11" vs 10.5" Flywheel Differences
 

Did a search on the forum and didn't see a clear answer to my question below regarding 2.75" register 65 and up flywheels:

Are all 11" flywheels heavier than 10.5"?

I bought an 11" flywheel at Norwalk last weekend (2.75" register, 166teeth). I see no identifying numbers on it but it has the same basic dimensions as a known 10.5" flywheel I have from my Mom's 69 GTO. Both fit on the end of my 65 crank (register/pilot and hole pattern).

The 11" flywheel is about 8lb heavier than the 10.5" according to an old bathroom scale.

Debating whether I want to use it on a 421 build I am about to start. I guess I didn't realize how heavy the 11" flywheels were.

I may just go with a billet steel flywheel that has both bolt patterns since I have a nearly new 10.5" RAM clutch in my car now. I could always put an 11" clutch in later.

Do you have a 11" disc and pressure plate to go with that flywheel??

Personally instead of going to the factory 11" cast iron flywheel, I would stay with the 10.5" RAM clutch parts
and put those parts on a SFI Billet flywheel that has both clutch bolt patterns (making sure it was SFI approved).

If you drive like a old lady and never beat on the engine/trans then either would work
BUT if you beat on the flywheel parts then go SFI approved flywheel with a Scatter-shield.

Are you launching the car where you really need that extra weight flywheel to get out of the chute??

Tom V.

Have owned a dozen & a half 11" cast iron flywheels. Original 11" Pontiac flywheels had the drilled & tapped holes further outward than on the 10.5" flywheels, yes they weigh more than the common '65-75 10.5" version. Have also had dual bolt pattern cast iron flywheels that accept both sizes of clutches. No date code cast into them, so I assume some 70's-80's aftermarket offering. In the mix, numerous '77-79 w72 11" flywheels, these only had the 11" pattern drilled & tapped.

Thanks OPH.

Tom V.

I thought they all had a four digit casting date code?
IIRC it's often hard to find and read...

Yes to SFI rated flywheels, don't skimp on this, or you may be using a crutch or prosthetic later.

It makes sense to use an SFI aftermarket due to the dual bolt pattern, increases you choices for clutches.

.

Thanks everyone! Tom, I drag race the car occasionally so I am running it pretty hard but I only ever race on street radials. I don't plan on running slicks anytime soon. With this next engine build I wanted to have a flywheel so I can get everything balanced. Also do not want to rip the car apart and have it down while I work on this engine build. Since the next engine is a 421 I just figured I would go with an 11" setup. But, the weight of the flywheel (this 11" has only the 11" bolt pattern) and the thought that my RAM clutch is nearly new is leading me the way you recommend. I ordered a new SFI flywheel with both patterns. That way I can run my current clutch and go with an 11" later if I ever need to replace it.

Daubert20, The worse Flywheel/Clutch/Trans explosion I have personally seen was a
first gen Camaro with a cast iron flywheel and aluminum bellhousing explode at US-131
Dragway in Martin, Michigan back in the mid 1970s.

It took out the whole right side of the car. Fortunately for the driver.

Have posted on this several times over the years.
Lakewood put that front plate and those fasteners around the Clutch Parts for a reason.

Are you running some brand of scatter shield currently??

Tom V.

One of my street racing friends in the 70s had a 65 GTO with a 455 on it. One day at the back of the parking lot at his work he side stepped it-street tires- grenaded the flywheel clutch. looked like on Uzi got the firewall and hood! messed his foot up a little. Later years he raced dirt spring cars!

made me go buy a good flywheel,clutch and scatter shield for my car!

The heavier flywheel would be an advantage on the street, with the additional inertia it provides to get the car moving. That said, I would not run it on the strip. Since you race the car, you made the right call not using it.

Thanks everyone! I haven't been running any kind of scattershield so it is time to step up the safety.

Thanks again.

Good job on that decision.

Tom V.

Dont trust the cast iron flywheels either. When it gets past the putt a round cruiser streetcar level, prefer a new a new steel flywheel in the build. Have a new 11" McLeod steel flywheel for one of the '71's. Another build has an old steel Weber 10 1/2". That's it, at one time, I'd considered buying a SFI bellhousing for my T-37 PureStock build, & may run one in my '72 T/A, but for the level of power & dedicated use of most of my cars. original bellhousings should be fine.

Scored an Aluminum Pontiac Flywheel in the early 90s. Nice. Buuut remained so TH400 minded that i sold the flywheel to a dad/son enthusiast from central PA.

Boy were they thrilled to buy it.

If i was Dry-clutch minded, the Aluminum Flywheel would be the choice.

I had never heard of it till it happened to me;
Then I started digging, and it seems to be a more common occurance than you might think.

https://forums.maxperformanceinc.com...1&d=1660881718

Aluminum flywheels are supposed to be regularly inspected so that this doesn't happen while your driving... like it did with me.

That there is the safest way to fail. buuut avoidable! I do remember my AL Flywheel was cut from the bolt circle like a Steel flywheel, and a sharp transition to the thick zone.

Definitely a poor design:Drawing to Machine work. AL needs flexure factured in. Like a Wheel Rim.

So who made that aluminum flywheel and did YOU buy it new?? Brand??? How Old???

I have never seen a Aluminum flywheel that bolted the friction surface to the aluminum wheel. UNTIL NOW


Tom V.

Aluminum flywheels belong on small block Chevy's being driven on dirt tracks. Totally useless on a Pontiac engine driven on the street, IMO. Kind of like having a 5,000 stall converter and street driving the car. Nonsense, IMO.

Yes, I bought it new;
I have understood that all aluminum flywheels have a bolted on steel friction surface.

Many early aluminum flywheels inserts were rivited on the steel to the aluminum wheel. NOT BOLTED.

The Chinese crap today may be different but the Weber flywheel and the Mcload flywheel I owned years ago and still have were not bolted.

Basically The flywheel typically does two things. It gives a lever arm for the ring gear to start the motor and stores energy for putting the vehicle in motion. Once the clutch is fully engaged, the flywheel could be gone because from that point on it is a inertia drag on the engine. When you step on the throttle it takes energy as it is restoring what it gave you to put the car in motion. Nothing is free. The reason you use a steel wheel in drag racing is typically because of slicks. You need more stored energy to launch with slicks. In the fifties and sixties aluminum flywheels were popular but many times "home made" because the vehicles had no tires. Late Sixties flywheels got heavy because we started have better tires. Some ran 40 pound wheels. I ran one for a while in my GTO. In the seventies flywheels began to lighten as the Doug Nash five speed appeared with a 3.25:1 low gear and we could lighten the flywheels again. I have a equal energy split Doug Nash 5 speed trans. Many vehicles had close ratio 2.20 first gears in the Muncie trans. Today it depends on what you are doing and how you want to drive. 5 speeds and 6 speeds being very popular. Sprint cars have no flywheels. They couple DIRECT as they push to start the car and have no clutch so no need for an hp robbing flywheel.

Today I would not buy a Chinese made flywheel of any material.

Tom V.