Is this how lightweight fly wheel should feel

[sms2022]

Nope. Cubic inches are cubic inches. As long as you're not shrouding the valves it won't matter.

This is absolutely not true.
https://www.hpacademy.com/technical-articles/rod-to-stroke-ratio-explained/

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[robvas]

This is absolutely not true.
https://www.hpacademy.com/technical-articles/rod-to-stroke-ratio-explained/

HPAcademy articles might as well be google blogspam

Go find me a dyno test between two engines that are within a percent or two total cubic inches, but have the same heads/intake/camshaft. And show me how the one with longer stroke or bigger bore (or whatever you think makes more power) making more power.

I'll wait. And please don't start talking about F1 engines or some other bullshit like that.

 

[Johnny maverick]

I'm no scientist. I think the heavier flywheel has more stored energy so you don't have the counter the lack of energy with more throttle. It heavier flywheel spins up slower but it also slows down slower. It's just a matter of getting used to. The pros of a light weight flywheel out weight the cons.

 

[K4fxd]

Drive some race cars with on off switch clutches and super light flywheels.

The heavy flywheels store energy and make the car a bit easier to get moving. Especially when starting up hill.


Smokey started the long rod thing and it might be true except we can't keep the rings from fluttering. Oops, got long rod confused with offset pins. Long rods work but so do short ones. just gotta get the cam timing correct for each. Long rods will make the engine last longer.

Tq and HP is fully a function of displacement. Air and fuel in = power out. We have come a long way in making these pigs more efficient. Everything equal, more cubes = more power

 

[sms2022]

HPAcademy articles might as well be google blogspam

Go find me a dyno test between two engines that are within a percent or two total cubic inches, but have the same heads/intake/camshaft. And show me how the one with longer stroke or bigger bore (or whatever you think makes more power) making more power.

I'll wait.

Since neither one of us is an expert and apparently this is something the experts disagree on, we’ll have to agree to disagree.
This is probably the most fair article I’ve seen on the subject
https://www.enginebuildermag.com/2016/08/understanding-rod-ratios/

 

[robvas]

Since neither one of us is an expert and apparently this is something the experts disagree on, we’ll have to agree to disagree.
This is probably the most fair article I’ve seen on the subject
https://www.enginebuildermag.com/2016/08/understanding-rod-ratios/

Which one are you trying to say is better, btw?

 

[sms2022]

Which one are you trying to say is better, btw?

Neither. I have no real opinion on rod ratio. I will admit I’ve used that term incorrectly throughout this discussion when I really meant bore/stroke ratio. I think a longer stroke allows an engine to produce more torque at a lower rpm than an otherwise equal engine of the same size with a larger bore and shorter stroke.

however, for a performance engine you usually want an over square or at least square bore/stroke. That way the engine can rev higher and make more hp since hp is a function of torque x rpm.

in terms of heavy rotating assembly and heavy/light flywheel I agree with Johnny maverick above. The heavier stuff stores energy, producing more torque at very low rpm. An engine with lightweight flywheel and rotating assembly has to rev higher to get the car moving for that reason. But that heavy stuff kills power overall because the engine can’t overcome its own mass to rev high enough to make good hp.

edit: I guess i shouldn’t say the heavier flywheel makes more torque because that’s not true. But it does distribute the produced torque over a longer duration which has the effect of feeling the same as more torque when taking off.

 

[Jpump]

I just had a McLeod RST installed 2 weeks ago. It's definitely different from the stock clutch. Takes a little more to get moving, but it does rev faster and the rpms drop quicker between shifts. Still getting used to it and finishing my break in period. Haven't been over 4k rpm yet.

 

[WildHorse]

Pick your poison:

Advantages:
Improved Acceleration: Lightweight flywheels reduce rotational mass, allowing the engine to rev up faster and accelerate more quickly.
Improved Throttle Response: The reduced rotational inertia of a lightweight flywheel can also improve throttle response, making the car feel more responsive to driver inputs.
Reduced Load on Engine Components: A lighter flywheel places less stress on engine components like the crankshaft and bearings, potentially increasing their lifespan.

Disadvantages:
Reduced Low-End Torque: Lightweight flywheels can reduce low-end torque, making it more difficult to accelerate from a stop or low speeds.
Rough Idle: The reduced rotational inertia of a lightweight flywheel can also cause the engine to idle less smoothly, potentially resulting in roughness or vibration.
Increased Wear on Transmission Components: Lightweight flywheels can place more stress on transmission components like the clutch and synchronizers, potentially reducing their lifespan.

 

[K4fxd]

I think a longer stroke allows an engine to produce more torque at a lower rpm than an otherwise equal engine of the same size with a larger bore and shorter stroke.

And you are wrong.

Cubic inches is cubic inches no matter how you get them The long stroke thinking was debunked in the early 70's but like the back pressure myth continues to pop up.

I have no real opinion on rod ratio.

I have a strong opinion on rod ratio, it reduces side loading allowing longer piston and bore life.

 

[WildHorse]

For 2-valve engines For high horsepower applications, an oversquare engine design (larger bore, shorter stroke) is often preferred. This allows for larger valves, better breathing, and higher RPMs, all of which can contribute to greater horsepower. A bore/stroke ratio of around 1.1:1 to 1.2:1 is common in high-performance engines.

2011-2017 have a 1.0027:1 ratio (slightly undersquare). Which is a very good compromise.

I have a strong opinion on rod ratio, it reduces side loading allowing longer piston and bore life.

A higher rod ratio, around 1.6:1 to 2.0:1, is often preferred in high-horsepower engines, as it can reduce side loading on the pistons and cylinder walls, improve piston dwell time near top dead center, and help the engine rev more freely.

Connecting rod ratio = 5.933 inches / 3.65 inches
Connecting rod ratio = approximately 1.624:1

 

[NightmareMoon]

Pick your poison:

Advantages:
Improved Acceleration: Lightweight flywheels reduce rotational mass, allowing the engine to rev up faster and accelerate more quickly.
Improved Throttle Response: The reduced rotational inertia of a lightweight flywheel can also improve throttle response, making the car feel more responsive to driver inputs.
Reduced Load on Engine Components: A lighter flywheel places less stress on engine components like the crankshaft and bearings, potentially increasing their lifespan.

Disadvantages:
Reduced Low-End Torque: Lightweight flywheels can reduce low-end torque, making it more difficult to accelerate from a stop or low speeds.
Rough Idle: The reduced rotational inertia of a lightweight flywheel can also cause the engine to idle less smoothly, potentially resulting in roughness or vibration.
Increased Wear on Transmission Components: Lightweight flywheels can place more stress on transmission components like the clutch and synchronizers, potentially reducing their lifespan.

reduce torque? Show me a dyno graph please, I’d like to see that.

theres a difference between storing inertia in a flywheel and engine generated torque.

The issue someone has with starting from a stop is not due to lack of engine torque from the lighter flywheel, its the lower rotating inertia isnt covering up for mistakes feeding in gas as they let off the clutch. The lighter flywheel car is happier to speed up AND slow down, which means that what you do with the gas pedal has a more immediate effect on RPMs. That’s not engine torque at all, its inertial mass. If you’re shifting right, you’re rev matching and none of that matters.

manufacturers put in telatively heavy flywheels to make the cars easier for lower skilled drivers to drive, its not to shift the power curve to the low end (thats cams and intake runner designs) and once the clutch is engaged the light flywheel car has less (although negligible) torque lost to spinning up rotating components as opposed to speeding up the car.

To be fair, most people who drive manuals cant realy describe the basics of how the clutch and transmission work together (for example, why a double clutch downshift technique is smoothest), so I’m not suprised to see some confusion about flywheels.

 

[WildHorse]

reduce torque?

Right. It's all about physics.
When you reduce the weight of the flywheel, you reduce the amount of energy required to accelerate the engine. This means that less torque is required to spin the engine up to a given RPM.

But there might be some confusion here.
The engine itself doesn't make less torque when using a lighter flywheel. Instead, the reduced rotational inertia of the engine assembly makes it more difficult for the engine to maintain torque at low RPMs.

 

[80FoxCoupe]

Yep. Torque is largely dependent on how heavy the reciprocating mass is on an N/A engine. That’s part of the reason why old big blocks would make 500tq but 150hp. They also had a flywheel that weighed 40lbs.

There’s an old wives tale about this that a guy swapped one of these flywheels onto his 396 Chevy and used to shut the engine down and let the clutch out and the car would still go 20mph down the street.

Pop a wheelie over a soda bottle. So much tq, popped the back window out. Hondo on the dash...

LOL

 

[NightmareMoon]

Right. It's all about physics.
When you reduce the weight of the flywheel, you reduce the amount of energy required to accelerate the engine. This means that less torque is required to spin the engine up to a given RPM.

But there might be some confusion here.
The engine itself doesn't make less torque when using a lighter flywheel. Instead, the reduced rotational inertia of the engine assembly makes it more difficult for the engine to maintain torque at low RPMs.

Yeah I hear you. my point was not to confuse engine output with the energy stored in the flywheel which only affects shifting and transient states. Saying 'low end torque' implies its an engine output thing.

A well tuned engine will maintain torque at idle just fine, but a massive flywheel will make idle more stable if the tune is sketchy for some reason.

my list of pros and cons are short -

Pros

• capable of upshifting and downshifting faster (if the driver can keep up)
• faster rev match blips if you're heel toe downshifting.

Cons

• harder for noobs to drive smoothly, and/or stalls easier if you F it up.
• Your average upshift needs to be a little faster.
• you really should be at least attempting to blip or matching RPMs on downshifts.

I love a lighter than stock flywheel because I feel it lets me do my job faster, but it does require more precision with the inputs

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