37 replies to this topic

[Joycey]

well i have been wondering about a straight cut boxes for a while and have been looking for info on them,

-how are they better than the conventional gearboxes?
-what are the advantages?

i know there have may been some light on this topic before but i would like to know you opinions..

cheers

Edited by Joycey, 02 October 2009 - 01:25 PM.

[Paul Wiginton]

You get closer ratios enabling the engine to stay 'on cam' after gearchanges and you get slightly lower transmission power losses

Paul

[george91]

Also correct if i am wrong, they are stronger than normal helical cut gears therefore can take the power of a modified engine etc. I was looking into these but was advised against it for the time being until i have a better spec on my engine where i would actually benfit from fitting one. One thing to bear in mind is that they are loud, they give a constant whine sound when any gear is engaged, you can get an idea of what it would be like by going to an open area and driving in reverse for a bit as the standard reverse gear is straight cut.

[Minigirl]

they sound awesome! although not good if you like a quiet ride

Edited by Minigirl, 02 October 2009 - 04:24 PM.

[LOWRIDERHORNET]

This aint me but you will no what they sound like

hUJvpWwLmHM

[project mini chris]

theres a red one round by me that has a straight cut box, it sounds gud and goes well

[Paul Wiginton]

SC boxes arent stronger than helical. A helical gear has a longer 'root' therefore are stronger than SC, but you still are quite unlikely to break one

Paul

[alexcrosse]

yep. helical are stronger, but you get more transmission loss through them, power is lost as it tries to push the gears to the side. But if you have an engine circa 100bhp this side thrust will push your drop gears through your casing... hence the 'need' for them with high powered engines, no need for a s/c box though.

[mini93]

not correct, dog box's as they do away with syncro allows space to use wider gears inside...if they did double helicle would be all together better

[Dan]

not correct, dog box's as they do away with syncro allows space to use wider gears inside...if they did double helicle would be all together better

Assuming I understand what you mean, and I'm not sure that I do because your reply seems to be missing several important words, the question is not about dog boxes it's about straight cut gearboxes. As you must know, these are not the same thing.

As said above straight cut gears have lower internal losses and offer more direct power transfer. The main benefit of them for gear makers and racers though is that they are far cheaper and faster to produce than helical gears. It is also possible to mix and match straight cut gears to some extent to allow for subtley different ratios, this cannot be done with helical gears. This allows racers to build gearboxes for specific circuits more easily than with helical gears.

Edited by Dan, 02 October 2009 - 06:44 PM.

[Lot]

Are SC gears made from stronger steel compared to normal helical gears?

It the materials were identical then helical would be stronger otherwise it's harder to judge. May be helical would still be the strongest but the margin is less if stronger steel is being used.

Edited by Lot, 02 October 2009 - 06:59 PM.

[Turbo Nick]

i always thought the benefits of a SC syncro box over a helical one were the better ratio's and the lack of side loading the bearings.

[Hughes]

I dont care what the beneifts are, that noise in the video is sexual.

I want one.

[TimmyG]

Advantages of a straight cut gearbox are;

closer ratios;-good to keep the engine 'on-song' when caning it, and generally nicer to drive when not caning it if used with final drive that is matched to your engine spec.

Longer first gear great for minimising wheelspin on fast starts, and means you can use it on tight corners/ hairpins and allows you to cover alot of ground (50mph with 3.4 fd) before changing gear

box will last longer/cope with more and consume less power as the straight cut gears don't produce side loadings on the bearings.

noise (if you like it like me!)

Disadvantages;

closer ratios;- because of the first 3 gears being much longer final drive selection is a much bigger compromise between cruising ability and acceleration especially with lumpy cams.

Longer 1st gear;- with a 3.44 fd is a pain to hill start (286 cam) AND very revvy on the cruise. Expect to be changing the clutch regularly!

Noise;- if you don't like it!

HOWEVER if you don't have very high power and don't use straight cut drop gears the noise is minimal, think of the wine in first gear (straight cut anyway) and double it, not that bad at all AND what many seem to forget in 4th gear you are not loading any of the straight cut gears anyway- the drive goes staight through the mainshaft to the final drive- so there will be virtually no more noise than standard, certainly not detectable at motorway speeds. Non intrusive gear wine in 1st 2nd and 3rd when you want it and none in 4th when you don't! Maybe?! happy days!

Edited by TimmyG, 03 October 2009 - 01:18 AM.

[TimmyG]

SC boxes arent stronger than helical. A helical gear has a longer 'root' therefore are stronger than SC, but you still are quite unlikely to break one

Paul

I think you meant to say that SC GEARS arent stronger than helical gears, as you say a helical gear has a larger tooth root to spread the load and is therefore stronger for a given material. However a gearBOX built with straight cut gears will be stronger i.e.more durable as the bearings are no longer having to cope with thrust loads.