Flywheel weight?

[xb-60]

What weight flywheel should I use?

My car’s total weight should easily be under 1100kg (2400lb)
Gearbox is a Toploader (WR)
Differential ratio is 2.92:1 (my choice)
Engine is a Tickford 302W with 220kW / 300bhp and 435Nm / 320 ft lb
My question…. What weight flywheel should I be using?
A friend who knows his stuff is suggesting a standard weight (28lb) flywheel.
My engine man is suggesting a light weight flywheel, reason being that with the car’s light weight, I'll benefit from a lighter flywheel.
He says that with a light flywheel, the engine will rev “like a Japanese engine”.

Bearing in mind my choice of a high diff. ratio, should I go standard weight flywheel, or light weight? 22lb and 14lb are available.

Cheers!
Glen

[Snake2998]

With your diff ratio I would stay standard weight especially for road use with lots of stop starts where the lighter the flywheel the more clutch slip you will need to get moving. Light weight flywheels are only of real benefit for serious track racing

To quote Google:
Cons of Lightweight Flywheels

Reduced Off-the-Line Performance. If you want to maximize performance from a standing start, a lightweight flywheel might not move you in the right direction. ...
Rough Engine Feel. With a lightweight flywheel, the engine will feel rougher while running. ...
Gear Rattle.

[Snake2998]

Read this for more info:
Light flywheels: pros and cons – Infinite-Garage

[1795]

Glen,

The article that Snake2998 provided is pretty much straight to the point. With my lightweight flywheel I have to make sure that I rev match when downshifting. With my street cobra when I had it with a heavier flywheel you did not have to. If you have a 22 lb option, that might be a nice in-between option. A little lighter than the standard, so the engine will rev a little quicker, but not so light weight that the car behaves like a race car.

looking forward to seeing what you decide on.

Cheers,

Jim

[t walgamuth]

My VSE weighs right at 2000#. It has an aluminum block 5.7 chevy taken out to 427 CI. I am running the 19# flywheel from a 67 Nova. Yeah, it feels a bit lumpy but isn''t that what these cars are supposed to be....race car like?

[Dwight]

a 302 will rev very quick with a standard flywheel.

I think you will need the weight of the flywheel to move you smoothly down the road.

I vote standard flywheel

[t walgamuth]

...in a tractor!

[patrickt]

Aluminum flywheel, please. If you do a search, you will find a quote from one of the Kirkham brothers saying you'd be nuts to put anything in a Cobra other than an aluminum flywheel.

[Alfa02]

Ok Glen, My $.03 Race car: yes Alum. Flywheel, as Jim said we're at high rpm's, quick shifts, etc. Not having to worry about coming off the line (Stop light) Std. flywheel: you're not gaining anything. Lightened: quicker revs, less internal mass, no slipping of the clutch coming off the line. I went from stock (28lbs) to a lightened (22bs) in the V-8 RX-7, made a HUGH difference without any drivable issues. You know I hate to disagree with patrickt, but sometimes you take your chances Cheers TommyRot.

[Gaz64]

Glen,

I would say aluminium if you went for a 5 speed and lower diff gears.

So a 22lb would be still a nice compromise for street, and occasional track.

Depends on the engine internals, and the whole car in combination.

Gary

[Dominik]

If your approach is merely to save total (curb) weight, you may find that your car comes easily under 2.200 lbs (1.000 kg). I had a, to you guys unknown make (LDS), 427 with cast iron 302. It did weigh 1.015 kg. With a single seater racing screen, T5 box and ally differential.

My RAM (from UK) with an all-ally 496 Chevy and Jag suspension & brakes was 2.015 lbs (917 kg)

If you like to reduce rotational weight, which performance-wise counts for much more than total weight, perhaps also consider lighter wheels and tires. I had Hoosiers on the RAM.

Drive a 302 with an aluminium flywheel. I haven't yet.
Get a shatter-proof bellhousing - (which does weigh extra).

I am dying to weigh my latest 427 with leightweight body but cast iron heads on a 427 FE.
Just for reference.

[xb-60]

I'm thinking that the safe option for my application (it's not a race car) is probably a standard weight (28lb) flywheel.
A possible alternative is the 22lb version.

A 14lb steel flywheel or an even lighter version in aluminium sounds like it would be too much of a compromise for my application... even if the Kirkhams would say I'm nuts.

The light weight flywheels would allow quicker 'blipping' of the engine, but I can't see how - apart from a tiny percentage of weight saving relative to the weight of the car - this would result in significantly quicker on-the-road performance.

I'm not too old to learn, so tell me if my logic is wrong

Cheers!
Glen

[t walgamuth]

Heavy flywheels are for smoothness, like in a Cadillac or truck. Light flywheels will allow quicker acceleration and deceleration. Take your pick. I'll always go for the lightest flywheel I can find in a car planned for high performance.

[patrickt]

An engine with an aluminum flywheel slows down faster as well. In a Cobra, I think that makes it safer. I can't think of any reason to put a heavier flywheel in a Cobra unless all you do is march in a parade line. Now, blipping the throttle when the car is not in gear is fun, especially with a big ol' FE (which you don't have). The engine does not go vroom-vroom, it just goes boom. You can't even tell that it's speeding up, it just sounds like it explodes. 800RPM to 3000RPM instantly, without ever going through 1000, 2000, or 2500. It's the magic of aluminum.

[xb-60]

Originally Posted by t walgamuth

....Light flywheels will allow quicker acceleration and deceleration.....

This is the bit I don't get.
OK, very slightly less gross vehicle mass with a lighter flywheel, but engine power and gearing are unchanged ..... so how does a lighter flywheel allow quicker acceleration?
Quicker to blip the engine - yes; quicker acceleration of the vehicle? ....no

I need a more convincing argument.

Cheers!
Glen

[eschaider]

Originally Posted by xb-60

This is the bit I don't get.
OK, very slightly less gross vehicle mass with a lighter flywheel, but engine power and gearing are unchanged ..... so how does a lighter flywheel allow quicker acceleration?
Quicker to blip the engine - yes; quicker acceleration of the vehicle? ....no

I need a more convincing argument.

Cheers!
Glen

So the argument goes, Glen, a reduction in the angular moment of inertia results in less angular momentum to accelerate during WOT operation.

If you do the math the overall difference (including vehicle mass) is skinny but — maybe. If you take a car to the track and try to read it on a time slip it is below the margin or error in the timing system, which begs the question why are we doing this again?


Ed

[t walgamuth]

Originally Posted by xb-60

This is the bit I don't get.
OK, very slightly less gross vehicle mass with a lighter flywheel, but engine power and gearing are unchanged ..... so how does a lighter flywheel allow quicker acceleration?
Quicker to blip the engine - yes; quicker acceleration of the vehicle? ....no

I need a more convincing argument.

Cheers!
Glen

Science my friend. It takes longer to accelerate a heavier weight. And it takes longer to slow it down. Newton's third law I believe it is. Why would it accelerate an unloaded flywheel faster but not the car?

I've no way to test it and prove it to you but if you are a racer you always want to reduce weight even if it is not by much. I have won and lost autocrosses by one or two thousandths of a second. You might not be able to feel it but the clock will measure it.

On my race car my rule is never put a part back on the car until I seek a way to reduce it's weight.

[patrickt]

Glen, you must be having a mental block on this. A heavy flywheel acts just like the friction toys we had as kids. You know, you would "rev them up" by moving them along the ground rapidly, then place them on the ground and they would zoom away on their own. But, if you placed your friction toy race car at the top of the hill and let gravity take it down, it would lose to every other toy car that was not a friction car (and sometimes it wouldn't even go down the hill without being revved up first). That is the difference between a light flywheel and a heavy flyweel.

[1985 CCX]

Ok, I'll try

I do not dump the clutch as I am not a drag racer. With alloy flywheel it hesitates a touch once you begin to move unless on the gas hard. Inertia is not there however once you start to move it rips like a rocket. RPM's fast!
Its like a two stroke dirt bike, pulls like a freight train.

Example the ACMKIV car, steel flywheel, almost can catch momentum if you let the clutch out slow with no gas.
The MKII will stall unless you give it some fuel.

Once moving the MKII is like a rocket where the MKIV is like a regular car and also smoother.

Granted the MKII is set up different, best I can do to describe it.

[xb-60]

Originally Posted by t walgamuth

Science my friend. It takes longer to accelerate a heavier weight. And it takes longer to slow it down. Newton's third law I believe it is. Why would it accelerate an unloaded flywheel faster but not the car?

I've no way to test it and prove it to you but if you are a racer you always want to reduce weight even if it is not by much. I have won and lost autocrosses by one or two thousandths of a second. You might not be able to feel it but the clock will measure it.

On my race car my rule is never put a part back on the car until I seek a way to reduce it's weight.

It's Newton's 2nd law .... the acceleration of an object depends on the mass of the object and the amount of force applied.
In my case (not a race car) the relevant mass is the total mass of my car, not the flywheel in isolation, and the accelerative energy applied to the car comes from the engine.

Cheers!
Glen