Still Pricing 428 Blocks
Post Fiend
Joined: Feb 2001
Posts: 6,624
Likes: 8
From: Missouri
Russ, Desktop dyno may not be right but it is definitely on the right track.
Increasing cubic inches HAS NOTHING TO DO WITH MAKING MORE POWER unless you upgrade the engine's ability to breath.
Think about it. Lets say with a given build on a 390 you run our of breath at 5,500rpm. Now you throw a 4.125" SCAT crank in the engine. What did you just do to the RPM that the engine runs out of breath? Yep, you lowered it. Probably by about 750rpm in this case. Now one thing you did do is increase torque and streetability.
The atmoshphere will only push air into a given set of heads so fast. The demand for air is determined by either the number of cubes below it and/or the speed at which the volume of air needs re-plenished.
HP = TQ X RPM / 5252
If your RPM decreases a little and your torque increases a little then you have about the same HP.
Increasing cubic inches HAS NOTHING TO DO WITH MAKING MORE POWER unless you upgrade the engine's ability to breath.
Think about it. Lets say with a given build on a 390 you run our of breath at 5,500rpm. Now you throw a 4.125" SCAT crank in the engine. What did you just do to the RPM that the engine runs out of breath? Yep, you lowered it. Probably by about 750rpm in this case. Now one thing you did do is increase torque and streetability.
The atmoshphere will only push air into a given set of heads so fast. The demand for air is determined by either the number of cubes below it and/or the speed at which the volume of air needs re-plenished.
HP = TQ X RPM / 5252
If your RPM decreases a little and your torque increases a little then you have about the same HP.
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