Horsepower explained
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Joined: Oct 2003
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From: Richmond Michigan
You will prolly never get a HP question without a real amount of controversy. Hp means different things to different people. the one given in HP is that it is impossible to make without Torque. and to my knowledge it is impossible to measure HP on a dyno. My understanding is that the dyo measures the torque as restictive force at RPM and then does the math.
For me it is where I make those torque #s that count. Take a motorcycle as an example. I ride 2 up on a heavy bike so I want to make my torque down low. The reason to make this torque down low is to take advantage of low end HP for gearing. so I put free flowing heads on with wiseco flat top pistons, Makuni Carb and a ,580 lift cam dropped the the front gear by 2 teeth and put an exaust system that would work within these parameters. Now you can make a number of assumptions about this set up but you still don't have the story. What about the duration of the cam and where do the intake and exaust valves open and close. Overlap? How does the LSA effect when we bring the power in. with all of these things in mind I make my torque on the low end of the rrrs and the end effect is that I can roll on the trottle and walk out pretty good without dropping a gear. (much more comfortable with 2 on). and it's fair in 1/4 to boot. In contrast the same .580 lift with different duration and LSA with a little different valve grind geared a little differently, jet the carb a little different, staight pipes tunned to the powerband and we have a great 1/4 miler ( get rid of the bags and weight) but it is miserable to ride 2 up and stumbles down low.
Like the motorcycle example I think it is unfair to compare torque and hp in a gasser and diesel when they are not in the same catagory. It is hard for a diesel to beat a gasser in the 1/4. now put some weight behind them and the gasser loses. the Motercycle is easier to see the immed, results from because of its weight and displacement but as an internal combustion engine the pricipals and dynamics are the same. I want a Truck that will give me long service. towing capability, a little kick(with bombs) and reasonable fuel milage. That spells diesel for me. If I needed to get there real fast I doubt I would have started with a 7,000 lb empty load. What makes go fast stuff fun to me , is trying to get that all around does everything combination I have found though that deciding where to make that power and concentrating on doing it is the most satisfiying. Trying to be strong everywhere only leaves me with doing all things only mediocre to just below great. To some that is what they want. and I guess that is my point. The HP debate is subjective to preference as it gets beyond the basics, one thing is certain one motor will not satisfy the needs of all drivers but around her the CTD is king.
I hope this made some sense.
For me it is where I make those torque #s that count. Take a motorcycle as an example. I ride 2 up on a heavy bike so I want to make my torque down low. The reason to make this torque down low is to take advantage of low end HP for gearing. so I put free flowing heads on with wiseco flat top pistons, Makuni Carb and a ,580 lift cam dropped the the front gear by 2 teeth and put an exaust system that would work within these parameters. Now you can make a number of assumptions about this set up but you still don't have the story. What about the duration of the cam and where do the intake and exaust valves open and close. Overlap? How does the LSA effect when we bring the power in. with all of these things in mind I make my torque on the low end of the rrrs and the end effect is that I can roll on the trottle and walk out pretty good without dropping a gear. (much more comfortable with 2 on). and it's fair in 1/4 to boot. In contrast the same .580 lift with different duration and LSA with a little different valve grind geared a little differently, jet the carb a little different, staight pipes tunned to the powerband and we have a great 1/4 miler ( get rid of the bags and weight) but it is miserable to ride 2 up and stumbles down low.
Like the motorcycle example I think it is unfair to compare torque and hp in a gasser and diesel when they are not in the same catagory. It is hard for a diesel to beat a gasser in the 1/4. now put some weight behind them and the gasser loses. the Motercycle is easier to see the immed, results from because of its weight and displacement but as an internal combustion engine the pricipals and dynamics are the same. I want a Truck that will give me long service. towing capability, a little kick(with bombs) and reasonable fuel milage. That spells diesel for me. If I needed to get there real fast I doubt I would have started with a 7,000 lb empty load. What makes go fast stuff fun to me , is trying to get that all around does everything combination I have found though that deciding where to make that power and concentrating on doing it is the most satisfiying. Trying to be strong everywhere only leaves me with doing all things only mediocre to just below great. To some that is what they want. and I guess that is my point. The HP debate is subjective to preference as it gets beyond the basics, one thing is certain one motor will not satisfy the needs of all drivers but around her the CTD is king.
I hope this made some sense.
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Joined: Apr 2003
Posts: 6,564
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From: Cummins Technical Center, IN
Originally posted by bigern24
Where's Hohn at, he's all over this stuff. That statement about the diesels not being able to make horsepower because of the RPM's being so low.... well maybe on the cummin's 5.9 that could SOMEWHAT be interpretted.... but a general statement that diesels cannot make high horsepower because they have lower rpm's is GENERALLY false. Different engine designs to different things. Take that monsterous 108 thousand hp engine... it runs at a RPM of 102... that's right 102 revolutions per minute.
So tell me again how that makes it difficult for diesels to make hp because of they're limited RPM?
HP is what sells cars and trucks in my opinion...people have become consumed with it.... the important figure is Torque. HP is simply the rate at which torque is force is applied...the force being torque.
Hohn has a great post on this over on the TDR.
A good example for some thinking is the difference in Dynojet and Mustang dynometers. Dynojets have a rep for being not as accurate....well they calculate how quickly an engine can accelerate a known load, which to me is very important. A mustang dyno is better suited for a static torque reading, which supports towing enthusiasts who what to maintain heavy loads efficiently. The Dynojet gives a true accelaration calculation which is what the engines ability to accelerate under load is like.
Where's Hohn at, he's all over this stuff. That statement about the diesels not being able to make horsepower because of the RPM's being so low.... well maybe on the cummin's 5.9 that could SOMEWHAT be interpretted.... but a general statement that diesels cannot make high horsepower because they have lower rpm's is GENERALLY false. Different engine designs to different things. Take that monsterous 108 thousand hp engine... it runs at a RPM of 102... that's right 102 revolutions per minute.
So tell me again how that makes it difficult for diesels to make hp because of they're limited RPM?
HP is what sells cars and trucks in my opinion...people have become consumed with it.... the important figure is Torque. HP is simply the rate at which torque is force is applied...the force being torque.
Hohn has a great post on this over on the TDR.
A good example for some thinking is the difference in Dynojet and Mustang dynometers. Dynojets have a rep for being not as accurate....well they calculate how quickly an engine can accelerate a known load, which to me is very important. A mustang dyno is better suited for a static torque reading, which supports towing enthusiasts who what to maintain heavy loads efficiently. The Dynojet gives a true accelaration calculation which is what the engines ability to accelerate under load is like.
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