Very Cheap and Easy MOD for more Horsepower and Torque (at ALL RPM) for ANY SAW!

[HuskyFan1977]

 While waiting for more parts for my Farmertec 372XP build "Farmer Dave" I got bored and saw my flywheel and my cordless drill and I figured I'd make a lot of holes in my flywheel. I should have 32 3/16" holes in it when all the way done with it. This is a cheap and easy mod that will add HP and Torque throughout the entire RPM band by means of reducing parasitic loss. Just be careful to keep all the holes as symmetrical as possible so you do not affect the balance of the flywheel. I also cleaned up the extra high spots that were in the casting to balance it better with a file and dremel tool. I'll put some pics up later when I get it done...   

[Al_Smith]

Now we get into a conversation of physics .Once a  flywheel(rotating mass )is  brought up to speed it  is potential energy until it reacts to a load then it becomes kinetic energy .
Old trick pulling antique farm tractors is to use a larger heavier flywheel which can often equate to a 10-15 feet longer pull on a transfer sled. Example a "war years" John Deere model B using an early 1950's flywheel which is heavier .

[HuskyFan1977]

That is very true, I hadn't considered that. Those kinetic log splitters are quite a good example of kinetic energy as well! Me I split my wood the old fashioned way. Always wanted a Ford 8N or 9N tractor myself. Good thing these famertec flywheels are cheap  8) Mine somehow has a bunch of holes in it  : 

[Al_Smith]

Usually a lightened flywheel might be on a racing designed chainsaw done by shaving the cooling fins. Which not only reduces the drag caused by the cooling fins but also lightens the entire mass .Keeping in mind these things are over bore over stroked engines running on racing fuel originally designed to fall giant red woods and Douglas fir trees on the west coast .These things are running short bars ,race chain and cutting 9 to 12 inch cants of poplar wood .

Add to that they are only cutting about 4 seconds at a time .The only reason the flywheels were lightened is to decrease the time it takes to reach max RPM's .On the subject those who build those 5,000 dollar hot rod saws don't always alter the flywheels ,some do some do not .On a working saw used in every day work it would be of little value IMO .To add to that the very idea of a flywheel coming apart at 12,000 RPM scares me and I'm almost fearless . :D 

[Jeff]

Reading this, my mind instantly went to that. Turning a saw into a potential grenade.

[Al_Smith]

I've never had a flywheel come apart but I did have one come loose .My fault forgot to tighten the nut .It came loose ,obited my garage about twice and just barely missed my wife's Cadillac with me on the floor fearing for life and limb .That was at around 4- 5,000 RPM not 12,000 .  I'll not soon forget that . 

[Grandpa]

I'm with Al and Jeff, I would be afraid to run it.

[gspren]

My brain cells are getting tired and forgetful but I think my physics class memories say that lightening the flywheel raises horsepower and lowers torque but that's just one of several variables. If simply removing mass (weight) improved performance across the board the flywheels would have been cast lighter initially. JMHO

[Al_Smith]

It was a practice by some in the 60's
 to replace the flywheels with aluminum flywheels so they would rev up faster at the drag strip .How effective that was I'm not sure of .What I am certain off was in more times than not the ring gears became loose and made starting them almost impossible .Not a very good idea after all .I can't imagine what might have happened if it would have tossed the ring completely  and it got hung in the clutch locking up the tranny and drive line at say 80 MPH .Not good !

[Bandmill Bandit]

While waiting for more parts for my Farmertec 372XP build "Farmer Dave" I got bored and saw my flywheel and my cordless drill and I figured I'd make a lot of holes in my flywheel. I should have 32 3/16" holes in it when all the way done with it. This is a cheap and easy mod that will add HP and Torque throughout the entire RPM band by means of reducing parasitic loss. Just be careful to keep all the holes as symmetrical as possible so you do not affect the balance of the flywheel. I also cleaned up the extra high spots that were in the casting to balance it better with a file and dremel tool. I'll put some pics up later when I get it done...  

Make sure you order a new fly wheel as you WILL need a new one.
Look at it this way. A 2 horse hitch of Clides may not start moving a load of 1000Lb as quick as a 6 horse hitch of Welsh Cobbs but the Clides will be moving very shortly and will be moving longer and farther and more times than the ponies.

RPM with out torque range is good for about a 1/4 mile if you can hold the rpm. Real easy to blow out the bottom end. It is really a rather dumb idea for saw that you expect to use on a daily basis.      

[Timberguytim]

I just grab a bigger saw. Theres no "replacement" for "displacement". It's called "torque" my friends. The Wright brothers flew an 800 pound airplane with 12 horsepower. Now that's called "engineering", my friends........don't think they drilled holes in the flywheel, but they HAD vaporized alcohol injection.....WHAT? YES......and a 4 cylinder overhead valve aluminum block......no spark plugs. You call what we got now "engineering". Ha!

[Greyman]

As an engineer myself, it's always best to ask yourself why they designed it that way.  Sure, some things are designed for liability and insurance reasons, but if they could get more hp and torque by reducing the weight they would have done it a looooong time ago.  Doubt it would hold together as long as it was designed to.

[Al_Smith]

Some many years a later as an experiment to see if the Wright flier could be duplicated  three examples were tried and two failed .One had a replica of the original engine no go .I forgot what the second example had but it failed too .The third had an 80 cubic inch Harley V twin engine ,it flew .Well,1903 ,the Wright flier,Harley Davidson and Ford motor Company .A lot going on that year .--and last but not least the US Model 1903 Springfield bolt action rifle .

[ehp]

doing this makes zero more horsepower, All it does is let the saw spool the engine up faster but it also comes back down to idle faster. Big thing like Al said is your lightening the driving mass that turns the chain, yes if your very carefull on how you run the motor you can keep the engine at peak power BUT by lightening the flywheel your taking weight which turns into torque if you dawg the saw down in a big cut , lighter  flywheel is going to allow the engine to loose rpms faster in the cut once you press hard enough to drawn the engine down. Also you would need to be very accurate on your holes to keep flywheel perfectly balance , just abit off is going to be very hard on the flywheel side crank bearing

[moodnacreek]

Getting rid of flywheel weight is done to increase response. This would be good on a short dirt oval track but not for keeping the chain saw in the wood.

[zimraphail]

while im sure you made a faster reving saw, Unless drilled in amill with depth gauge and 360 degree indexing chuck? Well certainly have affected balance of flywheell!  Reving fast doesnt help the effect of load as others have stated! I wouldnt do it! But thats my personalopinion, good luck

[ehp]

believe me I have lighten a lot of flywheels and I mean a lot of them but all on race motors and the only reason I did that was cause the motors spooled up so fast on the cold start you could kick the flywheel loose

[Bandmill Bandit]

During my Snowmobile racing years (72 - 76) I was one of 3 drivers for a local Arctic Cat dealer's racing team. I was also one of the shop mechanics. I started with the dealer (friend of my dads) during the late summer and fall assembling new sleds after school for 3 or 4 hours a day. 

The second year at 16 I started driving on the race team. We had a local machinist that did all manner of balancing and the engineering that went with that based on his knowledge and experience in high performance oilfield compressors and centrifugal separation systems  et el.

He did the balancing of EVERY motor/drive train we ran for racing right from the track,  drive sprockets back through the entire system to the pistons, including drive and driven clutch components. Stuffed the crank case, voluted the crank doughnuts, spiral polished the schnerll ports, slide polished the intake and exhaust ports, anodized interior of the tune pipes and I have probably missed a few things that I likely didn't realize he did.

I can tell you that you could fit the filing from the fly wheel balancing in a teaspoon with room to spare and you might get a 1/3 cup of filling from ALL the other machining/balancing he did for the whole sled. His accuracy target was plus minus .00005 through out the entire system.

The toughest part was building a drive clutch that would hold up at 12000 to 16000 RPM speed range for a day of racing, mostly running at 13000 to 14000 with cut in was 7500 to 8000.

We discovered that the harmonic balancing of the flywheel to crank to drive clutch was the most critical factor in endurance of the engine along with smooth fuel flow performance to max out system performance.

The best we ever did was a few 340  and 500 Spirits that would give us safely 18000+ RPM with excellent reliability but we couldn't build a clutch that would withstand that for a 7 lap race. 5 laps was about a 70% chance to finish. They would simply disintegrate. Under 16000 we could consistently go 3 to 4 races and then swap. 

Always had 4 clutches for each sled ready to go and installing a clutch wasn't just a matter of popping one off and installing a new one. We had a dial guage that screwed into the clutch side spark plug hole that would give us a zero TDC reading where we would lock crank and fly wheel and then install the clutch to alignment marks on the clutch  and crankcase.   

To get that kind of performance is not cheap and there is no way trimming a fly wheel will do it even if you did achieve a .0005 range in the process.

Building those race motors ran about $1200 to $1500 in 1970 $$ and thats when new sleds were about a $1000 average.

Racing performance is NOT the same as over all endurance and productivity performance. We built the sled driveline to last 3 x 7 lap  races on average on a half mile oval. Thats about 12 miles or about a $100 +/- a mile for engine cost.

While it was a lot of fun the racing costs were NEVER recovered the by receipts of a consistent top 5 winning team. The recovery came from the sales at the shop on Monday through Friday when the customers walked into the store and could have coffee and doughnut with the drivers and mechanics that also did the service work on the customer sleds. 

The race team was the marketing division.     

             

[Al_Smith]

Just as a general statement an out of balance flywheel on anything can cause all kinds of problems besides grenading .A little bit out can cause vibrations that on a modern saw will cause the mounts to go bad .On an older saw with a rigid mount can cause your hands to go dumb in about 5 minutes .Badly out of balance such as a broken fin can break out the key way or in some cases break the crankshaft end  ..
I had one on that  could be considered  an antique McCulloch which had been reworked that tore the key way out of three crankshafts before it dawned on me what was wrong with it .Changed the flywheel and never had a problem since .I nearly ran out of spare crankshafts by the time I figured it out .Some times I'm a little slow on the uptake evidently . ;)

[snowstorm]

18000 rpm out of a suzuki seems like a bit of a stretcher to me. when yamaha came out with there 4 stroke sled they had to use a gear reduction to get the clutch speed down to 8000 rpm. i had several new cats back in that era. i was never impressed with suzuki motors and the arctic hex clutch was junk. the comet was better mainly because it was a copy of a polaris. just got a new assault 800 havent had a chance to put many miles on it. i like 

[Bandmill Bandit]

I know exactly what you mean by stretch snowstorm. We were pretty surprised by the first one that did it. It blew up the clutch in quite spectacular fashion. Was a good thing we had the clutch/belt guard in place with the pins in stalled.

The 2 x 340cc and 1 x 500cc all blew up in the end but we got 2 weekends out of the 340s and 1 weekend and one heat out of the 500. An operation range of 8000 to max 14000 worked pretty good and on about a 1/3 of them 14000 was pushing it. You could feel it in the handle bars driving them. On the 500 the clutch gave out and that over revved the engine to failure.

Also those were upper RPMs max on bench on the Dyno, not operational on the track. Those 3 engines gave us about 1000 RPM more range on the track so max of about 15000. Also we ran about 60% Kawasaki engines too as the Spirits didn't come out officially till 75/76 even though we had access to them in the 74/75 season along with a whole whack of factory parts  because we were a factory sponsored team. If I remember right that was called "semi pro class".

Also on clutches we never did run the cat Hex clutch on the race sleds. they were worse than junk. Generally the NOS Securistat Powerbloc that was developed by the Rupp Factory team in a joint effort with Polaris and Comet if I remember right. 

The Heaton Brothers were more than Pithed with each other at the time so Arctic refused to be part of that endeavor and thats how that Hex clutch came into existence. 

West Yellowstone in 75 was not a great weekend for Team Arctic and that was mostly due to clutch issues. They did ok but Skidoo and Polaris kinda ruled the weekend.    
       

[ehp]

I ran arctic cat , skidoo, snow twister, and Polaris , skidoo and arctic cat were factory rides and if your 340 or whatever motor seen 18,000 rpms you had your tach wired wrong , the highest rpm motor of everything I ran was a rotax 340 super mod and that engine power band was 11,700 rpms and that motor had the best of everything that could of been done to it , the 440 rotax super mod was right at 10,000 rpms for power band . My older arctic cat sleds from the factory all had Kohler liquid motors in them , none had Suzuki engines until a lot later in factory race sleds

[snowstorm]

15 to 18000 rpm is a tough sell still not buying it. lets just say a hot rodded 340 piston ported twin makes a 100 hp at 9k at 9200 it may drop to 80 or less. at 16k it would be so peaky someone would have to push it off the starting line 

[scsmith42]

15 to 18000 rpm is a tough sell still not buying it. lets just say a hot rodded 340 piston ported twin makes a 100 hp at 9k at 9200 it may drop to 80 or less. at 16k it would be so peaky someone would have to push it off the starting line

Back in the early 1980's I owned an automotive machine shop that specialized in race engine assembly. We did balancing and blueprinting in house.

Formula 1 engines routinely used to operate between 15,000 and 20,000 rpm. The key for a high rpm engine is a short stroke, such as what motorcycles and snowmobile engines have.

There is no way that our common US hot rod engines would get close to that because of the longer stroke.

Honda CBR250RR motorcycles had a 19,000 redline back in the early 90's.

[snowstorm]

We are talking about a 2 stroke not a 4 stroke with a CVT  trans. I found  a article in a snowtec magazine  I have.this was about the polaris factory team in the 70s . They could not keep the clutches together at much over 9000 rpm

[Bandmill Bandit]

Yes EHP that little 340 Rotax was one tough competitor 11500 to 12500 was their sweet spot but with a Kawi and a Spirit you needed another 1200 to 1500 RPM to beat them.

There were few guys running Yammies in Sno Jets and Rupps that  would just scream in comparison but like us they had trouble holding the clutches together. Don't know what RPM they ran at for racing but it sounded like they topped us by at least a 1000 RPM.    

We didnt base our actual RPM numbers on an electronic tach on the sled. That came from the Dyno tests with a cable tach done on the bench before the motor was installed and we even assumed  a +/- 500 rpm error margin on that.  

That 9000 ish RPM limitation was one of the primary drivers for the development of what became the Comet Clutch. By 75 Polaris along with rest of the factory teams had some pretty impressive clutches running on their SnoPro Factory sleds and were running a lot higher than 9000 RPM. You couldn't get near the shop trailers in the pit for any of the factory teams. Polaris seemed to have the edge on clutchs in the semi Pro and Pro classes that season.  

I think the 74/75 season was the peak of those racing years. By 1980 factory teams were a shadow of their original glory days.         

[sawguy21]

I started my small engine career in Arctic Cat shops in the mid 70's, you guys are bringing a smile to my face. We weren't involved in serious racing but had a few tricks up our sleeves too. ;) And yes, clutches were a limiting factor.

[gspren]

  I'm afraid we scared off the OP , please come back and tell us what happened.

[Pine Ridge]

 smiley_horserider

[Al_Smith]

 I'm afraid we scared off the OP , please come back and tell us what happened.

Some times things aren't really a good idea once every thing is well thought out .It happens,been there .  ;)

[Northeaster]

As someone just mentioned a broken fin causing issues, i broke one on my early model 064 (which I just rebuilt and haven't run too much since rebuilding) and I thought I had read somewhere that the balancing was not precise enough on a saw flywheel to matter...for just a broken fin.
can anyone comment please? 

[Al_Smith]

My only comment is don't try locking the flywheel using a bar in a fin .If I get a broken fin on the used  saws I buy I replace the flywheel before I use it very much . I've got one right now as I type on a Partner P100 somebody evidently didn't know how to remove properly .I've also got a complete lower unit including a flywheel,clutch and rotating assembly to restore it .---some times a total restoration takes a long time especially on a less than popular saw because of a shortage of usable parts .If you do it right you'll never have to do it again ----but if you don't ----- :'(