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MG MGB GT V8 Factory Originals Technical - MGB Mazda RX8 conversion

About 18 m0nths ago I decided I wanted to put a rotary engine into my long-owned and much modified 67 MGB. After more research I decided the naturally aspirated EFI fueled standard power (192 hp) was the one to use. It is now installed and operational. Fly by wire, EFI, OBDII port all working. addressing overheating issues now. Have lots of pics of pieces and progress should anyone be interested.

JR Daugherty

Also I used the original Mazda RX8 ECU and Fuse/Relay box.
JR Daugherty

Looks good, what does it go like?
Allan Reeling

Alan,
Can't give you stats yet but she is very very quick, inaugural test run topped at 93 mph on public freeway. Was not pushing it. Still have some tuning issues to resolve, but overall she is a joy to drive. The mazda 5 speed is sweet, clutch activated by MG Clutch master to Mazda Clutch Slave.

Tuning issues at this point revolve around whether the inlet diameter modification I made to correct airflow (it did) reading is actually helping performance, and whether the high pressure fuel pump has enough capacity at full throttle.

Waiting for new radiator as we head into summer here!
JR Daugherty

JR,
My normally aspirated 3.9 V8 (220 bhp) runs quite happily on a standard SU pump. Their volume delivery is somewhere above 1 imp pint a minute.
Don't exactly know the capacity of your rotary, but it's probably no more than mine. If your HP pump can deliver that quantity at the right pressure I shouldn't think you would have a starvation problem.
Allan Reeling

The EFI requires 60psi at the fuel rail. Rotaries do tend to be thirsty esp when running in the 5 to 9k range. But if there is a problem it should show up in the OBDII problem reports. I just haven't checked it since right after I replaced the pump a week ago. Thank for the input!
JR Daugherty

JR
Mate, just be a little carefull relying on the OBD to notify you of low fuel pressure
Usually the only code that will come up will be------ O2 sensor showing lean, - and it usually takes a while running lean for the ECU to log this code
You run the risk of melting the cat or seal damage
Much better off checking fuel pressure - under load
cheers
willy

Does your system have a fuel return to the tank
If yes you can measure to see if fuel pressure is up to spec, and if it is - disconnect the return line and with the engine running measure how much fuel comes out the return
For an engine like that you would need at least300ml/10secs I would think
William Revit

Also
I have found (more than once) that if the engine you are using sat around for a bit with no fuel in it and it is a fuel return type system
The pressure regulator on the rail dries out and depending on how grotty it is ,when you start it up the reg can stick, the result of which is fairly normal fuel pressure depending on which position it stuck in, but as you feed the throttle in the regulator doesn't move and the faster you go the less fuel pressure you get The only way to test for this is a fuel pressure gaude in the HP line and up the road or on the rollers and check that pressure doesn't drop off against throttle movement ----
willy
William Revit

Much difficulty with the fuel system that to the point I could get half to one mile from home before the fuel pressure dropped to the point the engine would not work. this after almost a thousand miles of running well but lean. Long, very long story short, despite dropping fuel tank, and cleaning it, with no change in results, I converted the fuel tank drain into a new outlet ford the fuel system and my problems were resolved. Fly baby!

JR Daugherty

William, thank you for your helpful comments. I did in fact have a fuel pressure gauge installed on the pressure regulator so I could see the pressure fall off. I could also look into the fuel fill spout to see if the fuel was returning to the tank, which of course it stopped doing when the pressure dropped below the set psi level.

JR Daugherty

Interesting
I'm thinking it could have been a fuel supply problem in as much as---- Some efi pumps, although good high pressure supply pumps aren't very good suckers and by getting your supply from the bottom of the tank the pump is getting a better flowing supply
If it's fixed all good- but the Mazda pump would have been an in tank pump originally
If you still have trouble, like fuel surge when the fuel tank level is getting down a bit, maybee a lift pump into a swirl pot in the boot would be a good move
Or better still get the tank out and modify it for an in tank pump system
cheers
willy
William Revit

Ho there, I'd be really interested in hearing the details of your engine swap as I am considering the same swap.

Please could you provide some more information if you have the time?

Did you need to modify the shell much? What were those modifications?

How did you solve your fuel issues?

Did the gearbox fit well in to the transmission tunnel?

Thanks!
t rowley

This thread was discussed between 24/03/2015 and 13/04/2016

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