relation between engine size, hp and torque
farshidazimi
09-08-2005, 02:34 AM
Hey everybody ,
I am pretty confused about the relation between engine size, hp and torque.
For instance why a 3.8 L Buick engine delivers 200 hp while a 3 L Honda gives 244 hp. On the other hand both deliver almost the same torque of 230 lb-ft ?
What is more important factor in evaluating the performance of an engine ? hp or torque ?
thanx,
farshid
I am pretty confused about the relation between engine size, hp and torque.
For instance why a 3.8 L Buick engine delivers 200 hp while a 3 L Honda gives 244 hp. On the other hand both deliver almost the same torque of 230 lb-ft ?
What is more important factor in evaluating the performance of an engine ? hp or torque ?
thanx,
farshid
curtis73
09-08-2005, 04:54 AM
Its basically a balance of hundreds of factors. If you had a 2.0 litre engine making 200 hp and you could put that engine in a Magic Size Doubler machine, you would double all of its proportions; size, bore, stroke, intake and exhaust flow, fuel supply, etc. That theoretical engine should make 400 hp from its 4.0 litres.
Even if you kept the little 2.0 litre engine, by manipulating the components like cam specs, head flow figures, exhaust, intake, you could make that 2.0 litre engine produce 1hp or 1000 hp.
Engines are a huge air pump. In the process of pumping the air, they ingest and burn fuel to sustain their motion. A byproduct of this pumping is power, and torque. If you alter the amount of air the engine can ingest, you alter how much output it can ultimately make. In your example, the Honda engine was designed to flow more air than the buick so it can make more power in a car designed for a more youthful market. The buick was designed to give reliable power that performs well from 0-25 mph for the older market it targets. I use this analogy a lot, but think of it as a small hammer and a big hammer. Both can do the same amount of work, but you have to swing the little hammer a lot faster to do the same amount of nailing.
Your last question is tough to answer. The 3.0 litre Honda example you give makes about the same HP as a stock 8.2 litre V8 I have in my garage. The difference is that my V8 makes 550 ft-lbs of torque at a very low RPM. The Honda only makes 230 ft-lbs at a much higher RPM. My V8 is best suited to large cars that have a lot of weight, a lot of room under the hood, and have the ability to carry a 600-lb engine.
HP is a number that has become confusing thanks to the automotive marketing. HP is a number that is derived from torque and is a valuable comparison tool if you know how to use it. It is a number that relates torque to engine RPM. Typically a small engine with high HP needs to spin very fast to get it. The V8 I have only needs to rev to 3900 rpms to make all of its power. So, in choosing an engine, look at where the HP peaks. Is it 244 hp @ 3900 rpms, or 244 hp @ 7000 rpms. Typically the first, low-revving example is easier to drive on the street. For some it gets tiring to have to rev the engine every time just to get power to merge on the highway like the second example. As cars get lighter and lighter, however, that low-rpm oomph becomes less important. The thought behind that is that if you reduce the engine size and power while reducing the car's weight at the same time, the customer won't notice a difference in overall performance. The benefit there is the opportunity for better mileage and reliability among other things.
Even if you kept the little 2.0 litre engine, by manipulating the components like cam specs, head flow figures, exhaust, intake, you could make that 2.0 litre engine produce 1hp or 1000 hp.
Engines are a huge air pump. In the process of pumping the air, they ingest and burn fuel to sustain their motion. A byproduct of this pumping is power, and torque. If you alter the amount of air the engine can ingest, you alter how much output it can ultimately make. In your example, the Honda engine was designed to flow more air than the buick so it can make more power in a car designed for a more youthful market. The buick was designed to give reliable power that performs well from 0-25 mph for the older market it targets. I use this analogy a lot, but think of it as a small hammer and a big hammer. Both can do the same amount of work, but you have to swing the little hammer a lot faster to do the same amount of nailing.
Your last question is tough to answer. The 3.0 litre Honda example you give makes about the same HP as a stock 8.2 litre V8 I have in my garage. The difference is that my V8 makes 550 ft-lbs of torque at a very low RPM. The Honda only makes 230 ft-lbs at a much higher RPM. My V8 is best suited to large cars that have a lot of weight, a lot of room under the hood, and have the ability to carry a 600-lb engine.
HP is a number that has become confusing thanks to the automotive marketing. HP is a number that is derived from torque and is a valuable comparison tool if you know how to use it. It is a number that relates torque to engine RPM. Typically a small engine with high HP needs to spin very fast to get it. The V8 I have only needs to rev to 3900 rpms to make all of its power. So, in choosing an engine, look at where the HP peaks. Is it 244 hp @ 3900 rpms, or 244 hp @ 7000 rpms. Typically the first, low-revving example is easier to drive on the street. For some it gets tiring to have to rev the engine every time just to get power to merge on the highway like the second example. As cars get lighter and lighter, however, that low-rpm oomph becomes less important. The thought behind that is that if you reduce the engine size and power while reducing the car's weight at the same time, the customer won't notice a difference in overall performance. The benefit there is the opportunity for better mileage and reliability among other things.
2.2 Straight six
09-08-2005, 04:50 PM
and Brabham-BMW made a turbo 1.5litre engine for their F1 car, made over 1,400bhp, their dyno couldn'r read above 1,400bhp, an the figure was recorded with huge amounts of tyre slip i heard, you can tune tiny engine to huge amounts of power, i think someone estimated that 1.5L-T about something in the region of 1,600-1,800bhp, had massive amounts of tyre slip on the track.
and when you ask which is more important for evaluating performance is really based on its use, for example a Scania truck (swedich company) can make 570bhp, in 16litre V8 turbo (twin i think) but people may think that isnt a lot of power for such a big engine, but trucks need massive amounts of torque to pull the 35-40tons that the 570bhp unit-equipped trucks use, now you might think that it should make more power, but its a diesel, an they usually have a higher lb/ft torque figure than the bhp figure, but a 570bhp engine produces something like 1,600lb/ft of torque, an redlines about about 1,700rpm. so the vehicle's use an requirements determine the performance required an the kind ot lb/ft to bhp ratio.
i hope that makes sense.
and when you ask which is more important for evaluating performance is really based on its use, for example a Scania truck (swedich company) can make 570bhp, in 16litre V8 turbo (twin i think) but people may think that isnt a lot of power for such a big engine, but trucks need massive amounts of torque to pull the 35-40tons that the 570bhp unit-equipped trucks use, now you might think that it should make more power, but its a diesel, an they usually have a higher lb/ft torque figure than the bhp figure, but a 570bhp engine produces something like 1,600lb/ft of torque, an redlines about about 1,700rpm. so the vehicle's use an requirements determine the performance required an the kind ot lb/ft to bhp ratio.
i hope that makes sense.
farshidazimi
09-10-2005, 02:12 AM
Thanx folks for the breifing.
farshid
farshid
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