I have been in discussion quite a bit with a very knowledgable car tuner about whether or not a heavier or lighter flywheel is better for roadracing. My initial instinct tells me that the lighter the flywheel I have the better, but he begs to differ. He claims that because i'm basically never accelerating and i'm basically always at high rpms that it is better to have a heavier flywheel. His reasoning is because a heavier flywheel takes a longer time to slow down and therefore my rpms wont fall as much when i'm off the gas.

Thats the short story/explaination.

What do you all think?

 

lighter flywheel = easier to rev = easier to heel-toe = I like my light flywheel (9.5 lbs)

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by luder94si &raquo;</TD></TR><TR><TD CLASS="quote">lighter flywheel = easier to rev = easier to heel-toe = I like my light flywheel (9.5 lbs)</TD></TR></TABLE>

Right... but the opposite of "easier to rev" would be "harder to decelerate"?

If that truly is the case... perhaps my friend is correct. While going through braking zones and corners the engine won't lose as many revs as normal. I would lose acceleration, but thats only during the start (which is normally a moving start anyways)

??

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cyrio &raquo;</TD></TR><TR><TD CLASS="quote">

Right... but the opposite of "easier to rev" would be "harder to decelerate"?
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I don't think that is the case. Look at it in drive line loss.. everything between the piston and the rubber to the road will take power to move (called drive line loss). by reducing the drive line loss you'll "free" up some HP that can make it to the ground. Taking a few LB off the FW is a cheap place to free up some HP.

the only pro i can think of for a heavy FW in racing is for standing starts.. but will hurt in acceleration

 

Your friend has an interesting theory about it. Just thinking it out...would then be better to go out and buy a heavier aftermarket flywheel? Or is there a specific weight that would be optimum for road racing it is just happens not to be the lightest (or heaviest)?

I've had conversations with many people about the majic lightened flywheel mod. While it shows hp gains on some dynos, the type that actually places a load on the car (it mounts to the hub of car) doesn't.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cyrio &raquo;</TD></TR><TR><TD CLASS="quote"> He claims that because i'm basically never accelerating and i'm basically always at high rpms that it is better to have a heavier flywheel. His reasoning is because a heavier flywheel takes a longer time to slow down and therefore my rpms wont fall as much when i'm off the gas. </TD></TR></TABLE>

??Perhaps your pal has never driven on a road course??

A big part of making fast laps on a road course is how well you accelerate and decelerate. The fast guys take advantage of every (legal) opportunity to reduce rotating mass. Crank pulleys, flywheels, clutches, crankshafts, rods, pistons, wheels, tires and even lug nuts. An old car builder's rule says that reducing rotating mass by 1 lb is equal to removing 8-10 lbs from the car body. Dead weight hurts performance; rotating weight KILLS performance.

Keeping revs up is best accomplished with proper gearing, entry speeds and preservation of momentum, not heavy flywheels.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cyrio &raquo;</TD></TR><TR><TD CLASS="quote">

Right... but the opposite of "easier to rev" would be "harder to decelerate"?

If that truly is the case... perhaps my friend is correct. While going through braking zones and corners the engine won't lose as many revs as normal. I would lose acceleration, but thats only during the start (which is normally a moving start anyways)

??</TD></TR></TABLE>
Not true, there is a limit to how fast you can go through a corner. Let’s say you are going through the corner at max velocity. Since there is a connection between the engine and the wheels through the driveline, your RPM's will be the same for a given vehicle speed regardless of flywheel weight. Your ability to accelerate on exit makes the difference on how fast you get to the next corner, beat the other car to the next corner and you made a pass, making a pass gets you to the front. All things being equal, a lighter flywheel will allow the engine to accelerate faster (proven fact, less mass)..

Make sense?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cyrio &raquo;</TD></TR><TR><TD CLASS="quote">

Right... but the opposite of "easier to rev" would be "harder to decelerate"?

If that truly is the case... perhaps my friend is correct. While going through braking zones and corners the engine won't lose as many revs as normal. I would lose acceleration, but thats only during the start (which is normally a moving start anyways)

??</TD></TR></TABLE>

But a lighter flywheel has less momentum, and will decelerate faster.

the only time a lighter flywheel is disadvantageous is a standing start, becaus eit is easier to stall withotu the extra momentum. like you said, your starts are usually rolling.

I see onyl advantages to a lightened flywheel for RR/AutoX. drag racing, on the other hand....

 

[QUOTE=Safir]
the only time a lighter flywheel is disadvantageous is a standing start, becaus eit is easier to stall withotu the extra momentum.
QUOTE]

Depending on the car, standing starts are not an issue with light flywheels. Do soft clutch drop at a certain rpm, the clutch hooks up, get a little wheel spin, then it goes like hell. Once you've made it past the first 10 feet, the light flywheel is your friend.

 

It sounds like your knowledgable "tuner" isnt very knowledgable with all that misinformation he's been feeding you.

 

Agreed.. Thats a complete load of BS. A heavy flywheel will make your car slower everywhere on the track.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Track rat &raquo;</TD></TR><TR><TD CLASS="quote">??Perhaps your pal has never driven on a road course??</TD></TR></TABLE>
My thought exactly. He may be bright and have some talent as a tuner, but it doesn't sound like he's ever driven a car before and after installing a light flywheel... If he has, he's probably a drag racer who's never even thought about braking hard and downshifting at the same time.

You want a light flywheel. Period.

 

Lighter mean faster, period. If you want to keep the rev high, do a throttle blip while braking or changing gear.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thawley &raquo;</TD></TR><TR><TD CLASS="quote">he's probably a drag racer</TD></TR></TABLE>
I was just thinking that same exact thing.

 

I have done a few HPDEs using a 7.5lb flywheel. Heel-toe is soo easy and quick. Lightweight flywheel gets from me.

 

Would a turbo care what kind of flywheel is in there? ...on a road course

 

The only downside of a lightweight fw on a turbo car is when the revs drop, you may drop out of the power band and the turbo may lag. So then it will be your job to keep the revs up--left foot brake, power shift, and rev match during shifts.

 

A light flywheel won't give you any horsepower. But it will take less time to get the revs up where the power is at(like has been said). It increases the teansient response of the motor.

Especially with hondas where all the power is in high revs, a light flywheels can help alot. if the engine can take less effort and time to get to redline, where the meat of the powerband is, then you'll be faster. Sure the rev's drop faster, but they climb faster too.

 

I think your tuner friend has no idea what he is talking about. You are in a constant state of acceleration on a roadcourse, whether it be in the positive (gas) or negative (brake) direction. A lightweight flywheel is the ONLY way to go if you value performance and safety on course. From a performance standpoint the rpms will climb and drop faster which is good for acceleration and braking/downshifting for corners. Lighter flywheel = less rotating mass, and the quicker throttle response makes cornering easier to fine tune/modulate. You WANT the rpms to fall quickly when you are off the gas! The big negative of a stock or heavier flywheel is braking - you will be putting a heavier load on the braking system and actually be hurting your cars braking ability. The last thing you want to do is degrade your car's braking ability on track, which is what you would be doing with a heavier flywheel.

Even for drag racing a lightweight flywheel is better than a heavier one on a low torque higher revving motor. My brothers '90 Integra RS with ACT Prolite flywheel (8.8lbs) is quicker off the line at the drag strip than my V6 Camaro and can keep up until about the 1/8th mile. That's with a theoretical 5lb per lbft torque defficiency of the Integra verses the Camaro. A lightweight flywheel helps acceleration in a high revving engine. The engine won't make anymore power because of it, but you are freeing up the energy that would otherwise go into accelerating the uneccessary extra mass of a heavier flywheel, giving a noticable boost in performance from a dead stop that seems to equal a 4-5 lb per lbft torque power to weight ratio deficiency!

There are no positives with using a heavier flywheel on a roadcourse, only negatives!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JamesS &raquo;</TD></TR><TR><TD CLASS="quote">Would a turbo care what kind of flywheel is in there? ...on a road course</TD></TR></TABLE>

Lighter the better (to a point).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Vracer111 &raquo;</TD></TR><TR><TD CLASS="quote">You WANT the rpms to fall quickly when you are off the gas! The big negative of a stock or heavier flywheel is braking - you will be putting a heavier load on the braking system and actually be hurting your cars braking ability. The last thing you want to do is degrade your car's braking ability on track, which is what you would be doing with a heavier flywheel.
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Not trying to argue here, but driving these lightweight fwd cars I've found you try to use as least brake as you need to get you through a turn as fast as you can. If I'm still a bit too hot entering a turn, then my setup (with heavy flywheel) at least allows me (most of the time,lol) to use the throttle (off-throttle) to maybe still get to the apex. It works most of the time, and comfortably slowly at that. I guess my dumb point is that I thought these were "momentum" cars so you want to keep as much momentum in the motor as you can to get through the corners quickly.

The disclaimer is that I have zero experience with driving a light flywheel car on any course and thus the dumb point.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JamesS &raquo;</TD></TR><TR><TD CLASS="quote">N"momentum" cars so you want to keep as much momentum in the motor as you can to get through the corners quickly.</TD></TR></TABLE>

Every car is a momentum car. p=mv.

A lighter flywheel will give you better braking and better acceleration, make shifting easier, and it's lighter which is always good. You're WAY over-thinking this.

You want a light flywheel for some of the same reason you want light wheels. There's no 25 lb racing wheels available because they slow down acceleration.

-Chris

 

Huge spinning flywheel
Means more current going to
Your 5 subwoofers

 

My head assploding
Less weight is always better
Unless the car breaks

 

lighter is better,
no flywheel is the lightest,
yeah, thats the ticket.