Lighter Flywheel - Good or Bad?

L

Larry Brumfield

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I don't advise people on the exact best weight to remove from flywheels but this is how I see heavier vs. lighter:

To increase the engine RPM and accelerate the car, all rotating weight as well as the entire car must speed up. This requires power ..... and the heavier the parts the more power needed.

The less power needed to speed up a lighter flywheel the more power available to speed up everything else (clutch, driveshaft, wheels, tires, etc.).

On the other hand, what's wrong with a heavy flywheel? ..... The heavier the flywheel the smoother the idle, the easier it is to move the car from a dead stop and any slight throttle changes are smoother..... BUT, the slower the acceleration.

Because once that heavy flywheel energy is used up the engine has to provide more power to keep the extra weight spinning and the extra weight as compared to a lighter flywheel becomes an opposing force.

So how about a lighter flywheel? ......

No good some of you may say! ... because the lighter the flywheel the harder it is to get the car moving from a dead stop and a slightly higher RPM is needed before the clutch is let out to make it happen. So if you drive long enough it might wear the clutch out faster!

Also, the entire car might jerk a little with throttle changes while cruising and the idle might be a little rougher .... Who likes that?

So I guess one could say that it's a trade off ...... BUT .. the lighter flywheel is still necessary for the fastest acceleration once the car is in motion because it allows the engine to rev faster, which gets power to the wheels faster, and so the faster you go.


Larry B.
 
Good point. The heavier flywheel would tend to push the car forward.

Also, the energy of a heavier flywheel, once in motion, was considered a plus for moving the Model A and other old cars of the day through soft dirt, etc.. while in lower gear at slow speed.


Larry B.
 
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i had 20# taken off mine when balancing . works fine for me ........... steve
 
You can take a LOT of weight out of the flywheel and still have a very good driving Model A. Actually, it will feel a little more "Alive" and still Idle just fine. If you have a countered weighted Crank, I would definately lighten it. Just be sure to have it balanced AFTER you do any machining.

I believe Les Andrews gets into this in one of his books.

Chris
 
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Hi Larry, I think the issue of stored momentum in a flywheel weight difference of 20 pounds is overrated. Considering the weight of the car that that 20 lbs is affecting, I see very little effect of stored energy. However, the effect on engine performance can be considerable. My own feeling is that a non-slinged crankshaft needs the damping effect of the heavier flywheel. However, once slings have been added to the crankshaft and the damping effect has been located just under each of the four cylinders, the need for an oversized rotating weight at the end of the crankshaft is greatly reduced.
Some fellows have stated that the lighter flywheel causes loss of speed up hills. I've heard this any number of times. However, on my own roadster with a 40+ lb flywheel and the Burlington crank I have noticed no difference in climbing hills. HOWEVER, I HAVE NOTICED A HEIGHTENED SENSITIVITY TO IGNITION TIMING WHEN CLIMBING A HILL IN THIRD GEAR. The advance lever needs to be set just right for each climb!
Interesting topic...
 
CWPASADENA said:
You can take a LOT of weight out of the flywheel and still have a very good driving Model A. Actually, it will feel a little more "Alive" and still Idle just fine. If you have a countered weighted Crank, I would definately lighten it. Just be sure to have it balanced AFTER you do any machining. I believe Les Andrews gets into this in one of his books. Chris
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Never had much confidence in LESS Andrews.

My discussion applies to ALL engines, not just Model A's.

In addition, many people will oppose your view on idling just fine, i.e., the lever up tucka-pucka count the fan blade bunch.


Larry B.
 
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Larry one thing not considered in this discussion is the longer life of the rear main by not having to carry the weight of a stock flywheel
 
My 327 Chevy II has an 11 lb. aluminum flywheel that will shake your teeth out at idle, but when you hit the throttle...hang on! I like my Model A flywheel the way Henry made it; seems to work just fine for me. Several members of our club like the lightened flywheels, some with Model B clutches. I don't see either as good or bad - just preference. $0.02.
 
Larry Brumfield said:
Never had much confidence in LESS Andrews.

My discussion applies to ALL engines, not just Model A's.

In addition, many people will oppose your view on idling just fine.


Larry B.
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Sense this is a Model A Foreum, I was addressing my remarks in that direction.

I have lightened Flywheels in my Model As and am very happy with them.

I guess it gets to be a matter of opinion. ;)

Chris
 
ford1 said:
Larry one thing not considered in this discussion is the longer life of the rear main by not having to carry the weight of a stock flywheel
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I've thought of the rear main and the stock flywheel many times while accidently running over a jarring deep pothole in the road.

Larry B.
 
I have a B C/balanced crank, so 30# was removed. With the Lion Speed Head all I can say is WOW. Iceman
 
Larry, ford 1 has a good point that has been brought up many times. Someone mentioned the pot-hole jarring effect which brings up another aspect. I have seen stationary drilling rig engines and mud pumps that are of considerable size and weight that have been dropped due to moving equipment failure that have had to be shopped to check the cranks and bearings. I don`t know that it was necesary but was done as a precaution. Big bucks and down time! Food for thought. Monte
 
When Ford went to the counterbalanced crankshaft, the additional weight of the crankshaft was removed from the flywheel; the old way to lighten an A was to get the B flywheel. Also the old push to start overhead A speedsters used a 10 lb. aluminum racing flywheel (no ring gear). I'ts amaizing how a 40 lb. flywheel will wakeup a stock A engine.
 
I dont see much point of a light flywheel in a stock model A. Presumably, the driver drives it in a stock manner, but although it is fun to count the firing impulses at ultra low RPM that does not do much for oil splash and cam lube. A lighter wheel is not going to hurt, unless you are crawling in first over ruts in dirt roads as my pal Jerry and I did back before we had a license to drive on black top, but is not going to help things much either. I think that with a counterbalanced shaft, the wheel should probably be lightened because otherwise the weight of the entire assembly goes up too much. I had counterweights swedged on by Dan Price, (the "BB" style) and a 28 lb flywheel, and only saved about 20 lbs total, but it runs much smoother which is the real value. I understand in the day the dirt track guys used a light stock crank and light wheel specifically to get the quick accelleration.
 
I Have A's with Both Lightened and Standard flywheels.. I notice the lightened one seems to have a bit better get up and go in traffic, but the heavy flywheel seems to do better for hills.. Maybe it's just that between the 2 vehiclesIi am comparing apples to oranges, but the heavy flywheel does seem to have more torque getting onto a trailer or climbing a hill.
- Dave in Boise
 
PC/SR said:
I dont see much point of a light flywheel in a stock model A. Presumably, the driver drives it in a stock manner, but although it is fun to count the firing impulses at ultra low RPM that does not do much for oil splash and cam lube. A lighter wheel is not going to hurt, unless you are crawling in first over ruts in dirt roads as my pal Jerry and I did back before we had a license to drive on black top, but is not going to help things much either. I think that with a counterbalanced shaft, the wheel should probably be lightened because otherwise the weight of the entire assembly goes up too much. I had counterweights swedged on by Dan Price, (the "BB" style) and a 28 lb flywheel, and only saved about 20 lbs total, but it runs much smoother which is the real value. I understand in the day the dirt track guys used a light stock crank and light wheel specifically to get the quick accelleration.
Click to expand...


The ultra slow idle starves the cylinder walls for oil and for that reason it's not a good thing to do for very long. But in the last 35 years that I have been involved in Model A's I've seen people compare and judge their engines by the idle. Moreover, many will deliberately idle them slow, not necessarily for the tucka-pucka sound, but for easy shifting into first gear without a scratch (and they don't realize or care to fix or adjust the real problem).

Now whether they know what they are doing or not, if the engine won't idle slow and smooth they think something is wrong and many of them would automatically reject a lighter flywheel if the idle changed because of it.


Larry B.
 
Big, heavy flywheels used to be thought of as necessary. Have a look at the steam engines and early gas engines. The flywheel weights were measured in tons, not lbs.
As engines evolved from "undersquare" (Longer stroke than bore Dia) to "Oversquare" ( Larger bore than stroke length) It was found that flywheel weights could be lightened. It takes a lot of energy to rotate that mass. Energy that could be going to the wheels Furthermore, Road conditions improved. And the already mentioned weight on the rear main bearing. Myself, I would have to go with lightening the flywheel. Plenty of advantages, no disadvantages!
Terry
 
I have a 38# flywheel. Idle is not bad. It is very smooth. Probably won't idle below 300-400 but I don't see any significant advantage to that.
 
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