[Vid]

Doing my due diligence on replacing my OE cast iron flywheel and hoping for some useful advice.

Research seems to indicate that the standard weight of a factory flywheel is 29lbs. Most aftermarket billet flywheels seem to weigh in closer to 33lbs.

Aluminum flywheels weigh around 17lbs. My understanding is that aluminum isn’t really a good choice for typical high performance street applications when you factor in vehicle weight and inertia

Should I try to stay closer to the OE weight or is few pounds heavier preferred? Maybe I’m splitting hairs?

‘69 LeMans post coupe (3650 lbs?)
455 (500 hp ballpark)
Muncie with 9” Ford rear, 3:60 gears.

Thanks!


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[25stevem]

It's a case of 6 of one or a half dozen of another if you ask me!

Since the flywheel is considered rotating mass a reduction in weight from a stock one will allow the motor to rev faster and in turn the car will accelerate faster.
The down side to this is that the motor also looses rpm faster with less mass in the flywheel.
Depending on the ratio of gearing in the trans, like if it's a wide ratio type it may be more beneficial to run a standard mass flywheel to slow the drop off of rpm and keep the motor in its power band better during shifts.

What's most important if your beating on the car and you are not running a scatter sheild is to have a steel, not a iron flywheel in there!

[HWYSTR455]

Tom is spot-on, totally agree, but let me add, definitely run an SFI one.

Most say when it shifts, the aluminum flywheels can have a slight bog as the next gear engages and will required tuning adjustments when switching from steel.


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[Don 79 TA]

I'm gonna say heavier wheel, and billet (SFI approved)..... but read on from my experience

i used a stock flywheel, hays billet, and hays aluminum
each has a pro/con if you will, and each has its own place

when i had the aluminum holly cow would it wind up fast, like uncontrolled, and all i would do is blaze the tires
i'm talking like driving on the street and hitting the gas (maybe a safe maneuver or whacking the throttle)
would be a little scary, but keep in mind i run a 5spd and 3:7 gear with 440 compound tires and a very tight LSA cam so no..... not ideal, but at time... OMFG FUN as heck, and at times SCARY as heck...
starting off maybe here and there needing to feather the clutch a little

with the billet wheel now, starting, idling, loaded take off (up steep incline) and downshifting i'd say better for typical street driving. and less blazing of the tires, meaning instead of feeling like i am sitting and spinning, they will spin but i feel i am also going too (if you get what i mean)

this all also comes down to personal preference too
i'll be honest i liked them all, but with my setup i feel the billet one gives me more safety confidence in the event i hit throttle to hard for a move

now.... i have NOT used any great performance tires like a slick or drag radial, so maybe that would have solved my one concern, and suspension is basically stock, so yes for drag strip use it would need serious work

BTW
they also have aluminum pressure plates too

all i can say is that the aluminum would spin the engine so much faster
when i changed to the billet and my first at speed downshift which i was used to with the aluminum, the tires barked and it felt like brakes were slammed on, the aluminum would just spin up and didn't feel the brake effect (probably clear as mud, but if you experienced what i did you'd understand), i never experienced the tires barking on a downshift with the aluminum

again, just my experience with my setup (just a fun friday night toy car)

do watch your shimming with the starter gears

[Skip Fix]

My 64 Impala 409 car I drove in high school had an aluminum flywheel(went on the 79 Camaro's SBC in the 80s when I autocross it). Drove to high school and threw my paper route with it daily. Not much bog , reved pretty quick and why I think the Muncie lasted since it was a low 12 second car in the 70s with cheater slicks. Lasted 5000 side steps Car weighed 3850 at the track.

[tom s]

I had a alu wheel in a 389 in my 62 GP,If I did not know I put it in I would not have been able to tell.JMHO,Tom

[Vid]

Wow, it’s great to hear from you guys that ran aluminum flywheels. I’m pretty sure I’ll be going billet steel, but your experiences with aluminum are very interesting.

From what I’ve read, aluminum works best in big motor, light chassis situations. My 455 is fairly big but GM “A” bodies aren’t particularly light, and my 3:60 gears aren’t particularly tall.

My concern is that if I go with a 33 pound or heavier wheel, the extra pounds might cause the motor longer than necessary to get the revs up. My last Pontiac (67 wagon with a 400 and an auto trans) always bugged me because I’d “blip” the throttle in neutral and it would respond rather**s l o w l y**. I don’t want to experience that again.


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[Sirrotica]

I've run Pontiac dirt track cars we ran with aluminum flywheels. They definitely had an advantage off the corner with the lighter mass.

A friend ran an almost identical 61 Catalina to the one we had, without an aluminum flywheel, and could never beat our car off the corners. He also had a 400, where we had a correct 389 in our car, so he had 11 more cubes on us too, and we could always come off the corners faster.

Even limited to a 7 inch tire, it still beat the other car.

[Tom Vaught]

I have run an aluminum flywheel for 50 years without issues.
First a WEBER piece then a Hays piece with the insert in both cases.
Not an all aluminum piece.

Thousands of power shifts with the flywheels. Scatter shield installed always.
Ran a 40 lb steel flywheel for a short while when Hays was making a new aluminum flywheel for me.
POS for my set-up.

Might be great for drag racing or pulling a boat but lousy in my application.

Not Drag Racing or Street Racing so no need to run a steel piece.

5 speed trans with 3.27 first gear really helps get the car moving from a stop driving
around town.

My car was a 64 A-Body convertible, not a light weight Nova, the aluminum flywheel will go on the 455 engine to be installed in the car at some point down the road.

Tom V.

[70GS455]

If you decide on an aluminum flywheel, make sure you have at least 10:1 SLR (starting line ratio) which is rear gear times first gear ratio

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[Tom Vaught]

I have posted here about removing the 4:33 gear housing and gears and installing a rear with 2.56 gears prior to making the round trip (800 miles). Most driving was highway in Canada on a trip, so not many starts from a dead stop.

I took it easy on the clutch/pressure plate and never had any issues. But not the gear for around town. That combination was a about a 6.5 "drive away from the light" ratio vs the number recommended in by 70GS455.

Tom V.

[jhein]

Originally Posted by Vid

Research seems to indicate that the standard weight of a factory flywheel is 29lbs. Most aftermarket billet flywheels seem to weigh in closer to 33lbs.
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Hayes, McLeod, and Summit all have billet SFI flywheels that are 30 pounds. Others can go up to 35 pounds.

This RAM is 29 pounds:

https://www.summitracing.com/parts/r...w/make/pontiac

[tom s]

I had 8.75 ratio in a 4000 lb 62GP and a 30 over 389 and never had a issue.Small street hyd FT cam with alu flywheel.First gear was and is 3.42.Tom

[Skip Fix]

Mine was a Hays with an insert. Made before SFI ('71)but back then they advertised all the good flywheels and clutches as "blowup proof"! Not sure if they would certify it now if I sent it in

[Vid]

Originally Posted by 70GS455

If you decide on an aluminum flywheel, make sure you have at least 10:1 SLR (starting line ratio) which is rear gear times first gear ratio

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So… 2.52 (1st gear) x 3.60 (ring & pinion) = 9.07. That would be a fail if I did the math correctly?


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[Tom Vaught]

Tons and Tons of GTOS out there FROM THE FACTORY with 3.55 gears and 2.52 1st gear trans.

Not sure about your 3.6 gear ratio as most are called a 3.55 ratio. 8.946 ratio.

So I personally do not agree with post #10 if you have a factory iron flywheel.
But there might be some merit to the statement with the aluminum flywheel.

Tom V.

[Vid]

Originally Posted by Tom Vaught

Not sure about your 3.6 gear ratio as most are called a 3.55 ratio. 8.946 ratio.

Tom V.

3:60 Gears are from Motive for 9” Ford. They also list 3:50’s and 3:70’s.


The 3:60’s are my compromise between the 3:23’s I should use and the 4:11’s I want to use, haha.


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[Tom Vaught]

Apologize, Did not realize that you had moved up to a 9" Ford Rear like I did
later in my life. 1986 time frame. The trips I took with the 2.56 Gear (GM 10 bolt)
were years earlier when I was in college 1970 time frame.

If I did not have a Nash 5 speed and was running a OD type trans the 3.6 gear would be perfect. Again, I ASSUMED. I Apologize,

Tom V.

[track73]

My 79 TA has an aluminum flywheel. I can't really tell much if any difference. Remember the crankshaft weighs 75 pounds.

[HWYSTR455]

Crank may be 75lbs, but you add the flywheel, PP, and disc, and that's a considerable moving mass. 10-15lbs difference is noticable to me when shifting.

In some cases, the diff in mass can also affect shifts. A lighter assembly back there can cause a faster slowdown of all the mass, trans input shaft included (disc drag), and impact synchro speeds.

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