G50/20 or G50/21 which one?

[brdee]

I have managed to locate a G50/20 and a G50/21 today and I wondered what would be most appropriate for a 600+ SBC engine?

The ratios are as follows:

Gear G50/20 G50/21
1 3.818 3.818
2 2.047 2.150
3 1.407 1.560
4 1.110 1.242
5 0.921 1.027
6 0.775 0.820

Any opinions?

cheers

Brdee

[peterpsg]

Hi Keith,

my gtr has the G50/21 6 speed. Looking at the ratio differance, it seems like the G50/20 would produce a higher top end, as well as a lower cruising RPM...

The first gear is basically no use (except for push starts), I'd check out the G50/50 & G50/52 5 speeds if you can find them, as they have the larger & stronger diff, but also they may have a more usable spacing of gears - read the FAQ on transaxles.

These boxes are close geared in the ratios to suit the narrower power band of the turbo porsche motors, so it's quite feasable to skip over a gear... (Like first!) whereas our SBC's have a fairly wide torque band, and thus would benefit from a more spaced gearing arrangment.

Andy had the very strong 4 speed box but this is a pain to mount due to clutch servos, but it had much more suitable ratios for our engines...

At the end of the day, either will be fine, but you'll probably find you do a lot of shifting...

I'm about to rip my box out over the weekend so I can take it to Quaife and get an ATB LSD added, so I'll let you know how that goes, it should end up costing around £900, but it'll be worth it for the better handling & fast starts...

[G Man]

A 377 ci - I have that gearbox, on my 377 ci the torque is higher up the rev range so you won't bust the gearbox

[Dr Peter]

What sort of money can you expect to pay for a G50 box?
5 Speed and 6 Speed

[GTWayne]

You can expect to pay from £800.00 for a short tail G50 upto £1800.00 for a G50/52 (and anything around,in between,over or under depending on how greedy,switched on or dumb the vendor might be)The best advice I can give you is start looking for a box as soon as you decide to build the car,leave no stone unturned,ring everybody you can think of and keep ringing on a regular bassis and then ring again.Ask freinds,family,fellow builders and all of their freinds,post adverts,scoure the interweb,beg,borrow and steal(the last three are not really essential to the cause but often serv to release tension and anguish brought about by the seemingly never ending search for that elusive box of ever so sought after cogs).Or you might just get lucky.