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MG MGB Technical - Diff ratios....

Hi guys, another question I am afraid.....

I am wanting to increase my diff ratio to bring up the revs as I am currently doing just over the 100 MPH mark when I hit 7200 in 3rd.... Although great, it is just too fast to be able to enjoy 2nd and 3rd to their best on most roads!

I have a Salisbury axle running a standard 3.9 ratio and would like to switch to a 4.3 - 4.8 reducing that 100mph to around the 80 mark!

I have done a bit of research and am new getting the impression that no one makes this ration crown wheel and pinion for the Salisbury but it was available for the banjo.

Due to again MORE work and cost, I am loather to start to replace the complete axle for this. Does anyone have any ideas of how I can increase the ratio? Didn’t know if possible a Sherpa Van might have run on the same etc or if anyone has one of these in a box in their garage?

Any info as always greatly received

Cheers
Ed
Ed Braclik

7200!!!
Chris Currah

Is this a wind up or what ??
Iain MacKintosh

I gather it's not a B-series engine!
Dave O'Neill

May as well get a new rear-end; you're gonna need a new motor. ;)

IIRC, somebody asked the same question on an earlier thread, but I don't think he ever got an answer. You may want to ask the same question over on the Engine Conversions forum. Not all of those folks come over here regularly, and the conversion crowd may have more info.

R.
Rick Stevens

For those that haven't spotted the other threads, Ed has a K-series VVC engine so 7200 is no problem (althouh 200rpm higher than the stock rev limit!)

I think the Reliant Scimitar shared the axle type with the B, perhaps there is a lower axle ratio to be had from one of these? Probably not though, as they were light and had big lumbering engines.

Sherpa is a (non-MGB type) banjo axle I'm afraid - plenty of low ratios but they're for austin westminsters and FX4 taxis! Got a welded 4.8:1 in the Morris at the moment just so we can move it around after bursting the 3.9.

I don't see the problem with 100 in 3rd myself, it's a lot of fun! I think I *just* scrape it with the 6700 limit on the stock T16.

fwiw,
--
Olly
Oliver Stephenson

Ed has a K series engine in his B.

He confused me slightly (easily done) when he said here and elsewhere that he wanted to raise the axle ratio, he really means to lower the ratio so the engine revs more. The Rally spec Bs must have had a low ratio axle but I don’t know of a supplier around today.

Geoff
Geoff King

Thanks guys

My DVA K-Series engine actualy tops out at 7,800, but I normally dont go past 7,200....

Looked at the possibility of different axles like a Banjo, but want to investigate all routes with the easiest option of a simple diff change first!

I will post on the convession formum and see if anyone has any ideas!
Ed Braclik

That axle was used everywhere. The CW/Pinonin was 11/40 for the MGB and 1.8 Marina. The 1.3 Marina had about 4.11 to 1 if any stil lurk in scap yards
Stan Best

The trouble is ED if you lower the rear end first gear will be too low. Denis
DENIS H

I never investigated this, since I've been more interested in higher ratios than lower, but Volvo used a similarly Salisbury axle in the 60-70s, maybe later. Possibly the diffs will fit, or even the whole axle, since later ones had rear discs. They used a lot of different mounting/locating arrangements over the years.
FRM
FR Millmore

Ed,
How about really small wheels?
Neil

PS My GT running 185/60/14 tyres will do, what, 75mph ish, at 6000rpm in third so another 1500rpm or so would give say another 15mph tops...? Is your speedo okay? Is my speedo okay??
Neil

This thread was discussed between 26/01/2007 and 28/01/2007

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