Yes, and most people don't know that rpm has just as much to do with
horsepower ratings as anything else. They throw around horsepower numbers
like they mean something without the rpm. How many times have you heard
someone brag about the horsepower their engine makes? Want to shut them up?
Ask them what rpm that horsepower occurs at. Most often, they don't even
know. So what good is that number? Horsepower tells you nothing of the
engine's performance without knowing the rpm.
I'm glad you got a chuckle from the F1 guys. I do think they are better
engineers than comics though. I don't know what they say about the other
tracks. If you find out, let us know. Pick anyone to quote if you like, but
please use credible sources. Don't quote Joe Bling saying that the 22's that
he put on his Civic make 500 horsepower so it now goes 300 mph in the
straights. I will consider any comments from any credible source that says a
high horsepower number is more important than torque.
Those dynos still measure the engine's torque and then convert it to kW.
Also, I said "no matter what engine" and I should not have. I didn't intend
that to include jet engines, nuclear power plants, or other exotics.
Inertial dynos (Dynojet, for example) don't... they measure power (be it HP
or KW), and interpret torque based on engine RPM. This is why a lot of
times, diesel guys only get HP ratings from their dyno runs - becuase they
don't feel like setting up the cumbersome little optical sensor to read RPM
from the engine.
The Dynojet measures horsepower, but it has no idea what the rpm is?
Please explain how you can tell the hosepower without knowing the rpm.
I saw your dyno sheets. Quite impressive. What happened at 2650 rpm on sheet
I'm not ignoring the other questions, I just don't have time to answer them
Stop thinking that HP is _ONLY_ "torque times RPM divided by 5252". HP is a
measure of work done over time. Work is the moving of a load over a
distance. The dynojet knows the load (weight of the drum). It knows the
distance the load is moved (turned). It knows the time between samples.
Work done over time is power. It's a simple calculation. 1 HP equals
33,000 ft.lbs. of work per minute, or 550 ft.lbs. of work per second A foot
pound is the energy required to move 1 pound 1 foot.
I dunno... maybe some wheelspin/slippage? Those are also old dyno sheets,
before I put on twin turbos. I have to take the outer rear tires off to fit
the truck on the dyno, so my contact patch goes down by 50% :)
That is the point that I disagree with. A horsepower number does not
describe an engine's ability the same at different rpms. 100 horsepower at
1,000 rpm is 10 times stronger than 100 horsepower at 10,000 rpm. 100 lbs/ft
of torque has the same ability no matter what rpm it occurs at.
100 hp @ 1,000 rpm = 525.2 lbs/ft torque
100 hp @ 10,000 rpm = 52.52 lbs/ft torque
Um... no. 100ft lbs at 1000RPM is 19Hp. 100ft lbs at 6000RPM is 114Hp.
If it takes 100ftlbs to turn a shaft, one shaft will turn 6 times as fast,
meaning more work is done. Looks like different abilities to me.
Whats this for?
"There are four boxes to be used in defense of liberty:
Yep - and back to my F1 example... 270ft.lbs. at 8000RPM in a 3.0L V10
makes 411HP, where that same 270ft.lbs. at 2800RPM in a 4.7L V8 only makes
144HP. Which engine's going to move the same amount of weight faster?
I'm almost sorry to have started this, if in fact I did. My only point is
that Torque is the force that turns the shaft. it doesn't matter how fast
you turn the shaft, it is still torque that is turning it. At no point does
the force or even the name of the force change into something else, it is
always torque. HP never turns the shaft it is an expression of the
resulting motion. You must have torque to produce HP but you do not need HP
(or kW, etc.) to produce torque. Torque is the force at play and HP is an
expression of the work performed.
Yep... it's all your fault :)
Everything you say about torque is true - I'm not arguing that. The initial
statement was in reference to someone's claim that (and I'm paraphrasing
here) "the ability to pull [move] a load is all about gearing". I countered
that, "no - when it comes to moving a load, it's all about HP". Weights
being equal, the vehicle with the ability to generate more HP will go
What I WASN'T discussing was the ability to ACCELERATE a load to a certain
speed. That makes it a much more complicated equation, because then you're
usually talking about starting from a stand-still, which because of the
limitations of modern drivetrains, requires that the engine be able to
produce enough HP to overcome static friction/inertia/etc. (everything that
resists motion and acceleration), at a relatively low RPM. Since one
component of the HP equation is being limited, torque (the other component)
becomes the deciding factor in being able to overcome those static forces.
This is where gearing, torque curves, etc. etc. come into play. If we could
eliminate those artificial limitations (let's say we have an infinitely
variable transmission that would let an engine operate at it's peak HP
output all the time), then that little 800HP 3.0L V10 engine would out-pull
a big Cummins 600HP 14L I6 in every conceivable measurement: 60 ft. times,
1/4 mile times, top speed, you name it. The fact that the V10 would implode
itself before the Cummins reached full operating temperature isn't germane
to this discussion :^)
Back to my original statement... the vehicle that produces more horsepower
will be able to move a given load at a faster overall rate than the vehicle
with less HP.
And oh yeah.... my Dodge is better than Larry's Chevy - which is where this
whole thing started in the first place <grin>
What's this for? It's to show that a horsepower number alone does not
accurately describe the ability an engine has to do work.
You said "If it takes 100ftlbs to turn a shaft, one shaft will turn 6 times
as fast, meaning more work is done."
We'll use that same shaft again comparing the two 100 horsepower engines.
The engine that makes 100 hp @ 1,000 rpm has 525 lbs/ft of torque. That's
plenty of torque to do the job. In fact it can run 5 shafts each requiring
100 lbs/ft of torque all at the same time. The engine that produces 100 hp @
10,000 rpm makes less than 53 lbs/ft of torque. If it takes 100 lbs/ft of
torque to turn the shaft, it will not be able to turn the shaft at all. No
work is being done.
I'll give you another example. Say I'm out shopping for a new push mower. I
get frequent rain and one corner of my back lawn doesn't drain very well.
The lawn is always wet there and the grass grows very fast. My old mower cut
fine everywhere in my lawn, including the high wet grass. It had a good 5
horsepower engine when new but now it's old and uses too much oil. I leave a
trail of smoke behind every pass. I assume any 5 horsepower push mower with
the same size blade will work the exact same way, so that's what I go
shopping for. I want a brand new mower just like my old one, but the old
model is discontinued. I find the same brand mower with the same 21" blade,
a 5hp engine, and rear mounted collection bag. Same thing as the old one
right? Well, no. It looked the same and had all the same advertised
specifications, but it wasn't the same thing. I didn't realize that my old
mower was rated 5 horsepower @ 500 rpm and the new one is 5 horsepower @
1,000 rpm. The grass doesn't really care if it gets whacked by a blade
spinning around at 500 rpm or 1,000 rpm, so the end result should be the
same. It should make tall grass short.
I try out my new mower. I get the front lawn done and it looks very nice.
That 1,000 rpm mower cuts the lawn very cleanly and deposits much more of
the clippings into the bag than my old mower ever did. I'm very happy with
my new mower even though I still don't know about the higher blade speed. I
assume the old engine was getting weak and this new one is more powerful.
Now I go around back. I get three feet into the wet high grass and the mower
stalls. I have to drag it back out of the wet area to get it started again.
I push it another three feet into the wet grass and it stalls again. It
takes me hours longer with this new mower to cut the wet area than it did
with my old mower. 5 horsepower isn't always exactly the same as 5
horsepower. The old mower had twice the torque that my new mower has. The
new mower has twice the blade speed that the old mower had.
Which one gets more work done? If you ask the guy that has to push the mower
through the tall wet grass, it's the old one.
I'm not saying that horsepower ratings are meaningless. I'm only saying that
horsepower ratings are less meaningful without an rpm to go along with them.
No kidding, thats why they typically pair it with a torque rating. Note the
word "pair". It means both HP and torque are important. This is the point,
so let me repeat.....
It means both HP and torque are important.
Congrats, you can do the math. You still don't seem to understand that
torque isn't the only thing that needs to be talked about. If it were, we'd
be getting complete tables of torque and RPM.
No need, I already KNOW how the two work together. YOU were the one that
said torque was everything.
Ok........ 1000ft lbs.
Wow, thats useful......
Get it yet?
"There are four boxes to be used in defense of liberty:
19.4 MPG or so as I travel about 80% Freeway (68-70mph) and 20% city
(25-55mph, not to mention the times I go 0mph). The heated seats allow for
an extra .2mpg as I'm not shivering down the road. I also get 11-12 MPG
when towing my Arctic Fox 24-5N 55-65 mph.
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