Benefits of close ratio gearbox?

[VerySideways]

Hi,
I've been searching the forums because i figured this would have been covered by someone at some point but haven't been able to find anything.

I found on mytuscan.co.uk the gear ratios/speed between the normal gearbox and the CR box, but what's the benefit to the CR box?

4th and 5th are the same, it's 1st/2nd/3rd which are closer. What this means of course is that 1st is much longer in the CR box than the standard box. Whilst i can see the beenfit under race conditions i don't see what the improvement would be on a road car.

My 350hp 4.0 Tuscan with standard 'box doesn't seem to have any holes in the power delivery, when i change gear there's plenty of power in the next gear.

So what's the point of the CR for a road car?

[pete]

0-60 in first gear, and 0-100 in second

I've had a play in a friend's Red Rose with one of the first CR gearboxes, and the advantage seems to be that you change gear less between 2nd and 3rd when you're really pressing on.

Pete

[Fly Boy]

1st is a more useable gear
smaller rpm drop between gears, keeps the engine in the power band( I know its a wide band...)

change the diff ratio too(as most do ) then the acceleration is phenominal...

On paper it doesn't seem to be worth the hassle/money but...
in the real world it's MENTAL

Edited by Fly Boy on Friday 22 May 11:54

[Robertjp]

So what is the difference in acceleration to 60 and to 100 with the CR box then? I suppose its a long shot to expect someone to have measured it!!

and what difference does the diff make to acceleration? presumably it drops your top speed, which, i guess to 95% of us has never ever been reached anyway!!

[VerySideways]

CR box will do 60 in 1st so that'll be a gearchange quicker. Doesn't change 4th or 5th so top speed is the same.

[T450t]

All what you saying above is dependent on the dif ratio. Put a 3.9 in and 1st is not that long. The up side of a CR box and short dif is less drop in revs through the gears and more instant acceleration. The down side it runs out of puff quicker. Personally neither is any good without the other.

[Robertjp]

VerySideways said:

CR box will do 60 in 1st so that'll be a gearchange quicker. Doesn't change 4th or 5th so top speed is the same.

Yeah i worked out that the top speed remains the same with the CR box, just wondered what the combined affect of CR box and diff was.

Personally i think i'd rather have just the diff, or a combination of both, not just the CR Box?

Better acceleration at semi legal speeds and losing some top end...

Mind you this is academic for me, i have only had it three weeks and its quick enough just now!! Although...pending engine rebuild may well ruin the bleedin summer!

[MrsS]

Robertjp said:

VerySideways said:

CR box will do 60 in 1st so that'll be a gearchange quicker. Doesn't change 4th or 5th so top speed is the same.

Yeah i worked out that the top speed remains the same with the CR box, just wondered what the combined affect of CR box and diff was.

Personally i think i'd rather have just the diff, or a combination of both, not just the CR Box?

Better acceleration at semi legal speeds and losing some top end...

Mind you this is academic for me, i have only had it three weeks and its quick enough just now!! Although...pending engine rebuild may well ruin the bleedin summer!

You wont loose any top end with a shorter diff. The satndard car won't pull its gearing.

[GT TVR]

MrsS said:

You wont loose any top end with a shorter diff. The satndard car won't pull its gearing.

Using the Gearspeed calculator, a car with a 3.91 diff will do 167 mph at 7000 rpm while a 3.73 diff will do 175 mhp and a 3.46 188 mph. (The latter will never happen of course.)

But even if it loses this 8 mph, who cares, I love the short diff and CR box, especially the seemless acceleration in the first few gears, it's brilliant.

Edited by GT TVR on Sunday 24th May 08:17