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Speedy Squirrel Speedy Squirrel is offline
Rocket Scientist
Join Date: Jun 2008
Location: Detroit
Posts: 896
Originally Posted by 911st View Post
Another point of referance.

In Bruce Anderson's book he gives a formula for sizing the throat of carburetors. We might accept that this was to be the smalles restriction in a normaly asperated performance motors intake tract. From looking at Porsches EFI turbos the ports seem to be the same as there N/A motors.

The formula is: 20 times the square root of (one cylinder volume/1000 + RPM at HP peak/1000)

The results being for a 3.3:

At 5500rpm = 34.8mm
At 6000rpm = 36.3mm
at 6500rpm = 37.8mm

For a 3.5 at 5500rpm, 35.8

Most of us with SC and stock cams are making peak hp at 5500. If the C2's were timed to factory stock setting they could make HP at 6000rpm.

This is just a point of referance.

It might be this is the smallest we want to consider. Do not want pressure to build in front of the intake port as boost pressure builds should it become a restriction. We want it to build in the cylinder.
Insanely wrong ... again. I love the way you answer your previously incorrect posts with more mis-information.

The formula is based on the delta P needed to get a decent fuel flow at at the venturi, without too much pressure drop at max RPM. It is at least 50 years old.

For port injection the port can be sized for other things like momentum tuning (something you continue to ignore due to your mistaken belief that it requires really long ports), or reduced pressure drop (another point that you jack up by assuming that just because the port area is smaller than the valve curtain area it is a restriction. It's not. The is a thing called valve discharge coefficient. It represents the actual flow characteristic of the valve. It is different from the curtain area.)

Then there is your weird belief that the port velocity has a big effect on evaporation. It doesn't.
Old 02-07-2010, 02:08 PM
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