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MG MGA - Lighten the flywheel or not?

My Twin Cam engine is ready to go back together and i thought of following Barney's flywheel topic before reassenbly. I have had two knowledgeable people tell me to not bother as, although it will help the engine rev quicker, it will lose torque due to the light weight. Opinions?
Colin Manley

It doesn't lose engine torque, but it does lose inertia, which is exactly what allows the engine to rev up quicker. When the engine can rev up quicker it gives better acceleration, especially in the lower gears. It is almost the same as having extra power, because the engine can use its available power to accellerate the car rather than acccellerating the flywheel.

On the flip side, when reved to high speed the flywheel stores energy by way of inertia, so a lighter flywneel will store less energy. A certain amount of stored energy is good for giving the engine a smooth idle and for getting off the line from a dead stop when you let the clutch up. With a very light flywneel you can go from vroom-vroom at a stand still to "aws***, I killed it" pretty quick. That can make a super light flywheel very hard to drive on the street.

A heavy flywheel can also allow you to rev it up and spin the tires momentarily when starting from a dead stop with an otherwise low torque engine. Combined with a strong enough clutch it may also allow you to lay rubber momentarily when doing a swift upshift to 2nd or even 3rd gear after high revving. These effects of a heavy flywheel are all very impressive, but do not add much to competitive performance.

The "standard" MGA has a rather heavy flywheel, around 28 pounds, which is sort of overkill and makes the car seem more docile than it needs to be. The late production MGA MK-II used a lighter flywheel, about 20 pounds, which does give the car a more lively feel and slightly better accelleration in the lower gears. This must have been recognized to be a good thing, as the lighter flywheel was subsequeltly carried over into MGB production. I have the early MGB flywheel in my MGA, and I like it. You can find machining instructions to convert the early flywheel to later dimensions here: http://mgaguru.com/mgtech/clutch/ft_202.htm

If you had in mind to go a little farther you might lighten the flywneel a bit more to be a little friskier. Racing flywheels can be very light (like 8 to 10 pounds), given due consideration to the driving style. For street use I wouldn't recommend going below about 16 pounds, as it would become difficult to drive in city traffic.
Barney Gaylord

Thanks Barney, that's helped me decide to do it after all.
regards
Colin
Colin Manley

I use the lighter early B flywheel which was lightened further, on the street. Happy with it.
Steve
Steve Meline

Has anyone checked the weight of an A pressure plate vs a B plate? My A plate seemed very heavy but I have nothing to compare with.Could it be that the combo of B flywheel and plate you lose more than 8lbs? Gary
gary starr

I am running a MGB 5main motor with the stock 1600 transmission and 1600 back plate.

The MGA 1600 flywheel would not bolt on to the crank so I purchased a New MGA Ring Gear and had the 5 main flywheel O/D trim down to the MGA ring gear inside diameter.
This has lightened the flywheel by just less than half of the stock MGA. The only downfall is there is no land on the back face of the gear and ensuring straightness was a bit tricky.

I have'nt run this yet and am fully expecting the whole thing to explode once I hit 8500 rpm with my first missed shift.

I did'nt do this for performance, This was done as a way to make the combination of parts work.

Am I screwed?

Chris
Chris Hausbeck

I highly recommend a moderate lightening - it transforms even a standard 1500. It does make the clutch rather sharper, so don't go mad.
dominic clancy

I run the early 3-main flywheel on my later MGB, lightened to 15 lbs. I think the negative side-effects of using a lightened flywheel are all a bit exaggerated. They may be true for an 11 lb. aluminum flywheel, but not a 16 lb. lightened stock unit! The performance increase is something we all should have. A lighter flywheel means bettr fuel mileage AND acceleration?
Jeff Schlemmer

From 1964-1967 the MGB had the first 5-main engine mated to the 3-syncro gearbox. Use the flywheel from this model to install the 5-main engine in the MGA.
Barney Gaylord

This thread was discussed between 04/09/2006 and 06/09/2006

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