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Al. Flywheel

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M

MCS

Jedi Warrior
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Have a look at the eBay link; they claim a 10 to 30 horse improvement. Is that real, if you are out there Hap, could you please add your thoughts on that claim.
Just to recap my engine it is 1363cc, swift tune cam, Hap ported and built head and just about every performance option I could buy, 6 grand in total... That’s the very short list
Cheers Phil



item # 120325290504


https://cgi.ebay.ca/FIDANZA-ALUMINU...39:1|66:2|65:12|240:1318&_trksid=p3286.c0.m14
 
No way, what a lighter flywheel does is make the engine rev. faster. Does not change HP.
 
Correct Jack!
But reving faster makes it feel like more HP.
HP is a factor of Torque x Speed of the engine.
Under dynamic conditions (when the engine is changing speed) if the engine doesn't have to accelerate the flywheel, but only the load (car) the car will accelerate faster! In physics, HP (or kW) is only half the story.
 
Correct me if I'm wrong, but if the engine is already a little "cammy" and hard to keep a decent idle then a lightweight flywheel will make that idle more troublesome.
 
Thanks for the posts. Vizard says that the eng will rev faster and a lighter flywheel will take load off the crank, that is all I can find in his book. I have searched for more info but no luck so far.
Phil
 
The purpose of a flywheel is to store kinetic energy and maintain the revolving inertia of the engine. The key here is maintain the revolving inertia. Assuming two flywheels are the same shape, the one that is lighter will store less energy and thus maintain the revolving inertia less. This goes for increasing RPMS as well as decreasing. We need to flywheel to help the car idle and get the car rolling when starting up from a dead stop. Once the car is moving the flywheel is less important since it will slow the increase in speed (the engine needs to get the flywheel rotating, more work). Think of it as accelerating you car with and without a passenger. Your car doesn't have anymore horsepower but it accelerates better without a passenger.

If you do a lot of city driving an aluminum flywheel may be a bit of a pain, it you like a crisp throttle response it might be just your ticket.
 
Hello Chris,
thanks for the post, I do spend about 40% of my driving in the city. I saw a post somewhere on how to lighten the stock flywheel, maybe that would be the best for me. I am pulling the engine soon as I have a Datsun 210 trans a rivergate kit enroute so now is the time to tinker.
Thanks Phil
 
This is a comparison of one I lightened.
 

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Hi Chris,
Good pictures, I see it is just the outer edge that is machined. How much weight did you remove? Do you think I would need to rebalance my crank etc. if I go this route.
Thanks Phil
 
So... Chris. How much weight did it remove? Did you slot it too?
 
I don't remember the weights off hand but it was several pounds. I'll try to get some weight later. The reason the outside was machined is that it has the most impact; the moment of inertia is a function of mass times radius squared. If we get the radius down it has a squared effect on the moment of inertia. Removing 1 pound form the outside 1/2" of the flywheel has a lot more impact than removing 1 pound over the entire surface by skimming. After the lightening is done the flywheel needs to be rebalanced.

Trevor - I didn't slot anything, just removed the outer lip between the ring gear and pressure plate. I'm sure there is more material to be removed but at that point I just went aluminum. Something about that thing rotating at 7000 rpm next to my legs made me stop lightening.
 
I think that the increased hp is due to the way the roller or rolling road dynomometers work. Unlike a traditional crankshaft dyno or water brake type, these machines rely on accelerating a heavy steel roller and then extrapolating the hp from the torque value determined by the rate at which the engine speeds up the roller. The faster you accelerate the roller, the more torque and thus the more hp. A lighter rotating assembly will spool up quicker thus indicating greater hp.

The traditional type of engine or crankshaft dyno uses a brake or drag producing device to put resistance against the engine. The force needed to overcome that resistance is measured by moving a lever arm against a known weight. In a modern version a water brake provides the resistance and electronic load cells measure the force. These are steady state systems where the engine is held at a given rpm against the load during the measurement. In the Dynojet type dyno runs are just a matter of flooring the throttle and running up to redline, if one held the engine at a given rpm the indicated hp would rise during acceleration and then drop once the roller/drum reached the target speed.

As Jack said earlier, the flywheel does not make power although it does contribute to a tiny amount of parasitic drag, but that is not really what you feel when you swap to a lighter flywheel. BTW the same effect is seen when "wedging" a crank as per Vizards book, just like an alloy flywheel it lightens the mass of the rotating assembly and the engine becomes snappier and you think you have lots more torque and thus hp.
 
I am sold, guess I better add that to the Christmas list.
Thank you for the input, it has all been very helpful.
Phil
 
I have mine lightened similar to Chris_s, it is only champered on the back edge, with a little taken off the front (engine side).

Incidently it has a 276 cam in it, and a lightened rods.

I think I am weighing in at around 14 lbs and stock is about 18 or 20, if memory serves me.

P
 
As I recall from Vizard and another Spridgeteer's recommendation, taking 4 lbs off a 1275 flywheel improves acceleration from idle without excessive effect on the idle performance. I had my machinist take 4 lbs off the flywheels I use on the turbo Sprite and the 1275 I'm putting in the Morris truck. Neither is terribly "cammy" by design, since I only street drive my cars, but I have no problematic lumpiness at idle and both perform very well.

So, about 4lbs is not a problem unless you run a lot of cam.

Glen Byrns
 
I spoke with Hap today.
He likes the Fidanza Aluminum Flywheel it weighs in at 7lbs. He has never had a problem with a light flywheel on a street car.
Cheers Phil
 
I suppose with all this talk about the difference between steady state HP and rolling road dyno implied HP, one could wonder what the "real" world difference is. After all, HP is an indication of how fast the car accelerates, and therefore a rolling road dyno should give a better indication of the real world.
Thoughts?
 
There is no increase in HP only an increase in how fast the engine revs.
 
I run the fidanza and I saw an instant notice. The biggest feel was on the street when you take your foot off the gas while still in gear the car has much less lag. (Less motor braking) and the motor spools up faster from midrange up.

No problems with the idle.
 
I am convinced it will be a noticeable improvement for my 1363cc eng. going to order a Fidanza on Monday. It will fit great with the 210 transmission installation. At 7lbs I can hide it on the bookshelf; my wife will never suspect it is another sprite part.
Phil
 
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