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VOLUMETRIC EFFICIENCY/ENGINEs torque CURVE

grumpyvette

Well-known member
Joined
Apr 17, 2001
Messages
841
Location
Loxahatchee, FL, Palm Beach co
ever wonder why your engines torque curve gets higher with the engines rpm level untill about 4000rpm-5500rpm(DEPENDING ON YOUR COMBO) but fades above that rpm level?
well it depends on several factors, first as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires,THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds theres not enough air velocity to mix the fuel correctly or produce a effective ram tuneing effect but as the rpms increase the cylinders fill very efficiently untill the rpms reach a point where the cylinders just don,t have the time necessary to flow
enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs in each cycle opens for about 250degs of effective flow even with a hot roller cam, now thats only about 35% of the time and theres 41.6 intake strokes per second , thats only 1/60th of a second for air to flow into the cylinder, I found this graph that shows the relationship between V.E.(VOLUMETRIC EFFICIENCY) and AN ENGINEs torque CURVE http://www.n2performance.com/lectures/lect1/n2perf5.gif
WHAT THAT GRAPH SHOWS RATHER EFFECTIVELY is that its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can acomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp)so moveing the torque curve higher in the rpm range increases hp. btw heres info on how to find the effective tuneing lengths for th intake and exhaust lengths,
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ram tuned and rpm matched cam timeing for the effective use of the headers and intake system can get you to slightly over 100% V.E. at (1) rpm range where the tuneing is most effective, look here, http://www.grapeaperacing.com/GrapeApeRacing/tech/intaketuned.cfm
heres how to find the correct tuneing lengths http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html
 

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