82 replies to this topic

[Spider]

Here's another set to also consider

 

http://www.guess-wor...play.htm?id=114

 

(Sorry GW - didn't know you also had them)

[Ethel]

A wee point of interest for the OP,

 

First and reverse on the standard gearbox are straight cut. 

 

The available straight cuts can be stronger than the factory helicals, but that's down to materials and engineering. Closer ratios will also get less of a hammering when you change gear, but then you're also likely to have a snatchy race clutch if you're running them.

 

Getting the final drive right is the main thing 3.4 is great for a road Min, maybe 3.7 for a lairy 998.

[Cooperman]

I have certainly found a 3.44:1 FDR to be a bit too high when using a SC CR gear set on a 1330 cc 'S' with a 286 cam. In fact even a 3.76:1 can be a bit high and a 3.9:1 is best, but that means a lot of revs at cruising speed.

[Spider]

I have certainly found a 3.44:1 FDR to be a bit too high when using a SC CR gear set on a 1330 cc 'S' with a 286 cam. In fact even a 3.76:1 can be a bit high and a 3.9:1 is best, but that means a lot of revs at cruising speed.

 

If I recall, the works cars with fitted with 3.9's and 4.1's.

[Cooperman]

A lot of works rally cars had 4.3:1.

I did a couple of rallies in 18 CRX which was a works car sold to a private owner and fitted out to full 1275 works specs. It had a 4.1:1. My rally 'S' has a 3.9:1 and even then I find that a bit high if trying to pull away from rest up a steep hill as quickly as possible, as at the start of a test for example. I had a 1071 'S' with a 4.1:1 and it was very good. It had a 649 cam with little grunt below about 5000 rpm and it pulled best from about 6000 to 7500 rpm. Nasty to drive on the road, but on a tarmac rally stage on pace notes it was awesome. We had a good class win (up to 1200 cc) on a Belgian Historic International rally in that car.

Many people don't understand how gearing is directly linked to engine performance and the rpm's at which the power & torque is delivered. I've been out to a charity event today in my rally 'S' and really it doesn't go as well below 5000 rpm as it would with a 'softer cam' than the 286 it has. I cruised back at 5000 rpm which is about 73 mph in top with my earplugs in to mask the horrible straight cut drop gear noise!

[Spider]

 

Many people don't understand how gearing is directly linked to engine performance and the rpm's at which the power & torque is delivered. I've been out to a charity event today in my rally 'S' and really it doesn't go as well below 5000 rpm as it would with a 'softer cam' than the 286 it has. I cruised back at 5000 rpm which is about 73 mph in top with my earplugs in to mask the horrible straight cut drop gear noise!

 

Oh, they go hand in hand! 

 

I couldn't imagine trying to drive the streets on a 4.1 (on 10" sized wheels).

 

I think our Race Car had a 4.2, but that was a very long time ago!

[nicklouse]

I can't remember if I have a 4.1 or a 4.3 but I don't always need 1st.

Really should change the gearbox ratios at some time. But it works? But there is now way I would want to put it on the road. It is bad enough in the paddock. Hit a bump and it wants to take off.

[ryomini]

Hahaha

so reverse and first are already straight cut

so what is a good final drive ratio for a fast road mini

 

are we sitting at 3.9 - 4.1 ?

[timmy850]

Hahaha

so reverse and first are already straight cut

so what is a good final drive ratio for a fast road mini

 

are we sitting at 3.9 - 4.1 ?

You would really need to decide on your engine spec, particularly the cam before choosing the gear ratios as mentioned above. 

[Mini Manannán]

Hahaha

so reverse and first are already straight cut

so what is a good final drive ratio for a fast road mini

 

are we sitting at 3.9 - 4.1 ?

 

Decide how you're going to drive it to decide which camshaft you're going for, then look at the cam charts for that cam, that will tell you which FD would be best.

[ac427]

Why are straight cut gears now viewed as weaker the helical gears ?

 

What is the rough percentage power loss between a straight cut gear box and ahelical gear box, 10% ?

[Alex_B]

Why are straight cut gears now viewed as weaker the helical gears ?

 

What is the rough percentage power loss between a straight cut gear box and ahelical gear box, 10% ?

They aren't suddenly now regarded as weaker, they always have been if you take out material strength from the equation. 

It's physics at the end of the day, helicals have more tooth contact so can safely transfer more power. It's more the effect on the rest of the box that makes them less preferable. Helicals will try to drive away from each other and thus put side loadings on the bearings and casing which isn't ideal. Also straight cut gears are much cheaper to manufacture which makes them preferable for motorsport use where you are likely to run different ratios for different events / tracks. The loss of power transfer between gears is less with straight cuts as well which is another benefit for motorsport use as you mention however I don't know the difference of losses between both types. 

[ac427]

Thanks Alex, I was aware of the side loading but not about the material strength element. Being easier to manufacture you would think they might be a bit cheaper

[ac427]

Here's another set to also consider

 

http://www.guess-wor...play.htm?id=114

 

(Sorry GW - didn't know you also had them)

 

Swiftune have them also, manufactured by Quaife too.

 

http://www.swiftune....ansmission.aspx

[Guess-Works.com]

Thanks Alex, I was aware of the side loading but not about the material strength element. Being easier to manufacture you would think they might be a bit cheaper

 

They are considerably cheaper than getting a helical gear kit made... eg look at the price of a newly manufactured 22G1040 GT laygear, and 1st motion... 

 

http://www.minispare...C-AJJ4032A.aspx