82 replies to this topic

[carbon]

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 ?

Try driving without using top gear for a week (ie only up into third)

 

With typical Mini  2.7-3.1 final drive this will be like using a 4.1 diff

 

Good for acceleration, but very wearing if you're planning long trips...

[ryomini]

OK

 

so like many things, the car is a system, modify one area and you need to keep the other areas in 'balance'

- makes sense

staying with 1275 rather than boring out to 1380 but also looking to put in some kind of higher spec piston

a mild cam would suit me more - acceleration of course, acceleration over outright speed

 

people talk about metro cams and so on - I often forget the numbers but something smooth, I don't really want a crazy lumpy torque curve (like an old Ducati) and a top end only car - low end torque and changing up at low rpm is very nice I think

[timmy850]

If you aren't going with a crazy cam you won't need a close ratio gear set to keep it "on the cam". 

[Spider]

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% ?

 

I know some of the other guys have already posted on this, but to echo some of their posts, Gear for Gear, Straight have never been considered stronger than Helicals. Sure, maybe in some sets they may have them made in better materials or different heat treatment and that may make them stronger, but taking that out of the picture (hence what I mean by saying 'Gear for Gear') Helicals are much stronger because the tooth is not only longer, but also wraps over a longer part of the circumference. Not only does the tooth wrap further around but does so from the load side (or lagging side) to the un-loaded side (or leading side). As loaded Gears rotate, there is a pressure wave within the Gear set up, on smaller Gears, like those in the Pinions of our Final Drives for example, this Pressure wave actually causes a distortion in their shape as the Loaded Gear rotates. The Leading side tries to straighten or flatten out, while the Lagging side puckers up, on very small, high loaded gears, this continuous action tries to break the teeth off from fatigue.

 

 

 

The Power Loss of Helicals is not readily defined as a percentage as Helix Angles, Speed and Load factors come in to play, however it's less than 1%. To show that it really is that small, have a look at our Gearboxes, All the Shaftings are on Ball Bearings and Needle Roller Bearings, to carry the loading on them at the speeds they turn at yet, the Thrusts - which are there for the side loadings - don't nearly have anywhere near the load rating as any of the Bearings in the Gearbox. Have a look at the surface area of the small Thrust on the Layshaft and also those of the Idler Gear, yet, they last well enough. To further illustrate the load capability of these Bearings, in the very early Mini 850's they only had Bronze Bushes on the 2nd and 3rd Gears and yet, with these low powered cars, they burnt them out in no time, so the change to Needle Roller Bearings here happened fairly early in Mini history.

Edited by Moke Spider, 14 July 2015 - 05:39 AM.

[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% ?

 

I know some of the other guys have already posted on this, but to echo some of their posts, Gear for Gear, Straight have never been considered stronger than Helicals. Sure, maybe in some sets they may have them made in better materials or different heat treatment and that may make them stronger, but taking that out of the picture (hence what I mean by saying 'Gear for Gear') Helicals are much stronger because the tooth is not only longer, but also wraps over a longer part of the circumference. Not only does the tooth wrap further around but does so from the load side (or lagging side) to the un-loaded side (or leading side). As loaded Gears rotate, there is a pressure wave within the Gear set up, on smaller Gears, like those in the Pinions of our Final Drives for example, this Pressure wave actually causes a distortion in their shape as the Loaded Gear rotates. The Leading side tries to straighten or flatten out, while the Lagging side puckers up, on very small, high loaded gears, this continuous action tries to break the teeth off from fatigue.

 

 

 

 

The Power Loss of Helicals is not readily defined as a percentage as Helix Angles, Speed and Load factors come in to play, however it's less than 1%. To show that it really is that small, have a look at our Gearboxes, All the Shaftings are on Ball Bearings and Needle Roller Bearings, to carry the loading on them at the speeds they turn at yet, the Thrusts - which are there for the side loadings - don't nearly have anywhere near the load rating as any of the Bearings in the Gearbox. Have a look at the surface area of the small Thrust on the Layshaft and also those of the Idler Gear, yet, they last well enough. To further illustrate the load capability of these Bearings, in the very early Mini 850's they only had Bronze Bushes on the 2nd and 3rd Gears and yet, with these low powered cars, they burnt them out in no time, so the change to Needle Roller Bearings here happened fairly early in Mini history.

 

 

Where would i be able to see your gearboxes ?

 

So unless it is for Motorsport strightcut anything on a Mini is pretty pointless then?

 

Slightly off topic but would it be true to say the A+ Metro Turbo box has the strongest/largest input idler bearing ?

[Cooperman]

Straight cut gears are made with close ratios which are to enable engines with narrow power bands to keep and maximise the available power.

If, for example, you have a high-performance engine with a race cam (649/296, etc) the rev band at which good power happens may only be between 5500 and 7000 rpm. So with standard gear ratios at change up the engine revs would fall outside the best power band, so closer ratios are needed to optimise the performance and keep lap times to the minimum.

Such a cam on a road car would be virtually useless (despite what the two 'comics' may say) and a road cam will always give its power & torque over a wider rev band, so a standard helical gear box is ideal. If the engine is mildly modified, a change of gearing can be achieved by fitting a lower final drive ratio.

[ac427]

Straight cut gears are made with close ratios which are to enable engines with narrow power bands to keep and maximise the available power.

If, for example, you have a high-performance engine with a race cam (649/296, etc) the rev band at which good power happens may only be between 5500 and 7000 rpm. So with standard gear ratios at change up the engine revs would fall outside the best power band, so closer ratios are needed to optimise the performance and keep lap times to the minimum.

Such a cam on a road car would be virtually useless (despite what the two 'comics' may say) and a road cam will always give its power & torque over a wider rev band, so a standard helical gear box is ideal. If the engine is mildly modified, a change of gearing can be achieved by fitting a lower final drive ratio.

 

 I understand but is a close ratio helical box or gearset not available?

 

The A+ Metro Turbo box i have is ok but the ratios leave a bit to be desired.  First gear for instance is next useless because you are into second so quickly, even when not driving quickly.

 

Which gearset do people generally go for with a torquey wide power engine like a 1430cc for instance ?

[Cooperman]

It may be that the FDR is too low with a Metro 'box.

For a torquey engine a standard helical box with a 3.1:1 FDR is usually good or, for better acceleration a 3.44:1 FDR.

[ryomini]

Cooperman

thanks for that info

so your close ratio box is to keep you 'on the cam' just like a good 'ol 2 stroke with the super narrow power band

 

so in fact we have 2 modifications not one,

helical to straight cut is one modification

but standard wider ratio gears to close ratio gears is another

 

SC gears give better performance, but we are trying to compromise for 'fun' road use

is there a straight cut 'wide ratio' gear set that is of any interest or is that just bringing us back to square one with a standard set up

SC gears but not so 'peaky' that it's a pain in the butt to drive, the one's you see in the videos seem to perform very smoothly for road cars - would be good to know what 'set up' they are using

[nicklouse]

 

 

SC gears give better performance, but we are trying to compromise for 'fun' road use

is there a straight cut 'wide ratio' gear set that is of any interest or is that just bringing us back to square one with a standard set up

SC gears but not so 'peaky' that it's a pain in the butt to drive, the one's you see in the videos seem to perform very smoothly for road cars - would be good to know what 'set up' they are using

No.

 

they allow you to use the power from the engine that is all.

 

yes they will be smooth in a road car as the engine would have suitable cam in it. just dont go touring in it.

 

what are you trying to do? build? engine specs......

[Guess-Works.com]

is there a straight cut 'wide ratio' gear set that is of any interest

 

Watch this space....

[Spider]

 

what are you trying to do? build? engine specs......

 

 

 

Good point.

 

Rather than look at what parts you want to run with, decide what you want / expect from the Car and work from that.

[Cooperman]

I've always wanted a close-ratio helical gear set, but no-one does one with the same ratios as the SC CR set.

But to repeat, the ONLY true reason for a SC CR gear set is to keep a 'hot' engine with a narrow power band built for competition use 'on the cam' during maximum power use on a race track or rally special stage.

[Spider]

 

Where would i be able to see your gearboxes ?

 

 

Here;-

 

http://www.theminifo...version/?hl=4wd

[ryomini]

What's it for (everyday car) what are you trying to do ?

To be honest

I'm not sure myself, lol

not having done any racing

I've had enough high rev ie 20 000 rpm rice rockets in my time

just wanted to fiddle about with a 'dead' mini and produce something that

packed a kick in the pants with intelligent spending (is that possible) as I am not the owner of a 'fat wallet' ;)

(have fond memories of drive out's in a friends Ford Cosworth, now that packed a kick in the pants - and almost heart failure too)

 

another stupid very nooby question, can you drop the gearbox without taking out the engine

ie build up another gear box and swap it out and if you really dont like it swap it back in

with the engine in place  ???