So, as I get into my suburu tuning, I came across an interesting number. For every pound you shave off the rotating assembly (Ie lighter pulleys, or flywheels) your are supposed to net between 2.5 and 3.0 HP. I know that on my 4.9L m5od, my flywheel is well in excess of 20 lbs, and that 8-12 pound flywheels are not uncommon, so you are looking at a 20-35HP gain. Im sure it will be on the lower end because the motor doesnt rev as much as highersprung 4 cyls, but still. For you people looking to get the most power out of your 4.9, this might be an interesting idea to look into. If anyone has seen one, or has one, please post info on it, because I would be very excited to find 1.

 

it will actually be on the higher end. lightening the flywheel decreases the amount of rotating mass allowing an engine to rev quicker. You will loose some driveability as it will be easier to stall as the heavier flywheel actually helps keep the engine running at lower RPM's. For a race motor I can see it but for an everyday driver there are better ways to gain HP.

 

Lightweight flywheels are overrated on the street. You aren't going to see any measurable performance gain with a light flywheel. The flywheel is such a small percentage of the total rotating weight of the vehicle it is barely noticeable to the engine.

 

With a lightend flywheel, you'll probably loose grunt off the line. A heavy rotating mass is needed to get a heavy truck moving. We used to lighten flywheels from 20lbs to 10-12lbs for lightweight (and generally higher-revving) street & race cars but ALWAYS left them heavier for full bodied street cars or trucks/vans.

IMO, vehicle weight has more to do than anything with the effect of flywheel weight, and unless you have a severly lightened truck, then a lighter flywheel is going to hurt you.

 

if you really want one, Centerforce (www.centerforce.com) makes lightened flywheels and clutch assemblies. For what its worth (prolly 2 cents, just like everybody's opinion) you should focus on the core power builders (i.e. more displacement, more compression, ideal air fuel mixture, etc) before you start cutting weight. And as far as weight goes, a truck is the last thing that you should be concerned about cutting weight from. Trucks are designed to do work, not be light and go fast. It is a good idea in principal, but not in application.

 

I believe an aluminum SBF flywheel with the right imbalance/teeth would work.

 

This has great merit. When I changed from the daul mass flywheel to a one piece flywheel on my wrecker, I found it takes more throtle to get moving and my crawl speed increased quite a bit. This may be ok as long as you never intend to use your truck for work. Lighter wheels and tires will do more for you than a lighter flywheel. If power is what you are looking for there are much better ways to free up extra ponies, like removing the cooling fan and adding an electric unit.

Pat

 

Well as for the electric fan, its already there, and rarely used. Im only driving around 100 miles a month at the most, because I am at college and its all interstate driving. I knew about the driveability loss associated with removing weight from the assembly, but I am under the impression that it doesnt hurt anything, just takes time to get used to. I do plan on going with some lighter tires, because right now Ive got wrangler MTRs that are almost 7 years old by the dot date (but still half tread left) and are 8 ply sidewalls. I am looking for a good 28-30 inch tire with an agressive tread, directional if possible. Any suggestion for the stock 15 inch wheels, or will I need to get some 16-18s? I can drop the tranny and transfer case assebly with driveshaft and starter ect in about an hour, and change the clutch and flywheel assembly and have it all back together in about 4 hours now, after refining my methods (Ive done it 3 times now due to a throwout bearing failure and a slave cylender explosion). I figured that if I can drop it and gain 20 HP and a stronger clutch, in a day, why not. This mod will probably be more accepted than something like a cam swap (even though they dont equate to the same amount of power) because the ECU will just see less load on the motor because of the reduced rotational mass and the intake of air and fuel will remain constant.

Any suggestions on lightweight wheels and a decent aggressive tread patern?

 

I've been thinking about flywheel weight ever since I read this post last night. It makes me wonder how a heavier flywheel would respond to trucks like ours. An EFI 300 free-revs awfully quick, I was noticing today, so I was curious about the effects of slowing that down a little with a heavier rotating mass with the intent of getting the truck moving a little smoother.

 

these engines aren't designed to turn very high rpm's, for a lightened flywheel to really benefit you need an engine that can can churn a lot of rpm's such as race engines.

 

With a lighter flywheel you will accelerate faster, to a point. but the inertia will be less with the lighter mass. So if all you did was stop an go constantly (maybe) it would be a plus.
But most of our driving consists of rolling at a steady speed. Once this speed is obtained the heavier flywheel and it's stored energy (inertia) gain the advantage. One of our resident Physics guru can explain this much better than me.


Now as far as making the flywheel heavier it also has it's draw backs there is a medium I suppose. But if you add to much weight you get the acceleration of an 8N ford tractor and mopeds will be blowing your doors off on take off.

Pat

 

they already blowin my doors off lol. My 300 free revs good from like, Id guestimate 2500 RPMS on, below its like wait you want me to move? lol I odnt know, I was just tossing the idea around. I really think I am going to go standalone if i get another 500 or so though. Once I get that much, I can pick up a fully built megasquirt and shock with extra, and then spend another 100-150 on a nice big MAF tuned for some nice healthy (at least higher than stock) injectors, and then grab a wideband for another 200-300$. Then I can have fun. The flywheel was just something id been throwin around cuz i remember holding the flywheel up to install it with 1 hand while trying to get bolts on with the other, it was a blast, sitting under the truck in bell housing hump, oh the joys, when I was only 5'4.

 

Whats the mass air flow sensor for? Megasquirt is speed density, unless you wanna get really involved in it, so you'll be needing a throttle body, luckily a stock 302/351w or 460 throttle body would work well and be cost effective.

Theres a company that offers the wideband O2 and a controller (no gauge), that plugs right into the megasquirt for $199, its on the MS site.

 

WOOOOWWW this whole time Ive thought megasquirt was MAF, I feel like a NOOOBBYYYYY. Oh well. Yea im sure I can net a few more ponies by building my own tune, and if I am nice, im sure that I can maintain some decent mileage given that again, all my driving really is interstate, so Id just like something to mess around with at the lights, and maybe have a bit more on the top.