Do lightweight flywheels make much difference?

[steffen707]

Originally Posted by dcb

so you are saying you have no first hand experience with lighter flywheels in cars? Unlike steffen?

Well I do have experience with one car with a light fidanza flywheel and it did certainly accelerate faster than with the old one. But I never did a before and after mpg test because this was an autocross car.

Maybe he is right that it will require more throttle to keep a given speed and this decrease the mpg, but again no real life apples to apples data.

There has to be somebody on this forum that has tried this. I'm already going to compare stock Vx gearing in my 97 civic dx with vx engine to the same setup with Crx hf gearing, but don't feel like pulling the tranny a third time to swap in the light flywheel to maybe have to pull the tranny a fourth time to put the stock flywheel back if it loses mpg. But if nobody else has any data, then that can be my contribution to this great website.

[steffen707]

Originally Posted by autoteach

I would spoil you if I were to develop a graph that would show the power impulses from each cylinder (showing acceleration of the crank) and the coinciding compression stroke (deceleration) and how that effects fuel consumption. Imagine how strong the impulse has to be that is put in if the flywheel is to light. Imagine the impulse that needs to be put into the equation if the flywheel is heavier. Lower rpm use will require more throttle (%) to keep the engine overcoming the compression stroke. If you think I am bat **** crazy, or I am some type of moronic asshole (which you do as you believe a piece of data off a graph for HP seekers is also the data the mpg seeker should look at), take the blade off your lawmower (flywheel for most, besides the ultra lite aluminum "fan) and start it up. I am sure that it will respond quickly, but will require a higher idle speed and more throttle to maintain any given RPM. But, I am just some dumb fool, almost always "proven wrong" by my students (especially when it comes to how stupid humans can be). Give it the old college try, and start up that lawnmower (and tell me about your experiences with it).

I don't think you are bat **** crazy or a moron, I just think if you are gunna post on a forum answers like because I said so like you did on the first page, then you might as well not post at all. Forums are to help people and not discourage them. Your explanation above was great and I'm now doubting my own uneducated gut feeling, but I still won't be satisfied until I see real world results of mine or somebody else's from a car.

[S2k-Takara]

Hey guys! I'm fairly new to ecomodder, I just wanted to mention what I had found about this with my CRX. I had went from stock flywheel (I dont know the weight, but someone can look it up if they care to.) getting 37-39mpg on long LA drives to a 7lb aluminum flywheel when I replaced the clutch. It took me a good week or so to really get the hang of driving it. When another trip to LA (from Bay Area) came up 2 weeks after the new clutch and flywheel were installed, I was really excited thinking I would get more mpg. What I found was that I was getting 33-34mpg in my crude measurements. But another month later I got the same results. The car was more responsive, and accelerated faster..and revved up faster...but after hitting the gas in neutral...the rpms decreased much faster with the 7lb flywheel. I didn't care much at the time, I wanted good gas mileage, but at 20 years old, I wanted to have fun more.

[steffen707]

ecomodder.com/forum/showthread.php/test-alternator-vs-no-alternator-10-mpg-gain-98.html
Metrompg found a 10% increase from an already very fuel efficient vehicle from reducing parasitic drag on the motor and deleting the alternator. I'm curious how this differs from the extra weight of the flywheel on the crank.

Drag racers delete their alternator and run on battery often because it steals HP, and Metrompg found it also will increase mpg.

Maybe lighter flywheel will give more mpg and has already been dyno proven to increase HP??

[steffen707]

Originally Posted by S2k-Takara

Hey guys! I'm fairly new to ecomodder, I just wanted to mention what I had found about this with my CRX. I had went from stock flywheel (I dont know the weight, but someone can look it up if they care to.) getting 37-39mpg on long LA drives to a 7lb aluminum flywheel when I replaced the clutch. It took me a good week or so to really get the hang of driving it. When another trip to LA (from Bay Area) came up 2 weeks after the new clutch and flywheel were installed, I was really excited thinking I would get more mpg. What I found was that I was getting 33-34mpg in my crude measurements. But another month later I got the same results. The car was more responsive, and accelerated faster..and revved up faster...but after hitting the gas in neutral...the rpms decreased much faster with the 7lb flywheel. I didn't care much at the time, I wanted good gas mileage, but at 20 years old, I wanted to have fun more.

Thanks takara! Anybody else have similar results?

[S2k-Takara]

Originally Posted by steffen707

Thanks takara! Anybody else have similar results?

I think your question should be if anyone has similar experience....the results may vary by car?

[steffen707]

Originally Posted by S2k-Takara

I think your question should be if anyone has similar experience....the results may vary by car?

Very good point. My gf and I drove 3 hrs to Minneapolis and back this weekend. We started with a full tank drove 72 mph there got 22.5mpg in her 03 v6 camry. The tires were 8psi low at the gas station in minneapolis. Aired them up drove home without cruise cuz she was following me in the civic I just bought without cruise. We gassed up at home and she got 30mpg. I don't know if it was just the low tires or if she had the AC off the whole time, but wow!

Point being lots of factors go into mpg. With your experiences with the 7lb flywheel did you change anything other than the flywheel? AC use, drive faster, have more traffic or was it overall same conditions?

[ShadeTreeMech]

I'm of two minds on this one. If you're accelerating and decelerating a lot, a lightweight flywheel "may" help. But I wouldn't consider a heavy flywheel in the same class as a parasitic drag, such as a power steering pump or alternator. The reason being, if you had a motor minus the head so the crankshaft and pistons could spin freely, and you compared how long the crankshaft spun with a heavy flywheel vs a lightweight flywheel, I bet the heavy one would win. Following that line of logic, it can't be considered parasitic drag if it makes the crankshaft spin for longer.

It may not be parasitic drag, but how much does it cost the engine in fuel to keep a heavy flywheel turning? I don't know.

However a motorcycle engine does not have a heavy flywheel of any sort (unless you go into Harleys) and they tend to do well on fuel. But they do require a higher rpm to idle smoothly and tend to require a bit more feathering of the clutch.

To s2k-takara I would wonder if having the more lively throttle response may have helped him develop more of a lead foot?

To autoteach, as right as you may or may not be (I haven't a clue) you could have been a lot more civilized and diplomatic for certain. Honey attracts more flies than vinegar and all that....

[user removed]

In the Civic VX they went with a lighter flywheel and lower idle speed. Not the smoothest idle but at 450 RPM you can just about feel every power stroke, and idle fuel consumption is very low, probably about .12 GPH.

I have seen car with very light flywheels where the gears in the transmission rattled against each other in neutral, even at idle speeds above 1000 RPM.

I would imagine there would be a benefit up to a point in lighter flywheels. The question is where is the point where the consequences of a lighter flywheel become significant.

Only one way to find out, I guess, but you wont see me swapping flywheels to see which one gets me 1% better mileage. Instead I would do some research into the difference between the stock 94 Civic and the VX flywheels, which would give you a fairly good idea of what Honda did to get the best mileage possible.

regards
Mech

[steffen707]

[QUOTE=Old Mechanic;178620Instead I would do some research into the difference between the stock 94 Civic and the VX flywheels, which would give you a fairly good idea of what Honda did to get the best mileage possible.

regards
Mech[/QUOTE]

Oooh, great idea, i'll have to try and research this, may be difficult though.

At any rate keep the good info coming. What I might do instead of putting the vx trans in first with the stock flywheel, I may put it in with the light one, that way if all this info does point towards heaver ie 16lbs ish is best, then I have one less trans swap to do.