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Old 03-17-2006, 01:09 PM
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Lightweight vs Heavy Flywheel

I am in the process of dropping a 400 CI SBC in my 69' Corvette.
In order to save some $$, I'd like to use most of my existing pieces IE stock bell housing, 10.5" clutch (Sachs Power Clutch), starter and M-20 Muncie. Since the 400 usually comes with an 11", 168 tooth set-up (which isn't what I have), I need to utilize a 153 tooth flywheel and balance plate on the 400 so I can use all my old parts.
The question I have is:
What is the difference between the 'lightweight' 18 lb flywheel vs the stock 25-30 lb flywheel (other than the weight)?
I am leaning towards the stock 'heavy' unit but I'd like to know the advantages or disadvantages of each.
This will be used on a street driven car with 3.70 gears and a mildly warmed over 400 (about 400 horse).
Any advice would be greatly appreciated.
Thanks!
Elm

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Old 03-17-2006, 01:36 PM
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The lighter flywheels are mainly used for faster engine RPM acceleration, allowing the engine to "wind up" or rev faster than the same engine using a standard or heavy flywheel. Mostly meant for high performance and racing application's.

The heavier weight flywheels are mainly meant for smaller displacement engines (6 cylinder's or smaller than 300cid V-8 engines), and are more geared toward truck use or car light duty use, the heavier flywheels will also allow the engine to not "lug" or "bog down" when shifting to a higher gear.

The main thing between the two of them that you won't hear very often, is that if you have a driver that has a tendancy to "ride the clutch" a little too often or too much, the lightweight flywheel will warp, crack, or develop hot spots and glaze over MUCH faster than the ehavy flywheels.
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Old 03-17-2006, 09:22 PM
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The lighter wheel will increase the tendency of the engine to die if you let out the clutch too quickly from a standing start under light throttle. I ran one on a '69 Nova with 230, M-20, & 3.08's, and it was drivable, but it was a pain in the butt. With a 400 & 3.70's, you might get away with it OK.
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Old 03-18-2006, 01:51 AM
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As someone who has driven plenty of both light and heavy flywheels, trust me and do the heavy. If you're racing and need the lower inertia its fine, especially since you rarely stop, but on the street they are a PAIN. You have to carefully modulate your RPMs, throttle input, and clutch engagement. You also have to ask the friction surface of the clutch to take extra abuse since you are slipping it through more of the engagement period. Since your 'vette isn't a racer and isn't too lightweight, stick to the regular weight.

You're not losing any energy with a heavy flywheel. The heavy flywheel just stores more kinetic energy. You get it back when you release the clutch, but it can slow down acceleration by a little bit. Given the entire rotating weight of the transmission, crankshaft, driveshaft, and axle shafts, saving 10 lbs on the flywheel (to me) isn't worth the headaches and embarrasment you get from stalling your 'vette like an amateur.
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Old 03-18-2006, 02:34 AM
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Good advice Curtis, you'll also find that the heavy flywheel helps rpm recovery on gear changes. They can be a pain on ice or snow but tend to prolong clutch life and are more predictable in a slide. Think of them as a torque reservoir. Light fly wheels are great in neutral or with a 5:38 gear.
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Old 03-18-2006, 05:35 AM
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Thank You!

Excellent-
Thank you all so much for your input!
I was leaning towards the stock one but I just wanted to make sure I wasn't making a big mistake.
Thanks again!
Elm
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Old 03-18-2006, 06:39 AM
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Quote:
Originally Posted by ezobens
I am in the process of dropping a 400 CI SBC in my 69' Corvette.
In order to save some $$, I'd like to use most of my existing pieces IE stock bell housing, 10.5" clutch (Sachs Power Clutch), starter and M-20 Muncie. Since the 400 usually comes with an 11", 168 tooth set-up (which isn't what I have), I need to utilize a 153 tooth flywheel and balance plate on the 400 so I can use all my old parts.
The question I have is:
What is the difference between the 'lightweight' 18 lb flywheel vs the stock 25-30 lb flywheel (other than the weight)?
I am leaning towards the stock 'heavy' unit but I'd like to know the advantages or disadvantages of each.
This will be used on a street driven car with 3.70 gears and a mildly warmed over 400 (about 400 horse).
Any advice would be greatly appreciated.
Thanks!
Elm

An 18# flywheel isn't really very lightweight, and with 400 cubes, a M20 and 3.70 gears it would be very easy to control. We use a 10# Fidanza in a 331" motor, x-ratio T-10 and 3.25 gears and have had no clutch problems at all. One of the most noticeable differences is the behavior of the car when you let off the throttle, it slows down much quicker without using the brakes, and accelerates out of the corners quicker.
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Old 03-18-2006, 03:12 PM
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I like heavy flywheels, they drive better on the street and launch a car faster at the strip, controlling bog and spin is easier. Drag cars tested with both heavy and light flywheels, heavier are usually faster overall than those with light clutches/flywheels and are easier for the less experienced to drag race.

Light flywheels are good for circle track and road racing.
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Old 03-18-2006, 07:05 PM
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Quote:
Originally Posted by ezobens
I am in the process of dropping a 400 CI SBC in my 69' Corvette.
In order to save some $$, I'd like to use most of my existing pieces IE stock bell housing, 10.5" clutch (Sachs Power Clutch), starter and M-20 Muncie. Since the 400 usually comes with an 11", 168 tooth set-up (which isn't what I have), I need to utilize a 153 tooth flywheel and balance plate on the 400 so I can use all my old parts.
The question I have is:
What is the difference between the 'lightweight' 18 lb flywheel vs the stock 25-30 lb flywheel (other than the weight)?
I am leaning towards the stock 'heavy' unit but I'd like to know the advantages or disadvantages of each.
This will be used on a street driven car with 3.70 gears and a mildly warmed over 400 (about 400 horse).
Any advice would be greatly appreciated.
Thanks!
Elm
Just remember the 400 is externally balanced , you must use a 400 flywheel and a 400 balancer , unless it has been internally balanced.
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