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Old 12-13-2006, 05:28 PM   #1
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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? :

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

Or this :

http://www.spswebpage.com/store/inde...a26204d2c7dfc5


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
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Old 12-13-2006, 05:34 PM   #2
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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.
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Old 12-13-2006, 05:48 PM   #3
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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

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

Scroll down to martinq on Mon Nov 21, 2005. That's where it starts.
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Old 12-13-2006, 05:59 PM   #4
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Quote:
Originally Posted by theclencher
Could you expand on that theory?
Quote:
Originally Posted by thisisntjared
the benifits for racing are much more valuable.
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.
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Old 12-13-2006, 06:03 PM   #5
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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.)
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Old 12-13-2006, 06:06 PM   #6
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Quote:
Originally Posted by thisisntjared
to comment on the cylinder deactivation, it will be to no avail, unless there is a reduction in reciprocating weight.
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?
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Old 12-13-2006, 06:11 PM   #7
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Quote:
Originally Posted by theclencher
Why?
because its 10 lbs.
Quote:
Originally Posted by theclencher
This makes no sense at all. Do you know what I am trying to do with the cylinder de-activation?
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.
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Originally Posted by theclencher
Why?
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?

Quote:
Originally Posted by MetroMPG
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?
and what are the gains from cylinder deactivation alone?
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Old 12-13-2006, 06:53 PM   #8
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Quote:
Originally Posted by theclencher
Hardly. Pistons still go up and down; 4 valves and maybe rockers and pushrods would become stationary...
stopping valves from moving helps with reducing the wasted engery, definitely.
Quote:
Originally Posted by theclencher
No- having two working cylinders and two dead cylinders makes it rougher ie. it's lost two power pulses so it would have increased reliance on flywheel energy storage to smooth the crankshaft rotation.
and that is why i do not favor this development in leu of others.
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That may very well be but it should be mathed out or referenced or tested or something to really know before it is summarily dismissed. You know we need more than a simple statement of this or that around here before it is accepted as fact.
you are right. to fully think out of the box, all possibilities should be explored.
Quote:
Originally Posted by theclencher
I'll search and come back with the figure given by GM Engineering- it's on this site somewhere- but IIRC it was up to 20% FE improvement in some conditions?
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.
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Old 12-13-2006, 06:55 PM   #9
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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.
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Old 12-13-2006, 06:58 PM   #10
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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).

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

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