Kevin Cameron wrote great article about this for his page in Motorcyclist magazine. There’s more to how the engine runs than just the weight of the flywheel. The crankshaft accelerates at each cylinder firing event and then decelerates until the next firing event (90 degrees for a cross plane crank 8 cylinder). This creates a harmonic that transfers through the engine that effects all other engine systems, specifically the camshaft and valve timing. The heavy flywheel engine will top-end better due to the smaller deceleration btwn firing events because of the heavy flywheel inertia. This lessens the harmonics that effect the valve train. As with most things ICE related, there is no perfect solution, but compromise based on what the engine will be powering. Going to Bonneville or Talladega? Put the heaviest flywheel you can and send it. Road racing where the engine will be accelerating the vehicle out of many slow speed corners? Then a light flywheel will be the best choice.

Interesting thing is that old gassers in the mid 70s would use a 50 pound flywheel on a 292 cu in small block chevy because the increased moment of inertia increased the momentum of the system and helped the heavy cars launch off the line better

On my heads/cam LS7 I went from a stock LS7 clutch to a Mantic 9000 twin disc and the difference was crazy. The car was noticeably quicker. It makes a much bigger difference in lower gears where the RPM is climbing faster, but not as much of a difference in higher gears when it's not climbing as fast.

Back in the 1970' we used to un a Boss 302 in D / mofified production, in a Maverick. the car would launch at 7500 RPM. With a 25-pound flywheel the car would launch then pull down the engine so bad it was basically stalling. We changed to a 50 pound flywheel and the car Would carry the Wheels right to the third gear shift with a Nash 5 speed. Once the car was launched the big flywheel was no different than the small one. We picked up 3 tenths with the 50-pound Fly wheel! i know times have changed and no body run's a standard any more. but this is real facts with a real car.

I was hoping you’d run the tests at both 300 rpm/sec and 600. The engine with the same rotating mass will have a different curve with just the acceleration change. It would be interesting to compare the differing effect as acceleration rate changes. Thanks for another great video, Richard.

Having installed a lightweight billet flywheel I can confirm without a single doubt that it added absolutely no horsepower to the engine...... however it is abundantly clear that more power is finding its way to the wheels

From my experience drag racing a 600rwhp stick shift car and going from a VERY light flywheel & clutch setup to a pretty typical steel flylwheel and spec clutch: The heavier setup worked much better. Definitely enough so to overcome any single digit loss in power to the wheels. The launches were a LOT more consistent and I believe the torque hit on 1-2 and 2-3 power shifts helped with overall acceleration.

Love the Data!! Thank you Richard !

Nice! Thanks for this video Richard!

This is good stuff! Thanks, Super Richie! 👍

Excelent research as usual Richard, just what I needed to know.

Going from a stock c4 Corvette stock flywheel & clutch (45-50 lbs)to a ram aluminum flywheel & clutch 20-25 pounds. The car definitely accelerates faster. Less rotational mass helps it wind up faster, and if it's accelerated faster there is less parasitic loss.

The diameter deal is exactly why I don't run out and get the lighter aluminum drivelines right off the bat, because it is a small diameter not effecting rwhp / tq much at all.

Love your video channels, I was always interested in the result of such an experiment👍

Man I cant believe you have been making videos for three years already. I wish I knew what video I commented on and suggested you overlay yourself on the dyno results to make the video feel more personal and higher quality. I'm glad your still around posting entertaining and informative videos!

Instead of an acceleration test, do a step test. The difference will be negligible. Do the test at 200 rpm/min, 400 rpm/min and 600. The faster the acceleration rate the bigger the change. You will typically see a bigger number in a step test with the engine parked at a set rpm.

Great video 🤘🏻

GREAT LOOKING SHIRT BUDDY !!

Interesting i didn't expect an increase in tourge also. That was cool to see

I'd say it depends on the application. If you're drag racing, you're going to want that energy of the heavy fly wheel for the hit to the slicks on launch(depending on capable engine power, and launch RPM), otherwise your slicks could bog down your engine. If you're road racing, or on the street then you will be better served all around with the light weight flywheel.

Thanks Dr Richard, another interesting day of physics.

nice work!

You proved the point I tried to make for years to my friends back in the 80's. I ran a 462 Pontiac, 12.7 CR with 3.08 diff gears and a wide ratio 4-spd in my 1968 GTO. I also ran a schiefer 11lb aluminum flywheel vs. the std 30lb steel pontiac factory flywheel. My Pontiac engine revved like it had nitrous injection. When I would run people they would accuse me of such or of running 4.11+ gears because the car revved SO fast compared to engines with factory flywheels. My 3.08:1 rear gear did NOT hinder me in street driving in any way, allowing me to run high 12's. High compression, ported heads, light flywheel - that engine wanted to REV. Perhaps you can run a similar comparison on a larger displacement engine to see if the gains are even greater between them??? :-) Thanks Richard.

learnt this here back in the kart racin days . took off the cast flywheel , installed the aluminum flywheel and changed the rear gear meant faster laps

I ❤Love that you test TYPICAL stuff... not a bunch of exotic ex$spenive stuff... but TYPICAL drivers combos. Real applications. TY

cool video richard. I just got a lightweight flywheel and clutch for my 2018 camaro ss

Stock flywheels have heavy steel clutches. Flexplates get heavy torque converters. Lightening a flywheel/ clutch assembly often makes it harder to launch, do to rpm drop at clutch engagement. Though ususally the car will accelerate quicker. A smaller diameter torque converter usually stalls higher and accelerates quicker. Something to consider. Fox Mustang flywheels are 19 lbs, I never weighed the original clutch assembly, but I will, its in the box.

I used to play around with 5hp briggs and stratton go-cart motors. I did a light weight flywheel and machined much of the counterweights off the crank to lighten it up. That motor was a turd, and took forever to Rev up. Lesson learned, one stroke to make power and three strokes to consume. In a single cylinder engine, light weight rotating mass did not help.

Match the flywheel to the application is much more important than any minimal power gains.

I feel like the lightweight flywheel would be better for an everyday daily fun car. the lightweight flywheel would allow the motor to rev out in the lower rpm’s better and might even increase fuel economy because there’s less resistance in the drivetrain, but the heavier flywheel would be better in a drag application because it would keep the inertia going stronger off of a launch. Definitely something that is very application specific

Love your content. Can you do a video on the effects different tunes and high performance parts have on the volumetric efficiency on engines? Not sure how you measure that but i dont think it would be engine specific. Again really appreciate your work!

I reduced approximately 1.7 kilograms from the outer edge (in total it weighed 9kg) from the Sentra flywheel a year ago. It's only a 1.6L engine and of course I gained less than 7 horsepower compared to the LS (I guess) but the gain is notable. Soon I will reduce it to half the original weight or less if possible, I already found a place in Guadalajara to have the Flywheel balanced.

Yes, engine masters episode a couple years ago proves the results I had.

If you were to measure power at a static RPM with a brake, the flywheel weight should be inconsequential. Also, with a CVT, once at peak power, the effect of flywheel moment of inertia is muted (but we still hate CVTs).

Yep! My v8 trike Sbc is a direct drive th350. Flexplate and a TCI splined hub. 1,200 lbs. insane fast.

Had a 95 Mustang gt paper filter stock, it's best 15.40 @90mph. Put in aluminum flywheel, aluminum driveshaft k&n filter, it went 14.90 @92.5 mph

A 12" flywheel at 6000RPM is going 214mph. If you double the speed, you quadruple the energy it takes to get there. So, a lightweight flywheel with a low moment of inertia is a really awesome mod.

How about a test that shows how duration and lift effect vacuum.

Did it in a hopped up mustang with no other changes. Car seemed to rev up and accelerate faster. It also was easier on the street tires on shifts. Seemed improved for street driving on street tires? Unfortunately I never took it to the track and it had fried the stick clutch before I changed the setup.

I agree with this one centrifugal weight of a flywheel or a massive weight of the automatic torque converter weighs a good 20-30 lb

Rich, you can drill holes in the flywheel to lighten it. Big holes. Hp not so much but throttle response improvements

Make power? No. Free up power from driveline loss? Yes.

Engine Masters did this a couple of years ago and at 100 RPM/sec it only made a little difference, but at 600 RPM/sec it made something like 20 HP difference.

Road racing = light flywheel and drag racing since you just flat footing it and starting from a dead stop, you want a heavy flywheel ! In my opinion I feel diameter should have stayed the same for the comparison. Smaller diameter has more to do with leverage and makes that 16lbs seem like 12lbs. I would have liked fluctuating loads to see recovery between both at same diameter. Better yet a gforce in a given vehicle going through the gears. Dynos are great but the pathway oil takes during G-forces makes G-forces test more accurate unless you're losing traction 💁‍♂️

I've been running a light clutch since the 2000s in my 99 camaro ss....like really light. Complete clutch/flywheel is 16lb.

I learned this in real world. if car is light enough, the lightweight wins.. but there is something magic to inertia of flywheel . A modern example is a 96 gmc with 5 liters and 5 speed, and the same exact truck with 350 and automatic... climbing the maine coast line hills to the sea hauling aboat..the 305 brings the giggles.. it is THAT powerful in comparision. Yes, with that "boat anchor" engine morons quibble over. 😄

I was always under the impression that the stored energy in the heavier flywheels assisted with shifting into the next gear preventing the engine from "bogging"... I wonder if there is an actual downside...

Hi Richard, did you look at steady state power between the two?

In drag racing you need the heavy combination for the momentum between shifts and off the line.

Doesn't actually increase power, but it will rev much quicker in Neutral. Improves launching with some engines, but not in some others.

The power gain or loss will correspond to how fast the rpm is changing, whether that is at a prescribed rate on a dyno test or acceleration on the road in x gear (1st gear acceleration will create a different effect than 4th gear acceleration). The harder the rpm acceleration, the greater the inertia loss in the flywheel. Now if you are testing at a constant load at a steady rpm, the flywheel effect would null out, altogether. The torque (and calculated hp) would be all it's worth, and flywheel weight would not matter, at all.

Just thinking about torsional flexing when the crank rapidly changes speed during shifts.. the heavy flywheel stores inertial energy and protects the crank from Dangerous harmonics

I run road courses and the biggest improvement from swapping to an aluminum flywheel was much snappier blips when heel/toe downshifting. However, if you're someone only driving on the street, I would suggest to stay with steel. The lightweight flywheels are not as smooth to engage for daily driving.

Flywheel weight isn't about power, it's about responsiveness and enjoyability of sporty driving. Being rewarded for a crisp rev match downshift isn't something that shows up on the dyno and doesn't matter of you're just drag racing.

The rev step rate needs to be slowed down or even better , manually step the engine through the rev range so the engine stabilizes at 500 RPM steps for 2 seconds so we are not running into some sort of software artifact. Does this dyno have synthetic inertia measurement / correction or some other calc? Another test would be to have a single tooth crank sensor at each end of the crank then measure crank twist to determine if this is where the power is coming from. HBREPAIR has some old GM tests showing 0.35 to 0.45 degree crank deflection on a Corvair engine with 2 different dampers. A lower inertia flywheel allowing the engine to produce " more " power is dipping into the perpetual motion / run an engine on water realm as long as there isn't some other change in engine deflection.

Richard have you used a Quick Spool Valve?. it blocks off one side of a twin scroll turbo at low rpm and when the boost gets high enough it opens the other port for top-end power so you can run a big turbo without the turbo lag.

A Flywheel is for a manual transmission car a Flex plate is for an automatic transmission car and a torque converter is attached to the flexplate 🤔🤔 but in term of light vs heavy flywheels fir drag racing you want the heavy flywheel for road racing you want the light weight flywheel also weight of the vehicle matters so for drag racing a light flywheel in a light car could work

This is good but much more interesting on a turbo car. would love too see if lag improves or more lag

I don't know if it will make more power but from my own experiences the engine rpms seem to snap up faster. I mean definitely seems to rev quicker

How much locked in does your tune need to be given the engine's responsiveness to input? Could a higher mass flywheel effectively build in some forgiveness for error?

I like to think a flywheel is more or less a kinetic battery. It stores energy proportionally to the average mass from its center and its rotational velocity. Free revving or, say 1st 2nd gear pulls will need to "charge" that energy much more quickly than a slower rate of rpm change in higher gears. The impact of a fly wheels energy storage will be much more noticeable in cases where you're trying to accelerate the wheel's rotation quickly. In the case of my old 1995 bmw 540i I calculated that my LWFW dropping over 30lbs "free up" in the ballpark of 40hp in 1st gear (mid 20hp range for 2nd gear). In the case of my 540 the difference was quite noticeable until 3rd gear.

Suggestion. What I would like to see is how or what makes an engine rev more quickly and makes it more responsive. For example due to smaller and lighter flywheel, and other factors like exhaust and management systems. I’ve seen some Ford V8 engines that rev like Formula One engines. You touch the throttle and wham, it goes all the way to 8000 RPM quick. I know some racer who race shelby cobras and they use smaller, lighter cutches and fly wheels but but more importantly, it’s not about horsepower it’s about how quickly the engine revs and how responsive it is. Hopefully you consider doing this test. I think it would be very interesting. I think there are many factors that contribute to an engine being quick revving but it’s quite complicated.

Heavy cars dont work very well out of the hole with lightweight flywheels and numerically low gear ratios has been my experience.

It's not just size but where the weight is. A larger flywheel where all the weight is in the middle would be better than a medium size flywheel with all the weight at the outside rim of the flywheel. The distinction being that a flywheel big enough to engage the starter could still use a small friction surface (where most of the mass is) toward the middle to reduce the moment of inertia.

I run 5.5 kg flywheel, alloy and steel in a light car it is awesome, 408 ford .

Something I’ve been curious about is how much of a difference water/meth injection makes as well as just water in reducing knock as well as how much more timing can be added N/A as well as boosted and how much more power can be made with it.

I assume this would also apply to torque converters. My 9.5 inch Yank converter weighed significantly less than the stock 12 inch converter.

What was the difference in time to accel from load in to max rpm between these 2 setups?

Do steady state and see if they do same trq and hp numbers because the dyno software account for the inertia and measured trq and outputs the results

I weighed the 12.25” clutch and flywheel setup for my 87 F-250 behind a 7.5L with the ZF-S5 and it was about 82.5lbs without bolts.

Since the flex plate is bolted to the converter shouldn't the weight of the outside rotating housing of the converter be added to the weight of the flex plate ?

ran a 40 lb flywheel in my 396 chevelle stock eliminator car

Sweet! Hope your clutch skills are good when youre using that lightweight piece (in the car that is). 😎 haha.

This was not a test of automatic transmissions only flywheel weight

Doesn't make more power but it's less rotating mass that the engine has to spin up.

george bryce has a claim that lightweight flyweel doesn’t have inertia during the gear change and loses acceleration in a drag race butthats on a harley

Question, was the O-ring supposed to be glued, or does that matter? Paying attention down here in Arkansas. LOL

Ima guess before hand. Yes

It would've been interesting if you recalibrated the inertia factor in the superflow software then re-ran the test

Re-run the test, but slow down the RPM sweep speed down to 150 RPM a second, and I would imagine the difference would be less. There is a time and a place for each application.

What about when you add Clutch weight and Torque converter weight?

Hmm, word of warning for an everyday street car a light flywheel loses bottom end driveability. Mildly lightening and a lighter and better clutch can help. But maybe not. Drag racing generally likes a heavy flywheel. But then you have to keep the engine on the boil. Or accelerate that mass again. Circuit racing? most will use a light steel flywheel and a triple palte Tilton style clutch, generally 7 1/4" . Weighing between 16-20lbs. A 'normal' street clutch will weigh around the same weight as the flywheel. Any where between 20 and 30lbs. A speedway clutch for a sedan or modified is a tiny flywheel, with a tiny ring gear and a dog style clutch in the gearbox. Very light but only usefull for those cars. Beware, lightening and abusing a cast iron flywheel they can and will explode. And very occasionally just the ring gear can as well. That with high rpm. An alloy flywheel to replace an iron one is generally ok. Most have a steel section cast or bolted in for the clutch plate to grip too. NEVER use an alloy flywheel with a friction disc onto the alloy. They explode, I saw one once explode left [where they usually go] and explode the bellhousing, cut the header as well as the chassis rail. On a speedway sedan. Cast iron at the drags has been known to injure spectators 80 feet away. BIG explosion contained by steel bellhousing,, sort of! I have also seen a iron flywheel [V8 Ford]with clutch come off the crank, did a LOT of damage to the car. Killed the gearbox bellhousing, floor etc. Though conversely another where the crank flange broke off did very little damage,, engine sounded real strong with all that weight missing. That on a crossflow grey Holden engine. Speedcars and Sprintcars have no clutch or flywheel,, the reason they rev so quickly,, and the reason they have to be all pushed off to start,, sometimes many times a race!!

Yup more power, same as light weight crank but is not all positive

I was wondering if you have ever done tests on a 307 chevy? People hate that motor but I think it would out preform a 305. Bigger bore, shorter stroke. A 283 with a 327 crank.

RPM change per second should be specified to make this meaningful. A light flywheel wouldn't significantly help a truck pulling a heavy load up a hill.

The problem is, this isn't taking into account the extra weight from the clutch assembly, or the torque converter, which are both weights that bolt to a flex or flywheel, so by rights, without the entire weight, it's all irrelevant.

would a alluminum flywheel be good on a t56magnum 6-speed , turbo 20lbs 900hp foxbody twinn disc clutch

Now I’m super curious about a full lightweight rotating assembly, crank, rods, pistons. I wonder if weight off the internals makes more or less of a difference than flywheel weight.

Add on the weight of the torque convertor full of transmission fluid. The difference between flywheel+clutch+pressure plate versus flex plate+convertor+fluid isn't much different.

I’m just saying 6.4L Hemi vs 6.2L LS or LT Engine. If you’re able to get a 6.4L Hemi. Also many, many would like to see a apples vs apples Whipple vs ProCharger comparison. I know many would like to see these comparisons. Appreciate all your videos...

For one, a flex plate doesn't compare to a flywheel. A flex plate is lighter because the torque converter weight with all the fluid helps dampen power pulses. A flywheel has a typically lighter clutch to be the link between engine and gearbox. So this comparison honestly means nothing.

Needs a test with steady state/ steps, no acceleration.

Never use an aluminum flywheel they will break eventually catastrophicly. Only use lightweight chromoly steel flywheels.

On the dyno it’s kinda fudgin it some ain’t it. On an auto you have to spin the torque converter right? That has to be some resistance…

Well the flex plate has a heavy torque converter bolted to it. So in the real world it’s a wash.

So would a lighter flywheel/clutch combo on a street car (01 Camaro SS) be horrible then?

That's a lot more power than I was expecting. Still, I feel like the power isn't the point of this. A lightweight driveline will vastly improve throttle response, more than the bump in horsepower would imply, as it's not just reducing how much weight the car needs to push, it's also reducing the amount of weight the engine needs to directly spin without a mechanical advantage from the transmission.

Mr Holdener, good test, but you should have gone in depth. For example, if you held each of these at a constant rpm, there would be no HP gain/loss.

My HCI LS7 in the Corvette Z06 I picked up used had a McLeod RXT twin disc with an aluminum flywheel and it seemed like there was so little momentum that I'd stall the engine with the clutch pedal fully in when the power steering pump would struggle at full steering lock. It seemed like that was enough to kill what little momentum it had. Between that and just general driveability I'd rather take the slight performance loss for it to not be a pain in my ass.

Heavy vs light. How heavy is the car?