I am wondering how much difference it would make between using an aluminum or steel flywheel on a 3800?
Could you feel much difference in acceleration?

What would be the pros and cons?

Thanks, Steve

I bought an aluminum flyhweel from Spec when I did my 3800SC swap, but I haven't driven it yet so I guess I can't be of any help to you.

I have already been told I was better off with a steel one and after doing some more reading, it seems that it is good for road racing and maybe drag racing but for a DD, the steel one is a better choice.

Steve

The advantage of an aluminum flywheel over a steel one is that it is considerably lighter. This means your engine has to do less work to spin the weight of the flywheel, allowing more power to be put to the ground and allowing the engine rev up faster and more easily. We're not talking about a lot of power here, probably not even enough to actually notice without going to a dyno, but you will probably notice it revs freer. The idea is that every little bit helps. The disadvantage is that all the stored energy in a big, heavy, steel flywheel is what helps you start smoothly from a stop. An aluminum flywheel will have less stored energy, so you'll have to give it more gas when starting from a stop than you would with a steel wheel, and it may not be as smooth.

Ideally the outside edge of the flywheel is heavy and the center part is lighter. This is because your most effective weight is in the perimeter, as this results in more intertia/oz. That's why flywheels will have holes in them to lighten the centers.

Not sure if this is relevant, but I put a 5.5lb aluminum flywheel behind my wife's VR6 Fiero. The stock weight is 25lbs. I also dropped a 12lb crankshaft damper for a 500g damper. There is no driveability issues on the street. It is also a daily driver that sees about 800 miles a week....mostly just long drives through the countryside, but enough stop and go to shred a set of rear tires in 6000 miles.
The engine does not feel floaty or any have any stalling issues. I wished I went with a 15lb steel flywheel, but the donor car came equiped with the aluminum, so I left it.
JMO,
Dave

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1987 GT (my toy-see above), 1987 GT (daily driver), 1986 SE with a VW VR6, certified master technician/shop owner
www.njautobahn.com

Ok...I have decided. From what I was told,readings and posted here, Im going with a steel one.

Thanks for the input everyone.

Steve

There's only one person here who's ACTUALLY DRIVEN a car with an aluminum flywheel, and he says that there is no problem with driveability.

What caused you to make that decision?

I haven't used one yet, but from what I've read from people who have ACTUALLY DRIVEN cars with aluminum flywheels, the effect is very significant and very noticeable.

David Vizard published an investigation of how much lightweight flywheels actually help/hurt and found that a Mustang could dyno 85 HP higher in 4th than in 1st. Almost all of that is power that's sapped by moment of inertia of the driveline... and a LOT of it is recoverable by changing to lighter parts.

So don't take your advice from armchair theoreticians who don't grasp the physics of flywheels... go out of get info from people who ACTUALLY DRIVE cars with aluminum flywheels.

[This message has been edited by Will (edited 12-14-2008).]

quote Originally posted by Will: There's only one person here who's ACTUALLY DRIVEN a car with an aluminum flywheel, and he says that there is no problem with driveability. What caused you to make that decision? I haven't used one yet, but from what I've read from people who have ACTUALLY DRIVEN cars with aluminum flywheels, the effect is very significant and very noticeable. David Vizard published an investigation of how much lightweight flywheels actually help/hurt and found chassis dyno gains on a Fox body mustang in the neighborhood of 10 HP in 4th and 50 (FIFTY!!!) HP in 1st. So don't take your advice from armchair theoreticians who don't grasp the physics of flywheels... go out of get info from people who ACTUALLY DRIVE cars with aluminum flywheels.

I know my N* is going to sound great with the 7 lb Spec flywheel and free up some power .

[This message has been edited by Erik (edited 12-13-2008).]

I've used a bajillion 11lbs and 8lbs ones in my DSMs

They are great yo

[This message has been edited by RideZiLightning (edited 12-13-2008).]

I haven't driven any of the late model cars wilth aluminum flywheels installed, but in my younger days, we used Schaefer aluminum flywheels on the early Chevy V8's. There was a noticeable difference over the steel flywheel, with everything else on the engine being unchanged. Now, I'm talking 265's, 283's, 327's with 250 or better HP. If you gain 10%, that's 25+ HP, and pretty noticeable. 10% on a 140 HP engine might not be so noticeable.

The happy medium has to be determined since a flywheel can be to light or to heavy for a given engine. The difference and how noticeable it is will depend on the weight difference between the flywheels and how powerful the engine they are bolted to is. A 12-15 lb difference on a 500 hp engine may only show up in the quarter mile times, when you consider the heavy flywheel will offer an advantage on launch and between shifts as opposed to the faster rev with the lighter flywheel.

I know the heavier 25 lb G6 flywheel has a lot to do with the tire chirp on the 1-2 shift and the sustained surge between the following shifts before falling off in my car with the understanding that going to the 6spd in place of the standard V6 4 spd plays a part also . I can still sense the character difference between the two flywheels however once the bottom end performance is restored in my engine by advancing the cam, aggressive shifting is likely to result in even more tire spin and possibly a tire chirp in the 2-3 shift as a result of the heavier flywheel. My 3.1 couldn't chirp anything past first gear and it was closer in power to my 3.9L on take off due to the cam being fully retarded in the 3.9L biased towards peak power.

I had a modified 2.8L flywheel in my 350 car, I noticed the dive the car tended to take due to a more rapid decelleration when taking my foot off the gas pedal abruptly in the lower gears than how quick it revved up.

Just don't over do it since to much or to little of a good thing can be bad.

[This message has been edited by Joseph Upson (edited 12-13-2008).]

Being that the last manual 3800 swap I did, I used an alum flywheel, I will say that the only difference I noticed was more power, and faster revving when the motor was unloaded.... VERY impressed with the quality and accuracy from spec. Many people drove it and said that it felt similar to a light duty aftermarket clutch with semi harsh engagement. My programming and a northstar TB makes it nearly impossible to stall with any flywheel, and the alum seemed to preform the same as the heavier irons I have used.

In the time I had the car, it broke an axle and held down power that broke 275 series performance summer tires loose from a 30 roll with just the gas pedal.

I say for the extra few bucks go alum and dont look back.

quote Originally posted by darkhorizon: ...and held down power that broke 275 series performance summer tires loose from a 30 roll with just the gas pedal.

Dang. I know programming is everything but does that TB swap add that big a punch as well? Was that with stock boost?

quote Originally posted by Joseph Upson: when you consider the heavy flywheel will offer an advantage on launch and between shifts as opposed to the faster rev with the lighter flywheel.

David Vizard investigated this very item and found that in 1/4 mile acceleration, the lighter flywheel resulted in better times across the board.
The same launch technique with a lighter flywheel resulted in a bog, BUT by increasing launch RPM, the cars cut 60 ft times with the light flywheels that were as good as what they did with the heavy flywheels, AND were faster at the end of the strip.

http://www.popularhotroddin..._increase/index.html

quote Originally posted by Bubbajuju: Dang. I know programming is everything but does that TB swap add that big a punch as well? Was that with stock boost?

It was modded heavily, cam, ported blower housing, full headers, extremely complicated exhaust, 2.8/3.0 pulley, and no IC to be found anywhere . No headwork though, Ill save it for my next project.

I never did get timing and race gas in it, I expected 350-370+whp with tuning on real gas, but its just bench racing at that point.

The original purpose of a flywheel is to keep the engine turning when there is no power being applied. In a single cylinder 4-cycle engine (like in a lawn mower), a comparatively massive flywheel is needed (provided by the steel lawnmower blade), since power is only being applied 1/4 of the time. The more cylinders you add, the less un-powered time there is, and the less mass you need in the flywheel. With 6 or more cylinders, high mass is not needed at all, so aluminum should be better.

[This message has been edited by pswayne (edited 12-14-2008).]

My experience with lighter flywheel was better acceleration ,I noticed no difference in braking ,, a lighter flywheel will not neccessarily increase Horse Power it will bring the power on faster at lower and mid range ,,., the engine spins quicker,, this gives better performance around town and will give a slight increase in MPG..
The performance gain is from 10mph to 70mph ,,you want to improve drive line inertia,, this has no effect on top speed NON.. you have to lower the weight of the other components in the drive train to make best use of a lighter flywheel ,,the weight of the tires and wheels is crucial,, they are connected DIRECTLY to the flywheel,,Inertia is about acceleration,rapid take off,,
The easier the drive train spins the faster you accelerate //The flywheel is DIRECTLY connected to the driveshafts the wheels the rotors,,drilled rotors hurt stopping distance but help you accelerate faster..
Removing weight from the drive train is the same as cutting weight from the flywheel

[This message has been edited by uhlanstan (edited 12-16-2008).]

Idea: I understand harmonic balancers are used to improve the balance of an engine. This is conceptual out-of-the-box thinking: what about instead putting two very light flywheels? The flywheels would do the work of the harmonic balancers, as they'd be calibrated for the engine. You'd have less weight/more inertia. The idea just came to my head. Those of you willing to think outside the box and who know more about the physics of flywheels and balancers can contribute to the idea.

The best machines were once new ideas.

-Michael

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"A guy know's he's in love when he loses interest in his car for a few days." -Tim Allen

He who dies with the most toys... still dies.


Check out my restoration!

most harmonic balancers are the crankshaft pulley that drives the alternator. A light weight damper is a common upgrade on most cars. Like I stated before, I removed a 12lb crank damper and installed a 500g damper in it's place. I've heard some say that lightweight flywheels are only good for road racing, but it all depends on how the rest of the engine is set up. If you are planning a turbo setup, I'd stay away from a superlight flywheel. That would actually hurt the boost because there would be less mass loading the engine. Hell, if we are going to have a serious talk about flywheels, I need to grab a killians.
Dave

[This message has been edited by bmwguru (edited 12-14-2008).]

Don't forget that a lighter flywheel is less likely to cause tranny failure. When you drop the clutch the engine will slow down more instead of slamming the tranning with all that rotating mass. With our choices of strong trannies somewhat limited I think this is an important point.

quote Originally posted by bmwguru: If you are planning a turbo setup, I'd stay away from a superlight flywheel. That would actually hurt the boost because there would be less mass loading the engine.

LOL... That's absurd.

quote Originally posted by Will: LOL... That's absurd.

Just from my EXPERIENCE on German boosted engines. I assumed it would be the same on American stuff.

I've heard too about going too light with the flywheel hurts the high spooling with a turbo. I've got the Fierostore billet steel one that they claim is 12 lbs but come to find out, it's 14 lbs. It's still better than 17 from the original.

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Is there a correct way to lighten the flywheel?

skim off the top and make it thinner,,,,,,, put holes in it but make it balanced,,,,,,,,,,,,,,, or a donut grove trench centered on the flywheel

I have seen an archie flywheel that was dremeld like mad after the clutch was installed... Basically all you need are the bolt bosses and the friction surface, the rest can go.

quote Originally posted by bmwguru: Just from my EXPERIENCE on German boosted engines. I assumed it would be the same on American stuff.

If you need "more load" to make boost, change gears. VW has plenty of options.
More flywheel mass is never a good thing for going faster.
DSM's and turbo Honduh's LOVE lightweight flywheels.

So what performance increase have you seen by increasing flywheel mass?

quote Originally posted by Will: If you need "more load" to make boost, change gears. VW has plenty of options. More flywheel mass is never a good thing for going faster. DSM's and turbo Honduh's LOVE lightweight flywheels. So what performance increase have you seen by increasing flywheel mass?

I don't increase flywheel mass, I just have had happier results from using a light weight steel flywheel or a moderate aluminum flywheel. My 5.5lbs Fidanza wouldn't be the best option for a boosted VW, but then again, I am not comparing the cars on the dyno. I am discussing what feels better to the customer on the street on their daily driver. There are plenty of options to build better boost, but a lot are not for the daily driver.
I had a feeling that my post might stir the pot and I guess I was right. I also don't know what a DSM is and the only Honda I work on belongs to my wife.
Dave

Define "what feels best"? Easiest to pull away from a stop smoothly? Best "butt dyno" return? Coolest sounding BOV? Best 1/4 mile time?

It's been THOROUGHLY proven that lighter rotating assemblies make for better acceleration (see Vizard article linked above), but it's equally easy to show that ultra-light rotating assemblies are NOT easy to drive. YOU should have made it clear that was the distinction you were making when you said that.

DSM = Diamond Star Motors; usually refers to 89-98 Mitsu Eclipse, Eagle Talon or Plymouth Laser. They were available AWD and had turbocharged Mitsu 4G63 2.0 litre engines. The fastest with stock block are in the '8's... I think the fastest that's still AWD is in the 9's.

You know what a Honda is, at least... They've topped 700 HP from B series engines.

[This message has been edited by Will (edited 12-15-2008).]

Not looking to get into a pissing contest over something that I really don't care about. I know what works for the cars I work on. To get the best performance without losing reliability or driveability. I don't repair Jap cars, so I don't know much about them. Tuning a car doesn't mean to put the lightest flywheel possible and run the engine rich to compensate for the boost. There are a few tuning companies that make really good "kits" for the German cars that I have installed, fine tuned and for the five figure prices, the customer has been more than happy with the end results.
I know little about the 3800. I have no intention of learning about it. It won't make me any money, so what is the point? I thought I'd add my input for my experience with light weight flywheels and now it has gotten me into a discussion that is making feel the need to defend my 15 years as a tech....and 17 years as a Fiero owner.
Dave

For performance you take material from the outer edge of the flywheel ,, you scallop it , in 4 placesthis was common knowlege before so many performance parts were available ,,you lighten the whole drive train starting with the flywheel then lighten the clutch and pressure plate ,,you lighten the drive axles (I drill holes in mine ) Every thing that spins and rotates..
There is a price to pay but it is small and ignored by men who want smoke off the line and a faster car.. I did not notice any real change in braking but many do ,,but I have never had a real light flywheel and was not really concerned about the car as I was more into scooters/drinking/loose intelligent women in those days ..
BMW guru makes sense to me

[This message has been edited by uhlanstan (edited 12-16-2008).]

Its always a trade off somewhere. Aluminum may rev quicker, but it can make it run rougher. Mass will absorb some vibration that lightness wont. I never had an aluminum one myself to my knowlege, but Id have to think there is also more wear in use. Its not uncommon for old clutches to last 50 years. I had a friend with a 30? chevy with original clutch.

quote Originally posted by bmwguru: I didn't answer your question. What feels best is mainly what the customer wants to achieve with his car. The second question I ask is what they want the end result to be. The first question is how much they want to spend. From my experience, the VW 1.8t and VR6 turbo have performed better on the street and at the track with a 10-13lb flywheel. The 5.5lb one I am running is fine, but I think it could be a bit heavier. I've driven VR6 cars with the stock flywheel, a 15lb steel, a 10lb aluminum and a 5.5lb aluminum. The 10lb was the most beneficial IMO. Dave

I'm still curious about how "too light" a flywheel affects performance and boost.

quote Originally posted by Will: I'm still curious about how "too light" a flywheel affects performance and boost.

The numbers on a dyno will probably show better with a lighter flywheel, but as for actually driving a turbo BMW or VW on the street, a mid sized flywheel feels better. I should have never even stated my opinion for the cars "I WORK ON". I am not going to continue this debate. Just don't expect much help from me in the tech section in the future. I am not a GM tech. The cars I work on don't use pushrods, and I still don't understand why GM uses them.
Dave

yes, I cannot see any reason\cause for a heaveir flywheel EVER on a motor with 4 or more cylinders. yes, a rough running motor, a heavy flywheel may absorb some of the roughness - but - I would much rather fix the roughness, than band-aid it with a heaveir flywheel. and, I can perhaps see a preferance in downshifting/engine braking - but, again - preferance - nothing else.

but, if ya wanna get stupid - how's about a variable weight flywheel - which gets lighter as it spins up? so its nice & heavy for the clutch dump, and quickly moves the mass inwards for less wieght, as rpms climb. yes - just asking for more stuff to break.

quote Originally posted by bmwguru: The numbers on a dyno will probably show better with a lighter flywheel, but as for actually driving a turbo BMW or VW on the street, a mid sized flywheel feels better. I should have never even stated my opinion for the cars "I WORK ON". I am not going to continue this debate. Just don't expect much help from me in the tech section in the future. I am not a GM tech. The cars I work on don't use pushrods, and I still don't understand why GM uses them. Dave

Don't be silly! The information is most valuable to those who don't know as much as you or Will about the subject so keep it comming, I appreciate it. The more knowledge you have the less you tend to listen to others (I'm guilty of that), it is clear there is a benefit to the heavier flywheel beyond just getting down the straight as fast as you can favoring light weight, particularly since they continue to find their way onto stock cars. The cars you work on are different but the concept is the same. Maybe some formulas and more details associated with referenced examples will help give a better understanding of the differences that count over all.

[This message has been edited by Joseph Upson (edited 12-16-2008).]

quote Originally posted by Joseph Upson: Don't be silly! The information is most valuable to those who don't know as much as you or Will about the subject so keep it comming, I appreciate it. The more knowledge you have the less you tend to listen to others (I'm guilty of that), it is clear there is a benefit to the heavier flywheel beyond just getting down the straight as fast as you can favoring light weight, particularly since they continue to find their way onto stock cars. The cars you work on are different but the concept is the same. Maybe some formulas and more details associated with referenced examples will help give a better understanding of the differences that count over all.

I concider myself to be a pretty decent tech. I've had new car dealers send me electrical headaches that their head tech couldn't diagnose. My idea of tuning a car is not just rolling races and 1/4 mile times. I like to see a car that is fun to drive as well. I'm expecting a thread to start on RFT (no I am not a member there) about my insane BS and how the lightest flywheel obviously is the best. Maybe on a 3800 it is the best, but IMO there is a happy medium.
I also will never purchase a dyno for my shop. The last thing I want is to make $100 per hour of tuning when I can make 4x that using the flat rate system on a set of brakes or a tune up. We charge four hours to replace spark plugs and ignition wires on a 2000 V8 Benz. That is book time. I can do that in about 30 minutes. It has been discussed as to why I won't own a dyno, but I really can't see spending about $100,000 for an AWD dyno (50% of my tuning cars are AWD) and there isn't much call for it in my area......and everyone knows a friend that knows a friend that can sneak it in on thier Dad's shop dyno.
I'm getting off topic, but I'm pretty fed up with the new age technology of boost it until it blows the engine. I'd rather be consistant and be able to drive my car home.
Dave

quote Originally posted by bmwguru: I should have never even stated my opinion for the cars "I WORK ON". I am not going to continue this debate. Just don't expect much help from me in the tech section in the future. I am not a GM tech. The cars I work on don't use pushrods, ....... Dave

Don't be like that. Some people just have to hammer on those that have a valid opinion based on what they do all the time.

They try to beat up on the people who really do have some technical knowledge. They beat on you hard enough & long enough that you give up on trying to help people who ask technical questions.

Then they go on other forums & beat up on PFF & say that there are no good techs posting on here.

Archie