T5 box in an MGB, diff ratio's?

[3xpendable]

I read somewhere that if you use a T5 gearbox in an MGB V8 conversion instead of the LT77 that you can retain the 4 cylinder MGB's 3.9:1 final drive instead of having to change to the 3.07 one.

Is this true?

[sidecar]

Your best bet would be to check out the final drive ratio for both boxes, if they are similar which I believe they are then they would require the same sort of diff ratio.

I have a T5 but with close ratio gears, my top gear is a bit lower than the standard T5 and LT77, I can't remember what the standard T5 top gear ratio is. I know that first gear was too low for my needs, my first is now around 2.5:1 which allows me to get to over 50 in first if required.

[3xpendable]

Thanks, i'll look into it

[sidecar]

I used a gear ratio calculator to help convince me that the ratios in my R380 box were not really what I needed. (The first gear was a crawler gear of around 4:1!!!). The LT77 has a better first gear but its still not much good in my humble, from memory it is 3.3:1 or something like that.

When working out what diff to go for you need to be realistic about the top speed that your engine can push your car up to, with my Cobra replica I think my 300 BHP engine can push the car up to about 150 MPH so that's what I aimed for with my gearbox and diff. (I have stuck another 100 BHP NOS shot just for a laugh). Cobra's are NOT aero dynamic!

Some people would rather over gear their engine which is fine when cruising about but as the speed increases the drag increases quicker than the rise in power from the engine and due to the fact that the revs are low the engine gives up and can't get the car to its theoretical top speed.

You could gear the car for top speed in fourth and use 5th as an over drive but that's not my 'bag'.

Here is a link to a gear calc, it not the one I used but it will give you an idea what your diff swap will do...

http://westfield-world.com/gtc.html

You will find that a diff swap makes very little difference to the first couple of gears but can make a huge difference to top gear. Going from 3.9:1 to 3:1 is a BIG change

[richardpope50]

My World Class T5 ratios (from a TVR Griffiths) are 2.95, 1.94, 1.34, 1 and 0.8 but there seems to be loads of different ratios via
http://www.moderndriveline.com/Technica ... n_spec.htm