HP Limit MS 880 bottom end

[Stihlman441]

Shaun i will come and help you a $1000 week cash and he can have $1500 for doing nothing.:msp_thumbsup:

 

[porky616]

i be watching with great interest, will help me build this exploded 088 of mine. mind you i dont think id want to get as much out of an 880 as you are hoping too, they have enough trouble staying in one piece and not exploding as a stock unit.

 

[imagineero]

I've never owned an 880, and I've only ran one twice, for pretty short times. I wasn't hugely impressed, but maybe i had high expectations? I kind of get the impression that the 084 is the way to go, but this is only based on hearsay. I'd be seeking out opinions from one of the saw builders on the site (simonizer, blsnelling) who have real life experience and knowledge of the innards of these pricey saws before having a crack. There is precedent, and knowledge out there to be tapped, no need to try to reinvent the wheel.

Shaun

 

[mtngun]

I kind of get the impression that the 084 is the way to go, but this is only based on hearsay. I'd be seeking out opinions from one of the saw builders on the site (simonizer, blsnelling) who have real life experience and knowledge of the innards of these pricey saws before having a crack. There is precedent, and knowledge out there to be tapped, no need to try to reinvent the wheel.

Nothing special about the 084, and it's hard to get parts for.

I haven't seen the intake port timing #'s for the 088 and 880, but I'm guessing they're lame like the 084.

They also have a low compression ratio, though it may vary from one jug to the next.

The bottom ends are not known for holding up well at high rpms, hence the limited coils and the mild port timing.

Otherwise, there is nothing magic about them, it's just like doing a woods port on any other saw, except you don't want to set it up for 14,000 rpm because it won't hold up at that speed. 8000 - 10,000 in the cut is more realistic.

 

[imagineero]

That's the thing that gets me about the bigger saws, on spec they seem like they're underperforming and I have never really got my head around the why of it. There's a pretty clear relationship in all engines of the holy trinity of cylinder displacement - revs - torque. As displacement *per cylinder* goes up, torque increases, but revs drop. Seems to be all about speeding up and slowing down mass, and with enough mass you get great momentum (torque) but you can only do it so fast (revs).

Honda was pushing the limits in the 60's with their 125cc and 250cc 4 cylinder bikes that revved out to 24,000 for a displacement of 75cc/37.5cc per cylinder. At the opposite end you've got, say, 6 litre V8's displacing 750cc per cylinder that might rev out to 5k but have great torque. Any time you're getting up to the 800cc~1,000cc range per cylinder no matter what the design - single, twin, V4 or V8, you're well and truly in the range of low revving torque monsters.

When you're down to the under 125cc per cylinder displacement, you're expecting huge revs. That's a 500cc 4 cylinder, or a 250 twin, or a 125 single. I've owned motorbikes in all of these configurations, and they were all revvy. Modern engines are really pushing the barriers, some 1000cc 4 cylinder bikes are approaching the 20k mark now (yamaha R1) which is huge for 250cc/cylinder. These are mostly square motors.

So where does that leave the 100cc+ saws? Some of the older designs barely cracked the 6k mark. But a 660 at 90cc will do 14k? It just doesnt add up. I've owned a couple of single cylinder 600cc air cooled bikes that did better than 125cc saws rev wise. Seems that there's some limitation (beyond reciprocating mass) that is limiting these saws. Maybe it's a dry sump issue?

Shaun

 

[BigMoneyGrip]

I think that heat dissipation has a role. You have to be able to cool that baby!

 

[mtngun]

What I found while playing with MOTA is that there is only so much you can do to increase power at all RPMs. Muffler mod and pop-up. That's it.

Beyond that, you're tweaking the ports to work better at a particular RPM. If you change the port timing for more power at high RPM, then you lose power on the low end. Besides, there's no point in porting a 120cc saw for 14,000 RPM because it won't hold together at that speed, at least not for very long.

So I was quite limited in what I could do.

I haven't plugged in a tuned pipe to see how much that would gain. No doubt a pipe would help, but it's not very practical on a work saw.

As BigMoneyGrip suggested, heat is always a limiting factor on a saw. That's why they typically run lower compression ratios than bikes and carts. I'm tempted to put a 2-piece head on my 084, but I don't know how much compression it'll tolerate for real world use. Sometimes the only way to determine the limit is to exceed it. That gets expensive. :msp_ohmy:

 

[masculator]

I don't know whos advice you followed on the chainsaw forum but the port job you put up in your posts on there is absolutely nothing like anyone on there has ever been stupid enough to try let alone try to convince someone to do.

An MS880 will never lug 20 horsepower and if it does it will not do it for long! not only this, if it does you will be wasting at least 12 of them, unless you are running a bar of around 80 inches or bigger!

I agree with the other guys on here if it is just a tool that can pay for itself twice over in a week you would be better off buying either a lucas slabber or a bandsaw mill and making ten times as much with a tenth of the effort and wasted time and fuel!

pleasantly awaiting your rude response as you have done to all my other posts!

 

[masculator]

I've never owned an 880, and I've only ran one twice, for pretty short times. I wasn't hugely impressed, but maybe i had high expectations? I kind of get the impression that the 084 is the way to go, but this is only based on hearsay. I'd be seeking out opinions from one of the saw builders on the site (simonizer, blsnelling) who have real life experience and knowledge of the innards of these pricey saws before having a crack. There is precedent, and knowledge out there to be tapped, no need to try to reinvent the wheel.

Shaun

In most wood a 660 will outcut an 880 all day but bury a 36 inch bar on both of them with a full comp chain and the 880 starts to show its true colours. the 120 plus cc saws are not and never have been speed demons and were designed and built to lug big bars in big timber. If you wanted to build a race saw a 660 or 390 would be good starting points but if you want a saw for cutting big wood where you are going to have 40 plus inches of bar buried then you would look at a 3120 or 880. if you want to build a saw of big ccs that revs and has heaps of power buy a 250cc dirt bike engine and start there!

 

[imagineero]

I used to think that pulling full comp on bigger bars was all about power, but Matt said something to me about chip clearance that got me thinking. We've got a few 660s and 395's mostly with bars in the 28"~36" range with the shorter bars on full comp and the longer on semi skip. I thought the shorter bars were bogging down because of lack of guts to drive it, but after watching closer I found the kerf and the sprocket cover were just getting jammed up with noodles or chips, and that was what was bogging the saw. My current theory is that if you've got a bfg bar and power to drive it then go semi skip or full skip and jump up one tooth more on your sprocket.

I got that modded 660 that Matt had and I've been running it a fair bit the last few weeks. I don't know what was dont to it but it goes pretty good. The last week I was up the mountains doing storm damage and we had some good sized aussie hardwoods, the biggest trees were 5' DBH and 40~50m high. Lots of uprooted trees, and some snapped in the middle, some leaners. I felt a bit underbarred with the 660 and a 36", semi skip and an 8 tooth. I file my rakers down pretty low, but that saw stayed hungry. I went through about 10l of fuel a day running it, but we went through about 6 or 7 good sized trees each day. I don't know that more power would be a big plus at that bar size and chain combo, and the extra weight would really suck... but I'm looking for a 5 footer and I could see maybe you'd want a bit more saw there.

I'm going back up next week, I'll get some pics to show round. Mother nature can be pretty impressive.

Shaun

 

[David (saltas)]

Heat dissipation is the key

You have a air cooled stationary engine V's a water cooled engine that is moving at hi speed.
There is a massive amount Mega joules difference.

Some guys I met in the Royal Australian Electrical and Mechanical Engineers got the bright idea to use a V6 outboard engine as a power plant as it had a hi HP per CC. They put one then two then four of the biggest radiators they had (600hp Mack truck) along with a seperate engine powered fan for each radiator and they could not get the rated HP out of the V6 outboard engine as they could not keep it cool enough.

One of the biggest factors that they had ignored is as well as being corrosive as I-Iell salt water is a excellent conductor of heat.
The infinite supply of cool salt water and the delta T delta S of the total loss cooling system is massive compared to recirculating system.

A 50cc engine at a maintained -190 deg c would make more hp than a 8.25L supercharged nitro engine at ambient temp.

 

[imagineero]

A 50cc engine at a maintained -190 deg c would make more hp than a 8.25L supercharged nitro engine at ambient temp.

You sure you don't want to re-work those numbers a bit and get back to us?

Shaun

 

[BigMoneyGrip]

You sure you don't want to re-work those numbers a bit and get back to us?

Shaun

Yeah, that ain't gonna work. The metal would be like glass at those temps. Plus, you wouldn't get the fuel to light, even if you used a torch. So, I say again, that ain't gonna work.

 

[masculator]

Yeah, that ain't gonna work. The metal would be like glass at those temps. Plus, you wouldn't get the fuel to light, even if you used a torch. So, I say again, that ain't gonna work.

That said cold air induction does make a difference to the combustion process, don't believe it light some sawdust in your hand and then blow on it!!!

 

[BigMoneyGrip]

That said cold air induction does make a difference to the combustion process, don't believe it light some sawdust in your hand and then blow on it!!!

That's a different animal. The air being cold is good to a point. That's why they use inter coolers on some forced induction engines. You can have too much of a good thing and your example is more of "supercharging" than engine cooling.

 

[David (saltas)]

My example was not a practical one, it is a mathematical one

My whole post was about do some maths, or at least go read about it.

Much of the published work is on electrical motors

There has been a lot of work published on superconductors

Heat is the wasted energy from any motor electrical or mechanical

Lean an engine out and it will make HP but the combustion chamber will get too hot.
In the second WW they experimented with oxygen injection and NOS was ignored at first because they did not consider that it had enough oxygen.

Eventually they did discover that it add oxygen leaned out the combustion but it also cooled the combustion...

Back to practical considerations and a little thermodynamics
The fins on an air cooled engine have an optimum length.
Too short and they get hot and stay hot and don't cool enough.
Too long and they stay too cool and do not dissipate the heat from the engine.

My original point was that heat was the biggest limiting factor.
If the op was able to design a set of port timmings, expansion chamber for a two stroke engine of that amount of CC (the op gave examples of designs that have achieved this) then he should calculate how much waste heat was going to be produced and how in the sam I-Iell he would be able to cope with this heat. The saw would melt the piston set fire to the plastic and catch fire.

The saw is not going to stay cool enough for long enough for the crank or crankcase to be the limiting factor and break

 

[BigMoneyGrip]

Yeah, when you're dealing with electricity, the colder the better. Thats why the collider at CERN uses liquid He, to cool it so that the electricity is more efficient.
Internal combustion engines are designed to operate within certain parameters.

 

[tek9tim]

why wont it make the power of a dirt bike or kart..................

bore to stroke ratio

expansion pipe

power valve on ex

port area and port types.....have a look at the other 2 and compare to a saw.....

carb type

crankcase size

cooling

combustion chamber shape and size


they are completely different beasts.....


like I said in your other thread, Jennings is good but is bike focused....its not 100% apples to apples for a saw

If the saw is 8 or so hp stock and you want to use it for work/mill I think 10-11hp would be max

Don't forget reeds on the intake...

To beat a dead horse, milling is hard on saws. Heavy port work is hard on saws. Both together are a bad idea. Get a proper mill if you can pay for an 880 twice in a week.

 

[tek9tim]

That said cold air induction does make a difference to the combustion process, don't believe it light some sawdust in your hand and then blow on it!!!

Whoa. Missed that one. Being a professional in fire behavior, I will say that although you are right about cold air induction, you are using a poor analogy. You're adding wind to the reaction, not colder temperature. Your analogy would be better suited to whether a turbo works or not. Now, comparing how sawdust burns in your hand while in a walk-in freezer versus how it burns when you aren't in the freezer would be better, though still not good, because the fuel (sawdust) temperature would be lower, which does negatively affect intensity.

 

[trappermike]

My 2 cents on the original subject...
The 880 bottom end is very durable,I built an 084 race saw from a pre-production test saw in 1986 and it is still being raced successfully today,and it has never been torn down or rebuilt,in fact it did some logging work before it's racing career. So no worries there I think.
If you want to increase the power that's really easy with the standard mod tricks- porting,compression,carb mods,muffler mods etc., but if you are stihl :msp_biggrin: going to use it for milling and work I wouldn't go too hog wild on it just for the sake of durability and heat build-up.
A pipe on a work saw(?!),I'd like to see that successfully done,there is so much vibration and sonic activity going on in a pipe that they stubbornly resist your efforts to hang onto the saw for long,unless you are willing to build one with a spring-fastened mounting flange and good rubber mounts! Also a fairly hot pipe can create a heluva lotta heat in the motor amazingly fast(like 10-20 seconds). Finally from the awkward bulky pipe you may self-inflict a lotta burns trying to work around it. So I'm just saying a pipe's impractical as well as make you deaf fast,just a well modded free flowing muffler will give good power and help keep heat down in the motor.