Lightened flywheel.

big2bird

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John, Darrow, and I are debating the pros and cons of installing the GM Perf flywheel #3963537 on his '72 BBC.
Any real life stories about someone who has done this?
Pros and cons?
 
FYI, that's the same as 14085720 Mark IV internally balanced 15lbs nodular iron 153teeth 12-3/4" diameter 10,4" clutch diameter L88 flywheel jsut for ext. balanced (454) engines.
The flywheel stores energy as kinetic energy, the heavier the flywheel the harder the engine will pull when you let off the clucth. A lighter flywheel will allow the engine to rev faster. It will also rev down faster!
With a heavier flywheel it's easier to pull up from a traffic light without the engine lugging and it'll be smoother.

Question is, what does he want?? Just a nice cruiser with a lot of stop & go driving, low rpm? The heavier one may well be the best choice then.
 
Question

Tt The Real Question Is What Is Best For Low End Tork.

I Thought That The Lighter Flywheel Was For High End.
And The Stock Weight Was Good For Low End.
 
Tt The Real Question Is What Is Best For Low End Tork.

I Thought That The Lighter Flywheel Was For High End.
And The Stock Weight Was Good For Low End.


Maybe, you are confusing low end torque with the ability to launch a vehicle.

Heavy Flywheels will launch better, lighter will rev quicker.:beer:
 
I've got that flywheel on my '69 427 and my '84 turbo 355. The first couple of stoplights were interesting (killed the engine a couple times), but once I got used to it, I don't even notice it anymore. I do notice it when autocrossing or running on the track. The revs (up or down) happen faster, and the motor is a bit more responsive.
As the guy noted: What is the intended use of the car in question?
 
Its a street car mostely original 72 very good condition

But the question is will the origional fly wheel have more torq at low end then the light weight replacement? Or launch a vehicle better.
 
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My car is just a cruiser for me. It is not really fast but is a real stump puller. It is a little car with a huge motor which is really the fun part of it. It was rated at 270 HP new and dyno'ed at "Birdfest 1" at 264 HP so I think that is pretty fresh for 36 years old. It is not really fast enough to want to race or anything like that. You could do a burnout though as long as you want, serously until the tires melted. I stumbled on this car that is 95% original with 58,000 miles on it and so I feel like I should honor that the car has stayed this preserved this long and so I'm not going to start changing stuff too much. I am sure that any of you would do the same with this car if you had it. I just enjoy driving it to work and back everyday cause it is me and where I come from.

I tell you though, pretty soon I'm going to get a "project" car that deserves nothing but a bunch of chrome and all the HP stuff I can afford. The 502 looks good!

John
 
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I've got that light flywheel- I can say from experience- it's something of a PITA until you get used to it. Hard to get the car rolling. 2 choices- work the clutch or light the tires. With the 4.11's. I don't really notice the loss of low end torque. I'll tell you more about that later- I've got a 3.08 rear I'm going to put in to play with. We'll see how the light 'wheel does with those gears.
You saw how quick the RPM came up both on the dyno and on the road. :D

I've been playing with numbers too. The 4.11's top speed should be around 126 MPH. 3.08 should be kissin close to 170 MPH both at 7000 RPM. I don't think that's really right either- without admitting anything, the speedo was really close to 3 digits in 3rd a couple of times- and still pulling hard.
 
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True answer

Then if you have a stock flywheel you should be able to burn a lot more rubber on take off then a alum one?

Just need an answer to this question.


for birds sake
 
Then if you have a stock flywheel you should be able to burn a lot more rubber on take off then a alum one?

Just need an answer to this question.


for birds sake

Dumping the clutch from a stop, the heavier flywheel will break the tires loose easier.
Once the clutch is out and you're moving, a lighter flywheel will let you break the tires loose again easier, if that's what you want.
Remember, the flywheel just stores energy, it doesn't create it. A heavy flywheel decreases the likelihood of the engine bogging down at launch, but it also decreases the ability of the engine to rev up afterward. There's no free lunch here.
 
Thanks for the input. Some stuff I'd sure never thought of. I'm going to just have it resurfaced. Much cheaper and I like how the car drives now anyway.
 
My car is just a cruiser for me. It is not really fast but is a real stump puller. It is a little car with a huge motor which is really the fun part of it. It was rated at 270 HP new and dyno'ed at "Birdfest 1" at 264 HP so I think that is pretty fresh for 36 years old. It is not really fast enough to want to race or anything like that. You could do a burnout though as long as you want, serously until the tires melted. I stumbled on this car that is 95% original with 58,000 miles on it and so I feel like I should honor that the car has stayed this preserved this long and so I'm not going to start changing stuff too much. I am sure that any of you would do the same with this car if you had it. I just enjoy driving it to work and back everyday cause it is me and where I come from.

I tell you though, pretty soon I'm going to get a "project" car that deserves nothing but a bunch of chrome and all the HP stuff I can afford. The 502 looks good!

John

Yep - it would be hard to tear into that car -- it is in such incredible shape. :drink:

Project car Hmmm - don't be teasing now.
 
SOme projects are never complete. I keep thinking about building a 540- or a 632.

How many cubic inches can I get from a standard deck big block? :fishing:
I keep looking at Reher-Morrison's all aluminum 747 cube monster, but it's a tall deck :suicide:.
 
SOme projects are never complete. I keep thinking about building a 540- or a 632.

How many cubic inches can I get from a standard deck big block? :fishing:
I keep looking at Reher-Morrison's all aluminum 747 cube monster, but it's a tall deck :suicide:.


With out getting into major problems, 496 is concidered a good jump up. I have a 454 block and that's what I WOULD do IF I go BB for Jiggles.:bounce:


Now if you go GM crate -- then 502 is the most popular.:quote:

All short decks can go bigger but these are combo's that would be simple and safe.:beer:
 
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SOme projects are never complete. I keep thinking about building a 540- or a 632.

How many cubic inches can I get from a standard deck big block? :fishing:
I keep looking at Reher-Morrison's all aluminum 747 cube monster, but it's a tall deck :suicide:.

632 can be done, if you for example use 2.1" rod journals, these will allow even more stroke by offsetting. That's about as big as fits in a short deck.
 
I bet the bearing speed on a 2.1 journal with that much stroke would be off into big numbers..YYEEEEOOOOWWWW!

I suspect that if I ever do anything it'll be a 540. No hurry, I still have to squeeze some more out of what I have now. When I get to the end of that (or at least what's comfortable) THEN I'll look at the 540.
 
I bet the bearing speed on a 2.1 journal with that much stroke would be off into big numbers..YYEEEEOOOOWWWW!

I suspect that if I ever do anything it'll be a 540. No hurry, I still have to squeeze some more out of what I have now. When I get to the end of that (or at least what's comfortable) THEN I'll look at the 540.

Just gota have those big numbers?:amazed:
In some cases "size matters", that would be one of two.:bounce:
 
I bet the bearing speed on a 2.1 journal with that much stroke would be off into big numbers..YYEEEEOOOOWWWW!

I suspect that if I ever do anything it'll be a 540. No hurry, I still have to squeeze some more out of what I have now. When I get to the end of that (or at least what's comfortable) THEN I'll look at the 540.

Actually the radial speed is lower with a smaller journal. Same reason why cup cars use the 1.888 honda journal. Think about it, @ x RPM the bearing spins the journal x times per minute. For a larger diameter journal this means a larger circumference, and thus a higher radial speed required to cover larger circumference in same amount of time (revs)
The only major drawback is reduced journal overlap.
 
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