Flywheel Mass vs. Acceleration

Simply put...The "Quicker" an engine revs, the quicker torque/horsepower is developed...Mark

You have to try the aluminum flywheel to understand but I am not a believer in them.

A stock Cleveland is probably marginal for one. Something like a 427, sure it will help.

I prefer to lighten the reciprocating assembly internally and use a steel flywheel.

As it turned out, the piston that was available for my 347 engine, a Keith Black, weighed 368 g and the pin 102 g, vs 528 and 160 g for the stock pin.

That right there gave the engine the same acceleration rate as the aluminum flywheel but the engine doesn't have the tendency of stalling when you try to engage the clutch in first gear like it will with an aluminum flywheel.

That and a 3.27 first gear and a 3.50 rear gear gives the accelleration of something like a 5.00:1 would in a Pantera.

The nose of the car really comes up on acceleration.



I feel you NEED the inertia of the steel flywheel. I'm sure others will disagree but I can never get accustomed to them.

"We" currently have an aluminum flywheel installed in a 3.0 liter supercharged Contour SVT and if you ask me, it sucks.

I have to slip the clutch like crazy to make it move without stalling it in first gear.



Another thought that I had is that removing the mass of the steel flywheel is removing virtually all of the engine vibration dampening on that end of the crankshaft.

The Cleveland LIKES the heavy dampening in particular. For some reason it produces a destructive harmonic over 6,000 rpm.

The only way I know to get that under control is with the external weights of the flywheel and the balancer.

It seems to be more important for the balance to have the added mass. I don't know why.

Just my opinion. I am not the expert on this or anything else for that matter.

Rocky, it takes power to spin up any mass. A lighter mass spins-up faster, that's all. Same as swinging a rope with a plastic cat-toy on the end, or substituting a full-sized car tire on the same rope. One will obviously spin up much faster than the other, and take less (arm) power doing it.

quote:

it takes power to spin up any mass. A lighter mass spins-up faster, that's all.

I certainly agree here.

But if you could get quicker acceleration just by lightening the flywheel, I would have guessed that Ford engineers would have specified flywheels lighter than they are now, only heavy enough to keep the motor from stalling.

I guess I am not taking into account any clutch slippage in my thinking process, as one factor.

Interesting, though.

Thanks -

Or the added manufacturing expense.

my $0.02, as a machine dynamics problem and not as an experanced automotive expert.

the benifits of less flyweight mass is the reduction in inertia so power can be applied to acceleration. the 20# less at the motor is where the least amount of excessive weight (inertia) has the most effect. the increase for acceleration in increased by the gear rations so the 20# reduction would be like a #200 reduction at the drive wheels (in 1st gear)

the negative with a light flywheel is in the transfer of engine power into kinetic energy and its storage. a light flywheel will require a very experanice driver to be able to release the clutch and apply throttle to transfer the little KE of the crank/pistons, where a heavy flywheel will deliver the stored KE as the cluth is released.

so if the car was manufactured with a light flywheel, the car would not be drivable to the public and clutches would become a warrenty nightmare as over throttle slipping would be required

the ability for the rpms to spin up quicker would also apply when the cluth is disengaged and they would fall off, thus requiring experance with the throttle to match rpms

If you really want to break your brain, read the section on flywheels at this link:
http://hpwizard.com/rotational-inertia.html#flywheel

quote:

...break your brain, read the section on flywheels

Actually, that's a pretty good explanation. It jibes with JFB's explanation.

Thanks -

Rocky

PS. I enjoyed his example on how to make a 10 second 1/4 mile car by spinning up a huge flywheel before your run.

quote:

Originally posted by JFB #05177:
my $0.02, as a machine dynamics problem and not as an experanced automotive expert.

the benifits of less flyweight mass is the reduction in inertia so power can be applied to acceleration. the 20# less at the motor is where the least amount of excessive weight (inertia) has the most effect. the increase for acceleration in increased by the gear rations so the 20# reduction would be like a #200 reduction at the drive wheels (in 1st gear)

the negative with a light flywheel is in the transfer of engine power into kinetic energy and its storage. a light flywheel will require a very experanice driver to be able to release the clutch and apply throttle to transfer the little KE of the crank/pistons, where a heavy flywheel will deliver the stored KE as the cluth is released.

so if the car was manufactured with a light flywheel, the car would not be drivable to the public and clutches would become a warrenty nightmare as over throttle slipping would be required

the ability for the rpms to spin up quicker would also apply when the cluth is disengaged and they would fall off, thus requiring experance with the throttle to match rpms

This is an EXCELLENT reply & covers the many various facets of an aluminum flywheel.

Especially the experience necessary to properly utilize/drive an engine equipped with an aluminum flywheel. I believe that "Twitchy" is an accurate descriptive term.

Since aluminum flywheels are normally associated with performance engine/s ie; HIGH lift camshafts, which require a certain amount of rpms/throttle to initially gain inertia, it comes a rather nuanced/difficult dance between launching the vehicle( Not stalling) & NOT burning up the clutch.

I purchased an aluminum flywheel in my never ending quest for the lightest reciprocating mass in my new engine build.

I believe I will quickly learn, MUCH to my consternation, that I don't like it!

Also I'm believing, being further educated more in the destructive nature of "Torsional Vibration", thus the purpose/application of LARGE vibration dampers such as those found on the highly coveted BOSS 302 & 351 engines.

For these reasons my "Lightened rotating mass" focus has shifted to just the engine's internals plus the harmonic damper rather than the weigh savings of the usage of an aluminum flywheel.

I might even consider building my engine using titanium wrist pins.

You want to be shocked/surprised...weigh your stock wrist pin...Mark

Titanium connecting rods. They are actually Corvette rods. Since you have to recut the crank, you put lightening holes in it also.

When I got mine back from the balancer it looked like swiss cheese so now the fear is was the crank weakened by removing too much metal?

This stuff never stops. A solution in one area creates a "concern" in another.

You need a Porsche 918. Then you can go rev the hell out of it and it loves it.

I seriously doubt you will be happy with the aluminum flywheel in the Pantera. The clutch with it is either all the way in or all the way out and why that is a problem is you need to rev the engine and slip the clutch.

You are going to look like a 14 year old who stole his fathers car and never drove a stick before.

Try that on a hill waiting for the light. You will have to hold the car with the hand brake so you can work the clutch and the throttle simultaneously. Of course if you had a PK transmission in the car that could be a solution?

quote:

Originally posted by PanteraDoug:
Titanium connecting rods. They are actually Corvette rods. Since you have to recut the crank, you put lightening holes in it also.

When I got mine back from the balancer it looked like swiss cheese so now the fear is was the crank weakened by removing too much metal?

This stuff never stops. A solution in one area creates a "concern" in another.

You need a Porsche 918. Then you can go rev the hell out of it and it loves it.

I seriously doubt you will be happy with the aluminum flywheel in the Pantera. The clutch with it is either all the way in or all the way out and why that is a problem is you need to rev the engine and slip the clutch.

You are going to look like a 14 year old who stole his fathers car and never drove a stick before.

Try that on a hill waiting for the light. You will have to hold the car with the hand brake so you can work the clutch and the throttle simultaneously. Of course if you had a PK transmission in the car that could be a solution?

Yes Doug in regards to the titanium connecting rods being Chevy, to be more specific the connecting rods are Corvette LS7 rods & weigh 466 grams vs 685-700 grams for a 351C connecting rod.

That is a weigh saving of 220+++ grams PER connecting rod.

For those not familiar with buying drugs, there are 28 grams in an ounce, for a saving of 1/2 POUND PER connecting rod or a total saving of OVER 4 lbs in 8 connecting rods!!!

Since "We" are car guys most will understand that I sometimes drive my Sports Cars in San Francisco, I PURPOSELY AVOID driving in the hillier sections of San Francisco.

At a stop light on a 45 degree hill with a Muni bus right up my exhaust pipe, a FIRED clutch can ruin a date real quick!

As far as a Porsche 918, I must admit Ford got it RIGHT with the new flat plane crankshaft engine!!!...SCREAMING to 8,000 RPMS!!!...Mark

http://articles.sae.org/13709/

quote:

For those not familiar with buying drugs, there are 28 grams in an ounce........

Funny!

FWIW, my Pantera has a 383 stroker Cleveland with a lightweight crank AND an aluminum flywheel. Driveability isn't as big an issue as some in this thread are making it out to be.

Mark - If you find yourself in the San Jose area, ping me and I'd be more than happy to let you drive my car. Then you'll have real data on the driveability with an aluminum flywheel to make the most informed decision.

quote:

Originally posted by garth66:
FWIW, my Pantera has a 383 stroker Cleveland with a lightweight crank AND an aluminum flywheel. Driveability isn't as big an issue as some in this thread are making it out to be.

Mark - If you find yourself in the San Jose area, ping me and I'd be more than happy to let you drive my car. Then you'll have real data on the driveability with an aluminum flywheel to make the most informed decision.

Agreed Garth. That's the ONLY way.

quote:

Originally posted by garth66:
FWIW, my Pantera has a 383 stroker Cleveland with a lightweight crank AND an aluminum flywheel. Driveability isn't as big an issue as some in this thread are making it out to be.

Mark - If you find yourself in the San Jose area, ping me and I'd be more than happy to let you drive my car. Then you'll have real data on the driveability with an aluminum flywheel to make the most informed decision.

Garth's generous offering of allowing myself the pleasure of experiencing the nuances of an aluminum flywheel are reminiscent of Adam & Eve & the "Evil Fruit".

Once I'm behind the wheel, I sure HOPE that Garth doesn't miss his mirror!!!...Mark


https://www.youtube.com/watch?v=AjGXn249Fc0

Mirror? Forget that. Get in sit down, then take your index finger, lick it and mark where 8000rpm is. That gets them everytime. He'll never let anyone drive it again. I'll mark it at 8500. .

Hahahahahaha... You'z guys crack me up!

I never laugh at 8,500 rpm. It requires heavy concentration.

Chuck I agree with your logic entirely. Here's some additional food for thought.

There's three types of acceleration: (1) from a rolling start, or (2) from a dead stop at low rpm (stop light street racing, road racing), or (3) from a dead stop at high rpm (drag racing).

From a rolling start its generally the entire the weight of the vehicle. The vehicle acts as one.

From a dead stop at low rpm the clutch is the dividing line. Everything on the flywheel side of the clutch must have a certain amount of mass in comparison to everything downstream of the clutch.

In drag racing everything is made as light as possible, and tire traction, clutch slip/torque converter slip are juggled.

Very Important: In all 3 applications the larger diameter a rotating part is, the higher importance is plays due to inertia.

The explosive acceleration of a 351C 4V and the traction of street tires are at odds, and must be considered. My 351C 4V powered Mach I Mustang had a factory flywheel (and Shelby traction bars) and could take a Ferrari Boxer or a Countach from a stop light (as I proved on several occasions back in Long Beach in the 1980s).

A heavy reciprocating assembly will allow for relaxed driving whereas a lightened assembly may require more attentiveness. For this consideration the lightened flywheel is on the wrong side of the clutch. Same goes for poor traction conditions (wet pavement, dirt roads, etc). In those situations you want to be able to crawl away from a stop at as low an rpm as possible without the engine trying to stall, to control wheel spin.

I like the Yella Terra steel flywheel. Its a bit lighter than the factory unit, but a helluva lot sturdier. The factory flywheel is iron. The Boss 351 had a nodular iron flywheel. The Yella Terra is steel. Get the drift? Steel doesn't work harden & crack like aluminum. Durability is important for street cars, sports cars, road racing, etc. If I were to lighten the drive train, it would be via lighter rear wheels, they seem to provide the most bang for the buck ... refer to my "very important" comment above. They are larger in diameter than any other rotating part of the power train, and there's two of them. They are also on the "good" side of the flywheel for crawling away from a stop in bad weather.

I have a pretty big engine, an aluminum flywheel and I would rather have a heavier flywheel for street driving.

quote:

I have a pretty big engine, an aluminum flywheel and I would rather have a heavier flywheel for street driving.

I think cam specs will play a big role in driveability, especially with a lighter flywheel.

I was initially disappointed with the driveability of my 383 stroker Cleveland engine with lightweight crank and aluminum flywheel and thought about going back to the stock flywheel. But after discussing my cam specs with several folks more knowledgable than me, I now believe it's largely a product of my cam's LSA.

Added my cam specs:
Duration @ .050: 226 int / 334 exh
Lift @ valve: .576" int / .586" exh
LSA: 110

My driveability disappointment/concerns were largely around low speed idling through a parking lot or down the street where it seemed "herky-jerky" and wanted to chug. Keeping it in a lower gear and keeping the revs up a bit more seems to overcome the issue, or I've just become accustomed with how I need to drive my car now after 3500 miles on the new engine.

I still plan to dyno tune it in the next month to improve response when slowly rolling into the throttle, especially below 3,000 rpm, while crusing down the road.

I am getting ready to dyno mine in the next couple weeks also. My cam is probably smaller than yours (The cam specs are 244/254 @.050" 588/614 valve lift 106/114 CL) but I know what you are talking about.

Just my $0.02. I've always thought that my high HP V8s revved pretty quickly. Until my then boss let me rev his Ferrari 599. Different world entirely

quote:

Originally posted by No Quarter:
Just my $0.02. I've always thought that my high HP V8s revved pretty quickly. Until my then boss let me rev his Ferrari 599. Different world entirely

However the 12 little cylinders don't produce the same amount of tq so it's kinda apples/oranges but the sound wicked.

My experience with aluminum flywheels is as follows.

They are to make the engine rev faster, which they do.
They need help at low rpms, i.e., 1000 rpm to about 1,700 rpm because they lack inertia at that rpm.

Camshafts with something like over a 236 @ .050 and overlaps of maybe 70 degrees and up, lack some punch below 2,000 rpm and maybe even 2,500 rpm.

In a vehicle with total weight (with driver) of over 3,000 pounds (like a Pantera) or so, the combination of the cam, low inertia flywheel and the vehicle weight makes the launching of the car a little touch and go.

There is no way you would want to drive that car in any kind of a bumper to bumper situation.

Even if you don't normally, even just the traffic coming out of something like a car show will give your clutch leg quite a challenge.

On the other hand that combination on the track at some kind of a high speed event will be one heck of a lot of fun and you will love it.

These are just my experiences and my opinions. I am not stating this as scientific fact, just what I have experienced.

They are in no way intended to contradict others.


The best recommendation anyone can give anyone else is to drive a car with the aluminum flywheel and a similar vehicle weight and cam timing and make your own determinations.
You might love it or hate it but until you actually test one, you will have little or no idea what anyone is talking about here.

quote:

Originally posted by PanteraDoug:
My experience with aluminum flywheels is as follows.

They are to make the engine rev faster, which they do.
They need help at low rpms, i.e., 1000 rpm to about 1,700 rpm because they lack inertia at that rpm.

Camshafts with something like over a 236 @ .050 and overlaps of maybe 70 degrees and up, lack some punch below 2,000 rpm and maybe even 2,500 rpm.

In a vehicle with total weight (with driver) of over 3,000 pounds (like a Pantera) or so, the combination of the cam, low inertia flywheel and the vehicle weight makes the launching of the car a little touch and go.

There is no way you would want to drive that car in any kind of a bumper to bumper situation.

Even if you don't normally, even just the traffic coming out of something like a car show will give your clutch leg quite a challenge.

On the other hand that combination on the track at some kind of a high speed event will be one heck of a lot of fun and you will love it.

These are just my experiences and my opinions. I am not stating this as scientific fact, just what I have experienced.

They are in no way intended to contradict others.


The best recommendation anyone can give anyone else is to drive a car with the aluminum flywheel and a similar vehicle weight and cam timing and make your own determinations.
You might love it or hate it but until you actually test one, you will have little or no idea what anyone is talking about here.

quote:

Originally posted by 8pack:

quote:

Originally posted by No Quarter:
Just my $0.02. I've always thought that my high HP V8s revved pretty quickly. Until my then boss let me rev his Ferrari 599. Different world entirely

However the 12 little cylinders don't produce the same amount of tq so it's kinda apples/oranges but the sound wicked.

YES!!...I concur about the Sweeeeeeeeeeeet Sound of a HIGH REVVING Ferrari flat 12.

Here's my "modified" flat 12 SCREAMING at 7,500RPMS!!! with a custom exhaust of my design & fabrication

Notice how Smooooooooooothly the engine returns to idle.


https://www.youtube.com/watch?v=gmUpLypFts0

My White Testarossa at 2:11 of the video leaving the dealership & at 2:25 doing a drive-by, notice the front-end LIFT under the torque of the flat 12 & subsequently my lighting QUICK!!! shift from 2-3...TURN it UP...Mark

Ferrari puts on GREAT EVENTS!...notice how Ferrari paid the local police force to have the street blocked off for us!

https://www.youtube.com/watch?v=_UQkr_x-Y9k

About 50 years ago I associated with Reath Automotive in Long Beach and had the opportunity to try a Schaefer Aluminum flywheel and clutch assembly for drag racing. At the time I had a 10” M&H and 4:56 gears. To compensate for the Aluminum flywheel I would sidestep the clutch at approximately 6,500 RPM vs 4,500. Trap speed slightly increased as elapsed time slightly decreased. I loved the snap sound the engine made with the aluminum flywheel, but repair, replacement of the aluminum flywheel became a problem and I went back to Hays.