Quote:
Originally posted by Henry Schmidt
High port velocity is necessary for maximum volumetric efficiency. Port shape and size not just port size is important for engine performance. Bigger is better only in a full throttle situation. must engines don't run full pedal all the time.
I would recommend a maximum 40 mm port for a 2.8 SS with an intake manifold of 38 mm. This lip at the transition will assist in the control of intake pulses caused by cam overlap and is exaggerated by large duration cams.
Big ports = poor low end possible good high end
small port = good low end possible reduced high end throttle response
Calculate CFM for your projected max RPM and run the smallest port to accomplish that volume.
With a 2.8 @ 7600 RPM 38 mm manifold is appropriate. Add 2 mm to the port for pulse control and you win.
8500 race on a race engine with proper gearing and bigger is better.
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On my planned 3.0 MFI engine im using large port SC heads 39mm, as this is a mainly road car low end is important, do you think the 39mm port is sufficient? What should I open the exhaust upto? 37mm? Im using DC40 cams