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MG Midget and Sprite Technical - 3.5 crown wheel and pinion

I am running a 3.9 Finespline LSD at the moment in the V8 but it tops out at 85-90 mph.
Does anyone have a 3.5 crown wheel and pinion they would part with.

Dave Pratt

It won't rev more than about 5500rpm in 4th at 1:1 or 4,500 in a typical 5th or slightly more revs if you have very low profile tyres on a 13" wheel? It ought to rev to 6500 without any trouble.
Daniel Stapleton

Maybe I've been going down the wrong route and should get the Ecu remapped first as it may have a limiter mapped in.
Dave Pratt

What sort of revs do you pull with the V8?

I thought they weren't big on revs without some serious mods.

Also, which gearbox are you using?
Dave O'Neill 2

Hi Dave,
3.5 crownwheels and pinions (new) are available from a company in Germany. I learnt about it from posts on this BBS. I guess a search of the archives or some Google work should easily find the source. I can't remember the name of the company which is offering them for sale but I do remember being pleasantly surprised at the price. (about $350 US I think). I usually run 4.2 ratio in my s/c TC special but at tracks with very long straights I run a 3.7 ratio. I run the Sprite/midget diff so I have a great choice of ratios. They are easy to convert to fit the TC banjo. A 3.7 diff with my 15" wheels and tall (legal in Historic) tyres gives me about 120 MPH at 6250 rpm.

I could be barking up the wrong tree as you mention you have a V8 engine? My input above assumes you have a Midget/Sprite diff which probably would not carry the power of a 3.5 litre V8.

I would have the company name in my records somewhere. I could dig out the info' if you can not find what you need.

Bob Schapel

R L Schapel

In my mind, tiny as it is- 3.9 or even 3.5 are too spinny for a V8. - You spend all your time changing gears and going nowhere - You need to be somewhere above 3.3 before there is some more serious forward movement instead of revvy nothingness
Unless it is a serious racer being tuned to a particular track,
In my opinion only of course----

What size wheels / tyres are you running
4speed or 5speed g/box

William Revit

Ref a supplier in Germany:


(BTA520) Crown wheel & Pinion 3.55
required quantities: 1
Doug Plumb

Thanks for the replies guys I need to do some more investigating.
Willy that's exactly what it's like, it is a 5 speed lt77 box. Out of a 3.5L rover sd1. You put your foot down step up through the gears in what seems like seconds and your revving the ar*e of it doing about 85 mph
Dave Pratt

What size wheels / tyres
William Revit

Thanks Doug I'll look into that and willy they are
13 inch wheels with 175/70/13
Dave Pratt

My MGB V8 (3.9 litre) has the Rover 5-speed box too, and with independent rear suspension runs a Ford 3.14 diff with 15" wheels, and it is still too low geared in my opinion. The engine is not a revvy unit and I don't suppose I have ever had it above 5000 rpm, and normally not above 4000 rpm. It has so much torque that it pulls away in second gear with no clutch slip necessary, and it could easily pull away in third. I only use first gear on hill starts. MG themselves used 3.07 on their own MGB V8 with 14" wheels.

I'm not surprised that with a 3.9 diff and 13" wheels you find the car much too low geared. How does your axle take the torque? Mine is producing around 200 lb.ft, rather a lot more than a Spridget engine!
Mike Howlett

What is the letter at the end of the gearbox serial number? The later Rover SD1 (Vitesse) had a higher 5th gear, with a larger o/p bearing and a diff ratio of less than 3.00. If you have PRE 'D' letter, it'll be the lower 5th. Some years ago I built a MGB V8 roadster with this later ratio box and 15" wheels but even then, as Mike said, first gear was rarely used.
Motley 5

Ha ha - You'll laugh at me
I took it that the 77 in the gearbox No. gave it a .77 overdrive in 5th-----
By coincidence one of them is--but not all, as you mention
But there isn;t a big, big difference in them so really it won't affect the result Dave's looking for here all that much
I feel his main prority is to get a diff ratio into it as high as he can find, like 3:25 or thereabouts or maybee even higher
William Revit

If anyone is thinking of swapping to the taller 3.5 CWP (as I did) it might be worth your while looking at the Bastuck range. The Euro to pound exchange is currently very favourable, and these babies work out at about half the price of even the ordinary versions available through our UK retailers.

Thanks again guys
I have contacted bastuck to see if they can do other ratios and as expected the answer was nein.
I will probably order the 3.55 and give it a go.
I do have a 1500 anglia English axle which I was originally going to use so I will do some more digging into that aswell but that looks like the lowest ratio is 3.5 at the moment.

3rd option is start from scratch as mentioned with a different axle that can get the lower ratios.

Fun fun fun
Dave Pratt

This thread was discussed between 25/03/2016 and 29/03/2016

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