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MGB Roadster conversion

18454 Views 18 Replies 6 Participants Last post by  Rf 4.3
I'm now planning for my next Conversion, which is going to be a 1979 MGB Roadster. This is a rear wheel drive.

I wanted this to be a fast and high performance drive. I just bought a Remy HVH250. I'm close to getting a rinehart pm100dz. I'm planning to run it close to 500V.

I need your guidance on the reduction ratio for this setup. MG diff is 3.9:1. I read up few threads about 2 speed Powerglide trannies and I don't think it is a good idea to go for Powerglide tranny, as its final ratio is 1:1. I don't want to spend too much money on tranny/reduction

Miz, RobA, Duncan, and all other experts, please share your thoughts
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Thanks guys. I'll do some Calc and decide on the gear ratios. I'm leaning towards using a powerglide tranny without torque converter. Anyone thinks I shouldn't use tranny?
MM - Thank you and I hope mine is WEG cooled, I don't have it with me yet, but will let you know once I have it.
Fascinating read about this on the motor forum- never seen these Remy motors before now. Appears that the highest output ones use active (forced) oil cooling, including flow between the rotor and stator if my brief scan of the thing was correct. Apparently they sell motors that are designed for 50% water/ethylene glycol (WEG) cooling which have sealed bearings, and oil lubricated + oil cooled units which give 40% higher heat dissipation performance because of the vastly greater surface area of cooling surfaces available when nonconductive oil is used as the coolant.

Which cooling system is your motor designed for? If it's one of the cartridge units and it's oil cooled, there's a whole lot of work required to integrate this into a housing, as the oil drains out of holes in the end of the motor cartridge...
I did some more research on the motor that I'm getting - Its HVH250 90SOM which is Series wound, Oil Cooled. I need to figureout how to take care of Oil drains..
I don't think I'm an expert but here is my tuppence worth

Top speed - what do you want?
What is the motors max rpm?

Divide A by B - and you get your maximum reduction ratio

any greater reduction than that will reduce your top speed

Sit that to one side

Weight of vehicle (MGB) - weight on rear axle
Size of tires

My tires are almost exactly 2Ft in diameter - so each Lbft of axle torque = 1Lb of force at the road surface (and at the axle)

General rule of thumb road tires have a max coefficient of friction of 80%

So if you have 1000lbs on the back wheels the most force you can apply is 800lbs
So the most torque is 800ftlbs (2ft tires)
If your diff is 4:1
You need 200ftlbs at the motor - to MAX out less is OK

Just plug your numbers in - see what you want and then have a look at what you can get
Thanks Duncan.
Remy can go upwards of 10000 rpm. So I'm not worried about Max Speed. My interest is to keep a good torque in freeway speed (~60mph) as well
Here are few numbers
Constant Torque up to 4000RPM is 184 ftlb
Diff Ratio 3.9
Rear end Weight 1100 lbs
Tire height is 2 ft
I wanted to see if I can do direct drive, today I saw the Latvian RX8 thread, which assures me of going Direct Drive. With rear diff ratio of 3.9:1, with 2ft tall tires, Rear weight of 1100 lbs, Max Torque of 880 ftlb here is what I got:


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Duncan, I don't think they have much choice in mg, I've to go custom for that kinda ratio.
Thanks Duncan. Will see some local shops this weekend
Yes, I'll limit the motor rpm under 7K through controller
No, that's the VW Doka project. There is at thread in the forum
The MGB used a lot of Austin/Morris parts as MG was part of the Austin/Morris/Leyland.... conglomerate

I think you will be able to go to at least 4.4:1 with standard bits
And with the long history in motorsport there may be higher ratios available

It may be worth "Going Custom" as you will end up with impressive performance
I found out that I can swp the diff with a Ford 8.8 Diff. I can get the Gear Ratio of 5.71:1
Here is what I can get and I think this is gonna work better fine for me..


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