gavinnz Posted March 4, 2006 Posted March 4, 2006 I am making a 1923 Fiat 501 enigne go better to get a more comforatable crusing speed...And one thing I am after info in is this question..What is the relationship (on a long stroke engine) to compression ratio and the amount of flywheel weight you need to have to make it run nice and idle?I figure a lot of flywheel weight was in the 1920's... their for low speed tracking in mud so in modern conditions it is only going to slow the gaining and droping of revs and add to the overall weight of the car.Am I missing the point of something major here???RegardsGavinNew Zealand1915 Fiat 52B1923 Fiat 501
Layden B Posted March 5, 2006 Posted March 5, 2006 My experience is that the larger flywheels on early cars is a function of the clutch! The idea was to let out the clutch with little slippage while the engine was above idle but not turning particularly fast. This allows minimum wear and chatter of the clutch, the mass of the heavy flywheel gets the car rolling without stalling the engine, and the low range torque of a long stroke motor is intended to accelerate up from there. Big trouble is todays drivers that want Jack Rabbitt starts and fast acceleration thus slipping and burning a clutch that was never intended to be used that way ( nor built with materials to survive it). An unintended consequence is however that a heavy flywheel is hard to stop! In the old days the speed was not great and drivers anticipated driving situations and slowed down much earlier. Today the heavy flywheel acting with about a 4 to 1 advantage ( the rear axle ratio) tries to drive the car on and the brakes get to do the work of stopping the flywheel as well as the car ( the job the engine used to do when you let off the gas). This all makes for a tradeoff between getting started and getting stopped.
Aanderson44 Posted March 6, 2006 Posted March 6, 2006 <div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I am making a 1923 Fiat 501 enigne go better to get a more comforatable crusing speed...And one thing I am after info in is this question..What is the relationship (on a long stroke engine) to compression ratio and the amount of flywheel weight you need to have to make it run nice and idle?I figure a lot of flywheel weight was in the 1920's... their for low speed tracking in mud so in modern conditions it is only going to slow the gaining and droping of revs and add to the overall weight of the car.Am I missing the point of something major here???RegardsGavinNew Zealand1915 Fiat 52B1923 Fiat 501 </div></div>The flywheel is there for one purpose, and one purpose only, beyond providing a friction surface for a clutch, and that is to ensure the engine stays running, and smoothly so at low rpm's. The higher the performance of the engine, the smaller and lighter the flywheel--for example, most 91-110cid Offenhauser Midget engines were run WITH no flywheel at all, which of course, gave a wicked windup upon acceleration, but we aren't talking Offies here.If your intention is to have a car that somehow manages to keep up with "modern" traffic (damn those kids and their "rice rockets", huh?), then lightening the flywheel is only part of the equation: Stronger, lighter connecting rods, and a stronger crankshaft would also be necessary. And, what about brakes? Wheels? Wood spoke wheels won't take nearly the abuse that modern wheels take, and those beautiful, old tall, skinny wire wheels? Fuggedaboudit as well!Why not keep that Fiat as it was built, restore it exactly, and enjoy it for what it was then, and can still be today?Just a few thoughts.Art
gavinnz Posted March 6, 2006 Author Posted March 6, 2006 Thanks guys! Some great food for thought their. I can really see what you mean by the getting off the mark with the momentum of the flywheel... I have a Motor Guzzi 500 single motorcycle with a huge outside flywheel and thinking about it does the same thing....I have two Fiat flywheels which is lucky as I can remove metal in stages and have the luxury of going back to the older one when I go to far with the first one!!I weighed the flywheel tonight and it was 25kg bare!! Thats 55 pounds!!!Which seem HUGE for a 1460cc four cyclinder engine? I think I could lose 10kg (22 pounds) and still have a resonable thing.... the open two seater sporting body I am building is MUCH lighter than an original sedan which will make the getaway easyer also.One advantage of the lower flywheel weight I would think would be less twisting stress on the crank... The Fiat was a multi plate clutch runing in air but with a mixture of oil and kero "washed" through it.RegardsGavin
Guest De Soto Frank Posted March 6, 2006 Posted March 6, 2006 The idea of a fly wheel comes from stationary engines of the 19th century, particularly steam engines, and helps provide enough momentum to carry the engine past "dead-center".It also helps "smooth -out" the power-impulses...The fewer the number of cylinders in a four-cycle internal combustion engine, the more important the flywheel is to smooth operation, especially at low rpms.I'd be careful about trying to make an old (pre-Depression) long-stroke engine try to spin too fast... especially if you've got poured (babbit) bearings and splash lubrication... lightening a flywheel can improve acceleration; the model-T Ford guys used to do by replacing the trembler-coil ignition with a distributor and "battery ignition", and they'd remove the magnets from the fly wheel, to lighten it, and in place of the magnets install "fins" to pick-up oil from the flywheel housing and dump it in the "funnel" that fed the cam and mains... or they'd rig an oil=pump and relieve the flywheel of all lubricating duties...Might be worth some research to see what Fiat did with some of their racing engines of the same period as your car...Good luck !
gavinnz Posted March 6, 2006 Author Posted March 6, 2006 I here what you are saying about not going to high revs...I am aiming for no more than 3000 rpm max and crusing rpm of 2500/2600 which is what Fiat got out of the road going 503 engine of 1926. (standard 501 like mine were 2500 max, 2000 crusing).So I think it will... with attention to detail and some slight upgrading cope ok with that. Add to that the extra light weight of the body and it should be quite a lively little car! I have the 503 cylinder head already so thats "heading" in the right direction!.Gavin
Guest De Soto Frank Posted March 7, 2006 Posted March 7, 2006 Also bear in mind how much "brake" you have to get you stopped...
gavinnz Posted March 7, 2006 Author Posted March 7, 2006 Yup I am working on that one too... the last of the 501 Fiats built had front brakes and I am onto a front axle from one of those. Standard it has two sets of brake shoes in the back.. one set foot and one set hand operated. I am also thinking about moving the gas tank from the scuttle to the rear of the car to get more weight over the rear wheels to improve braking and balance... as it has a two seater only body... with the spare wheel at the back also...Great forum this!! I am enjoying myself and getting some really good info.. thanks guys!!RegardsGavin
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