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Guys,
I have a question. When we use a horsepower calculator like Comp Cams or other various programs like Virtual Engine Dyno the results we get are somewhat close in comparison. My question is this. How can you use SCR to determine horsepower when DCR is the true measure of compression. When Virtual Engine Dyno uses an SCR of 10.5 to figure my horsepower, it comes to 403. If I use the true 7.8 DCR in the compression ratio space, the horsepower would be 290. What am I not seeing here. Jim
 

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As RPM rises toward peak torque, so does the DCR because the engine reaches a point where it actually compresses all the air it has ingested(complete cylinder filling). At that point, DCR and SCR are equal. BELOW that specific RPM, the piston pushes some of the A/F charge back out the intake tract before the intake valve can close, thereby reducing the DCR. ABOVE that specific RPM, the cylinder operates at a slight vacuum due to intake tract restriction, which also reduces the DCR.

The point is to remember that the DCR is just that....dynamic...it changes due to operating conditions. So the HP calculators should be taking this into account.
 
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