Super Jet How do you measure ports?

[Quinc]

Trying to figure out what kind of porting was done on my blaster.

Can you measure the porting with a basic set of calipers? If so where do you measure from?

 

[TheBuzzard]

porting is measured with a degree wheel. its pretty easy to tell if the main exhaust ports have been widened just by looking at them. its harder to tell if they have been raised unless its been ported to the moon. the distance from the top of the port to where the head bolts on will be less if the ports have been raised. raised ports is all top end porting. wider ports is for bottom end. the transfer ports and main ports need a degree wheel for accurate #s.

 

[Nuklear6]

A degree wheel will work but there is a more accurate way. I prefer to measure the ports with a caliber and use computer software to calculate the actual port timing. There are a few more variables but you end with a more accurate finding. I use a software program similar to this: http://www.torqsoft.net/piston-position.html. Biggest factor many people forget to include is the +or - deck height. To make an accurate calculation of your port timing your measure down from the deck surface to the top / opening. Lets say exhaust port opens 1.525" down from the deck. If the cylinder is stock height and hasnt been cut (at stock stroke) the piston will be .030 to .035 - deck height (in the hole). So you'll take 1.525" - .030"= 1.495"/.03937" (1mm)= 37.9mm port opening. Input this info into the software gives you 88.63 deg. atdc. Take the port opening degrees multiple by 2= 177.26 which is the degrees of crank rotation that the port is NOT open subtract that from 360 deg and thats is your port duration (182.74 degrees). All and all that would be a decent freestyle exhaust port timing for a 85mm ss bb. But then again it all depends on how the intake measures, which also effects the blow down........