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| Understanding The Dyno |
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| Many people do not understand what the torque and horsepower numbers actually mean. Torque is the twisting force measured in foot pounds. Horsepower is the actual amount of work produced. The calculation for horsepower is: Torque X rpm divided by 5252. In other words, the engine produced 400 foot pounds at 2000 rpm equals 152.3 horsepower. (400 X 2000= 800,000 / 5252 – 152.3) if the same engine produces the same torque (400 foot pounds) at double the rpm (4,000) it will make double the horsepower (304.6 horsepower). Also, I have included two graphs on the left to explain why two engines close in horsepower can have different torque numbers. The 350 Magnum and the 383 Hot Rod are identical engines except the Hot Rod is a stroker. At lower rpm the stroker (Hot Rod) has substantially more lower rpm torque than the non stroker Magnum. The drive-ability of the stroker is substantially better than the non stroker, especially if you have tall gears or an overdrive transmission. The extreme opposite would be a high revving import engine that produces small amounts of torque but revs at very high rpms. If you take 200 foot pounds X 8000 rpm, it would produce 304.6 horsepower. The same engine at 2000 rpm produces a measly 76.2 horsepower. |
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| As hobbyists we have all learned that horsepower is king. Here is an example of the importance of not just looking at peak horsepower, but also really understanding how an engine gets to that apex of the curve. For this example, we will have two engines: we will call them engine A and engine B. Engine A has a peak horsepower of 525 at 6000 rpm, and engine B will have a peak horsepower of 505 at 5500 rpm. Now most people will say, “I want the 525 horsepower” Who wouldn’t? But, let’s examine how each engine gets to the apex. |
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| Notice that the graph for engine A has a peaky power curve. Starting at 150 horsepower and slowly climbing up to 525. Engine B has a much broader power curve starting at 220 and quickly building power up to the 505 horsepower. Now what is the big deal? Well the issue is performance through the power curve. If I told you engine A only produces 150 horsepower |
| at 2,500 rpm and engine B produces 220 horsepower at the same rpm you would naturally assume engine B will produce more peak horsepower. In this example, we obviously know this is not the case. Ok, so lets really break down the numbers. If you take Engine A and add up the numbers at every 500 rpm and all the way through 6000 rpm. And then divide that number by the 9 readings; you’ll get an average of 377 horsepower. Do the same for Engine B and you’ll get an average of 410 horsepower. Engine A even though it has high peak horsepower, has less overall horsepower. |
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| Why is this important? Most hot rodders spend most of their time driving in the idle to 5,000 rpm range. Image driving down the freeway at 2,500 rpm with engine A producing only 150 hp or engine B producing 220 hp that’s a 47% increase. |
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