| Re: 2 part question |  | ||
| Re: Re: 2 part question -- Ken Merring | Post Reply | Top of thread | Maverick Message Board |
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Posted by: Rob Riffle ® 2001/09/11, 08:53:17 Author Profile |
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:: ::What exactly makes the car faster. I mean i think i understand it. Say all my (238ft/tq) tq comes into play by 2900 rpm, then slowly decreases till 5500 rpm. Now when i add mods, doesn't that broaden the curve and increase it? i.e. after modes it peaks at (for the sake of numbers) 3200 at say 250 ft/lbs and remains above the stock curve to 5500 now. Isn't that the "felt" increase in speed? or what makes 0 to 60 quicker? and where exactly does HP come in? i know tq is a product of HP.... <------ very confused.... : :..David, The engine is just an air pump that works by expanding air that is heated by the combustion of the gas-air mix that is taken in. As the rpm goes up, the (pumping losses) that occurr thru the intake passages 'after' the peak torque (2600 and 2800 rpm, for your engine, start to increase at a more rapid rate and the torque starts to drop. :..Pumping losses are caused by valve diameter,port shape/size,length,change in direction,carb size and a number of other factors that act to limit the maximum amount of air that can be drawn in. Some major limiting factors are the camshaft timing events and the amount of carb area. :..Having said that, with your carb change you now have an increase in airflow into the engine so torque production will increase but still in the same rpm range and perhaps broaden just a small amount. To raise the rpm of peak torque, the cam timing event would have to be lengthened. :..The improved exhaust allows the combustion by-products to clear the cylinders more completly therefore make more room for the increased new air-fuel charge. Result is more torque produced. :..Horsepower is a figure that is derived from the torque and rpm numbers. For your engine at stock peak torque the HP would = :234 x 2200 = 514800 divided by 5252 = 98 HP at peak torque. So you can see that if more air and improved breathing is given the engine, the torque value will rise at the same RPM thus equals a higher HP figure. It can also be seen that torque is what turns the crank and moves the car. :..Peak HP occurrs higher in rpm because the rpm rises faster than torque is lost, until the ability to injest air becomes so low that the torque value in the figures above cannot support the increasing HP result, and that figure starts dropping very fast. :If you take a look at a HP/torque vs RPM graph some other interesting info can be seen. Peak torque occurrs around the straightest portion of the HP curve and the torque will tend to be flat over that portion of the curve. Another interesting point that shows for stock and near stock engines is that the HP and torque curves alway cross each other very near the 5252 RPM point. This is the figure that is used in HP calculations. :..To find the torque produced by your unmodified engine at 4200 rpm would be 5252 x 138 hp divided by 4200 rpm = 172 lbs. ft. of torque. So it can be seen that torque does indeed fall as rpm increases due to the engines increasing pumping losses. :..These are the reasons why better flowing heads are installed with more carburation, cam duration and exhaust. :..Hope this helps in understanding without causing to much confusion. :..Good luck, Ken Man!! WHew!! You even rattled my brain a little with that one Ken. Poor boy will start drivin Chevys if we aint careful now LOL!! No, Its good to have such a wealth of information such as this just there for the asking. Again, This board is great!! Rob!! |
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