Flywheel weight
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Better throttle response...depends on how light. I run a 12 pound flywheel with a 4 speed.
Dave
67 Nova Boy
Dave
67 Nova Boy
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3,089 Posts
Many variables including counterweighted flywheels for strokers, internal and externally balanced engines (350 vs. 400), the lower mass of the flywheel in a lighter model creates a condition where the engine does not have to overcome the mass to spin freely. Mass = work. However, it only works to a point and depending on the cam you have, it can drastically alter your idle characteristics due to not enough mass allowing the mass to carry the rotation of the engine between cylinder firing. A 4/7 swap helps but still the lighter flywheel on a manual car can alter your idle. It really depends on many things but as @67 Nova Boy stated, a 12 lb would be a good place to land and would absolutely add to the throttle response and rev factor of your motor.
Here's a pretty straightforward article on it, not too much science.. LOL
Lighter flywheels advantages and disadvantages
A lighter flywheel can make a massive difference in the way the car engine responds and revs. We look at the advantages and disadvantages of a lighter flywheel. We discuss the pros and cons from light flywheels and DMF conversions.
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870 Posts
Stock 350 street driver I say stick with the 30 pounder,especially if you have a close ratio trans with the taller 1st gear. I went from a wide ratio 4 speed and 30# flywheel to an 18# with a close ratio 4 speed. 4.10 gear and 28" tire. It sorta reved quicker and I got used to it but the previous combo drove way nicer and stop/go traffic was much simpler. The taller 1st gear and lighter flywheel required a lot more clutch fussing. I eventually went back to the 30#/wide ratio combo and as soon as I backed out of the garage I noticed the difference. Got going much easier and gurgled down the lane with less rpm. No bucking or herky jerky. Gear changes were also more forgiving if you weren't right on with rpm and clutch release. I put a lot of street miles on my car every year and this made it fun to drive again. Launched better at the track too. Expensive lesson learned for me personally but I know some people prefer the lighter flywheel.
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44 Posts
A heavy flywheel is better on the street. Think of it as stored energy. So, taking off from a dead start, it will carry the launch better. Also, driving down the street where you on and off the gas will be a smoother ride because of the energy stored in the rotating mass. A lighter flywheel will rev quicker but carry less energy. So, harder to launch from a dead start, and when you are on and off the gas the car has a tendency to buck more as there is less stored energy to keep things smooth. All depends on what you like and how and where you do most of your driving. To a lesser degree how much your car weighs. You can lopped off a pound or two without much ill effects, in a light car for the street. But, big changes will as the previous posted stated, suck.
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1,480 Posts
Unless you’re road racing the car I wouldn’t worry about going lightweight on the flywheel.
I'm using one of the stock light flywheels from a third gen Camaro, it for sure makes the car harder to drive if you are not used to it. I'm also running the stock cam from an L31. I like this combo well enough (sorta put it together by accident picking parts from rockauto) but I think if I had any sorta cam lope it would be really tough to drive.
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Anytime your clutch is engaged, the flywheel is just more weight you have to accelerate. I used a 9# Fidanza wheel in our 331" Durango Deuce motor. It had two noticeable effects on the car - faster acceleration and easier cornering. You accelerate faster because the drivetrain weighs less. You corner better because the gyroscopic effect is less.
It was very easy to drive if you paid attention. We used an X-Ratio ST-10, so first gear was pretty quick.
It was very easy to drive if you paid attention. We used an X-Ratio ST-10, so first gear was pretty quick.
A light flywheel is a great change to make on a hot rod or even a street car. I recall the Chevy 350 engine uses the same flywheel for a trailer towing truck as for the base model Nova or a High output Corvette, and everything in between (sorta true - always have exceptions). Flywheel weight only makes a difference when you are at idle, clutch disengaged, with a non smooth running engine. Remember anything hooked to the front of the crank is "flywheel" i/e your A/C compressor, your water pump, a big bumpy cam and stiff valve springs, etc so the rotational torque to drive all that mass easily exceeds the torque load presented by the flywheel. So if you cut the flywheel weight in half you still have a far larger load remaining to keep the engine running smoothly. Conserved energy to smooth out power pluses from the cylinders firing can be increased by slightly higher idle speed. Maybe go from 650 RPM to 800 RPM. Nobody thinks twice about going from a 10.4 inch clutch to an 11 inch HD unit. But the reality is the 11 inch clutch "adds in" about as much flywheel mass as a light flywheel "takes out". So lets all put in 11 inch clutches and talk about how slow we can go. NOT. Anyway, so now you are getting ready to start off from a light at 800 RPM. Your half second to one second more clutch slipping made the disc wear about 7 to 13 revolutions more than before. Yawn.
And anything hooked to the tires is also "flywheel load". Once the clutch is locked up the driveshaft, U-joints, gears, axle shafts, wheels and tires are all additional flywheel load resisting acceleration. So you have the HD larger diameter driveshaft, the posi carrier, big thick axles and most of all - you put on wide rally rims that weight 40 lbs vs. the OEM narrow ones that weigh 25lbs and big tires that are twice the weight of OEM tires. So you added 50 lbs of tire weight, 30 lbs of rim weight and 10 lbs of everything else weight and worry about cutting 15 lbs off the "flywheel". What ?? me worry ?? Seems I heard that somewhere before. Anyway, don't be afraid to lighten up the flywheel. Have some fun with it instead.
I personally run light flywheels on the street in my BMW M3, Corvette, and GTO with various sized engines from 3.0 liter to 7liters. I have installed them in race winning smaller displacement foreign cars. i/e 1310cc Mini Cooper and TR250 liter engines in TVR sports cars. I also lighten crankshafts as much as possible. All efforts have been very positive experiences and none created any negative issues. Except for the Mini Cooper. It had a hard time starting out of the grid uphill into turn 1 at Sonoma. But it was tuned to run from 5000 to 9000 RPM and had very little torque below 5000 RPM. On that car we had to try and qualify sorta back of the pack then jump the start so we could run past the pack on the flat grid / pit row into turn 1. But we always qualified near the front so the first lap was a bit rough on the button clutch...That car had a rotating weight reduction of more than 50% from stock while running heavy axles. Equivalent to maybe a 7-8 lb Chevy flywheel and 20 lb crank in your Nova. Radical.
Have some fun with it. You will notice the difference - then try some really light wheels.........
And anything hooked to the tires is also "flywheel load". Once the clutch is locked up the driveshaft, U-joints, gears, axle shafts, wheels and tires are all additional flywheel load resisting acceleration. So you have the HD larger diameter driveshaft, the posi carrier, big thick axles and most of all - you put on wide rally rims that weight 40 lbs vs. the OEM narrow ones that weigh 25lbs and big tires that are twice the weight of OEM tires. So you added 50 lbs of tire weight, 30 lbs of rim weight and 10 lbs of everything else weight and worry about cutting 15 lbs off the "flywheel". What ?? me worry ?? Seems I heard that somewhere before. Anyway, don't be afraid to lighten up the flywheel. Have some fun with it instead.
I personally run light flywheels on the street in my BMW M3, Corvette, and GTO with various sized engines from 3.0 liter to 7liters. I have installed them in race winning smaller displacement foreign cars. i/e 1310cc Mini Cooper and TR250 liter engines in TVR sports cars. I also lighten crankshafts as much as possible. All efforts have been very positive experiences and none created any negative issues. Except for the Mini Cooper. It had a hard time starting out of the grid uphill into turn 1 at Sonoma. But it was tuned to run from 5000 to 9000 RPM and had very little torque below 5000 RPM. On that car we had to try and qualify sorta back of the pack then jump the start so we could run past the pack on the flat grid / pit row into turn 1. But we always qualified near the front so the first lap was a bit rough on the button clutch...That car had a rotating weight reduction of more than 50% from stock while running heavy axles. Equivalent to maybe a 7-8 lb Chevy flywheel and 20 lb crank in your Nova. Radical.
Have some fun with it. You will notice the difference - then try some really light wheels.........
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I'm not questioning your race experience, but that statement is not true
A flywheel is a mechanical battery, an energy storage device
there are many drains or loads on an engine, it doesn't make them a flywheel
they do all have effects on acceleration, throttle response, etc
all the loads on an engine are like resistors in an electric circuit, a flywheel is like a capacitor
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My left foot is a flying short
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A true street car involves lots of compromises for ease of use. Everybody has a different discomfort level they're prepared to deal with to eek out that last bit of performance you'll only get to use 1% of the time and suffer with the other 99%. I have no doubt a good portion of my improvement came from the 2.56 first gear as opposed to the 2.20 previous;however,with the heavier wheel the idle sounded slightly different (again...kinda...smoother probably) and there was no doubt the car gurgled along happier/smoother off idle where you spend a lot time in city traffic. I sold that 18# steel SFI flywheel to a buddy to replace his OE unit. He used it for a few months and didn't like it. Put the OE back in. Swap meet,sold. If you have the cash to buy the parts and don't mind the ugly wrenching yanking big things apart to experiment,I say go for it and try multiple combos till you find your Shangri-la. I guess flywheels are another thing like pizza,one guy's favorite is another guy's dog food. Good luck.
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All depends on how you want to use the car, what engine it is hooked to and/or how it makes power, and what your comfortable with.
For a snappy, high-revving engine with power up top and a short rear gear, a lightweight flywheel makes for a really fun, complete package, but may be a pain at low speeds due to less stored energy.
For a mostly stock or mild motor with tall gears, a heavier flywheel will make starts and stops easier, but may also make the setup slower to rev and "lazier". But, it will be easy to start and stop.
My only real source of input is from my own experience. I have a Honda Prelude with a high-revving (read: 8,000RPM) H22 and short gears. I went from the stock 20lbs flywheel to an 8lbs billet aluminum flywheel. The difference in the overall "snappiness" between the two was night and day. The biggest difference to the average Joe is the ability to highlight your shortcomings as a driver if you short-shift, let out the clutch too quickly, or aren't smooth with articulation.
For a snappy, high-revving engine with power up top and a short rear gear, a lightweight flywheel makes for a really fun, complete package, but may be a pain at low speeds due to less stored energy.
For a mostly stock or mild motor with tall gears, a heavier flywheel will make starts and stops easier, but may also make the setup slower to rev and "lazier". But, it will be easy to start and stop.
My only real source of input is from my own experience. I have a Honda Prelude with a high-revving (read: 8,000RPM) H22 and short gears. I went from the stock 20lbs flywheel to an 8lbs billet aluminum flywheel. The difference in the overall "snappiness" between the two was night and day. The biggest difference to the average Joe is the ability to highlight your shortcomings as a driver if you short-shift, let out the clutch too quickly, or aren't smooth with articulation.
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