Talk Morgan Forums Morgan Sports Cars Morgan Plus Four, Supersport & Plus Six (CX & CXV Generation Vehicles) OBD tuning Plus Four

Hi Guys


Has anybody have any experience with this? The B46 is what I can find easily tunable to 310bhp and 500nm of torque. If they use the stock BMW box this should be ok too. I have no idea if the diff can handle this kind of power.

Isn't the B46 the super low emission version of the B48 to satisfy tighter emission regs in some US states, and not the B48 version used in the Plus Four?

Hi Richard


My mistake it is indeed the B48 engine.

No problem PiGo. Not sure if this has been discussed but MMC usually use a custom version of fimware in engine suppliers PCM (ECU) and then have production versions locked down as supplied by MBE. If this is not the case then tuning would seemingly be very easy.

Regarding transmission chain, still a little suspicious why the manual Plus Four has engine mapping that significantly reduces torque compared with auto version.

The Auto/Engine combination is mapped to let the auto climb up to the highest gear at lowest revs as fast as possible to reduce fuel consumption/emissions. As they control the combined map of the two this is practical however when you put the MkI human in path there is a pattern that tends to hold lower gears and avoid labouring the engine?

Any changes to the map will be visible to engineers who inspect it which will bin your warranty. It has been a common issue on turbo engines for a long time now.
Also don't forget that whilst they appear to be the same engine with different bhp there is often a different piston/turbo/boost control valve for the higher powered ones which is not so visible?

Don't take that as "I think people who adjust boost etc are evil" quite the opposite. I find the economy minded engine map on most modern cars a royal PITA. It makes the throttle feel like a dead cat. You then have to hit the sport button to enjoy yourself again. Thems the rules, thems the results. It is totally possible I might have done some of my cars in the past.

Oh, don't forget your insurance. If there is an RTA they WILL inspect it.

I recall something said along the lines that the clutch and gearbox cant take the full torque of the engine, whereas the autobox can. I may be wrong, but it stuck in my mind.
Going back to Alistair's comment, modern turbo petrol engines have so much low end torque that the ca be "laboured". The AMG 63 4L V8, in comfort mode, rarely gets above 2000 rpm, yet it is happy to rev to 6500. As they say "The torque curve is synonymous with good drivability: the maximum value of 650 newton metre (480 ft lbs) is on hand in a wide range from 1,750 to 4,750 revolutions. So, like a diesel, it doesn't need to rev, although it can.

I ysed to love engines that reved sweetly. and that had to be kept "on the boil", but those days are gone...

Those days still exist in this house.

Sounds like an advert for a 1.6 Sigma engined 4/4.

Yes I read the same Peter but the explanation seemed a little too convenient. Why would BMW offer a manual gearbox that had so little torque handling in reserve that a reduction was required from the engine, especially in such a light car. Surely they had a manual box in their arsenal that could cope with that engines torque and more.

Reminds me of a Cobra replica I was building many years ago. I queried whether the supplied ZF gearbox could cope with the torque from the Ford 350 cu in. V8. The answer was it should be fine as the light car would break traction before the engines full torque was transmitted through the box.

I think it has more to do with emissions and making the auto car far better & thus the car of choice.

Sorry John but I find it difficult to accept that argument. Why would MMC offer a manual version to satisfy demand at a lower price than the auto? If they really wanted to steer us towards the auto there would be a premium for the manual version.

Since the auto has manual override that will probably be regularly used by many in this sports car application, I don't see the emissions argument either.