Ok, here is the deal. I am a little confused and I really want to understand this... And I know this isn't exactly the right place to ask, but the tech forum didn't even respond.

If a lightened flywheel doesn't substantially change how fast a car physically accelerates (I know it does to some degree but mostly its the feeling of accelerating faster that people talk about) but it does make the RPMs increase faster, how doesn't it make a vehicle's 0-60 or 1/4 mile times noticeably better?

I say this because at redline (or at any RPM rate for that matter) in 2nd gear a H22 with a stock flywheel and a H22 with an 8lb. flywheel are both going the same speed. So if the H22 with an 8lb. flywheel gets to redline considerably faster then the H22 with the stock flywheel, how isn't it accelerating considerably faster also?

Be nice to me. lol.

 

i have a theory about lightenend flywheels that matt (mgags) doesnt exactly agree with. IMO i believe that the lightened flywheel increases piston acceleration (not speed) which increase intake velocities which makes it easier for the engine to spin. Basically saying that it takes less punch to get the motor moving.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 98vtec &raquo;</TD></TR><TR><TD CLASS="quote">i have a theory about lightenend flywheels that matt (mgags) doesnt exactly agree with. IMO i believe that the lightened flywheel increases piston acceleration (not speed) which increase intake velocities which makes it easier for the engine to spin. Basically saying that it takes less punch to get the motor moving. </TD></TR></TABLE>

i agree. i have an 8pd flywheel and after putting it on the car seems to be real touchy. if that makes any sense. and on free reving the car does rev up a whole hell ove alot faster in free reving. but everybody has there own opinion.

 

The engines' rotating assembly just has less resistance to rotation. Engine revs easier and faster and the car accelerates faster.

People with heavy big brake kits and big heavy wheels always seem to make less hp on the dyno, so why would things like lighter wheels and lighter engine parts (flywheel for example) not make more power?

 

It's just less rotating mass in your drivetrain, less rotating mass means less lost horsepower from the engine to the ground. (Hawkze beat me)

 

I don't think you guys understood my point.

There are two sides to the argument here, and there is the somewhat unrelated fact that the engine revs faster with one.

The engine's faster revving when not in gear is having to do with the fact that a lighter flywheel reduces the moment of inertia about the crankshaft, so when you have a smaller moment of inertia, less energy is lost to the weight and can go into angular momentum (rpm). Therefore the engine can accelerate faster.

Blake I think you and I are thinking of different things when we say the words "piston acceleration". The higher piston acceleration I believe you're talking about is due to the fact that the rpms are changing more quickly, correct?

The term "piston acceleration" refers to the rate at which a single piston accelerates, and is greatest when coming off BDC (bottom dead center) in most engines. The rpm you're currently at matters in this, because it dictates how fast the crank is pushing the piston away from BDC, but the rate of change of rpm does not matter in that.

The only thing that can effect piston acceleration is the dimensions of the bottom end (mainly rod/stroke ratio)

With that said. The two sides to having a lighter flywheel can be summed up as follows.

The engine will make more torque due to the fact that the decreased moment of inertia about the axis of the crankshaft and transmission shafts in the transmission (because when the clutch is out, they act as one) takes less energy to accelerate, therefore more energy can go into the angular momentum, aka torque.

The other side of the story is that the smaller moment of inertia carries less momentum. So where torque would let off up top due to the engine's powerband, a heavier flywheel would be moving at such rpm that it would have a large amount of momentum, which would contribute to the torque, since it is part of the crankshaft.

This is shown in sr20s well, if you put a lighter flywheel on those things, they lose big torque up top, because the engine won't push hard enough up there to keep going, especially under boost.

A good example of this would be a fan. Turn your living room fan on high and stick your hand in there. Yeah it hurts a little. Now tape 2lb sand bags to all the blades, turn it on. See it takes more time to get going, but once its going, I dare you to put your hand in the way. That would really hurt.

(Yes I know that electric motors and internal combustion engines behave very differently, this is simply a demonstration of angular momentum)



Personally, I'm along the same lines as you guys, especially on our honda engines, I believe the lighter crankshaft benefits more than the loss in angular momentum.

 

Inertia - An object at rest will remain at rest unless acted on by an outside force. An object in motion will remain in motion unless acted on by an outside force.
Its all about reducing inertial drag on the motor. Ive got a 11.5 chromoly on my turbo h23 and when i put it in i noticed that the car would reach full spool much quicker then with the 21 pounder. Since the engine wouldnt have to stress as hard on the flywheel...basic physics.

 

i have a 8lb on my h22. i love the acceleration increase. theres less mass so the engine can turn up faster. only thing i hate about the 8lb if i shift wrong into second it drops out of vtec but if i shift right its all hell :D

 

I read all the reasons. But 7,800 in an H22 in second gear is about 62mph. If a car with a lightened flywheel gets to 7,800 considerably faster than a stock flywheel, how isn't it getting to 60mph considerably faster? I say this because an 8lb. flywheel might make you a tenth or to faster but not a second like it seems.

 

the engine really doesn't rev amazingly faster than a stock flywheel. its not like the car goes from revving like a mini van to revving like an indy car. it was a slight difference in feel if you ask me. a noticable, but slight change.

like people have said before, a lighter flywheel will give you a few more horse. a few horse isn't going to make a full second difference in 0-60 time. trying my best to explain, but i just got off 12 hour shift at work so i'm a little burnt out right now.


Modified by BB6racer at 8:31 PM 4/4/2007

 

The only difference that I noticed with the 10lb flywheel that I have now and the OEM flywheel that came with my H22 is that it stalls out much easier. My motor does rev a little quicker though and I have to rev a little higher when I take off to prevent stalling out. IMO, the $200 that I spent on the lighter flywheel should have been put towards my TB or cams. This is on a H22A with stock internals, I/H w/2.5in collector/E btw. Maybe others notice a difference with more mods than me.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94GSRCivic &raquo;</TD></TR><TR><TD CLASS="quote">The only difference that I noticed with the 10lb flywheel that I have now and the OEM flywheel that came with my H22 is that it stalls out much easier. My motor does rev a little quicker though and I have to rev a little higher when I take off to prevent stalling out. IMO, the $200 that I spent on the lighter flywheel should have been put towards my TB or cams. This is on a H22A with stock internals, I/H w/2.5in collector/E btw. Maybe others notice a difference with more mods than me.</TD></TR></TABLE>

I had a 8lb. ACT flywheel in my last motor. It made a considerable difference in how the car felt. I am not doubting the significant difference it makes. In my opinion it's the single most effective mod you can buy for $160, plus install costs I guess.

Except don't buy a Cromeoly flywheel if you don't have to, I am going with a Fidanza now.


Modified by slim9300 at 8:48 AM 4/5/2007

 

I've got a lightweight fidanza on my h23 and i've noticed a big difference. It's all about torque and momentum. For example, a car with a lightweight flywheel will be slower uphill because of the reduced torque caused by less mass. Less mass = less momentum which means it takes less resistance to slow the rotating assembly. It's mostly a supporting mod though. By itself it doesn't do much, but remove the balancing shafts, the ac compressor, and put on some lightweight pullies, and you'd be reving even faster. But none of those things are really power adders. Once you turbo an engine the torque numbers can be huge, which creates a lot of stress on the drivetrain, a lightweight flywheel can reduce the stress experienced by the drive train.

 

I like my fidanza 8lb. Like others said, it is easier to stall, has less ***** going up steep hills, and I have to rev it to nearly 2k to get a spirited start, but I think these negatives are outweighed by how much easier it is to rev match going into a turn and rev up quicker coming out. I think its a helpful mod if you're into being fast around corners. If you want to be fast in a straight line where launching a car effectively is involved, stay with stock. Although the FW frees up whp (doesn't add hp), the lesser amount of force you have to actualy set the car in motion and get out of the hole, is not compensated for my a few extra horses at the wheels. So to answer one of Slim's questions, a lighter FW may not improve your 1/4 mile or 0-60 time bc there is another factor involver besides acceleration: setting the car in motion. I think the answer would be different though, if we were comparing cars in a rolling start.

 

It's effect not affect.

 

That would be sweet if someone had done a comparison of say a 10-70 mph rolling start with stock versus lightened.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BlownH23a &raquo;</TD></TR><TR><TD CLASS="quote">Inertia - An object at rest will remain at rest unless acted on by an outside force. An object in motion will remain in motion unless acted on by an outside force.
Its all about reducing inertial drag on the motor. Ive got a 11.5 chromoly on my turbo h23 and when i put it in i noticed that the car would reach full spool much quicker then with the 21 pounder. Since the engine wouldnt have to stress as hard on the flywheel...basic physics.</TD></TR></TABLE>

Read my post dude

and on a side note: I seriously doubt that your h23 reaching "full spool" much quicker, unless of course you mean it reaches a certain rpm faster, there is no way at all that a lighter flywheel could directly effect the spooling of your turbo since that is just a function of rpm and constants such as your head flow and cams, etc.

Personally the main reason I enjoy my lighter flywheel is because I can rev match more easily and because its easier to install and remove. Heavy flywheels FTL!

 

Here's my thoughts. You have to seperate this into a couple scenario's. A lighter flywheel will accelerate faster when you are on the gas. All the rest of the time the heavier flywheel will have more momentum and carry the energy further than a lightened flywheel. The one caveat is that when you drop the clutch in first or gas the car in any gear the heavier flywheel obviously has more momentum and will for a split second produce a little bit more torque until the clutch fully catches. At this point and still under accerleration it is a closed system from the wheels to the crank in your engine. So now it's simple rotating mass and ofcourse the less the better.

Now these are my thoughts, I can't back this up with dynos but then again most of us probaly can't. To me however, this makes the most sense. Opinions welcome.

 

Holy ****. That is one of the best explanations I have read in regards to this issue

Matt

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hu &raquo;</TD></TR><TR><TD CLASS="quote">Holy ****. That is one of the best explanations I have read in regards to this issue

Matt</TD></TR></TABLE>

x2

That seems to make sense but im no expert on the matter.

 

Its considerably quicker because there's less rotational mass. Think of it like a lightweight wheels vs chromes, you get more acceleration with the lightweights even if its the same size. I have a 8lb flywheel and accelerates considerably faster but the speeds stay the same, same principal with deceleration. Just my 2 cents.

i didn't really read the thread to the bottom but what ^ said

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Import_Fan &raquo;</TD></TR><TR><TD CLASS="quote">It's effect not affect.</TD></TR></TABLE>


Unless the effect you're trying to generate is affected by an outside source.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 &raquo;</TD></TR><TR><TD CLASS="quote">I don't think you guys understood my point.

There are two sides to the argument here, and there is the somewhat unrelated fact that the engine revs faster with one.

The engine's faster revving when not in gear is having to do with the fact that a lighter flywheel reduces the moment of inertia about the crankshaft, so when you have a smaller moment of inertia, less energy is lost to the weight and can go into angular momentum (rpm). Therefore the engine can accelerate faster.

Blake I think you and I are thinking of different things when we say the words "piston acceleration". The higher piston acceleration I believe you're talking about is due to the fact that the rpms are changing more quickly, correct?

The term "piston acceleration" refers to the rate at which a single piston accelerates, and is greatest when coming off BDC (bottom dead center) in most engines. The rpm you're currently at matters in this, because it dictates how fast the crank is pushing the piston away from BDC, but the rate of change of rpm does not matter in that.

The only thing that can effect piston acceleration is the dimensions of the bottom end (mainly rod/stroke ratio)

With that said. The two sides to having a lighter flywheel can be summed up as follows.

The engine will make more torque due to the fact that the decreased moment of inertia about the axis of the crankshaft and transmission shafts in the transmission (because when the clutch is out, they act as one) takes less energy to accelerate, therefore more energy can go into the angular momentum, aka torque.

The other side of the story is that the smaller moment of inertia carries less momentum. So where torque would let off up top due to the engine's powerband, a heavier flywheel would be moving at such rpm that it would have a large amount of momentum, which would contribute to the torque, since it is part of the crankshaft.

This is shown in sr20s well, if you put a lighter flywheel on those things, they lose big torque up top, because the engine won't push hard enough up there to keep going, especially under boost.

A good example of this would be a fan. Turn your living room fan on high and stick your hand in there. Yeah it hurts a little. Now tape 2lb sand bags to all the blades, turn it on. See it takes more time to get going, but once its going, I dare you to put your hand in the way. That would really hurt.

(Yes I know that electric motors and internal combustion engines behave very differently, this is simply a demonstration of angular momentum)

Personally, I'm along the same lines as you guys, especially on our honda engines, I believe the lighter crankshaft benefits more than the loss in angular momentum.</TD></TR></TABLE>

That's a pretty good example of momentum about an axis.

 

best damn flywheel thread yet. Good explaination +1

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BB6racer &raquo;</TD></TR><TR><TD CLASS="quote">the engine really doesn't rev amazingly faster than a stock flywheel. its not like the car goes from revving like a mini van to revving like an indy car. it was a slight difference in feel if you ask me. a noticable, but slight change.

like people have said before, a lighter flywheel will give you a few more horse. a few horse isn't going to make a full second difference in 0-60 time. trying my best to explain, but i just got off 12 hour shift at work so i'm a little burnt out right now.


Modified by BB6racer at 8:31 PM 4/4/2007</TD></TR></TABLE>

My buddy put a twin plate in his gsr turbo eg and that thing really did go from revving like a mini van to revving like an indy car!! Actually more like a street bike!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BB6racer &raquo;</TD></TR><TR><TD CLASS="quote">the engine really doesn't rev amazingly faster than a stock flywheel. its not like the car goes from revving like a mini van to revving like an indy car. it was a slight difference in feel if you ask me. a noticable, but slight change.

like people have said before, a lighter flywheel will give you a few more horse. a few horse isn't going to make a full second difference in 0-60 time. trying my best to explain, but i just got off 12 hour shift at work so i'm a little burnt out right now.


Modified by BB6racer at 8:31 PM 4/4/2007</TD></TR></TABLE>

i agree. if your expecting big gains like a sec. u will be disapointed.