Lighter Flywheel for Manual Transmission?
 

Hello -

This is an expensive mod, so I am not seriously considering it. Will a lighter flywheel like this one improve MPG? :

https://cgi.ebay.com/ebaymotors/FIDAN...mZ140063164938

Or this :

https://www.spswebpage.com/store/inde...a26204d2c7dfc5
https://www.spswebpage.com/images/products/AFSAT115.jpg

It claims better HP. I don't know what the average weight difference is between OEM and performance flywheels, but the SPS one claims from 18 lb OEM to 8 lb (i.e. one beer gut saved).

This is the age-old question, which HP mods can lead to improved MPG, aka 2 for 1?

CarloSW2

in theory yes it will improve mpg, but the amount is definitely uncertain. one thing is for certain: it will have NO effect on the mpg upperbound aka highway mileage, it will only improve the acceleration.

the benifits for racing are much more valuable.

There was a long debate about this on teamswift a while back, each side arguing opposite (!) sides. Nobody was able to present their argument in terms simple enough to convince me one way or the other :)

https://www.teamswift.net/viewtopic.php?t=19413

Scroll down to martinq on Mon Nov 21, 2005. That's where it starts.

when i said the gains are uncertain, i meant that the only thing certain about them is that they will be very small

to comment on the cylinder deactivation, it will be to no avail, unless there is a reduction in reciprocating weight. EDIT: to anyone who reads this post and not the rest of the thread, this statement is wrong.

back on topic, lightweight flywheels wont be worth the research. there are far too many unexplored areas of efficiency that should be explored before this becomes worth studying.

It seems to me that if all you ever did was pulse & glide, a lighter flywheel would benefit, because the car could pulse up using less energy.

But the question that came up in the teamswift thread was whether more or less mass would help or hurt on the open highway at more or less constant speed (and with changes in grade, etc.)

I would have said the gain from cyl deactivation would only come with a reduction in pumping losses (ie valve deactivation). We know it works without reducing reciprocating weight - Honda, GM and DCX are using it, aren't they?

because its 10 lbs.
yes i remember reading it earlier and i think you will need to get more creative to make it worth while. so are you cutting down in reciprocating mass? are you cutting down rotating mass? are you smoothing the harmonics of the motors vibration? i dont remember the specifics on your project. if you are just cutting the fuel to some cylinders and calling it a day the gains will not be impressive.
because there are so many other areas that will provide better results. e.i. aerodynamics, raising the air/fuel octane, reducing the weight of some of the engine internals, etc.

did i hit a nerve? who pissed in your cornflakes?

and what are the gains from cylinder deactivation alone?

stopping valves from moving helps with reducing the wasted engery, definitely.
and that is why i do not favor this development in leu of others.
you are right. to fully think out of the box, all possibilities should be explored.
i am very skeptical about such statistics. the 20% improvement will be a 20% between the two modes of a motor that was designed to do this from birth. with that in mind the manufacturors could make the motor more agressive to make the motor more versitile. what i am trying to say is that i am more interested in what happens in the grand scheme of things and more importantly, are there any diy mods that really help me?

if its going to be an up top corporate engineer's decision, then why not cut to the chase and bring all of the existing known efficient techniques together??? hybrid, direct injections biodeisel, with variable valve timing and cylinder deactivation???

in the end though, my posts are not worth getting upset about. i am just exploring the physics, not emotions.

Does the amount of rotating mass influence bearing friction in an engine? That's the only thing I can think of that would influence engine efficiency wrt flywheels. A flywheel is only an energy storage device, so unless that additional weight makes the engine more than proportionally harder to turn, it don't matter.

Honda attributed a 2.65 mpg (US) improvement in highway fuel economy from cylinder deactivation in its V6 Accord hybrid over the non-hybrid (but only accounting for that technology, not any of the other hybrid tech).

https://www.hondanews.com/CatID2131?m...46959&mime=asc

The non-hybrid hwy figure was 30 mpg, so that's an 8.8% claim.