Do lightweight flywheels make much difference?

[steffen707]

Originally Posted by dcb

from the link:
Dyno Comparison
Lightweight Flywheel
+8.35WHP and +8.10TQ

Win win with the lightweight flywheel, that extra rotational mass takes a big bite. The launching doesn't bother me, I'll get the hang of it.


re: baseline, can't do, the car is screwed and needs a clutch (isn't disengaging) not apples to apples after I get a new clutch in.

The baseline of the dyno above was 111 tq and 126hp BTW. So a gain of 8 is quite a bit. The extra hp and tq has to equate to better mpg. Hopefully somebody can show some apples to apples figures.

I've driven a stock crx with stock flywheel and then with 7lb light flywheel, it takes some getting use to, but if the main use of your vehicle is for highway driving, then you don't come to complete stops often.

[autoteach]

Originally Posted by Ryland

I'm sure if you look around there is a formula out there as to how heavy you need a flywheel of a given size for an engine of a given size at a given speed, having it hard to drive to me would be a giveaway that it's to light as it's not absorbing and giving back the energy between firings, this was part of the idea behind having multi piston engines and the V8 engine design is that you have the firing of pistons happens often enough that your power output over the rotation is high enough.

someone gets it.

[autoteach]

Originally Posted by steffen707

The baseline of the dyno above was 111 tq and 126hp BTW. So a gain of 8 is quite a bit. The extra hp and tq has to equate to better mpg.

Originally Posted by steffen707

I've driven a stock crx with stock flywheel and then with 7lb light flywheel, it takes some getting use to, but if the main use of your vehicle is for highway driving, then you don't come to complete stops often.

someone doesn't

[Phantom]

The fly wheel holds(keeps) momentum. So think of it this way if you physically push a 1000lb car up to 10mph and then stop it by running to the front and pushing the other direction, now try the same thing with a 4000lb car.

What one is easier to start moving?
What one will you get to 10mph faster?
What one will be more likely to keep moving and run you over?

[busypaws]

My normal commute is 5.5 miles and 22 stop lights. I'm getting good at timing the lights but I'm still start/stop/start/stop. For me the lightweight flywheel would help (once I got good at driving it). If your vehicle is more often driving open highway then it won't help as much. I take energy to start the flywheel spinning every EOC/Bump start I do. Open highway then you've got the flywheel to speed once and you are not accelerating/decelerating every 3 times every mile.

Last weekend I took a grinder to the smaller pully on the crankshaft. (I did A/C and P/S delete last year). I took between 1 and 1.5 lbs of rotating mass off of the crank. Can't feel a differnce yet.

[steffen707]

Okay many of you missed the point here. I want to know if somebody has done a light flywheel and what their apples to apples findings for mpg were. NOT, I believe this and think ur wrong. You guys think it will hurt mpg, I think it will help. Now who has done the swap and has real results?

Also, you shouldn't attempt to reduce weight on integral parts of the motor like the crank pulley unless you are precise, like maybe a machine shop. You could end up making it unbalanced and break your engine.

[dcb]

I think a "real hypermiler" can make use of a lighter flywheel, especially around town. Someone who is more concerned with ease of use wont.

[steffen707]

Originally Posted by autoteach

someone doesn't

Explain to me in your awesome wisdom how an increase of 8 HP will mean you will lose mpg without changing anything but the flywheel?

[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).

[dcb]

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