should I lighten the flywheel?

General discussion about our beloved Tercel 4WD cars
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NWMO
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should I lighten the flywheel?

Post by NWMO »

Hey Peter,

As I undertake the 4ac swap, I see you have recommended lightening the flywheel some. From internet searches, it seems this is more common in "quick" cars for quicker revving, better response, etc. It seems the heavier flywheel is preferred for easier starts etc. during daily driving, though a few pounds might not make much difference. I'm certainly not looking for a race car, but if you think taking a few lbs off is worthwhile for a DD, I would consider it. Daily driver, mostly highway - how much would you recommend removing?

TIA,

Chris
Psalm 37:4 "Delight yourself in the Lord and he will give you the desires of your heart"

In remembrance of my friend ARCHINSTL:

T4WD augury?
"Oh, do not ask, 'What is it?' Let us go and make our visit."
T.S. Eliot - "The Love Song of J. Alfred Prufrock"

"Now and then we had a hope that, if we lived and were good, God would permit us to be pirates."
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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: should I lighten the flywheel?

Post by Petros »

good question, most people do not understand the reason to lighten a flywheel. It does not give you more power, it gives you an engine that revs up faster. On an under powered engine with an oversized flywheel (like our 3a engine) it will be noticeable and worth having. if you use advanced driving techniques like double clutching, heel-toe the brake and throttle, and other such methods in your daily driving, a lighter flywheel is a must.

The stock flywheel is a whopping 19 lbs, the corolla flywheel, with a bigger more powerful engine is only 16 lbs. Most 4 cylinder engines have factory flywheels in the 14-16 lb range. Performance cars, race cars, other high reving engines use flywheels as light as they can get them. I have helped design a 3 liter racing engine that put out about 980 hp that used an 8 lb flywheel (including the clutch weight). The flywheel itself must have weighed only 3 lbs (all titanium). This is to demonstrate that there is no such thing as making the flywheel "too light", as I have seen on some car forums.

The purpose for the flywheel is to smooth out the pulsed input from the 4 cylinders, and to prevent it from stalling when sloppy clutch technique is used. Since the Tercel was their entry level car, I have to assume Toyota considered that an inexperienced driver would be test driving them, and if they stall out the engine too often, they would not buy the car. So I suspect it was marketing decision to cater to their target market.

That being said, I always lighten the flywheel of any engine I rebuild if I intend to keep the car or truck it goes in. It must be rebalanced, and the crank, rods and pistons all should be carefully balanced as well to help smooth out the engine when at high rpm.

There are not a lot of shops around that know how to do this properly, but custom machine shops that regularly do hot rod work are around (ask around at auto parts stores, local car shows, etc. on how to find them). They can also balance the rotating engine parts as well, and the other parts if you do not want to do it yourself (not difficult if you have access to an accurate gram scale). It can be costly if the shop sees themselves as a high end custom machine shop, but ask around you often will find a serious engine hobbyist working out of a home shop with a lot of serious auto machine shop tools who will do a good job for a great price. In the several places I have lived, there was always one of those guys nearby, and well worth using. They usually are knowledgeable on what to do, how far you can go, and will do a great job. The normal retail auto machine shops usually have techs that will only do "factory spec" work, avoid that type. Also, no matter who you talk to, if they are reluctant to do the work, if it takes any effort to talk them into it, better find someone else. There are many who take on jobs they should not, and can make a mess of it. I know of people that ended up having to find another flywheel to replace the one messed up by a machine shop that clearly had no clue about what do with a flywheel.

The more weight you can remove from the outer edges of the flywheel, the more effective it will be. If you only have budget to lighten it a little bit, take it all off the outer edge near the ring gear. Front or back side does not matter, where ever you can get excess weight off that does not affect function. by taking it off the outer edge you reduced the rotating inertia of the flywheel faster and more effectively. Once all you can safety take off the outer edges is done, than you can go to the back side, and last to the hub area.

but do not waste a lot of money around the hub area removing weight, you will hardly notice it. the formula for rotational inertial is I = mr(2), meaning is the product of the mass times the radius squared (radios out from the axis of rotation). so taking mass off the rim at say 7" vs. taking off at 2" (near the hub) is 12 times more effective (ratio of 7 squared and 2 squared). That is 1200 percent more effective.

I was able to get my stock Tercel flywheel down from 19 lbs, to about 14, and I would have gone more if i thought I would notice it. I would also consider taking it off the ring gear as well, it too is heavier than it needs to be. but that adds cost unless you can do it yourself.

good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
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NWMO
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Re: should I lighten the flywheel?

Post by NWMO »

Thanks a ton!!
Psalm 37:4 "Delight yourself in the Lord and he will give you the desires of your heart"

In remembrance of my friend ARCHINSTL:

T4WD augury?
"Oh, do not ask, 'What is it?' Let us go and make our visit."
T.S. Eliot - "The Love Song of J. Alfred Prufrock"

"Now and then we had a hope that, if we lived and were good, God would permit us to be pirates."
Mark Twain
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