines power transferred to the wheels, helical gears can take up to 20bhp from the engines output.........sometimes more, if you are worried about the noise of straight cut gears then just fit a sccr gear set and leave the drop gears helical, I have a sccr gearbox with helical drops and it does whine in 1st, 2nd and 3rd gear but is totally silent in top gear.

I have attached a video of mine so that you can hear what the sccr gearbox sounds like with helical drop gears.

 

 

[Cooperman]

In theory helical gears are stronger than straight-cut as the shear area of the tooth is much greater. However, with a helical gear there is an end load.
The reason SC gears have become popular is because they are cheaper to machine and thus can be made with different ratios as options. SC gears are now normally in one or two closer ratio sets and this is to close up the gear ratios to enable a 'cammy' engine to stay 'on cam' and in the optimum power band at each gear shift. The it is normal to use a lower FDR as well to keep 1st gear at a sensible ratio - try a hot cam with a CR box and a high FDR and you'll be slipping the clutch for a long way in 1st (been there, done that!).
The idea is the same with SC drops. They were developed for racing where a slightly higher or lower drive ratio might be needed for different circuits and it is easier to change the drop gears between race meetings than to remove the engine and change the diff ratio.
For road use with a road-useable cam, a normal helical box is usually fine, although the original Cooper 'S'/1275GT helical box had closer ratios, but not as close as a SC CR box.
SC gears do reduce the end thrust loading on the gearbox and drop gear bearings, but not alarmingly so unless the car is used in competition.

[oltonlad]

I run a sccr box in my road mini (only because my old gearbox was knackered and the straight cut box was dirt cheap)...........and I use a 3.6 diff In it, I find it totally usable and I don't have to slip the clutch at all to pull off in first, I was going to use my 3.1 diff in it but i'm glad that I never now.

[MIGLIACARS]

In theory helical gears are stronger than straight-cut as the shear area of the tooth is much greater. However, with a helical gear there is an end load.
The reason SC gears have become popular is because they are cheaper to machine and thus can be made with different ratios as options. SC gears are now normally in one or two closer ratio sets and this is to close up the gear ratios to enable a 'cammy' engine to stay 'on cam' and in the optimum power band at each gear shift. The it is normal to use a lower FDR as well to keep 1st gear at a sensible ratio - try a hot cam with a CR box and a high FDR and you'll be slipping the clutch for a long way in 1st (been there, done that!).
The idea is the same with SC drops. They were developed for racing where a slightly higher or lower drive ratio might be needed for different circuits and it is easier to change the drop gears between race meetings than to remove the engine and change the diff ratio.
For road use with a road-useable cam, a normal helical box is usually fine, although the original Cooper 'S'/1275GT helical box had closer ratios, but not as close as a SC CR box.
SC gears do reduce the end thrust loading on the gearbox and drop gear bearings, but not alarmingly so unless the car is used in competition.

 

 

 

 

cooperman.

 

In my race car i used to run a fd 3.4 and 1-1 drops.   dogbox and s/c drops

 

ive 170 hp and lots of torque as its supercharged

see this link to see it.

 

 

as you will see it doesnt really drop off the cam anywhere but there is more power the higher you rev it.

 

As the dogbox and drops destroyed them selves im going to try.

a cooper s c/r 1040 gearset with a 3.9 fd.

 

 

how will it compare to how it was, will i ever use first on a British circuit.

will it be undriveable 

will the drops in the revs when changing gear be to much????

[Cooperman]

A 3.6:1 with CR gears should be fine. I have a 3.9:1 with a 286 cam and it's OK, although initial acceleration would be better with a 4.1:1. That's a rally car where off-the-line is important. I once tried a 544 cam with a SCCR box and a 3.44:1 and it was not good at all and 1st gear seemed to go for ever to the detriment of both clutch and test times.

[minilee94]

Thank you everyone for the help I'm not worried about the noise from them.

I just don't know if to spent that sorta cash on a gearbox or not that's all if I'm guna have sccr gears I don't want sc drops will be way to noisy

[minilee94]

Also I was going to keep my standard 3.21.1 final drive will this be okay car won't be going on long drive that often

[Cooperman]

Hi Miglia,
With forced induction the issues are a bit different, but so long as you have the revs available a 3.9:1 should be OK. You'll be getting around 14.5 to 15 mph/1000 rpm in top, so 7000 rpm is around 100 mph. You might need a bit more top end speed.
Let us all know how you get on. That sounds an awesome track car.