Why does my 920 destroy my mt8200?

[bplust]

Hi all,

I've had an Efco my8200 (80cc) for a little under a year, have done a lot of work with it, and am very happy with it overall.

However, I just picked up and fixed a Jonsered 920 (87cc). I put the two to a test, five times, of using an 18" bar (both had new bars) with Oregon ripping chain (both had new chains), and various diameter logs. I would have the two saws milling slabs off of the same canted log (at the same time! just kidding), so they were doing the exact same task.

And, I'm sure you're surprised based on the title of the thread, that the 920 destroyed the Efco. Not much of a competition. I do recognize that the 920's 7cc's bigger, but still, it was much more than a 9% milling speed increase.

What's going on here? Superior torque on the part of the 920 due to a heavier crank?

Thanks,

Bryan

 

[HUSKYMAN]

Because Jonsered's rule and Efco's drool! Kidding

The 920 is a heavy duty saw designed to run long bars and has port timing that is designed all around low rpm grunt. The Efco is a high speed saw designed to run at peak rpm and be a fast saw for bucking, felling, etc.

920s are bad asses

 

[mtngun]

The Efco is a high speed saw designed to run at peak rpm and be a fast saw for bucking, felling, etc.

Nah, Efcos have tame port timing.

Dunno about Johnny.

 

[SawTroll]

I don't understand why you are surpriced - the larger Efco saws are not known to be very good performers.......:help:

 

[HUSKYMAN]

Nah, Efcos have tame port timing.

Dunno about Johnny.

Compared to the Johnny 920, a saw designed in the 70's to never see more than 10000 rpm, I bet that Efco has a lot more aggressive timing, thats my point. Compared to a Dolmar 7900, you are probably right, the Efco would look pretty tame

 

[SawTroll]

As far as I know, the 920 was made 1982 - 1986, and had a max rpm rating of 12,200 rpm and max power output at about 9,000 rpm.

 

[mtngun]

I bet that Efco has a lot more aggressive timing, thats my point.

I don't have the numbers at my fingertips, but I've posted Efco timing numbers on AS before. They're very mild. Otherwise, the jug design is similar to a Stihl, and they respond nicely to a woods port and muffler mod.

Bryan, if your Efco doesn't already have a muffler mod, that would be the easiest way to boost the power.

 

[ray benson]

I'm surprised - especially with short 18" bars. With 32" bars and big wood the 920 would be expected to dominate.

 

[sachsmo]

I'm surprised - especially with short 18" bars. With 32" bars and big wood the 920 would be expected to dominate.

Sounds like he's milling Ray.

Rippin' takes a bunch of power.

 

[spike60]

The Jonny 900's are very strong saws, so your 920 is running right where it should be.

And the 930 Super is even more impressive. :msp_w00t:

 

[WoodChuck'r]

I want a mint 930 so darn bad...... Those saws are frikkin' BOSS!!

 

[bplust]

Sounds like he's milling Ray.

Rippin' takes a bunch of power.

yessir, I am testing them via milling

 

[bplust]

I don't have the numbers at my fingertips, but I've posted Efco timing numbers on AS before. They're very mild. Otherwise, the jug design is similar to a Stihl, and they respond nicely to a woods port and muffler mod.

Bryan, if your Efco doesn't already have a muffler mod, that would be the easiest way to boost the power.

Beyond removing the spark screen, there have been no mods.

Suggestions?

And how about the 920, any suggestions on mods ideal for that?

Thanks,

Bryan

 

[HUSKYMAN]

Beyond removing the spark screen, there have been no mods.

Suggestions?

And how about the 920, any suggestions on mods ideal for that?

Thanks,

Bryan

Just mod the mufflers on both and be sure to point the exhaust in a direction that it will not burn your hands when you are milling.

 

[bplust]

Just mod the mufflers on both and be sure to point the exhaust in a direction that it will not burn your hands when you are milling.

So basically create/enlarge existing openings in the mufflers to create more flow?

I've been reading this a bit:

http://www.arboristsite.com/chainsaw/178738.htm

Don't think I'm quite qualified just yet to be porting, maybe just some muffler work. Let me know if there are any other good threads to check out.

Thanks,

Bryan

 

[SawTroll]

Beyond removing the spark screen, there have been no mods.

Suggestions?

And how about the 920, any suggestions on mods ideal for that?

Thanks,

Bryan

Put a 930 cylinder on it, isn't that right Spike?

 

[bplust]

I looked at Chainsaw Collectors Corner and compare the specs of the 920 to the 930.

I've never had a 930 in my hands, so I haven't witnessed the power difference, but on paper, what's giving it the difference? Based on stroke, bore, and the fact that the piston's interchangeable, I'm not sure what the difference is, but I will admit that I am a newbie as well. Just curious, piston's are easy enough to grab, and I do have a good 920 jug lined up for $20, but if it's worth putting in a 930, I'll find one.

Thanks.

 

[SawTroll]

We need one of the true Jonsered(s) experts here - I think I know something about it, but my memory could be wrong, or the knowledge not complete - and thereby misleading.......

 

[Chris J.]

I just spen the last 20 minutes going through previous threads regarding differences between the 920 and 930, but didn't find any definitive info.

Maybe someone else will have better luck?
http://www.google.com/#sclient=psy&....r_gc.r_pw.&fp=18006656ae9954f0&pf=p&pdl=3000

 

[bplust]

Based on CCC as my only resource, an answer that aligns perfectly with the information presented there is that the 930 started being produced in 1986, after the 920 stopped being produced. That might be it.

As I said in my last post in this thread, I've never had a 930 in my hands, but there might be some body styling differences. Looking at the photos provided of the two, everything looks the same as mine, besides the skinnier chainbrake, which is shown in both saws' pages. I have the fatter one.