26 replies to this topic

[danny164]

taken on what is for me a massive task of rebuilding a mini, this is my first project but im still motivated and positive (for now) and was wondering what the benefit of straight cut gears are compared with other?? any help tips etc would be great thanks

[Cooperman]

Straight cut gears are designed for competition where the use of really 'hot' cams means that the power band is narrower and closer ratio gears are needed to keep it all 'on the cam'. The big disadvantage for anything other than competition is that a low final drive ratio is needed which reduces the the cruising speed at given revs and means that a high top speed means really 'serious' revs.
With a really strong high-revving engine with, say, a 286 cam, the SC box is lovely in competition as you can keep it revving and always be in the right gear. On my 1964 'S' which has the 286 and a SC box, it accelerates fantastically, but cruising at 4000 rpm gives just under 60 mph.
They are also noisy which is a bit wearing on a long road section or in general use. Withj cfrash helmets on is is not noticeable, however.

[bardan]

Because straight cut gears have no or less of a hypoid angle, they don't load the layshaft to the side of the case. This side loading causes drag and uses more power to turn the gear clusters. Without this side loading the trans is also stronger. Why have this side load on the stock trans? To quiet the gear meshing.

[Wil_h]

Straight cut gears are designed for competition where the use of really 'hot' cams means that the power band is narrower and closer ratio gears are needed to keep it all 'on the cam'. The big disadvantage for anything other than competition is that a low final drive ratio is needed which reduces the the cruising speed at given revs and means that a high top speed means really 'serious' revs.
With a really strong high-revving engine with, say, a 286 cam, the SC box is lovely in competition as you can keep it revving and always be in the right gear. On my 1964 'S' which has the 286 and a SC box, it accelerates fantastically, but cruising at 4000 rpm gives just under 60 mph.
They are also noisy which is a bit wearing on a long road section or in general use. Withj cfrash helmets on is is not noticeable, however.

Why do you need to use a low diff ratio?. I presume because of the tall first gear. All the high power turbo boys us 2.9 diffs with straight cut.

Unless you have serious power or really need the close ratios the helical box is ok.

[Cooperman]

With a NA but well-modified A-series engine the power band is relatively narrow compared with forced-induction engines where the power is available from quite low revs. Thus an engine with a narrow power band needs a close ratio box to keep it on-the-cam, hence the SC/CR box's suitability for that type of engine. However, since power will probably not be really available below around 2800 - 3000 rpm, 1st gear is far too high on a normal diff of maybe 3.1:1.
Forced induction units are another matter, of course, and it's quite correct that a high FD ratio can be run even with a 'long' 1st gear without causing clutch issues.
In this case, the OP has not suggested that he'll go forced induction in his initial post. If he does super- or turbo-charge, then he can run SC/CR with a higher diff ratio.

[roofless]

blah.....blah....blah......blah........they sound nice

[maggies_minder]

blah.....blah....blah......blah........they sound nice

im not sure im with you on that one, maybe for a short journey but every day?

[roofless]

blah.....blah....blah......blah........they sound nice

im not sure im with you on that one, maybe for a short journey but every day?

fair comment - you either love it or hate it......I love it

[mini93]

everyone always says straightcuts are such a pain...you guys must be wimps, i used my dogbox daily for a while and that was fine and im not deaf!

[maggies_minder]

everyone always says straightcuts are such a pain...you guys must be wimps, i used my dogbox daily for a while and that was fine and im not deaf!

your shouting just dont realise (your exclamation mark)

[mini93]

nope, its just some people seem to be forever going on about how there so bad and painful on your ears, i however drove from warwickshire to newquay and back and a week down in and around the area, i was just fine and didnt get bothered by it at all. only annoying thing was my car doesnt have a setrio and quite like to listen to music on journeys, point still stands though

[Shifty]

nope, its just some people seem to be forever going on about how there so bad and painful on your ears, i however drove from warwickshire to newquay and back and a week down in and around the area, i was just fine and didnt get bothered by it at all. only annoying thing was my car doesnt have a setrio and quite like to listen to music on journeys, point still stands though

Thats because you've also got an incredibly loud exhaust as well!!

One drowns the other out!!

[mini93]

its rather loud on th rev-limiter but its not to bad ordinarily, twin box set up...its the webbers which are most prominent but thats obviously only under load

[roofless]

Compared to the cabriolet I reckon Earl's straight cut box n drops will be positively refined in comparison

[Shifty]

Compared to the cabriolet I reckon Earl's straight cut box n drops will be positively refined in comparison

Don't forget to tighten his rack!!