why the lost hp

[CamaroSpike23]

Originally Posted by theholycow

Are you saying that the formula is wrong? Mathematical formulas work just as accurately no matter which variable you're solving for. I am not an engineer and don't know much about this, so I can accept that the formula may be wrong, but I know enough about math to know that a formula is just as accurate no matter which way you figure it.

Another possibility is inaccurate dyno readings, which I'd guess probably explain the discrepancies you've noticed. How accurate can a random ricer on a random chassis dyno be?

im saying that those calculators take peak hp numbers at X rpm and give you a torque value based on that. but if your dyno curve isnt just a steady rise to peak hp (which most are, cus thats more efficient to gain hp as a motor spins faster, until the rotating mass of the motor overcomes the gains in speed) but imagine the peak hp is only 3 hp higher than the average hp over the whole rpm band, the formula is not setup for that. the formula's are to give you a torque value at a certain rpm based off of the hp number you put in. not what the peak torque number truly is.

Originally Posted by knowitman

I believe that you don't know what you are talking about. The relationship between power and torque is just a unit conversion taking the engine speed into account.

http://www.howstuffworks.com/question622.htm

im well aware of what im talking about. what im saying is that Horsepower is calculated from a given torque value. when doing it the other way around, using the supplied calculators, it gives you a torque rating from the peak hp at a certain rpm.












but when have you ever seen a peak torque # and a peak hp # occur at the exact same rpm?

[CamaroSpike23]

Originally Posted by rayhawk

Camarospike, it's ok, I don't take it as an attack. Hp and torque are not independent of each other. Basically, as has been said, they are dependent on each other. At 5250 rpm, torque=hp. As a matter of fact, a dyno really measures the torque output and horsepower is calculated from it. The number you start with makes no difference to the outcome.

HP=Torque (ftlbs)*rpm/5250

So if you were to take 422 hp at 5000 rpm, you would get 443.1 ft lbs of torque, which is higher than the peak even for the Corvette LS3. Torque is a unit of work, hp is a unit of power, or work per given time period, which is basically figured out by the rpm which the torque was generated at. And I think they test the engine with all accessories and full exhaust as it will be installed in the car, but I could be wrong.

Try the formula and you will see the 432 hp at 6400 rpm does come out to 354 ft lbs. The peak torque, however is typically at a lower rpm, which is why most times you see the two listed at two separate rpms's.

yeah, i was trying to say something along those lines. i keep forgetting that everyone else cant read my mind when i dont post up every single reason behind a post. lol



but you got me thinking about something else to keep in mind is that these calculations do not take into account frictional loss. which is why the calculated torque appears high, but yet will be lower in reality.

[theholycow]

Originally Posted by CamaroSpike23

but you got me thinking about something else to keep in mind is that these calculations do not take into account frictional loss. which is why the calculated torque appears high, but yet will be lower in reality.

I'll attempt to read your mind here: You mean frictional loss in the whole drivetrain. That would be the difference between engine dyno and chassis dyno.

[CamaroSpike23]

Originally Posted by theholycow

I'll attempt to read your mind here: You mean frictional loss in the whole drivetrain. That would be the difference between engine dyno and chassis dyno.

that too,

but im actually meaning for just the engine having frictional (and now that we are talking about it) and rotational loss. that as the motor speeds up to a certain point, it is losing a small % of delivered power as it has to use part of its force to overcome its own rotational resistance

[Crowley]

Lets just get this thread closed as it has gone way off ... lol

Crowley

[theholycow]

If we're talking about output measured at the crankshaft...how could it not include the frictional loss? "Delivered power" is what's being measured.

Interesting note: I'm told that engine internal frictional loss goes up as a square of RPM, rather than directly proportional. That's an important consideration when thinking about engine torque, gear ratios, and fuel economy.

[jordan 572]

if an auto l99 raced a ls3 same weight how good would u have to be at driving a stick to get that little edge on the auto

[CamaroSpike23]

Originally Posted by theholycow

If we're talking about output measured at the crankshaft...how could it not include the frictional loss? "Delivered power" is what's being measured.

Interesting note: I'm told that engine internal frictional loss goes up as a square of RPM, rather than directly proportional. That's an important consideration when thinking about engine torque, gear ratios, and fuel economy.

thats what im getting at, is that even tho you are creating more power as you increase in rpm, you are losing a larger percentage of power as you increase in rpm.

now, when it is actually measured on a dyno, you wouldnt know this from that.
but what my point is, is that the conversion tables that were listed are just formulas to find torque for a given hp/rpm. it wasnt an actual measurement of the torque just a quick equation to guesstimate it.

but if it were on an actual dyno it would read lower than the equation gives you as the rotational loss is factored in.

[CamaroSpike23]

Originally Posted by jordan 572

if an auto l99 raced a ls3 same weight how good would u have to be at driving a stick to get that little edge on the auto

well, with no lift shifting, im sure that a good driver will be able to get the edge over the auto.

i wouldnt say that you would need to be a full blown manual racer, but be experienced in powershifting.

[Jamestwilliams]

Originally Posted by headpunter

these are fly wheel tests that arent in the car so i dont know if there is even an exhaust on them

The new SAE numbers require that the engine is run as is in the engine bay. In other words with all accessories being attached to the belts. So it's supposed to demonstrate what your actual fly wheel horse power would be if you were some how able to dyno the engine while installed.

[rayhawk]

Originally Posted by CamaroSpike23

thats what im getting at, is that even tho you are creating more power as you increase in rpm, you are losing a larger percentage of power as you increase in rpm.

now, when it is actually measured on a dyno, you wouldnt know this from that.
but what my point is, is that the conversion tables that were listed are just formulas to find torque for a given hp/rpm. it wasnt an actual measurement of the torque just a quick equation to guesstimate it.

but if it were on an actual dyno it would read lower than the equation gives you as the rotational loss is factored in.

From my days in Internal combustion engines, the split of energy typically goes as follows:

1/3:Shaft power
1/3:Friction
1/3:Heat loss to radiator and exhaust

That is the distribution on average of the amount of energy available in the fuel itself. This is in general as every motor has it's points where it is most efficient, that is where you get the most out of a quantity of fuel. As I said before, hp is not measured directly, it is an indirectly measured quantity based on the torque output per unit time (which is completely dependent on the rpm). Horsepower is always calculated, it can't be measured.

[knowitman]

Originally Posted by CamaroSpike23

now, when it is actually measured on a dyno, you wouldnt know this from that.
but what my point is, is that the conversion tables that were listed are just formulas to find torque for a given hp/rpm. it wasnt an actual measurement of the torque just a quick equation to guesstimate it.

What do you mean it isn't an actual measurement of the torque? That's exactly what it is. When an engine is making a certain amount of horsepower at a certain RPM, there is only one value of torque that it can make at that same RPM. How are you guesstimating?

[CamaroSpike23]

Originally Posted by knowitman

What do you mean it isn't an actual measurement of the torque? That's exactly what it is. When an engine is making a certain amount of horsepower at a certain RPM, there is only one value of torque that it can make at that same RPM. How are you guesstimating?

you are taking a hp number and calculating it in a formula to get the torque number.

you are not actually putting the motor on the dyno and getting the real torque number for that rpm.

[headpunter]

Originally Posted by Jamestwilliams

The new SAE numbers require that the engine is run as is in the engine bay. In other words with all accessories being attached to the belts. So it's supposed to demonstrate what your actual fly wheel horse power would be if you were some how able to dyno the engine while installed.

so that accounts for the accesory drive but not the mufflers and catalytic converters which arent in the engine bay