What is Horsepower?

[SawTroll]

The most accurate way to measure HP on a saw is using a torsion bar (small diameter shaft) set-up and a brake. You can measure the RPM very accurately with a laser tach on the shaft. The shaft will deflect a certain amount from one end (pto) to the other (brake) measuring the deflection at various rpms at wide open throttle shows a torque at an RPM. The rest is simple math. (2*pi*rpm*torque(ft*lbs) divided by 33000 is HP. Cheers, Simon.

..but the question is what kind of hp? :smile2:

 

[ozflea]

Depends on if your using draught horses or shetland ponies

 

[SawTroll]

Depends on if your using draught horses or shetland ponies

Yup, that is about it! :hmm3grin2orange::hmm3grin2orange:

Then, max hp is just a small part of how a saw performs in wood - just a rough indication on what to expect!

 

[indiansprings]

Thanks for that information, so with a simple dial indicator and magnetic base I can see a person making a relatively simple fixture to measure hp, you could use a modified chain brake to control the amount of braking. Do you have any idea what size shaft should be used?

 

[Gologit]

Yup, that is about it! :hmm3grin2orange::hmm3grin2orange:

Then, max hp is just a small part of how a saw performs in wood - just a rough indication on what to expect!

Exactly. The only real test of a saw is how it cuts in the wood. Things like type of wood and the sharpness of the chain can make mere numbers completely meaningless. Cutting technique counts for a lot, too.

For instance...My main saw is a lightly modded 660 that TreeSlingr did for me. A friend that I work with has a 390 that's been modded radically. If we're in the same kind of wood a small difference in chain type and sharpness brings those two saws back pretty close to equal. He's running bigger hp, rpm, and torque numbers than I am but it's surprising how often those two saws, one supposedly numerically superior to the other, even themselves out.

 

[indiansprings]

Exactly Troll, the hp number is just one measurement, torque has a lot to do with the performance as well. That's why when you compare a diesel tractor and gas tractor of the exact same hp almost without fail the diesel will outperform the gas unit, the diesel having a better ratio of hp and torque.
It's just my opinion that many builders make the mistake of building for top end rpms, sure it looks good on a tach and sounds impressive, but more than likely at the expense of torque (working saws). I guess it's just a matter of what you like in a saw. Sustained rpm in the cut would be important for me.

 

[indiansprings]

Gologit, excellent post. Tried to rep you but it says I got to spread some around.

 

[SawTroll]

Another thing; Most of the "testing" done on here are done with one single bar, chain and gearing both before and after, and in one type and size of wood - there is no way to know if the times really represents the capasity of the saws(s)!

This is one of the cases where the KISS rule doesn't work too well! :rolleyes2:

 

[SawTroll]

Exactly Troll, the hp number is just one measurement, torque has a lot to do with the performance as well. That's why when you compare a diesel tractor and gas tractor of the exact same hp almost without fail the diesel will outperform the gas unit, the diesel having a better ratio of hp and torque.
It's just my opinion that many builders make the mistake of building for top end rpms, sure it looks good on a tach and sounds impressive, but more than likely at the expense of torque (working saws). I guess it's just a matter of what you like in a saw. Sustained rpm in the cut would be important for me.

Well, imo top end (higher rpm than max hp rpm) is way more important than low end (if that matters you use a too small saw) - but opinions on this will always differ!

 

[Kemper]

Yup, that is about it! :hmm3grin2orange::hmm3grin2orange:

Then, max hp is just a small part of how a saw performs in wood - just a rough indication on what to expect!

It's actually everything in how a saw performs in wood.

The Horsepower rating on saw specs is under a load at a certain rpm,(curve) so if a saw has 4.2 HP at 8500 rpm in the cut,then you have a baseline when building a saw, so if one could mod the saw to have 4.2 HP @10000rpm then it would be a measurable increase,....waaaay better than a timed cut...Timed cuts have too many variables.

 

[SawTroll]

It's actually everything in how a saw performs in wood.

The Horsepower rating on saw specs is under a load at a certain rpm,(curve) so if a saw has 4.2 HP at 8500 rpm in the cut,then you have a baseline when building a saw, so if one could mod the saw to have 4.2 HP @10000rpm then it would be a measurable increase,....waaaay better than a timed cut...Timed cuts have too many variables.

I agree on the "too many variables", but not really if the wood is uniform and various size, and all relevant gearing and cutting attachment options are tested. Most often, that is not the case.

 

[indiansprings]

Simon, being a mechanical engineer, with a desire to produce consistent results from saw to saw, so users can expect a consistent product, you have to know what kind of hp your getting out of a 372, come on unless it is a trade secret it would sure help your marketing. On you everyday in and out work saw modification what kind of gross hp gain is to be expected for a customers hard earned dollars?

 

[drkptt]

The most accurate way to measure HP on a saw is using a torsion bar (small diameter shaft) set-up and a brake. You can measure the RPM very accurately with a laser tach on the shaft. The shaft will deflect a certain amount from one end (pto) to the other (brake) measuring the deflection at various rpms at wide open throttle shows a torque at an RPM. The rest is simple math. (2*pi*rpm*torque(ft*lbs) divided by 33000 is HP. Cheers, Simon.

Can you describe how you measure the deflection of a spinning shaft? Are you referring to the use of a torque transducer?

 

[TreeClimber57]

Lots of good info here.. and frankly is it ONLY horsepower that matters in a saw.. no..

But.. interestingly enough that is usually the only thing you see advertised on saws in the way of rating.

So .. are all saws of equal horsepower equal then ?

Back to the original question.. what is horsepower :

Mechanical horsepower: hp(I) = 33,000 ft-lbf/min = 550 ft·lbf/s = 745.699872 W

Metric horsepower hp(M) = 75 kgf·m/s = 735.49875 W

Electrical horsepower hp(E) = 746 W

Boiler horsepower hp(S) = 33,475 BTU/h = 9,809.5 W

Hydraulic horsepower = flow rate (US gal/min) × pressure (psi) × 7/12,000
or = flow rate (US gal/min) × pressure (psi) / 1714 = 550 ft·lbf/s = 745.699872 W

So.. as you can see.. just as the rating of a saw is horsepower does not tell the whole story about the saw.. neither does the term horsepower even tell you the whole story.. about work energy provided

 

[Blowncrewcab]

So, Really what we have learned is that if you "Hop UP" a Chainsaw to Increase HP & RPM, Your Chain is going to get Dull Faster



ps, don't mind me, I'm sick with a fever & feel Like ####

 

[Terry Syd]

Going back to the early posts in the thread - I'd like to know what the temperature differences are between a rough cast jug and one that has been coated with black paint. - that might be useful information I can use.

Perhaps Simon can give us some recorded observations (or is it just hype to sell mods)

Any difference in a thin coat of flat black paint, versus a died aluminum oxide (like for gun parts)?

 

[SawTroll]

Lots of good info here.. and frankly is it ONLY horsepower that matters in a saw.. no..

But.. interestingly enough that is usually the only thing you see advertised on saws in the way of rating.

So .. are all saws of equal horsepower equal then ?

Back to the original question.. what is horsepower :

Mechanical horsepower: hp(I) = 33,000 ft-lbf/min = 550 ft·lbf/s = 745.699872 W

Metric horsepower hp(M) = 75 kgf·m/s = 735.49875 W

Electrical horsepower hp(E) = 746 W

Boiler horsepower hp(S) = 33,475 BTU/h = 9,809.5 W

Hydraulic horsepower = flow rate (US gal/min) × pressure (psi) × 7/12,000
or = flow rate (US gal/min) × pressure (psi) / 1714 = 550 ft·lbf/s = 745.699872 W

So.. as you can see.. just as the rating of a saw is horsepower does not tell the whole story about the saw.. neither does the term horsepower even tell you the whole story.. about work energy provided

Looks like that info is from the site I referred to - but there are even more variants!

Mechanical hp (Hp(I) or Imperial hp) is what Stihl refer to in the US, and what Dolmar pretends to refer to. Oddly, Dolmars numbers are the same as the PS (Metric hp) that they refer to in Europe - the numbers really should be different then....:msp_rolleyes:

Anyway, those differences are small and of little importance (maybe a bit more in marketing than in reality), considering how little the max hp specs really tell us!

Here are some interesting specs, where both the kW and two kinds of hp are posted. Hp(M) obviously is Metric, the other kind obviously is hp(I), or what (inaccuratly) often are called bhp in the US.

 

[promac850]

What the ####? Who the hell brought this old ass thread back from the dead?

1 Horsepower=745.699872 Watts

(Torque x Engine Speed)/5252=Horsepower

I sometimes refer to horsepower as horsies.

----------
Here are the formulas for calculating motorcycle and automotive performance.

-Many of the formulas use the value of pi which is 3.1415927
-Some formulas contain notation such as ^2 which means "squared" or ^3 which means "cubed"
Formulas for Calculating Performance

Convert between 1/4 mile and 1/8 mile ET's

1/4 mile ET = 1/8 mile ET x 1.5832 (thanks to Bobby Mosher for this formula)

1/8 mile ET = 1/4 mile ET / 1.5832 (thanks to Bobby Mosher for this formula)

Calculate 1/4 mile ET and MPH from HP and Weight

ET = ((Weight / HP)^.333) * 5.825

MPH = ((HP / Weight)^.333) * 234


Calculate HP From ET and Weight

HP = (Weight / ((ET/5.825)^3))



Calculate HP From MPH and Weight

HP = (((MPH / 234)^3) * Weight)




Formulas for displacement, bore and stroke

pi/4 = 0.7853982

cylinder volume = pi/4 x bore^2 x stroke

stroke = displacement / (pi/4 x bore^2 x number of cylinders)



Formulas for compression ratio

(CylVolume + ChamberVolume) / ChamberVolume

cylinder volume = pi/4 x bore^2 x stroke

chamber volume = cylinder volume / compression ratio - 1.0

displacement ratio = cylinder volume / chamber volume

amount to mill = (new disp. ratio - old disp. ratio / new disp. ratio x old disp. ratio) x stroke

Formulas for piston speed

piston speed in fpm = stroke in inches x rpm / 6

rpm = piston speed in fpm x 6 / stroke in inches

Formulas for brake horsepower

horsepower = rpm x torque / 5252

torque = 5252 x horsepower / rpm

brake specific fuel consumption = fuel pounds per hour / brake horsepower

bhp loss = elevation in feet / 1000 x 0.03 x bhp at sea level

Formulas for indicated horsepower & torque

horsepower = mep x displcement x rpm / 792,00

torque = mep x displacement / 150.8

mep = hp x 792,000 / displacement x rpm

mep = hp x 792,000 / displacement x rpm

mechanical efficiency = brake output / indocated output x 100

friction output = indicated output - brake output

taxable horsepower = bore2 x cylinders / 2.5

Formulas for air capacity & volumetric efficiency

theoretical cfm = rpm x displacement / 3456

volumetric efficiency = actual cfm / theoretical cfm x 100

street carb cfm = rpm x displacement / 3456 x 0.85

racing carb cfm = rpm x displacement / 3456 x 1.1

Formulas for tire size & their effect

effective ratio = (old tire diameter / new tire diameter) x original ratio

actual mph = (new tire diameter / old tire diameter) x actual mph

Formulas for g force & weight transfer

drive wheel torque = flywheel torque x first gear x final drive x 0.85

wheel thrust = drive wheel torque / rolling radius

g = wheel thrust / weight

weight transfer = weight x cg height / wheelbase x g

lateral acceleration = 1.227 x raduis / time^2

lateral weight transfer = weight x cg height / wheel track x g

centrufugal force = weight x g

Formulas for shift points

rpm after shift = ratio shift into / ratio shift from x rpm before shift

driveshaft torque = flywheel torque x transmission ratio

Formula for instrument error

actual mph = 3600 / seconds per mile

speedometer error percent = difference between actual and indicated speed / actual speed x 100

indicated distance = odometer reading at finish - odometer reading at start

odometer error percent = difference between actual and indicated distances / actual distance x 100

Formulas for MPH RPM gears & tires

mph = (rpm x tire diameter) / (gear ratio x 336)

rpm = (mph x gear ratio x 336) / tire daimeter

gear ratio = (rpm x tire diameter) / (mph x 336)

tire diameter = (mph x gear ratio x 336) / rpm

Formulas for weight distribution

percent of weight on wheels = weight on wheels / overweight x 100

increased weight on wheels = [ distance of cg from wheels / wheelbase x weight ] + weight

Formulas for center of gravity

cj location behind front wheels = rear wheel weights / overall weight x wheelbase

cg location off-center to heavy side = track / 2 - [ weight on light side / overall weight ] x track

cg height = [ level wheelbase x raised wheelbase x added weight on scale / distance raised ] x overall weight


This all is from here: http://www.nightrider.com/biketech/calc_formulas_page.htm

 

[RiverRat2]

Heh heh heh,,,, Picking on 04Ultra 4 years ago!!!!

 

[promac850]

Heh heh heh,,,, Picking on 04Ultra 4 years ago!!!!

Picking on you right now!! :msp_flapper:

:fart: :check: :deadhorse: otstir: :sword:


he he he... he...