58 replies to this topic

[minilee94]

As many people have seen me putting stuff up on here I can't remember if I posted this already but
Are straight cut gears really worth it

The week end I was going to order straight cut gears , re con kit and a x pin diff but do you really get anything out of straight cut gears

Not that it matters but in my box now I have a few damaged synchros And iv sen the price of standard synchros so I was guna go all out and have straight cut

Engine wise it's a well speced 1380 road / track

Edited by minilee94, 17 September 2013 - 05:19 PM.

[AVV IT]

With straight cut gears you reduce transmission loss, meaning that the BHP at the wheels becomes closer to that originally produced at the flywheel. Now whether you consider that power gain (or reduction in power loss as the case may be) to be worth the cost and effort of fitting them is really a matter of personal preference. The other issue is the noise of straight cut's, as they produce the same whining noise that you get when reversing. Personally, even if I had the time, money and inclination to fit straight cuts, I wouldn't bother because I couldn't stand the noise they produce!

[minilee94]

Okay thank you very much I don't mind the noise it's not an everyday thing so I don't mind

[diogoteix]

I made the choice of a straight cut gearbox a couple of years ago and to be frank, I don't know what choice I would make today , but I tend to think I would revert to a "standard box".

 

On the good side:

- a straight cut gearbox has no side thrust so you will never end up with the so famous problem of a 2nd gear popping out, because the gear cannot stand the torque!

- on a circuit, the very close ratios are a real fun to play with, you really feel like in a "rally car" without the engine dropping 3000RPM between 2nd and 3rd...

On the bad side:

- the noise is quite annoying, I tend to drive in 4th gear even at low speeds to avoid the winning sound of the gears (on 4th gear you're on "no gear" to a SC box makes the same noise as any standard box)

- The "close ratios" are not at all adapted to an every day drive. I'm living in Lisbon,a town with 7 (steep) hills and you better not get into a traffic jam with a nice climbing street: you will pretty soon start smelling your clutch burning... Even with a 3.4 diff, 1st gear is almost equivalent to a 2nd gear on a classic gear box.

- Because of the previous, you tend to stick to high ratio diffs. There is no way you can use a 2.9 or 3.1 diff if you don't want to ask for a "little pushing help" at every traffic light! So you can forget about cruising on highways!

 

So as with many things on a Mini, you need to take some time to consider how you will use your car, so that your box choice takes into account all these parameters!

[Noah]

If it was me, it's all about having the close ratios, C-STN77 is a lovely set up, I'd be using helical drop gears to reduce noise, and the C-STN77 Gearset, you'll still get the reassuring whine, just not the deafening clatter of straight cut drops. 

 

[minilee94]

Hmm I don't know what gears set you have out up Noah but I'm going for the mini spares ones

And as said the car is not guna be used everyday so I don't really care about the noise

[Noah]

Hmm I don't know what gears set you have out up Noah but I'm going for the mini spares ones

And as said the car is not guna be used everyday so I don't really care about the noise

 

Those part numbers are Mini Spares ones, the C-STN77 is the ST close ratio rod change gearset. 

C-STN39 is another alternative, not close ratio however. By all means go hard or go home if you wan't to but, if you like drivability then, you have to take into consideration your ears. 

There are plenty of cars around with Straigt Cut boxes, straight cut drops and straight cut CW&Ps, but there is a reason they're usually race cars. 

Edited by Noah, 17 September 2013 - 07:36 PM.

[Barman]

I made the choice of a straight cut gearbox a couple of years ago and to be frank, I don't know what choice I would make today , but I tend to think I would revert to a "standard box".

 

On the good side:

- a straight cut gearbox has no side thrust so you will never end up with the so famous problem of a 2nd gear popping out, because the gear cannot stand the torque!

- on a circuit, the very close ratios are a real fun to play with, you really feel like in a "rally car" without the engine dropping 3000RPM between 2nd and 3rd...

On the bad side:

- the noise is quite annoying, I tend to drive in 4th gear even at low speeds to avoid the winning sound of the gears (on 4th gear you're on "no gear" to a SC box makes the same noise as any standard box)

- The "close ratios" are not at all adapted to an every day drive. I'm living in Lisbon,a town with 7 (steep) hills and you better not get into a traffic jam with a nice climbing street: you will pretty soon start smelling your clutch burning... Even with a 3.4 diff, 1st gear is almost equivalent to a 2nd gear on a classic gear box.

- Because of the previous, you tend to stick to high ratio diffs. There is no way you can use a 2.9 or 3.1 diff if you don't want to ask for a "little pushing help" at every traffic light! So you can forget about cruising on highways!

 

So as with many things on a Mini, you need to take some time to consider how you will use your car, so that your box choice takes into account all these parameters!

 

What an excellent, reasoned response!

[minilee94]

This is the kit I was guna fit

http://www.minispare...|Back to search

[Cooperman]

The use of SC gears is to keep an engine 'on the cam' when a cam with a narrow power/torque band is fitted. It is used with a low ratio final drive and is intended for competition.

So, for example, if a 286 or hotter cam is fitted, it will only give real power from about 5300 to 6800 (for a 286). Yes, it will run outside this rev range, but the power given will be no more than and usually less than a softer cam at those revs.

However, a SC gear set has a very high 1st gear compared with a standard box, so a low FDR is needed to enable the car to pull away from rest under competition conditions. With an engine able to pull up to c.7000 rpm that will present no problem and the mph/1000 rpm in top will be low, but the engine will then need to run at high revs to get to max. speed. It is not intended to 'cruise' on the road, so on-the-road revs will be high.

It is great to drive a 'cammy' engine with a sccr box and a low (3.9:1 probably) FDR and when keeping the revs at 5500 to 6500 it is very rewarding, especially on a twisty special stage.

Edited by Cooperman, 17 September 2013 - 06:51 PM.

[minilee94]

Pete I do love your info but confuses me to the max lol

[Midas Mk1]

SC gears get annoying, followed a car on l2b this year and it was doing my head in. Even with a 286 cam a std 3.44 box is great for road driving.

Yes peak power is higher up, but then it still has more power at 3000rpm than the max power from my 266. 

Edited by Midas Mk1, 17 September 2013 - 07:01 PM.

[minilee94]

Some straight cut gears aren't even noisy I got in my mate mini and couldn't even hear it he has similar spec to me

[Cooperman]

I just checked the cam graphs, and at 3000 rpm even a 276 cam is giving 50% more bhp than a 286, so a 266 will be giving more than a 276 at those lower revs. The 276 and 286 give the same power at about 4500 rpm, then the 286 is better right through the rev range. The 266 gives max power at 5700 rpm, the 276 at 6100 and the 286 at 6400.

So a 276 will run OK with a standard gear set, so long as a reasonably low FDR, like a 3.44 is used.

I tried a 544 (similar to a 286) with a 3.44:1 and a SC CR gearbox. The clutch didn't last long as it had to be slipped a lot to get good acceleration off the line!

[Gulfclubby]

276 works fine with a 3.44 final drive and standard helical gears. However, the rev drop between shifts is quite significant, so you would arguably want a closer ratio box for competition use.

For road use, the 276 is a fine cam though.