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----- Original Message ----- From: "Jim Adney" <jadney@vwtype3.org> To: <type3@vwtype3.org> > So if you want to go from 1600 to 2100 cc then you should increase the fuel > pressure from 30 to 39.4 psi. Is this possible with the stock pump? > > Suppose we have 5" of vacuum driving along in our 1600. That means that each > cylinder is pulling in 400 cc of air an 5" of vacuum (less some pressure drop.) > If we then look at our 2100 cc engine also running with 5" of vacuum we now > have each cylinder pulling in 525 cc of air at the same pressure. The only > change is that we now have more of it, in proportion to 525/400. If we change > nothing, the FI will still meter out the amount of fuel that would be required > by 400 cc of air at this pressure. Seems correct to me. > > If you could find injectors that metered more fuel by exactly the ratio of > 525/400 (2100/1600) then this would also work, but it's a lot simpler to just > dial up the pressure to 39.4 psi. This is exactly equivalent, and it has the > advantage that you can dial it in to whatever you want. Am I correct in assuming you're referring to Lbs/Hr ? > > There's one uncertainly, and that's the fact that this assumes that the > pressure drop between the IAD and the combustion chamber is linear with > airflow. I seem to remember that it is not but probably close enough for our purposes. >I don't know if that's true or not, but even if it's wrong, the linear > assumption for small % increases of displacement should be pretty good > approximations. I hope so! 8^} "....the whole world , Chico. And everything in it." David V. Nelson 1969 Fastback FI (no matter what!) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org