The calculator in EngMod was added by Neels after I had done dozens of tests with tripple and T port designs.
The calculator simply uses 75% of the total effective port area as a guide.
This always works and always makes alot more power and generally I found that the duct exit should be about the area of the main port alone.
This usually ends up around 75% of the total ( by taking away the extra area of tripple ports) needed for lots of blowdown - thus power.
It was never intended to be used with a single port only as I havnt tested that at all, apart from years ago on TD3s etc, and we always went bigger back then, not smaller.
Theory says that having a smaller duct volume changes the Helmholtz frequency ( higher ) , and reduces the amount of exhaust residuals able to be stored in that duct ( meaning more clean mixture sits close) , but im not sure this theory will apply to making more power with a single port.
Having said that, a 40mm pipe entry on an engine only making 30 Hp is way too big, so reducing the duct and or header area, or maybe both, will very likely work real well.
Did you model the nozzle as a short tapered section ( 30mm say) from the duct exit up to the header dia ( as the first section of the pipe) and this is made as an oval to round transition in the flange on T port and tripple port designs.
Be real interesting to see if the sim reflects reality on a dyno, in your single port scenario TeeZee.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
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