stihl 660 magnum mods

[bigjayfromwa]

I run a 660 mag with a dual port muffler and i leaned the carb out a bit to get some more power out of it. I was wondering what else i can do to it to get a little bit more out of it. I dont want it so modified that its a total hotsaw, but just curious if there is anything else i can do.
I run a 36in bar with full skip 3/8 chain.
Or if there is anyone out in my neck of the woods that has an 88 for a decent price to turn into a hotsaw. thanks

 

[Lakeside53]

You've done the easy stuff... if you don't want to start grinding way at your cylinder, then keep the chain sharp. A sharp chain will double HP, or should say, halve it if dull! Don't believe me, time the cuts - might even be three times... up to infinity is really really dull!

With tongue firmly planted in cheek, the only reason I bring this up is that for a working saw, not one that just make a couple of cuts in nice clean wood for a race, the condition of the chain has much more to do with cutting speed than porting... What can you do with a port than will double cut speed? Let's assume you can raise your 066 from 7.7hp to say 9.5 HPwith a major port and considerable $$. What will this do to your cutting times that a touch up now and then with a file won't do?

O.K., hot saw fanatics, jump all over me!

Hmmm, I have an 088 in your neck of the woods, completely rebuilt, but.. not ready to part with it, yet...

 

[tek9tim]

You leaned it out to get more power? Either you have your terminology or your understanding of engines bassackwards. Leaning it out after already creating a lean running conditon (by opening the exhaust) would make your saw rev out stupid high, but have no power in the cut.

 

[NWCS]

leaning the saw out can and lead to destroying the piston and cylinder, remember that fuel is your oil supply also! running a bit rich is always better than lean. i would pull the muffler cover to inspect for any piston scoring that may have already happened. if you want more power i would have it modified by one of the companies around that specialize in that work. opening up the exhaust port and intake tract help greatly, and tuning the transfer ports all add up to great power gains. coupled with a dual port muffler and a full woods port job you can see 25% or more power and have the same or more life to the saw. there are several places around with great service, Northwest Chainsaw (me!) and Washington Hot Saws are my choices PM me and i'll give you a call or give you my home number and we can talk a while if you want.

 

[bvaught]

You leaned it out to get more power? Either you have your terminology or your understanding of engines bassackwards. Leaning it out after already creating a lean running conditon (by opening the exhaust) would make your saw rev out stupid high, but have no power in the cut.

Chainsaws use fuel to cool the engine. Any mixture richer than "somewhere in the neighborhood of 12:1 air:fuel ratio will decrease the power produced by a chainsaw. Perhaps someone can enlighten me, but I am assuming that a chainsaw runs in the neighborhood of 7-10:1 fuel air ratio. So you would increase the power produced by leaning the saw a bit, you will also increase the flame propagation rate. So there would be at least two reasons why the engine speeds up when leaning the high speed screw at WOT. One is that you have more gas expansion energy, and the other is that you have a flame propagation that is doing more buring during the power stroke before the exhaust port is open, which relates to engine ignition timing.

 

[timberwolf]

The fuel ratio changes in a curve accross the powerband, the idea is to have about a 20% rich mixture (12:1) at the RPM where you will be cutting. At other RPMs the saw will be a tad rich or a tad lean, but when it is set right on at the cutting RPM you get the best cutting speed.

For gas mean effective pressure (MEP) is produced 20% rich go above or below that and the prressure produced by combustion drops as will HP.

The 12:1 is a bit of a rough number, extra fuel is required to make up for fuel that does not get burned 100%, so it will vary depending on the burning efficiency of the engine, how well the fuel is atomized and how well it is kept that way, scavenging, losses in the squish area....

066 has less left on the table in terms of mods than many other saws, the saw comes stock with pretty good numbers and casting work.

 

[Lakeside53]

Bigjay - did you really mean what you said? I read it as you tuned it, so did you really "lean it out" beyond the max WOT allowed, or not?

 

[klickitatsacket]

066 has less left on the table in terms of mods than many other saws, the saw comes stock with pretty good numbers and casting work.

The 066 like you said has much less room for improvement than other models but does have quite a bit of room. If you want to put the time into it you can still find 25 - 30%. The MS660 on the other hand, has reverted into something that resembles, well you fill in the blank. They have the intake and exhaust so stoved up that it should be some what embarrassing.

 

[timberwolf]

With the new saws 20-40% gain in cutting times is possible just by dealing with the muffler and carb caps.

Why is it that with car engines they can get more HP out of less displacement year after year while still meeting polution standards? Fuel injection and computer control?

 

[klickitatsacket]

With the new saws 20-40% gain in cutting times is possible just by dealing with the muffler and carb caps.

Why is it that with car engines they can get more HP out of less displacement year after year while still meeting polution standards? Fuel injection and computer control?

I completely agree with the cut times increased but HP and cut times are not the same critter either. Interesting you brought up the fuel injection topic. I was talking with some one the other day that mentioned a new saw that is fuel injected by computer and feeds from the top of the cylinder.

 

[Lakeside53]

Why is it that with car engines they can get more HP out of less displacement year after year while still meeting polution standards? Fuel injection and computer control?

yes, mainly injection and computer control (closed loop control), and that cars aren't 2 smokers..

 

[timberwolf]

I am finding that the gain in cut time keeping the same chain and gearing = the % gain in HP + the % in RPM. So far this seems about right to me. So if you bump the saw up 10% in HP and the sweat spot in the cut moves from 9.5k to 10.5k you gain 10% for the HP and ~10% for chain speed or a total of ~20% cutting speed.