Port Modifications
When a modification is decided upon through careful flow testing with an air flow bench, the original port wall material can be carefully reshaped by hand with die grinders or by numerically controlled milling machines. For major modifications the ports must be welded up or similarly built up to add material where none existed.
The Ford two-liter shown above in stock trim was capable of delivering 115 horsepower@5500 rpm for a BMEP of 136 psi. Contrast this with the Pro Stock ports shown below.
This aftermarket racing GM Pro Stock head was capable of 1300 horsepower@8500 rpm with a BMEP of 238psi. Since BMEP is an excellent efficiency measure and closely related to volumetric efficiency, the aftermarket Pro Stock head is vastly better than the stock Ford. In fact a BMEP of 238 puts it near the top of the racing engine world. It is close to the limit for a naturally aspirated gas burning engines. For four-valve/cylinder engines the BMEP limit is about 265 psi.
Of course cam profiles, engine rpm, engine height constraints and other limitations play a role in this difference as well but the difference in port design is a major factor.
Read more about this topic: Cylinder Head Porting
Famous quotes containing the word port:
“In the midst of this chopping sea of civilized life, such are the clouds and storms and quicksands and thousand-and-one items to be allowed for, that a man has to live, if he would not founder and go to the bottom and not make his port at all, by dead reckoning, and he must be a great calculator indeed who succeeds.”
—Henry David Thoreau (1817–1862)