Please help! Whats crankshaft Horsepower?

[supadupasupraman]

where is horspower measured? I am always hearing crankshaft or wheel hospower. What is it?

[ccc880]

When you see a hp rating, it is usually hp at the crankshaft (hp before it has to spin the tranny, driveshafts, axles, and wheels). The real hp (or hp at the wheels) is usually around 20hp less than the hp at the crankshaft because it (hp at the wheels) is the total power left after it has moved the drivetrain. Hope this helps (because I am bad at explaining things)!!

[jeffescortlx]

Most car manufactuers rate there vehicals in crank hp, but when you get a dyno reading it's wheel hp.

[V-8Fan]

Since I rarely read car magazines anymore, I dunno what they are saying these days, but they used to (maybe still do?) quote what they called "bhp", which means brake horsepower---and that means horsepower delivered to the wheels. I remember being very shocked at some of the brake horsepower figures I saw published...don't recall exactly, but they seemed at the time to be up to around 100 or more horsepower less than what an engine put out at the crankshaft. This was back in the 60s...maybe drivetrains are just more efficient these days. Or maybe my feeble memory just doesn't recall.

[supadupasupraman]

Thanks! That info is awsome. This may sound stupid, but i'm only 13 ok. Whats torque?

[Fliquer]

Torque is twisting power. Horsepower is simply a function of torque

[jeffescortlx]

Originally Posted by V-8Fan

Since I rarely read car magazines anymore, I dunno what they are saying these days, but they used to (maybe still do?) quote what they called "bhp", which means brake horsepower---and that means horsepower delivered to the wheels. I remember being very shocked at some of the brake horsepower figures I saw published...don't recall exactly, but they seemed at the time to be up to around 100 or more horsepower less than what an engine put out at the crankshaft. This was back in the 60s...maybe drivetrains are just more efficient these days. Or maybe my feeble memory just doesn't recall.

People in the UK call it bhp, in the US I see a lot of whp (wheel hp)

Usally a FWD 5 speed takes away about 12-15%, auto are as high as 20%.

[supadupasupraman]

C'mon somone, in detail, what the hell is torque? Or do none of you so called " car experts" know!

[SaabJohan]

Bhp means braked horsepower and that means just like it sounds like, that the engine is braked in a dyno, the power is not just a guess or similar.

All car manufacturers measure the power on the crankshaft, the powerloss to the wheels is usually 10-20% depending on the transmission.

There are several standards how to measure the engine power, there is also something called net and gross power depending on what help equipment that was used like generator, AC compressor and so on.

When an engine is braked this can be done in two ways, static or dynamic. With a static measurement the engine is held at a constant rpm for a time while a dynamic measurement is done by accelerating the engine through a given rpm range under a time. Car manufacturers usually use the static method and this is done under a long time since that will give the largest heatproblems and the lowest power.

[pimpmaro]

Originally Posted by supadupasupraman

C'mon somone, in detail, what the hell is torque? Or do none of you so called " car experts" know!

Wow... pushy for a 13 year old... BTW, your question as already been answered. Torque is the twisting power of an engine or anything that turns. When measured in Ft-lbs, it is measured as the force (in the direction of rotation) produced at a point, that is 1 ft out from the center of rotation. Imagine a lever in a tangential position to the driveshaft that measures 1 ft long. Torque is the force put on the end of that lever.

BTW, horsepower is a made up number. Torque (ft-lbs) = (hp x 5252)/RPM. If you ever look at a dyno graph, torque and hp always cross at 5252 rpm. Basically this means that you can find one number from the other and that you cannot change the torque without changing the hp.

If you'd really like to get into a complex engine discussion, I can start next with BMEP, which is the Brake Mean Effective Pressure that an engine operates at, and which is the limiting factor of the power that an engine can reliably produce.

[LancasterWannaBe]

Well shoot, I want to know about BMEP.
Tell me something about it if that isn't too vague.

[ivymike1031]

Originally Posted by pimpmaro

BTW, horsepower is a made up number. Torque (ft-lbs) = (hp x 5252)/RPM. If you ever look at a dyno graph, torque and hp always
cross at 5252 rpm....

Hmm, what if my axes are not in units of ft-lbf, rpm, and hp? Say, for example, they were in SI units, like N*m and kW, the way you're most likely to find them at an engine OEM? Then my dyno graph wouldn't follow your rule, would it? Heck, unless you're looking at a US hotrod magazine, chances are your dyno graph won't conform to the above...

Originally Posted by pimpmaro

If you'd really like to get into a complex engine discussion, I can start next with BMEP, which is the Brake Mean Effective Pressure that an engine operates at, and which is the limiting factor of the power that an engine can reliably produce.

BMEP? That's another made-up number! It's just the work per cycle divided by the fluid displaced per cycle! You can calculate it from displacement and torque, in much the same way that you can calculate power from torque & rpm... I wouldn't say that BMEP limits the power output of an engine, but it is a good indicator of how hard an engine is working.

[supadupasupraman]

Heh, being pushy got me an anwer didn't it. You saw the numbers? 30 views and 4 replys. Crazy
( Thanks)

[pimpmaro]

Originally Posted by ivymike1031

Hmm, what if my axes are not in units of ft-lbf, rpm, and hp? Say, for example, they were in SI units, like N*m and kW, the way you're most likely to find them at an engine OEM? Then my dyno graph wouldn't follow your rule, would it? Heck, unless you're looking at a US hotrod magazine, chances are your dyno graph won't conform to the above...

Obviously there are conversion factors for those numbers to correct for using metric units. I haven't ever tried N*m and kW in that formula, but I'll tell you what. I'll take a dyno graph I have here and do the calculations later on and get back to this thread to see how accurate it is and whether or not they still cross at 5252.

Originally Posted by ivymike1031

BMEP? That's another made-up number! It's just the work per cycle divided by the fluid displaced per cycle! You can calculate it from displacement and torque, in much the same way that you can calculate power from torque & rpm... I wouldn't say that BMEP limits the power output of an engine, but it is a good indicator of how hard an engine is working.

Exactly right, I wasn't meaning to say that it is a limitation on the power of the engine, but you are right in that it does indicate how hard an engine is working. What I was trying to say was that using the BMEP, you can determine how hard an engine is working, and figure out how hard an engine can reliably work (for lack of a more eloquent way to put it). The rule I've heard is that an engine in stock form can be modified to handle up to 300 BMEP reliably (simply power adders, not strength components), while in fully stock form, it may be at 170 BMEP. This way you can calculate your maximum torque and then your maximum horsepower off of that giving you an idea of how reliable your engine will be at that power level. I'm personally not fully sold on the idea, but I find it very interesting and I am looking into it further here and there to see exactly how reliable these numbers are and how meaningful they are.

[ivymike1031]

an engine in stock form can be modified to handle up to 300 BMEP reliably

I assume that when you say "300 BMEP" you mean 300psi BMEP. 30bar BMEP (441psi) is a very hard number to reach, but a modified diesel can get pretty close. Many stock diesels run in the neighborhood of 20-24bar (294 to 353 psi) BMEP.

14bar (205psi) BMEP is a pretty decent rating for a naturally-aspirated gasoline engine.

there are conversion factors for those numbers to correct for using metric units...I'll take a dyno graph I have here and do the calculations later on and get back to this thread to see how accurate it is and whether or not they still cross at 5252.

Don't bother. 1/5252 is just a conversion factor to convert units from ft*lbf*rpm to HP. It doesn't matter what units you put on a dyno graph, or where the lines cross each other, as long as the units are shown on the plot. Heck, even if your graph was in ft*lbf and HP vs RPM, your lines wouldn't necessarily cross at 5252. The only time they would is if both of your y-axes had the same scalar values (as is commonly done). If it was useful, you could use different values on your torque axis than on your power axis, to exaggerate the scale of one versus the other (maybe to highlight a dip in the torque curve), and then the place where your lines cross would be arbitrary, depending on what range of numbers you picked on each axis.