22 replies to this topic

[haz]

Ayt people, I'd like to know your thoughts on straight cut 5 speed boxes

I've seen the minispares SC 5spd box, and looked at various 4 speeds, inc JK and the 'Mutts' from guessworks among others

My main concerns are, are they as reliable.. do i have to change anything else to fit one? appart from the 'H' ofcourse. And, are they worth it for pretty much an extra 1k?!

The box will be going on a 1380 - circa 100bhp at the fly

[Baldspeed Racing]

ive got a 4 speed box which is more than fine for road and track use on my 1380 running 115bhp at the wheels. I do think a 5th gear would be nice for motorways tho imo

[haz]

whats ur FD ratio and top speed??

115 at the wheels, v.nice! what cam u running?

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Have a look at this

http://www.guess-wor...arbox/ratio.htm

Put in your tyre size etc, then which gear kit you plan to run, and you can calculate speeds in each gear, very useful!

[Guess-Works.com]

Thanks Simon, wasn't expecting that

what I would say tho, if you do loko at a 5 speed, you don't want to end up with too much overdrive in 5th, as then it'll become a wasted gear as you'll not be able to accelerate in it...

So treat a 5 speed as trying to fit an extra ratio in which the 4 use to cover.... ie a 4 speed has a final ratio of 1:1 in the box and then the diff factor, say 3.4 for arguments sake... If the final drive in a sc 5 speed is ( looked on MS site ) is 0.865 then ideally you want to adjust the final drive so the end result is the same as the 3.4 with a 1:1... does math in head so something like a 3.9 would achieve that result ( also reduce stress on the case and gears )

Simon, do you have to hand the ratios for your 5 speeds ( helical and SC ) and I'll see about adding them to the calculator...

Edited by GuessWorks.co.uk, 07 February 2008 - 01:20 PM.

[Baldspeed Racing]

whats ur FD ratio and top speed??

115 at the wheels, v.nice! what cam u running?

er I think a kent 286 rings a bell, been a while since ive talked specs

[GraemeC]

Guessworks - if you do it that way then you would see no advantage on the motorway would you - you'd just be swappping cogs more often to achieve the same top speed at the same revs?

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The advantage is you would still have the acceleration ability of a 3.4 for example, but the cruising ability of a 3.1.

[samwell]

Guessworks - if you do it that way then you would see no advantage on the motorway would you - you'd just be swappping cogs more often to achieve the same top speed at the same revs?

an get more accelleration in each gear. I dont think anyone who spends 2k on a 5speed box woud prefer a slightly lower rpm on motorways in exchange for better acceleration

[Guess-Works.com]

This is true... but assumption is, based on the fact it's a SC requirement, the intention is to 'give it some beans'.... and I would be warey of that with a long final drive and an overdrive gear...

We all know what a long final drive does to MPi gearboxes...

However, if it were a cruiser for the motorway, then yes make use of the extra legs provided by the overdrive.... but would you want a SCCR gearbox for that ???

[GraemeC]

The advantage is you would still have the acceleration ability of a 3.4 for example, but the cruising ability of a 3.1.

Not if you adjust the final drive of the diff as GW suggests. You'd get the accelleration of a 3.9 with the cruising of a 3.4(ish) assuming the first 4 gears in your kit are standardish ratios.

an get more accelleration in each gear. I dont think anyone who spends 2k on a 5speed box woud prefer a slightly lower rpm on motorways in exchange for better acceleration

Beg to differ, but its not a factual point. I believe most people buying a 5 speed will be doing so for better cruising (and for bar points). If people just want hard accelleration then they'd change the diff ratio alone.

[GraemeC]

True GW - I was missing the point that this was SCCR.

In which case I would say 5 speed is again bar points. A car that warrants SCCR is usually powerful enough to accellerate pretty handily in the existing 4 gears without needing a 5th ratio. I would much prefer to stay in a gears longer than change an additional time. But yes that would be more stressful on the box.

Edited by GraemeC, 07 February 2008 - 02:41 PM.

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The advantage is you would still have the acceleration ability of a 3.4 for example, but the cruising ability of a 3.1.

Not if you adjust the final drive of the diff as GW suggests. You'd get the accelleration of a 3.9 with the cruising of a 3.4(ish) assuming the first 4 gears in your kit are standardish ratios.

an get more accelleration in each gear. I dont think anyone who spends 2k on a 5speed box woud prefer a slightly lower rpm on motorways in exchange for better acceleration

Beg to differ, but its not a factual point. I believe most people buying a 5 speed will be doing so for better cruising (and for bar points). If people just want hard accelleration then they'd change the diff ratio alone.

The boxes we supply come with a 3.4 diff, hence my example albeit for a helical kit. S/C would give more like 2.98

[Guess-Works.com]

Just incase you're wondering what "The Mutts" is....

[attachment=49774:07022008344.jpg]

[samwell]

True GW - I was missing the point that this was SCCR.

In which case I would say 5 speed is again bar points. A car that warrants SCCR is usually powerful enough to accellerate pretty handily in the existing 4 gears without needing a 5th ratio. I would much prefer to stay in a gears longer than change an additional time. But yes that would be more stressful on the box.

brilliant for acceleration if you have a ludicrously wide power/torque band such as a turbo but most engines tend to have fairly compact power band so more gears means better acceleration