Please give advice------Briggs and Stratton power chart

[bertsmobile1]

And you sound suprised ?
Horse power can be calculated at least a dozen different ways and there are almost as many different ways to measure it.
Mower engines are by and large not high horsepower .
Further more the world finally came to an agreement as how to rate the energy developed by small engines, one of the nice spin offs of the WTO so I have been told.

So when you are measuring a small item it makes good sense to use a small unit of measurement.
Under the old system those motors would have been rated as 3.75 , 4 & 4,5 Hp respectively.
Under the new system they would be rated something like 2.75, 2.9 & 3.1 Hp so naturally the need to change the publicised power measurements.
Much like the old days when cc for cc Honda engines were around 10% to 15% lower rated Hp than Briggs because principally they were being measured differently.

Nothing has physically changed, just the way we describe them but it is almost impossible for Joe public to backwards convert their old engines power ratings to compare them with the modern ones.
Under the new systen the Powertorque figures I quoted before would be around 30% lower, but that is not the way I remember them.

For industral engines you want flat power delivery at the best or a strait upward curve at the worst.
You do not want your mowers power to halve suddenly when you push it into the tall tufty wet grass and it slows down the engine slightly.
So if you for instance push your mower hard and regularly submit it to high loads that are likely to slow it down then you need the engine which developes peak power a bit lower down so as the engine is slowed by the load it adds a bit more oomph which is what the latter two curves show.

Back in the bad old side banger days you could get engines in 0.25 Hp increments but when you had a good look there were 6 to 8 different engines that all had the same piston, stroke, compression ratio, valve size , cam & carb size.
The difference ?
The size of the main jet.
The actual difference in performance 5/8 of SFA
But the sales person could convince you that the extra 1.5Hp was worth the extra 20% on the price tag.
Remember the mower engines are made for the mower companies not the end user.

 

[efc1978]

And you sound suprised ?
Horse power can be calculated at least a dozen different ways and there are almost as many different ways to measure it.
Mower engines are by and large not high horsepower .
Further more the world finally came to an agreement as how to rate the energy developed by small engines, one of the nice spin offs of the WTO so I have been told.

So when you are measuring a small item it makes good sense to use a small unit of measurement.
Under the old system those motors would have been rated as 3.75 , 4 & 4,5 Hp respectively.
Under the new system they would be rated something like 2.75, 2.9 & 3.1 Hp so naturally the need to change the publicised power measurements.
Much like the old days when cc for cc Honda engines were around 10% to 15% lower rated Hp than Briggs because principally they were being measured differently.

Nothing has physically changed, just the way we describe them but it is almost impossible for Joe public to backwards convert their old engines power ratings to compare them with the modern ones.
Under the new systen the Powertorque figures I quoted before would be around 30% lower, but that is not the way I remember them.

For industral engines you want flat power delivery at the best or a strait upward curve at the worst.
You do not want your mowers power to halve suddenly when you push it into the tall tufty wet grass and it slows down the engine slightly.
So if you for instance push your mower hard and regularly submit it to high loads that are likely to slow it down then you need the engine which developes peak power a bit lower down so as the engine is slowed by the load it adds a bit more oomph which is what the latter two curves show.

Back in the bad old side banger days you could get engines in 0.25 Hp increments but when you had a good look there were 6 to 8 different engines that all had the same piston, stroke, compression ratio, valve size , cam & carb size.
The difference ?
The size of the main jet.
The actual difference in performance 5/8 of SFA
But the sales person could convince you that the extra 1.5Hp was worth the extra 20% on the price tag.
Remember the mower engines are made for the mower companies not the end user.

So if the 6.5HP Powertorque you mentioned would be rated as 30% lower by these days measurements, it would be rated today at 4.55HP (6.5 x 0.3 = 1.95, so 6.5 - 1.95 = 4.55), which would still make those older engines more powerful than todays residential push mowers (you said the 675EX would be around 3.1 HP in todays measurements), although I did read somewhere back then (around 20 years ago), a lot of the HP ratings given were gross, not net as it is today?

 

[bertsmobile1]

Nothing has really changed physically.
Just the numbers and how we get to them.
Guestimates from old to new are just that, rough calcs .
The original Villers on the original Victa 18 was around 1.75 Hp from memory measured on the old Pommie scales which were a little lower than the USA scales but higher than the Japaneese.
Somewhat meaning less for a mower.
Important for a brick elevator or pump but not much good for vague application with so many variables as powering a mower.

How many Hp do you need to mow a lawn ?
And to get back to our original question.
For low mowing on a cleanish lawn there will be little to no advantage to ordering a mower with the bigger engine.
It will not mow your grass 1 second slower than the bigger engine and most likely use a little less fuel to boot.

 

[cpurvis]

There is only one way to calculate horsepower. It is a function of two measured units, torque and rpm, multiplied together and divided by a constant to get the measurement units into the same form as the definition of horsepower. Namely, the ability to lift 550 pounds one foot in one second is the definition of one horsepower.

efc 1978, you might want to check your math as to the percentage difference between those two engines. It's small, but much larger than a few tenths of a percent.

 

[efc1978]

efc 1978, you might want to check your math as to the percentage difference between those two engines. It's small, but much larger than a few tenths of a percent.

Sorry I meant there's 1 tenth of 1 horsepower difference, not 1 tenth of a %, pretty sure I got it correct. eg.
-------------------------
Well that's interesting, unless I got something wrong....
If you read the fine print at the bottom of those power charts I posted from the Briggs and Stratton website, it says HP is measured at 3600 RPM, so looking at the charts I posted the 625EX 8.5Nm 150cc is a bit above 7.6Nm at 3600, and the 675EX 9.1Nm 190cc is about 7.8Nm at 3600, so when I used the converter at the below link to convert 7.6Nm and 7.8Nm at 3600 RPM to HP the 625EX is 3.84 HP and the 675EX is 3.94 HP, just 1 tenth of a % difference between the 2, according to the B&S website if I correctly understood......
WEN Technology - Calculators
-------------------------

 

[bertsmobile1]

There is only one way to calculate horsepower. It is a function of two measured units, torque and rpm, multiplied together and divided by a constant to get the measurement units into the same form as the definition of horsepower. Namely, the ability to lift 550 pounds one foot in one second is the definition of one horsepower.

efc 1978, you might want to check your math as to the percentage difference between those two engines. It's small, but much larger than a few tenths of a percent.

And if you do not have a dyno to measure torque ?
Formula Horsepower which is what Briggs use.
This then had to be reduced because the new world standard requires the MEASURED Hp to be at least 95% of the CALCULATED Hp

The RAC (British) formula for calculating tax horsepower which was used in both the USA & the Commonwealt for far too long.

Hp =DxDxN / 2.5
where
D is the diameter (or bore) of the cylinder in inches
n is the number of cylinders

Then there is Nominal Hp
nhp = 7 x total piston area x equivalent piston speed / 33,000

I have a couple of others kicking around that take compression ratios into account.

And the 550 pound one foot is a rounded simplified calculation.
The Germans, French & Italians all had different ways of determining HP which was one of the big EEC problems.
The Japaneese had a different method again that gave a much bigger number
The SAE abandoned the BHP method in the 60's from memory.
And then we have brake Hp
Crank Hp
Gross Hp
Net Hp
Hp calculated from time traps etc, etc, etc, etc.

Hp was obsolete and should have been abandoned when we stopped using horses which was basically around WWII

it is slowly being replaced with kW which is a better measure and much easier to measure accurately.

How many on this list can visualise how much work a horse can do ?
And if you can do that can you equate that to the rotating blades on a mower?

 

[cpurvis]

Uh, no. 550 ft-lb/sec is the definition of one horsepower. There is no 'rounding' to it. Horsepower in other units, such as watts, BTU, or whatever are derived from the 550 ft-lb/sec definition and may have some rounding but the original definition of horsepower contains no rounding.

Any of those other formulas you mention are horsepower estimators. You can get a 'ballpark' figure from them as to what the horsepower might be but actual horsepower can only be calculated from measuring torque and rpm. That's what those Briggs charts are--dyno runs. If they were estimations, they'd all have the same curve shape, and they don't.

 

[bertsmobile1]

Watt rounded off the original numbers to make them easy to work with.
One of the Pommie museums has some of the original work done by him & Stevens ( I think )
It happened to be on display one time when I was in the Old Dart.
Apparently there was a lot of contraversy at the time and the "std" horsepower did not become "std" for quite some time.

And yes the charts should come from a dyno but the dyno is a fairly new tool.
Engine designers use one of the desk top dynos now days to replace the formula Hp calculations done back in the days of the slide rule.
The former should give a reasonably accurate "estimate" as the new computer formulas can take phnumatics, friction & heat into account where as the old formulas I learned at college conviently overlooked them.

This had to happen as you can not fabricate and test 22,000 different head variations on a dyno. They all have to be simulated on screen before being committed to metal.
BSA ( motorcycles ) had a dyno shop from around the late 30's but it was never used to test any of the production engines and none of the production engine prototypes till the late 50's.
It was used excluseivly by the competition department and in particular to produce power curves for actual engines fitted to the Gold Star Competition range so you gat ypur chart with every competition engine.

No arguement about REAL figures needing to be the results of actual testing .
However the numbers on the engines are not real, they are now 95 % real whereas the previous standard they only needed to be 85% real and the % variation is the difference between what the computer calculates and what the dyno measures under the conditions the dyno is set to, then "corrected" for air pressure , temperature etc ,etc, etc and has little resemblance to your motor on your mower in your garden.
They used to do consumption tests very early in the morning so the fuel was cold , thus denser so once the engine had warmed up you had in effect 5% more fuel in the tank than you would have had if the tank was filled in mid morning and the fuel was at air temperature.

Spin , and manupliating the testing proceedue to obtain results to your advantage is not new.

 

[efc1978]

From memory the power torque series II came in two outputs.
A high compression which was rated at 6.25Hp and the low compression rated at 5Hp
Never seen a torque curve diagram for one as they had way more power than was needed for the application.
AFAIK the difference was all in the head the high comp one has a decompressor and the low power one does not but the castings are the same, you can see the unmachined space for the decompressor to go.
Never bothered to compare them and have no idea why they made them 2 different ways.
However you have to remember that blue smokes are all revs, so comparing the power torque to the equivalent 4 stroke is very difficult.
The 24" came with a power torque , Honda c160 or B & S and both the 4 strokes were hopeless where as on the std 18" mower deck there was little difference till you got into wet grass or mulching.
The big trouble with comparing power torques is much like trying to comparre Hondas.
Each engine ran for a very long time and often the produced 4 different identical looking engines at the same time.
A lot of the changes were quite subtle like variations in the port size & shape while the Mk I to Mk II was quite dramatic as the latter had 1/3 of the finning as the former which actually cooled too much, not bad for an alloy headed iron motor.
If you are trying to remember how yours went back then, try to remember what it was like new out of the box, not what it went like 20 years latter having never been serviced.
The big problem was they very rarely broke down so never got serviced as they slowly deteriorated and became almost impossible to start.
A $25 set of parts brings them back to almost as new provided the bore is not scored.

Hi,
Here's 2 photos of the 1994? Victa Mustang, can you tell if it has the high or low compression output? 2 photos attached.
As you explained previously, I think it's hard for you to make a clear torque Nm comparison with the Briggs and Stratton 625EX / 8.5Nm / 150cc OHV engine?
Would either be clearly the more superior at cutting patches of 2 inch wet grass?
Thanks

 

[bertsmobile1]

That is a high compression engine.
The pie shapped thing top right on the head is the decompressor.
It should be able to cut 2" of wet grass with no problems at all if the mower is in reasonable nick.
Pop off the muffler and have a look at the bore.
If it is clean and oily then good chance the engine is ok and worth fixing.
If it is scored then it goes in the recycle bin.
a rebore new piston & rings, bearings , seals , O rings & fuel lines runs about $ 150 and despite making the mower good for another 30 years very few will pay the price.
They want a nice new Chineese one from Bunnings that will cut the grass badly for 2 or 3 years.

The steel deck handles wet grass better than the alloy deck.
Put the heavy duty high lift blades on it and that will make it even better.