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MG MGB GT V8 Factory Originals Technical - 675hp 3rotor conversion

i have a 68 mgb roadster with no engine in it and a mazda 20b 3rotor engine jus sitting around in running condition due to a wreck i got into with my converted 1995 3rd gen 3rotor conversion. the engine was dynoed at 675 hp and looks like it could fit with just a few modifications. has anyone ever put that much power behind a MGB before? has anyoned ever done this exact conversion? potential what type of speed and modifications would have to be done to make my MG SAFETY FAST? and if not exactly safe then what would need to be done to get the most out of it

I have not seen a B with that much power but a few years back I did SEE a MGB with a rotary in it.. Talk about lots of room to work!!! Unfortunatley the owner was not the convertor and had little info to offer..

I am guessing by your power number she was a TT set-up.. You should still have plenty of room, but may need/want to make custom header/manifold to better place the turbo's in the B's engine bay...

Defintely keep us posted, I would love to have pictures and info on my website about it..
Larry Embrey

Check out the link below. It's a midget with the smaller 13B engine. Grassroots Motorsports magazine featured an early B roadster with the 13B rotary in it about 2 years ago. It looked like it was an easy conversion other than some firewall mods.
If you could overcome the turbo plumbing problems, the
20B would be an impressive piece. Getting the power to the ground would be another issue!
Phil O

I would put a 2x4 under the gas pedal. You take your moder cars vipers, corvetts, porshe, none of these have that kind of power from the factory. You will need to put an after market front end in and some independent suspention in the rear. You could also some how fit the body to a custom frame but since the mg dosen't have a frame this would be harder. Or just atatch a bungie cord to the cas pedal so when you pass out from fright from goinging 400 mph it will automaticly let the pedal come back to the top. All kidding aside you don't have to use all the power but you sure could do some nice burnouts. Remember no matter what you do your car is still 37 years old. Denny
dbw morris

375 hp is impresive, but not amazing.
The rotary engine does not have the torque of a push rod engine, the rotary would have to be wound up high in the revs to produce any decent torque #'s.
The output shaft in the rotary is high and does represent a problem when doing a swap.
I did a Bug Eye with an early rotor engine,exhaust is critical. I would suggest to stay with the V6/V8 swap or another 4 cylinder engine.
Bill Guzman

Bill its 675 hp not 375 u still think it will have the torque problem? as far as the aftermarket front end i wouldnt be able to afford it (i dont think anyway about what would that cost?) but if i decided to leave it stock like it is w the exception of the engine obviously and with the tube shock conversion for the rear that i have alredy converted(Moss Motors kit) what would or could happen?

Chuiming in again, JUST DO IT!! I got the same line of why bother when I started my SBF conversion back in 2000. Now everyone wants to do them. If I had another choice for more of a "road racer" type car it would be the rotary..
Larry Embrey

I agree too, just do it. Sure the driveline angle may be an issue, but you can weld right? So if the crossmember is in the way just weld in appropriate reinforcements for what you have to cut out and carry on. As for the power, your biggest issue will be getting it to the ground. That much power has the potential to fry the tires at any speed. So pay attention to your air management and try to generate some downforce.

Jim Blackwood

Yeah you will be LUCKY to get half that power to the ground in all honesty, but it will be darn fun trying!! My meager 195RWHP can tear the stock tires loose fairly well, can;t wait till I get over 300!!!
Larry Embrey

The best way to experience anyhting , is by doing it.
Have a good plan and work the plan. Not a problem with the chassis in the MGB with a rotary engine.
HP numbers are just that numbers.
A few years back an MGB with a rotary engine was feature in Grassroots magazine, I think it was in 01 or 02.
Larry, the small block Ford swap into an MGB was done in the early seventies in North Hollywood in Ca. several B's were done. That B was also feature in a magazine, I think it was Hot Rod. I think the shop was Hollywood Motors, the owner of that shop is the same person who build "Old Yeller" He did several swaps. One of his swaps was a Ferrari with a small block Chevy and a muncie four speed. I also saw a B that was done by Moody in one of my trips to Orlando Florida, it had a top loader 4 speed and it had the Moody 289 around 350 hp and about the same in torque. It had the Weber down draft carbs. The car was a very well done.
The B had Halibrands wheels of the knock of type. It was for sale at the time (1981)at a high end dealership.
I truly believe that the Ford was put in a B before the Buick/rover V8
Bill Guzman

I know they were done Bill, but back then people were still "BOP/Rover or bust" in terms of what they knew or accepted in the MG community. I have a scanned copy of that ford article heh pretty interesting install. After I had my car done, I found a local guy that has had a 302 in his B since the late 90's, not a MG guy at all, just a guy with a motor and a chassis heh. Now he just built a GT with a 383 stroker!!

When I started the only widely known example was Dale's car and I followed his layout fairly closely. He probably still remembers the endless emails asking him, what where, how....

I think we all can agree, build it and the grins will come...
Larry Embrey

Joe, considering that 3 rotor is a turbo engine, my recommendation if you do this conversion is to at least initially set the boost at zero. Then after you've gotten used to the power gradually increase it. A turbo engine is *not* a good candidate for use in an MGB because of turbo induced loss of control. You may have experienced this phenomenon, how did you say the donor was wrecked? A blower would be a much better option.

Jim Blackwood

i was doing 140 at 2 in the morning in the rain on the way to vegas and lost control spun around off the freeway and rolled the car quite a few times luckly enough i had no serious injerys thank god for 5 point harness seatbelts

"I truly believe that the Ford was put in a B before the Buick/rover V8"


Not sure I agree, but it would make for an interesting argument. In fact, documenting the history of American engines in British cars would make a great book.
Carl Floyd

"I truly believe that the Ford was put in a B before the Buick/rover V8"

I don't know about the "B" but I do know for a fact that a Ford V8 was put into a "T" series MG well before the BOP/Rover.

It was a flathead, but a Ford nevertheless. In the early 50s, a relatively unknown driver named Phil Hill ran a TC with a transplanted Ford flathead, and stomped the competition. If I'm not mistaken, Phil went on to some degree of success as a driver (an understatement if there ever was one), but the car has been pretty much forgotten.

The Ford engine, in 261ci capacity, was introduced in 1961. The BOP engine was introduced in 1962. I'd say it would be pretty hard to determine which engine went in first, as records for this sort of thing aren't kept.

The SB Chevy was introduced in 1955, and I think it's a pretty safe bet that this engine beat both the Ford and the BOP as the first MGB transplant.

I wish I hadn't written this. I can remember when the SB Chevy was introduced, and looking back on it, I sure feel like an old timer now. Dang!
Dan Masters

As another old-timer, I don't recall Phil Hill racing a TC with a Ford flathead. Of course I am probably wrong due to being an old-timer.

If I were a betting man, I'd suggest the SB Chevy was the first transplant into a TD, and less confident regarding the B.

Edd Weninger


Looks like Carroll Shelby had his fair share too with a Ford Flathead V8 powered MG TC


Pete Mantell


The SB Chevy didn't come out until '55, so Phil's flathead TC beat it by a few years. As for a TD, who knows?

If you're interested in the early days of sports car racing in the US, pick up a copy of "American Sports Car Racing In The 1950s" by MT Lynch, W Edgar, and R Parravano, ISBN 0-7603-0367-3. When you get it, don't have anything else planned for the rest of the day, as you won't be able to put it down.

For the rest who might not want to buy the book, check it out at your local book store, and turn to page 55 for a picture of the car with Phil driving at Torrey Pines in December, 1951.

Check the rebodied MG on the same page and on page 98.

Check the 148HP supercharged TC on page 50.

Or the Mercury powered Kurtis on page 98.

Oh, hell, buy the book, you'll be glad you did. It's been a couple of years since I read it, but I'm going to go read it again.
Dan Masters


Shelby's in there too. Stuffing big motors into little cars is not new. Get a copy, you'll thank me for it.
Dan Masters


Looks like this book retails at $264.71 from Amazon !!!

Pete Mantell

WHAT!?!?!?!?!? WOW!

I guess I'd better go lock my copy up in a vault!

I can guarantee I didn't pay anywhere near that for mine. Wow!

I guess that just goes to show how good the book really is if it has appreciated that much. I only paid $39.95 for it new in 1998.
Dan Masters


I did the usual book shopping bots and was starting to think that it was out of print. Then I believe I hit the jackpot. Get yerself a personalized, autographed copy. You can thank me in Terre Haute. :)
Carl Floyd

Thanks, Carl, you just did me out of $224.76! :)

Seriously, though, I'm glad it's still available for those interested, because it realy is a good book on the subject.
Dan Masters

Great !
Thanks Carl.
I will give them a call.

PJ Mantell

Thanks Dan,

I'll get a copy. Anything similar about the early 60's ? I was helping a friend wrench an AH3000 then when we had much racing around SoCal at Palm Springs, Santa Barbara and such. Never won anything, Hollywood Sports Cars had the hot set-up then and we didn't have near as much money. Fun anyway. Glory Days I guess.
Edd Weninger

Joe, you should have plenty of room considering the past E-Mod solo II champ has a N/A 3 rotor in a bugeye. The major areas of concern will be the rear suspension, rear axle, and brakes and cooling. You could easliy retrofit a domestic solid axle rear, add some lower links to control spring wind up and a panhard bar.

You will definalty want better brakes to slow you down from the much higher speeds you will attain. You will want vented rotors to help with cooling. Also consider 4 wheel disks.

Cooling may be tuff since the B has a small area for the radiator. I'd fit the largest radiator you can find since the rotory does make some heat. I found a VW radiator works well with a NA 13B motor.

I would add a roll bar with some extra bracing to stiffen the chassis a bit around the front leaf spring and panhard bar mount.

The fact that the ecentric shaft exits higher up in the motor is not a problem in my Midget conversion and I do not se it being a problem in a MGB.

I wish you luck with your project. I want to do a Turbo II transplant into my 70 BGT sometime.

Here is a link to some newer pics of the RX-Midget:
Brian Kraus 1

Oh Bill, torque will not be a problem. The 3 rotor motor came froma heavy luxury car and it pushed it around without any problems.

Pettit racings 3 rotor specs as follows:

2 Sequential Turbochargers
2.0 Liters
550 HP @ 7500 RPM
460 Lb-Ft @ 5500 RPM

It pushes a 2735 lb car to an 11.4 second 1/4 mile at over 126 mph.

I think that is more than enough torque.
Brian Kraus 1

wow, if you do this i really really really have to see it. i always wanted to put a rotary into an mgb. but i changed my mind not so long ago to the ford 302. but a rotary has always been in my heart.

This thread was discussed between 20/03/2005 and 26/03/2005

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