If your looking to build a rather serious 283 sbc in a light weight car sq inches.port ccĮdelbrock performer rpm. (measured at the smallest part of the ports) Here's a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes Smallest cross section without losing HP is the best size.Small Cross Section: Works better on smaller CID and lower RPM.Too large of a cross section can cause reversion and less power.Large Cross Section: Works better on larger CID and higher RPM.
Short Port Length: Improve high RPM range.Long Port Length: Improve low RPM range.Note: You can also save this link to a handy Gear Ratio calculator.ĬCs of Deck Clearance = Bore x Bore x 12.87 x Depth of Deck ClearanceĬCs of Head Gasket = Bore x Bore x 12.87 x Thickness of Head Gasket Rear Gear Ratio = (RPM at Finish Line x Tire Diameter) ÷ (MPH x 336) Rod Ratio = Rod Length ÷ Crank Stroke LengthĪverage Piston Speed = Crank Stroke x RPM ÷ 6 Gross Valve Lift = Camshaft Lobe Lift x Rocker Arm Ratio Tire Diameter = (MPH x Gear Ratio x 336) ÷ RPM Note: You can also take this Compression Ratio Calculator tool for a spin. 7854 x Bore2 x Stroke x Number of Cylinders Note: Summit Racing also offers this CFM Calculator to make the job easier.ĭisplacement =. Racing Carburetor CFM = RPM x Displacement ÷ 3456 x 1.1 That’s why we’ve put together this list of 13 key performance formulas you should know when building or tuning your street or race vehicle. While cheat sheets might have frowned upon in your sixth-grade classroom, we strongly encourage them in the garage, shop, or pits. but keep in mind valve lift and port flow limitations USE THE CALCULATORS to match port size to intended rpm levels. If you do the research youll find that carefully matched cam timing,and header design can be used to increase the cylinder fill efficiency. The bore size of the smaller SBC engines like a 265 or 283 won,t physically allow the use of the larger 2.02" intake and 1.60" exhaust valves, especially with longer duration high lift cam profiles. The cylinder head port size required can be easily calculated,many guys seem to think your limited to a certain size port for a certain displacement, but the fact is that theres far more factors that effect the correct port configuration and port size than engine displacement alone. You might want to read through this thread also.Ī couple KEY factors in getting any smaller displacement SBC engine to perform well, is your going to have to get the static compression ratio up in the 10.5:1 or higher range and match the cam duration and lift to maximize the port air flow rates in the upper rpm range, and that will generally require selecting a solid lifter cam, use of tuned headers with a low restriction exhaust, and gearing the cars drive train to allow it to maximize, the engines ability to breath in the 4500 rpm-7500 rpm, range that a short stroke 3"-3.25" SBC engine is capable of if properly designed and constructed
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