Engines and horsepower ratings

[FlipTrac_511]

When a particular engine is given a horsepower rating, does the weight of the vehicle it is mounted on a factor? I'm reading all these auto magazines and I'm continously amazed at how Japanese engines are putting out greater power with smaller displacement compared to domestic ones. The Japanese vehicles do tend to be relatively lighter so I was wondering if this was the catch, and not simply engineering superiority.

 

[Todd Z]

Nope, Those numbers are taken at the flywheel of the engine...



The clearances, materials used and computer controls gives the foreign companies the advantage, and they know how to do it right and make the smaller engine produce more HP..



Todd Z

 

[Allen]

No, weight is not a factor in HP ratings alot of it has to do with they are just designed better so they can reach higher rpm which is a factor in HP. However these engines don't have that much torque which is what is important to get the car moving. American manufacturers are finnaly catching up tho.

 

[Todd Z]

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[FlipTrac_511]

I've read that Ford's new Duratec 3.5 produces 265 horses, and I thought, finally an American V6 that can match what the imports have been putting out. But then I compare the displacements and the imports are 3.2s and what not. Then I was like, dammit.



Thanks for the clarification!

 

[Tom Schindler]

Our motorhome has a 7.5L V8 in it. It has 230 HP.



It will push our 17,000 LB motorhome with a 3500 LB car on a 1400 LB trailer 80 MPH on the interstate.



That is with only 230 HP. Take the engine from a Honda S2000 (2.2L with 240 HP) and try to do that. It isn't going to happen.



One of the reasons the Japanese have higher HP numbers is by the way they calculate the numbers. I know a while if they used the new formula, they lost on average 10+ HP. Many of GM's vehicles actually gained HP.



There is more to an engine and its "power" output.



An engine with 230 HP can pull 22,000 LBS at 80 MPH.



Don't be misled by HP numbers and HP numbers alone. There is more to an engine than the HP alone.



The Honda S2000 has an impressive engine. When it first came out, it had a 2.0L engine with 240 HP. Later they increased the displacement to increase the torque. If you shifted the S2000 at 7,000 RPM, you were driving a 17 second car. Shift the engine at redline and you were into the 14 second range. To get the tires to break loose, you had to sidestep the clutch at 9,000 RPM.



What fun is that?



To compare the two, don't look at numbers, drive them.





Tom

 

[Jacob Dryer]

There is an old saying but I'm not old enough to know it. It has something to do with HP is imaginary, torque is real.



What I pulled from that is that HP has to do with RPM's therefore if RPM's get higher HP gets higher, in calculations that could go to infinity and therefore so could HP. Torque is a real figure not calculated by some increasing factor and is therefore a REAL figure of power.



But I don't know anything about much so take it for what it's worth.

 

[Travis Munday]

Well, not really JD. You can derive HP from torque and torque from HP. They are related. They are simply two different ways of measuring two different motivation forces, namely twisting power and pulling power.



The 'problem' from different HP rating is because different parts of the world use different units to express HP, there is a conversion factor to go between all of them.



Japanese and Eurpean engines tend to have higher compression then American, usually because of the lower-grade gas America uses compared to Europe and Japan. The higher compression ratio mixed with better engine management and the 'guts' to make different and new engines (which tend to have better tech) leads to more power per litre then American engines.



There are some Japanese engines that have impressive HP numbers AND torque numbers, but no one really wants to point that out. As an example, Nissan made a 2.6L inline-6 with 276 HP and 260 ft-lb. The engine in my Ranger has 3.0 liters, makes only 150 HP and only 180 ft-lbs. Of course, being a V6 it'll be down in torque a bit compared to an inline.

 

[EddieS'04]

One thing you have to consider is some jap V6's have higher compresion and rpm's. Therefore requiring Premium fuel only. Put 87 octane in them, they run like shit.

 

[Michael Cacioppo]

In general, if you want to accelerate faster you need higher torque. If you want to go faster (top speed) you need horsepower. American moteor heritage was designed around moving big heavy cars which requires torque and its relationship to cubic inches. The offshore autos where designed around smaller. lighter autos. They have a lot of experience tweekingsmall cI motors. Also one must be careful of the actual HP curve profile. Where does it come in hard? The 2000 is a good example. Yah, it makes horsepower but at what RPM. The BMW Z3 produces less HP but out performs the Honda.