litefoot
Addicted to ArboristSite
I guess we're giving up torque for chain speed these days, but what's the difference in the engine configuration. I assume that it has much to do with the porting, but I'd like to hear more.
Why do the old saws make more torque?
- Thread starter litefoot
- Start date
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Longer stroke
I think the biggest reason would be the longer stroke, long stroke means more leverage = more torque or twisting force all other factors being equal.
I always suspected that when the reed valves were in good condition in those engines they may have been a bit more efficient at charging the crankcase/cylinder but I am not sure that would apply with the high level of technology and engineering that goes in to today's high speed piston ported models.
Mark
I think the biggest reason would be the longer stroke, long stroke means more leverage = more torque or twisting force all other factors being equal.
I always suspected that when the reed valves were in good condition in those engines they may have been a bit more efficient at charging the crankcase/cylinder but I am not sure that would apply with the high level of technology and engineering that goes in to today's high speed piston ported models.
Mark
:agree2:
the 'long stroke' is a common but wrong assumption. like the old 4 stroke motorcycles of the 50's. But think about it: for the same displacement, longer stroke means smaller bore, so less area pushing, which exactly cancels out the longer crank radius. area times stroke is displacement.
The big single 4 stroke motorcycles had several reasons for low end torque: 1. long stroke = small bore = not much room for valve area, so they had to be tuned low end, they ran out of breathing at high rpm.
2. long stroke = rpm limited due to piston speeds, so had to be tuned to low end.
3. long stroke = vibration = limited crank balancing, or simply move vibration from vertical to horizontal. thus again, rpm limited.
to say 'more torque' really means more torque RISE as the rpms drop off. This feels like more lugging ability as the rpms drops off the torque rises and the saw carries the load. a flatter curve means very little rise, then it goes over the top of the peak and the engine stalls down.
My guess is that higher torque was a result of lower rpm tuning, because the metals and oils could not take 14000 rpm. The engines were tuned lower, thus the porting and exhaust was different. Also, with less sophisticated designs, before computer simulations, etc. engines were not really optimized, but were designed by experience and history of what worked, so not so optimized to a narrow range.
kcj
The big single 4 stroke motorcycles had several reasons for low end torque: 1. long stroke = small bore = not much room for valve area, so they had to be tuned low end, they ran out of breathing at high rpm.
2. long stroke = rpm limited due to piston speeds, so had to be tuned to low end.
3. long stroke = vibration = limited crank balancing, or simply move vibration from vertical to horizontal. thus again, rpm limited.
to say 'more torque' really means more torque RISE as the rpms drop off. This feels like more lugging ability as the rpms drops off the torque rises and the saw carries the load. a flatter curve means very little rise, then it goes over the top of the peak and the engine stalls down.
My guess is that higher torque was a result of lower rpm tuning, because the metals and oils could not take 14000 rpm. The engines were tuned lower, thus the porting and exhaust was different. Also, with less sophisticated designs, before computer simulations, etc. engines were not really optimized, but were designed by experience and history of what worked, so not so optimized to a narrow range.
kcj
kevlar
Addicted to ArboristSite
heavier rotating masses. ie flywheel,clutches etc.
Lakeside53
Stihl Wrenching
uh oh..... Deja vue...
A couple of years ago there was a long and heated thread debating whether a heavier flywheel "increases" torque.... I'm with the "Not so" crowd....
A couple of years ago there was a long and heated thread debating whether a heavier flywheel "increases" torque.... I'm with the "Not so" crowd....
stevethekiwi
Addicted to ArboristSite
torque on older saws? hmmm... Lack of EPA c(lean) burning BS, Reed valves (yes reed valves increase torque), heavier rotating mass...
part of the reason why old saws S U C K for limbing. also why they weigh a tonne and my daddy looks like stone cold steve austin with wrinkels
stk
part of the reason why old saws S U C K for limbing. also why they weigh a tonne and my daddy looks like stone cold steve austin with wrinkels
stk
motosierra
ArboristSite Guru
piston + rod + crankshaft + flywheel + clutch + chain + stroke = torque..???
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Given that the old saw has the same power as a new saw,
it has more torque if it has lower rpm since:
Power = Torque * rpm
Power is the interesting thing, it defines how much work (=cutting wood) per
time unit you can do. Hence, a 14 000 rpm 346xp will cut as much wood as an older
bigger displacement saw with lower rpm and higher torque.
it has more torque if it has lower rpm since:
Power = Torque * rpm
Power is the interesting thing, it defines how much work (=cutting wood) per
time unit you can do. Hence, a 14 000 rpm 346xp will cut as much wood as an older
bigger displacement saw with lower rpm and higher torque.
Torqued Off
I know there are a lot of variables, and all posters so far won't be there, but...........
I'm taking some saws to sell at Spikes GTG and among the saws I'm taking up are:051, 056 Mag II, and an 066 mag. All good strong saws, and folks are welcome to run them one after another and see what they think. All around 90 ccs and what a great excuse to cut cookies and throw insults. Anyone in foir it?
Rob
I know there are a lot of variables, and all posters so far won't be there, but...........
I'm taking some saws to sell at Spikes GTG and among the saws I'm taking up are:051, 056 Mag II, and an 066 mag. All good strong saws, and folks are welcome to run them one after another and see what they think. All around 90 ccs and what a great excuse to cut cookies and throw insults. Anyone in foir it?
Rob
if some one has one fine. These are 3 different series, same make & cc range. I do have to get a longer bar foir the 051 (3002 mount ?)so we can try these in bigger wood. 32-36 maybe .How about throwing in a 9010 dolmar because it has a different stroke!!
I would love to attend the tests but Im only 2000 miles from you!!
Right now Im staring at a new dolmar 9010 on the lobby floor----should I???
Or should I not because my wife will throw me out and god knows what else. If it wasn't for females I would have way to many saws.
whoops, sorry to hijack this thread. Any how--when I was running my 2100 husky I though it always out pulled my 3120. I think that was possible because compression was greater on most of the older saws compaired to the new stuff. I remember running a stock Jonnyred model 90 that had 200 pounds of compression when tested hot!!!
The only old saw I've found to have higher compression on so far is the Homelite SXL-925. The first one I removed the base gasket on and it has 200 PSI. The other is stock and has 165 PSI, but the cylinder on it has pores in it from the factory. And it still makes that kind of compression.
Peacock
Addicted to ArboristSite
Agreed.
A heaver flywheel holds the rpm better if you dont believe my ask the drag racers with the big hemis
Lakeside53
Stihl Wrenching
Which has nothing to do with "torque". A flywheel is "stored power".
Before you guy launch off into a discusion on this, you might want to read the prior very long thread on this matter..
Before you guy launch off into a discusion on this, you might want to read the prior very long thread on this matter..
Stored power, that is a better way of putting it, thank you for the expanded volcabulary
