SC Drop Gears or SC Box
Turbo Mini Forums

As per a budget point of view what do you folks feel is more important?

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


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How much power are you hoping to run? What is the car to be used for?

I'd always do them both together but in my experience the drops start to suffer before the box.

Every day is a school day ...........

How fast and how expensive ...... the same question...

the first this that will break when the horses and torque go up are the drop gears so i would go for those.
i,m planning to do the same think. standerd box with straight cut drop gears. and when the funds allow straight cut all the way

there is nothing wrong with a A-series that a turbo can't fix.

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I am not of the opinion that SC gears in the box add that much strength, they just give better ratios. If you are upgrading the box I would say in order of importance is Diff, drops, box.

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could i fit Sc drops to the box myself though? what about a diff?

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you need a x-pin diff, even a stock 998 will eat the standard one, never taken one to bits that isnt ****ed!

Slaters not wrong...

Every day is a school day ...........

How fast and how expensive ...... the same question...

Bit of thread excavation here but I can't find the answers to my questions using search and this thread seems closest.

I'm building a fast road car (not the cooper) and don't really want noisy SC drops.

I've seen Robert's car and he runs an SC box with standard helical drops. We all know he is putting out some serious billies and curly's and his drops seems to be taking the abuse.

It maybe that Robert is an exception to the rule but would this be a good setup for say 130-150 billies/curlies in a road car.

I know most people go for sc drops before box but perhaps the sc box first approach may be beneficial in some situations?

I basically want to be able to get in and go and not have to wear ear defenders!

If something is worth doing, it's worth doing half of.

Then limit the power to around 120, run std drops and a std box....

Alex

AlexF

Thanks for the input but I want it bit more power than that really. With the current spec of the engine 120bhp would be a waste.

If something is worth doing, it's worth doing half of.

Ear plugs then :)

Its a tricky thing - but the problem lies with the original design.

Helical gears made of the same material as stright cuts are stronger - but there are side load issues with helicals as they push apart from each other.

AlexF

in theory they should cancel out on the drop gears though...

I'm assuming (possibly wrongly) the twisting effect on the helical idler causes the problem with a helical box as it will transfer this load to the layshaft via the input gear. then cause the engaged gear to climb the headset and possibly strip the teeth.

If something is worth doing, it's worth doing half of.

no? Why not? to qoute TD:

First thing about helical gear trains that is mis-understood:
They do indeed impart forces other than radial. The axial force is as a result of the helix, and as it is applied to the tooth, generated a bending along the axis of the shaft, which because the shaft (gear) is supported on bearings, translates to an axial force.

So, what happens with idlers?

Well, think about the way the idler train is laid out. You have three gears, with the idler in the centre. The driver and driven either side of the idler are the same size and helix - and as a result, the magnitude and direction of the force on the (top) of the idler (against the driver gear) is equal and opposite to the magnitude and direction of the force on the driven gear.
In short - if you have a helical idler geartrain with the same driver and driven gears either side of the idler, and with the idler axis symetrical about the driver and driven axes (so you could hold a straight edge between all three axes), then you would see zero axial forces.
That's right, ZERO axial resultant force.

However, the shaft axes in a mini are not in a straight line - hence you do see a resultant axial force about the idler axis, which reverses in direction between drive and coast.

If you want a little more evidence, just look at the thrust washers against the alloy casing - do you REALLY think this could take all the thrust of the helix if it wasn't in an idler train??? It is not a huge force.

Back to SC's - of course they eliminate ever last little bit of this axial resultant.

Ben's idea of installing a bearing into a helical is certainly do-able, but I am pretty sure a cylindrical bearing is not going to work in this application, because a cylindrical will happily take a thrust, and / or a radial, but the bending moment from the idler application in a transverse A-series is not going to cut it...

All is not totally lost; if you can fir two narrow (back-to-back) tapers in there, then you have about as stong a bearing as you could want.

Can you fit them in there? I don't know... There is also the small problem of keeping everything perfectly concentric.

If you want a little more evidence, just look at the thrust washers against the alloy casing - do you REALLY think this could take all the thrust of the helix if it wasn't in an idler train??? It is not a huge force

this is the problen though Andre, the washers can and do weld themselves to the casing in high torque motors,
iv'e had it myself on NA engine,

carl

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There not that loud anyway

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

On 14th Dec, 2009 MikeRace said:
There not that loud anyway

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On 14th Dec, 2009 fastcarl said:

On 14th Dec, 2009 MikeRace said:
There not that loud anyway

true, i have two sets in the twinnie and i just can't hear them when iv'e driving it,

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I ran mine with 140+ nanas as my daily drive a few years back, and never had any problems.

I put about 15-20k on the engine in that time. Being a daily drive I didn't tend to drive it that hard, only the odd thrash here and there on sunny days. I think a bit of mechanical sympathy plays a big part in how long it lasts tbh. :ohell:

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1/4mile in 13.2sec @ 111 terminal on 15psi