5252 Ever wonder where that came from ?

Was looking through a book I have . It's called "How to build Big-Inch GM LS -Series engines" . SA Design SA203 Stephen Kim if anyone is interested. It's a very good book with lots of pictures and good explanations of the hows and whys. Thought I would give him credit for what I'm posting so maybe some of you will be interested in getting a copy.

Anyway he has the best explanation I've seen on how the number 5252 came about. Thats the point where (on a graph) torque peaks and begins to decline........

It also explains why HP can continue to rise when torque is falling.

There are only 2 ways to increase HP. Increase torque OR Increase RPM

5252 is the rpm point where an engine begins to benefit more from RPM than from Torque. But WHY is that the same in all engines ?

Here is a simple dyno chart that demonstrates the 5252 principle.

Here is the explanation..........







And now ya know............. (Again, an excellent book for learning about building LS engines and which parts you should and should not use)


Let me make a point here to clarify something. If you have a specific RPM where you want to increase your HP, then you MUST increase the Torque at that RPM to derive more HP. There are only two variables . Torque and RPM. People rev their motors higher to gain HP..........That simply means if an engine is producing X torque at each revolution......more revolutions will produce that X Torque more times in one minute......so more HP.

If you want more HP for your midrange, say at 2500 RPMs. Each rpm level will need more TORQUE at that RPM to increase the resultant HP at that rpm. You can increase Torque at a specific RPM many ways. Using a larger displacement, or adding a super charger or even tweaking the compression or camshaft....but you must increase torque to increase HP at a given rpm.

 

Yes HP is a function of torque and RPM. Always cracks me up during the torque and HP debates when someone says they would rather have torque versus HP or vice versa. I think the toque crowd really wants a flat torque curve starting at low rpm. At the end of the day or race the car with the most HP will be faster and quicker if said car is set up right. It’s simple physics horse power is work done over time.
Dan

 

My reasoning has always been torque gets you to where you can really start using the horsepower.

 

The reason the number is 5252 is because James Watt decided that a horse can sustain a rate of energy production of 33,000 lb-ft per minute. If you divide that by 2π, you get the 5252 number

Since that number is a constant in the equation to calculate HP from Torque and RPM, torque and HP always have to be equal at 5252 RPM. It has nothing to do with how a particular engine is built, it just has to do with some simple math.

 

I had a customer whom i had done a proposal for a hydraulic system (Indian engineer) ask me, "what is this 5252?" I had to take him through all the calculations to derive it. I wasn't long out of college at that time and it was pretty easy for me to do. His employer overheard the conversation and later told me, "I knew I was in trouble when he didn't know what 5252 was!"

 

When I saw the****le, my dislecsia thought of the old tune "in the year, 25, 25"

I don't race, but on the street I love torque. 5,252 RPM is rarely much of an issue in suburbia.

 

Also: it depends on what units of measure you use. For instance, 5252rpm is the engine speed at which 0.7456999kW translates to 1.35582Nm. The 1-to-1 correspondences will happen at different speeds for all the various combinations of units.

kW = lb.ft @ 7043rpm
hp = Nm @ 3874rpm
kW = Nm @ 5195rpm

This also highlights how peak power and peak torque happen at specific speeds. So when figuring out how a torque converter is going to behave using its K-factor, it is necessary to consider the torque it sees at that engine speed. It isn't seeing peak torque all the time.

 

2π (2 x 3.14) is 6.28 as mentioned in the article, and yes it is a constant. I think the beauty in the thing was that Watt recognized that using a 1 foot radius and then calculating the distance it travels (the circumference) AND how many times it travels that distance (1 rpm X ? rpms) he could come up with a usable way to accurately calculate the resulting force available. What I wonder about is why he used "lbs/ft" as Scotland (where he lived) used the Metric system. Up to then, I don't know of any other method of comparing output. He was a brilliant guy.

Yes, thats the point I'm making ..........but most of us only knew that it happens that way..........but not why it happens that way.

 

Don't confuse me...............

 

When I visited Scotland about 25 years ago, they used miles....

 

Indeed: https://en.wikipedia.org/wiki/Scottish_units

Watt would have lived in the midst of a process of standardizing Imperial units.

 

He only missed the metric system by about 145 years...

James Watt
Born: 19 January 1736, Greenock, United Kingdom
Died: 25 August 1819 (age 83 years), Heathfield Hall

The British Imperial System of weights and measures was used officially in Great Britain from 1824 until the adoption of the metric system beginning in 1965.

 

Well that explains why he used "foot" instead of "meters" , thanks for the explanation. I know there are historically lots of "systems of measurement" and variations of those systems that have come and gone. The Metric System also has/had variations as well. I remember that while working as a Machinist apprentice at the Naval Ordnance Station we used to get drawings for parts for an Italian weapon, and the drawings and documentation were not always accurate, requiring us to contact the engineering department for explanation. That was 1966 or so.


I'm glad Watt chose a horse for his basis to calculate power............otherwise we might not have Hot Rods today because there would be no such thing as "horsepower" Think about it, at the time he invented his equation, there were no engines that turned 5252 rpms. I just think what he was able to****imilate into a usable equation was pretty remarkable for his time.

"Imperial System:
.
The Imperial system was officially adopted in Great Britain in 1824 and defined by the Weights and Measures Act. It includes units like the inch, foot, yard, mile, ounce, pound, and gallon"

I was in Scotland in the sixties courtesy of the USN. Only thing I think I remember was that beer was served in pints...........but my memory of that time period is hazy due to consuming that beer. I think I'm still having lingering effects.

 

Good to see that author use ft.-lbs. instead of modern pounds feet. You can pounds yer feet all you want; it will always be ft.-lbs. to me.
I`ve also seen dyno graphs where the two don`t intersect and find that odd.

 

Now how much of an increase in RPM does it take to make up for the lack of torque to get an equal ET and/or MPH out of the same HP number?

 

I don't know..........

 

What ever RPM is required to get the HP.
Two engines:
1 torque monster makes peak HP of 400 at 4500 RPM
2 high winder makes peak HP of 400 at 7200 RPM
Both engines powering the same car should have equal ETs and top speeds if they are set up set up for the power curve, that is gearing etc has to be maximized to take advantage of the curve.
The engine producing the HP at lower RPM should be easier to drive and attain its best ET.
If you ever rode an old school dirt bike you’ll understand.
Dan

 

Like the old 2 stroke bikes when they’d hit their powerband. I remember riding Honda CRs and how they’d take off once you got the revs up.

 

However you measure it, it all goes down the same lol

 

It is great to see the metric system stole the use of his name [for a unit of power]

I had that discussion 50 years ago with one of my dad's friends.
He said truck horsepower is totally different to car horsepower! [comparing a 300hp****mins with a 300hp Chevy]
The truth is truck [diesel] torque curve is different, the units of energy are exactly the same.

If you had 2 different engines with the same HP but at different RPM's the torque curve would be different.
BUT if you geared both engines so the wheel speed [output] was the same. The torque multiplication would equalize on both.
200hp @ 3000 rpm = 350 ft/lbs at 3000 rpm x 2:1 ratio = 700 ft/lbs at 1500 rpm
200hp @ 6000 rpm = 175 ft/lbs at 6000 rpm x 4:1 ratio = 700 ft/lbs at 1500 rpm

I've always said the cheapest modification on a car is "mechanical leverage" [gear it for it's purpose]

And the famous words of "Keith Duckworth" of Cosworth fame "Horsepower is the size of the bang ,multiplied by the number of bangs per minute"

Squirrel is correct about it being an equation.
James Watt's horsepower was a Dray Horse lifting 550 lbs vertically 1ft in 1 second [multiply 550 by 60 to get minutes = 33000]
Divide 33000 by 2π to convert linear lift to torque = 5252 [the constant]

 

That was weird
Thanks @Kerrynzl
Your description is much better than mine.
Dan

 

Thanks mate
Here's the kicker to those equations
the rear wheel horsepower is identical to engine horsepower [in theory]

200hp @ 3000 rpm = 350 ft/lbs at 3000 rpm x 2:1 ratio = 700 ft/lbs at 1500 rpm
200hp @ 6000 rpm = 175 ft/lbs at 6000 rpm x 4:1 ratio = 700 ft/lbs at 1500 rpm

700 ft/lbs x 1500 RPM ÷ 5252 = 200 hp [actually 199.92]

If the 200hp @ 6000 rpm engine had different gearing [2:1 instead of 4:1] the torque output would be 350 ft/lbs at 3000 rpm
350 ft/lbs x 3000 RPM ÷ 5252 = 200 hp [also 199.92] less torque /more rpm
So gear ratio shouldn't affect horsepower output on a rolling road dyno [except for mechanical losses]


Kerry

Torque is just a force [rotational] but similar to leaning against a wall.
When you get movement [velocity or distance/time] it is power.

So these cliches are the wrong way round.
Torque is how hard you lean on a wall, Power is how quick you push it over

 

So why is a "torque wrench" not called a "horsepower wrench" since you have to apply a force thru a distance to tighten a bolt ?

 

Because the force is applied and measured at a pivot [the bolt]
Power is the movement from your arm [try torquing a head in 30 seconds ]

If you simply "leaned" on the bolt it would be torque/force from your arm
Once the torque /force exceeds resistance you factor movement /velocity which is power [up until it is met with an equal/opposite resistance]

This ^^^^ also explains why a car accelerates faster in lower gears [with the same power]
The torque is multiplied to exceed resistance .
But the velocity is lower, so the power is constant.

Terminal velocity is when power meets equal/opposite resistance from aerodynamic drag.

referring back to this

If you leaned at the top of the wall vs the base of the wall, you'd have more chance of pushing it over
[torque is increased]
OR if you applied more force ..... Maybe!!

 

I was just kidding Kerry.......... But its still takes applying a force thru a distance about a pivot just like a piston does to a crankshaft pivoting about a center. We just don't concern ourselves with the rate of motion (rpm).

 

I realize you're kidding, but I responded purely for clarity to others [the Torque vs Power argument has won and lost a few arguments]

We should "UP" the discussion from physics to quantum physics [aka quantum mechanics] which is the study of nature at the atomic and subatomic level.

The universe has an abundance of Protons, Neutrons, Electrons, and******s

 

Getting pretty math heavy and dry (technically speaking) so I thought this little joke might lighten things up, it's a bit juvenile (heard it over fifty years ago) but here it is......................
Old guy told me the true definition of torque is when you wake up in the morning and you need to pee reeeeealy bad and when you push down on your your heels lift off the floor..........that's torque!
Laugh or I'll tell it again!

 

now you're taking me back to "dimensional*****ysis", which we spent a little time on back in engineering school so many decades ago.

But to answer the question, you have to be "on the clock" to call it a horsepower wrench. Time would be involved. Just how fast can you torque all 17 bolts on an SBC head?