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MG MGB GT V8 Factory Originals Technical - rotary engine conversion

i have a 1968 mgb rd and i want to put in a 13b fuel injected rotary engine out of a 2nd gen rx7. what steps would be involved in doing this? what would i have to change? and about how much money and time will it take?

thanks everyone

Scot Hamm

An easy question to ask but not to answer!

The rotary engine is a lot lighter than the B motor so new springs and shocks to start.
Probably a new gearbox (use the RX 7?)and definitely a new tailshaft / driveshaft and possibly a new diff of a suitable ratio.
New radiator (again RX 7? if it will fit) maybe and some new electrics to match the Mazda side to the 12 V Positive to earth wiring of the B.

After that it is really how far do you want to go?
New interior , brakes , external cosmetics etc.

How much depends on: 1) how professional the end result is intended to be and b) how much you want to have done by someone else.

No idea of where you stand on the legal side of things and what if any certification and permits are required there so I cannot comment on that part.

One point is you are probably treading new ground so you will need to blaze the trail rather than follow a well documented path of Rover V8, Ford V8 etc.

Good luck, Cheers, Pete.
Peter Thomas

There was a rotary conversion MGB in attendance at
MG 92 in Peterborough, Ontario, Canada (1992). It was blue. I have no clue who the owner was. Perhaps, if someone from that region reads this post, they can comment. It did have a definite HUM.....

rick ingram

Are you planning on doing the work yourself, if so figure the cost to be the price of a complete salvage RX7 and then multiply by three. You might run over or under, but this is a pretty good guess for your project budget. I recommend finding a complete car for the donor as it will definitely save you time and money in the long run. There are photos of a midget with a rotary on the MG Engine Conversions web page which might be of help. Don't forget that you're dealing with a computer controlled engine, so if there are not pre-computer distributors and intake systems availabel to fit, then you'll have to integrate the computer into the system and make provisions for all the input sensors and emissions devices.
Bill Young

yeah i plan on doing all the work myself. on the midgets did they have to put in the computer system? what would i get the driveshaft out of? im buying an rx7 that is in running condition for $600-$1000 that way i know the engine doesnt overheat or anything. the radiator,trans and rims will fit. my rims are shot and definatly in need of replacing. so i figure getting a running car is well worth it to start.


The rotary-engined midget:


Alexander M

The blue B may have been the same one I saw at Bronte a few years ago. The problem with the rotary is that it is quite wide at the front lower end: it all wants to fit in the front where the frame narrows and the steering and crossmember all come together. The car in question had a compromised front crossmember that the owner had been trying to re-inforce for more structural integrity.

The Midget does not narrow at the front of the frame rails and hence does not need much work in the engine bay. As a personal aside, the rotary conversions never "look: the part in a brit car. They just go like hell and sound neat!


The above Midget and another as well as a few others can be found at
Marc Judson

I saw a '69 B roadster with a rotary at the Bellvue field meet last year. The car looked perfectly stock on the outside, except the shifter was a little different. There was an acre of room all around the motor. The guy didn't really get into too many particulars about how it was done; he might have bought it like that, but he said it went fast and he liked the sound of it. Joe
Joe Ullman

Only thing wrong with a rotary is when the apex seals finally wear out they are EXPENSIVE to repair. Usually have to replace most of the engine.

Good luck!

G.P. Copes

I bought an 82 RX7, 5 speed, 12A engine, to put in my 73 Roadster about 5 years ago. When I trial fitted it, I started with the complete engine/trans and took everything off the engine that got in the way to put it down in the engine compartment. What I found was that the exhaust ports were pointing directly at the RH frame rail and were too close for me to believe anything would fit. This was with the engine sitting straight up - perhaps I could have turned it to clear. Not being willing to cut up the car for that, the four cylinder went back in, and now my B is dreaming of four cylinders on each side.

Wayne Pearson

That is not an exhaust note you is a call....a call to come over to the Dark Side!

Cheers, Pete
Peter Thomas

has anyone ever even trial fitted a 13B engine? i want to put in the 13B that way i can at least say im putting a B engine back in. that and i hear they have more HP

Scot Hamm

i just realized something. the fuel injected 13 b requires a computer system to regulate the spray and the fuel pressure. is it hard to transfer the computer? is it wired throughout the whole car? can i just hook up the wireing for the fuel injectors and pump or does it all have to be hooked up?

thanks everyone


Peter, more like a scream. I saw a midget with one at an autocross years ago and it hurt your head to hear it run. 'Course it didn't have mufflers...

Jim Blackwood

I have seen a rotary, not sure what version, but pretty sure it was car'b, in a MGB GT, saw no fitment issues at all, thing was TINY!!
Larry Embrey

Transfering the ECU and whatever other computer needed bits is fairly straightforward.
You may want to check the wiring and see if the codes are in English or Japanese.
I am not being funny. Having an ECU multi pin labeled in Japanese when you do not read or write the language is a real frustration and it wouldn't be the first time it has happened!
Cheers, Pete.
Peter Thomas

This thread was discussed between 04/08/2003 and 12/08/2003

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