New speed vs old torque question

[bplust]

So I've been around a few older saws and a few newer saws, all of the being direct drive, and my general observation is that the newer ones have greater cutting speed, and the older ones have more torque. I can understand how gear drive would greatly increase torque, but what is it about the older direct drives that give them more torque than the newer saws (all direct drive as far as I know)? Heavier cranks?

And why can't the older saws be tuned to run regularly at the new saws rpms? Tolerances?

Thanks in advance for any replies!

 

[blsnelling]

A lot of it has to do with the old saws having reed induction and the new saws being piston ported.

 

[bplust]

I understand the basics of how the two work. How do different intake methods affect speed or torque?

 

[Dan_IN_MN]

Here's a thread I started that might answer a few questions: http://www.arboristsite.com/chainsaw/123923.htm

 

[woodyman]

If you want them to run faster porting would not hurt:hmm3grin2orange:

 

[bplust]

Ya, it's not that I really want the old ones to run like the new ones, I was wondering why they run so much slower but have more torque. Gearing makes sense regarding torque to me, it's a reduction. And by the way, that thread manyhobies recommended was great, lots of good stuff to learn. I was trying to find the "missing piece of the puzzle" as to why the older saws couldn't produce the rpms, and maybe it's in the porting. Displacement/Stroke/Bore can match up between old and new, my 1-72 has the same stats in these as a Husky 288. And I cannot image that a carburetor as big as the McCulloch flatback (not in my 1-72, but I'm just saying) couldn't deliver as much air & fuel as any other carb fitted on a saw. So I guess it's in the delivery, and how much can get in there (better porting through R&D, I suppose?)?

I'm not making proclamations here by any means, if you didn't notice the question marks, just intuitive remarks based on the minimal amount I know on the subject. Please correct me at will, just tryin to learn stuff here.

 

[roostersgt]

Not a lot of mystery here. A lot of the torque is brought about soley by the weight of moving mass. The greater moving mass stores more kinetic energy. Newer saws shed weight and are designed for higher rpm's. Older saws had longer strokes and heavier flywheels / cranks.

 

[blsnelling]

Also, I suspect today's lubricants allow higher RPMs.

 

[Danno]

I know Brad said it early, but reeds do play a big part in this. Those older reeds will start to fluttering at any RPMs that are close to today's saws.

I think if you could port it properly and replace those reeds with some of those new fancy carbon fiber ones and adjust th a/f ratio on it to account for better lubricants, then you could get an old Mac like mine (stock is like 6,000rpm) up close to 10K and it would probably be fine.

But I'm just an armchair mechanic, so this is all just hypothesizing.

 

[NORMZILLA44]

Plus they werent all choked up trying to pass smog!

 

[Justsaws]

Mcculloch 250 versus Dolmar 7900, which one do you think with pull a 36" bar better?
Mcculloch Super 250 versus a Husqvarna 385, same question.

At the end of the day which saws will make more cuts?

Hype is hype, the rest is the chains, bearings, seals and the chain is going so slow it seems is more powerful. A 250 will run out of gusto long before a 7900.

And before people get all pissy about the good old days, I own and use lots of Mccullochs, Poulans and Homelites and I do not currently own a 7900 or a 386.

 

[Modifiedmark]

Depends on how old of a old saw your talking about. There are several saws from the late 70's through the 80's that will hang with most modern saws of the same displacement.

Yes they turn slower no load speeds, but they dont lose as much of the no load speed when put in the wood.

 

[old 040]

So I've been around a few older saws and a few newer saws, all of the being direct drive, and my general observation is that the newer ones have greater cutting speed, and the older ones have more torque. I can understand how gear drive would greatly increase torque, but what is it about the older direct drives that give them more torque than the newer saws (all direct drive as far as I know)? Heavier cranks?

And why can't the older saws be tuned to run regularly at the new saws rpms? Tolerances?

Thanks in advance for any replies!

as others have said in this thread, longer stoke and or conn. rod, heavier flywheels and cranks, these saws will still cut very well, just finished a refurb on a very nice 041av, it had been a while since i've run one, boy did it bring back the days i remember, runs awsome, and i know i will hang with many of my newer sawsopcorn:

 

[igpoe]

And please remember that the old and torquey saws used bigger pitch chains even with direct drive so as make use of their torque. If we change sprockets on a 770D Homey down to a 3/8, even a square grind chain will suffer extreme embarrassment compared to the original 7/16 or
.404, unless........................8,9, or even 10 pins of rim sprocket can be mounted!
I'm thinking this would have to be true, but then, I've never tried it!
Igpoe

 

[sawmandave]

I have put a 404 full skip square grind chain on a super wiz-66 with a3 ft. bar not much gain also but cool..:msp_tongue:

 

[Eccentric]

Depends on how old of a old saw your talking about. There are several saws from the late 70's through the 80's that will hang with most modern saws of the same displacement.

Yes they turn slower no load speeds, but they dont lose as much of the no load speed when put in the wood.

Yep. I'll bet some of these 'modern saw' guys would be surprised by a PP 655BP or a Homelite 750.

 

[Modifiedmark]

Yes Aaron those would fit the bill but I was thinking like a Poulan 4200. Andyshine was telling me he put the tach on one of Mikes at a GTG and wasnt inpressed at the no load speed of it. He then put the tach on it when it was buried in the wood and was floored to see it only lost like 4-600 rpms (if I remember right) under load.

 

[Rounder]

Strokin'

 

[ncsawguy]

which is better torque or rpms. i have never run any new high rpm saws. but i got a super xl 925 that has handled any thing i throw at it.
i am looking to but a new saw but dont know what to get. i am very satfied with that 925.

 

[roostersgt]

The only downside with the older reliable saws is the lack of parts and the WEIGHT. If you're happy with the 925, why get a new one? CAD?