58 replies to this topic

[minilee94]

Not all straight cut gears are close ratio are they ?

Edited by minilee94, 19 September 2013 - 06:42 PM.

[Cooperman]

For the Mini I've not seen any SC gears which were not part of a close ratio set. The reason the close ratio gears are straight cut is because they are cheaper & easier to machine than the stronger helical ones and the sales volume for close ratio gears is small. If they made them I would buy the SC ratios in helical form, but no-one does, so far as I know.

It would be uneconomical to have a batch of helical close ratio gears machined up and they would be very expensive if that were done.

[minilee94]

Oh right okay so with my cam Pete will straight cuts be okay

The power band cam I am going to get is 2000 to 7000

I have not chosen a FD if it helps I'm going to use helical drop gears

[Cooperman]

I think you will probably be OK with a standard gearbox and a 3.76:1 FDR, especially if it is to be a road car. No point in spending money for no actual performance gain.

If the power band is 2k to 7k then it's a fairly mild cam, so the power band will not be narrow enough to justify CR gears.

[minilee94]

Well I was only guna go straight cut as

1 I wanted to
2 because 2 of my gears are ruined

[MIGLIACARS]

I was speaking to a guy the other day and he tells me nowadays f1 cars used syncro mesh gears that are helical, and not s/c dogs anymore

[Gulfclubby]

f1 cars all have electronic sequential gearboxes now too. There's really no point in comparing that in any way to a 1960s design of a budget road car.

[MIGLIACARS]

f1 cars all have electronic sequential gearboxes now too. There's really no point in comparing that in any way to a 1960s design of a budget road car.

It wasnt meant as a comparison, just letting people know.

 

Its quite interesting as most people think s/c gear are the be all and end all.

[Cooperman]

For the OP's car, the best gear ratios would be the original Cooper 'S' ones. There really is little point in having SC gears for a road car with a fairly mild cam. In fact the high first gear will reduce the acceleration compared with a standard gearbox, a 3.76 FDR and a fairly mild cam (up to a 276 for example).

[MIGLIACARS]

I have a cooper s gearbox foresale too.

[minilee94]

The kit Im thinking of buying doesn't come with 1st gear. So I use standard 1st gear that's in the box . So as your saying about the acceleration will be poor because of the cam .

So as I'm keeping the original 1st gear surely that's cured the problem or not ?

[cian]

Loving this topic as this is what i amcontemplating i have an sw5 and a 3.4 fd, i just cant get the power down in first have the drag the clutch to get a descent start

[Cooperman]

The kit Im thinking of buying doesn't come with 1st gear. So I use standard 1st gear that's in the box . So as your saying about the acceleration will be poor because of the cam .

So as I'm keeping the original 1st gear surely that's cured the problem or not ?

 

Surely the low 1st gear with the higher 2nd gear from a SC CR set will give a HUGE gap between 1st & 2nd.

If fitting SC CR gears they must be fitted as a complete 4-speed set so that they perform as intended in keeping a narrow power band high-revving engine 'on the cam'. With a standard low 1st and the high 2nd it will quite simply 'bog down' when the change to 2nd is made.

[minimaxie]

Well I was only guna go straight cut as

1 I wanted to
 

You've answered your own question there

[diogoteix]

 

The kit Im thinking of buying doesn't come with 1st gear. So I use standard 1st gear that's in the box . So as your saying about the acceleration will be poor because of the cam .

So as I'm keeping the original 1st gear surely that's cured the problem or not ?

 

Surely the low 1st gear with the higher 2nd gear from a SC CR set will give a HUGE gap between 1st & 2nd.

If fitting SC CR gears they must be fitted as a complete 4-speed set so that they perform as intended in keeping a narrow power band high-revving engine 'on the cam'. With a standard low 1st and the high 2nd it will quite simply 'bog down' when the change to 2nd is made.

 

Yes a SC 2rd gear ratio (about 1.7) is quite close to "standard A+" 3rd gear ratio (1.45) ... So just try jumping from 1st (3.6 ratio) to 3rd gear on a normal box and you'll get an idea. Basically if you push 1st gear to 6000RPM you would get down to 3000RPM, not very advisable...