Moss Motors, Ltd

Hello all:  I plan to have the flywheel lightened from my 1275 '71 midget.  Can anyone tell me what the ideal weight/percentage should be when it comes to lightening the flywheel for fast highway use?  Any other recommendations, suggestions or advice is also welcomed.  Thanks to all who reply.

mgmotoring,

The amount you remove is not so easily determined. It depends on what you are trying to achieve. For the retention of a reasonable idle, I would not advise taking more than 25% off the total. Where you remove it can be just as important. The further out toward the edge the weight is removed, the greater will be the effect. The only thing you gain is response. No horsepower or top speed gains will result from this modification. 

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Thanks motorbill66 for the informative response.  Based upon your response I have to ask you if this is something you would suggest doing.  Do you think its better to leave as is to avoid possibility of causing other problems.  Thanks again for the insight.

mgm,

If you have access to a machinist who will perform this operation at a reasonable price, go for it. He may have a hard time finding enough "meat" to remove to achieve a full 25% weight reduction. That's OK. What he SHOULD NOT DO is remove metal where the ring gear seats, or anywhere else he thinks will in any way weaken the part. If I were building a street performance Midget, I would consider a weight reduction for the flywheel, but I'd keep it modest. 20% is plenty. Enjoy.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Thanks yet again for great advice.  The machinist plans to reface the flywheel as well.  Any problems with doing that?

Nope.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

mgmotoring:

Hello all:  I plan to have the flywheel lightened from my 1275 '71 midget.  Can anyone tell me what the ideal weight/percentage should be when it comes to lightening the flywheel for fast highway use?  Any other recommendations, suggestions or advice is also welcomed.  Thanks to all who reply.

Just my 2 cents here, but, I notice you say that it's for "fast highway use." IIRC, the idea of using a lighter flywheel is to increase the flywheel's response to changes in engine acceleration, not as an improvement of any kind for mostly steady-state speed. That is, with less mass to accelerate, you can get the revs up quicker going through the gears, as you would if you were coming out of a corner, etc. Also, I've read that using a lighter flywheel has something of an impact on driving style, as not only does the flywheel respond quicker to acceleration, but also to deceleration. So the revs drop quicker and lower when you let off the throttle during gearshifts, so the interplay between throttle, clutch, and gearshift will be different. And more revs are required taking off from a standstill, as the flywheel doesn't carry the extra mass to help get the vehicle going, so the clutch suffers a bit more wear.

Anyone know more about this?

Goodwood,

If you'll check my response to the poster's initial question, you'll see that I pointed this out to him, warning him that response would be better but that power would not increase. The fact is, having lightened a lot of flywheels over time, I can tell you that reducing the weight by 20% will not introduce any truly adverse drivability problems or premature clutch wear. Most all earlier British flywheels were WAY too heavy in the first place. The driver has MUCH more influence over clutch wear than the weight of the flywheel.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

anyone know how much lighter a alum flywheel is compared to stock? ok for street?

Tony-

On my Lotus with a 1565 cc twin-cam motor the aluminum flywheel is 10 lbs. lighter than stock. I doubt it is much bigger than one on a Sprite so this should be in the ball park for weight difference.

 

LCJUTILA 

yeah its a lot lighter, what was the effect on engine? I have  one and want to make sure it will not make the car no fun around town,although I defently want the pull of the corners when trying to keep up my friends in there bigger cars!

Tony-

I had a 67 Sprite as my first car back in the stone age. It was very easy to drive off from a standstill and the clutch was nicely progressive. I think you will be very pleased with an aluminum flywheel in yours. The first couple of take-offs from standstill may be a little tricky but you will quickly get used to it. The only negative may be a less smooth idle, as the cast iron flywheel does smooth out the motor pulses more. If the car goes significantly out of tune it may not hold an idle. You will really feel the difference in second gear as the weight saving in the flywheel is multiplied by the gear box and differential ratio.

As an aside, it was mentioned in an earlier post that lightening the fly-wheel does not increase horsepower or torque. It in fact does.

 

LCJUTILA 

anyone else have experience with a alum flywheel in a 1275? I had a few people tell me I will hate it in a street car! way to light, bad idle and hard getting going and up hill, uneven cruzing on fwy?