chainsaw horsepower

[oakman]

hello all,
recently there was a post about an 088 clutch slipping, and or chain stalling. i know this may open a can of worms, but here it is anyway. i know most of us, MYSELF included, tend to think of our saws as high performance machines, especially the larger displacement saws. however, in the world of two-stroke motors, they are actually more towards the bottom of the totem pole, power wise. now i believe this is mandated by several things. weight,size, longevity, user friendliness, noise, and epa regs. just for an example, look at the specs for a stock 088, 121cc's, 8.5 hp, stihl doesn't say how many rpm's, but i'd guess around 12,000. now look at a stock 2001 honda cr125 dirt bike. almost exactly the same displacement, but an amazing 33 hp at 11,500 rpm, and can go up to 40 hp or more modified! i'd lay odds that, if you stuck the stihl motor in the bike, it would barely move. i don't mean to offend anyone, but next time you wonder why you can stick the chain on your monster saw, think about the differences mentioned here. this is only my opinion. tim

 

[dbabcock]

Oak,
Ken Dunn can explain all of the in's and out's in regard toward comparisons and tradeoffs of saw, cart and motorsicle 2 strokes. It's really interesting stuff and certainly worth some discussion. A good topic for sure.

 

[sproston]

gotta be at the wheel hp behind a 6 speed trans? huh

 

[oakman]

sproston,
so you're saying the 088 has comparable horsepower at the crankshaft with the cr125 bike engine? i highly doubt that it's even close. tim

 

[dbabcock]

You're correct about the horsepower difference, Oakman. 125cc cart and bike motors are making in the 40 HP range, modified. With a pipe, head and serious other mods, Ken tells me that really hopped up 3120's, 088's and the like can make over 25 HP. What keeps 120cc chainsaw engines from being not quite as potent as the others, may lie in part to the fact that modern chainsaws rely on piston port rather than case reed or rotary valve induction used on the others. Piston port engines can be made lighter, less bulky and cheaper, but are compromised by considerably more restrictive port timing. Another reason has to do with air versus water cooling, I suspect. I'm certainly no engine guru, but this is what I have heard and read.

 

[Gypo Logger]

Hi there, here's a picture of an 084 by Ken Dunn that ran really fast at Clearwater. Not sure but I think it winds out at 14,000 rpm and 22 hp. With the Maxima 927 Casterbean mixed at 23:1 it smells like burning nitro, plus there is not much chance of blowing it up, even if its up on the pipe for some time.
John

 

[Gypo Logger]

More Saw by Ken Dunn

Here's the saw that Ken Dunn built that I mentioned above. Although Ken likes to build full fledged racing saws he also builds the fastest wood saws I know of which last longer than stock.
Instead of trying to keep it all to myself, get hold of Ken at: [email protected]
John

 

[dbabcock]

More like 16,000 according to Ken, as I just this minute asked him.

 

[dbabcock]

And, of course, a repeat performance of Ken and Linda's favorite pic...

 

[z4lunch]

Don't forget about the variable exhaust port on the Honda too.
Steve
025
088

 

[bwalker]

What keeps 120cc chainsaw engines from being not quite as potent as the others, may lie in

Also in the fact that the cr is liquid cooled and is built with very little regard for reliability/longetivity. BTW exhaust valves dont give an engine more peak horspower. They just allow for a fatter torque curv which makes the bikes easier to ride.

 

[tony marks]

outa my league here ,but them dam chips
coming off that saw could be used for firewood dn this neck o the woods.
guess they just dont have a dept gauge,on the chain.

 

[oakman]

heres another piece of horsepower trivia sure to get yer chain speed up. did you know that one cylinder on a top fuel dragster produces more horsepower than the entire engine in a winston cup stock car? potent stuff, that nitro. i'll bet it can't do it for 500 miles, though. now how bout a top fuel chainsaw?

 

[Tzed250]

More power

The CR125 and its cousins are not even at the top of the 125 two-stroke hill. A 125 roadracer makes even more power. The bike makes more power for several reasons. 1. The bike is liquid cooled. An engines ability to make continous power is limited by the amount of heat it can eliminate. 2. The carb on the CR is either a 38 or 39mm. Huge airflow compared to the dinky carbs on a saw. 3. The variable exhaust valve. The valve lets the engine make the max power level while still letting it pull itself out of the basement. 4. Port size. The bike has ports that will flow all of the air that the carb will feed it. 6. Tuned exhaust. the bike uses the pipe to supercharge the engine.
A 500cc Grand Prix roadrace bike can make over 200 HP. That is 50HP per cylinder on a bike that has a 3000 RPM powerband. Modern saws are the best that the engineers know how to build within the parameters of saw operation.

 

[ccicora]

One thing that no one has talked about is exhaust duration. The longer the burn the more power you can make. Although, this factor is limited by all the other factors that you have already talked about. Those hopped up 125 motors have a round 200 degrees of duration. Also If you put a 125 crank next to a 3120 crank the chainsaw crank is half the size. You do the math... chansaw go boom if not done right.

Later,
Chris

 

[bwalker]

The longer the burn the more power you can make.

Duration has nothing to do with "burn". Duration is a refferance to the time a port stays open. Be it exhaust, intake or transfer. If you lenthen the combustion event you simply allow the piston to be exposed to more heat( ie advanced timing) which inturn increase the risk of seizure and detonation. In any case longer "burn" is a bad idea.

 

[ccicora]

Go ahead and keep that stock duration, I don't care because in a race that just more money for me in the end. You need to burn all the fuel and air mix you squish together with that piston. And if you are burning holes in pistons then your too lean. The most importaint issue is the balance of all the aspects that make that saw run.

Later dude!
chris

 

[bwalker]

port duration, yes. "burn" duration, no.

 

[bwalker]

port duration, yes. "burn" duration, no.

 

[tundraotto]

yes b - agreed - the fuel burns at a set rate - the port durations set the possibilities for whatever may happen in this duration - get a saw done by greffard or ken dunn and itll never be the same again.