i am pretty pleased - new motor coming together Options

[Scott S]

I just finished the final grinding on the new fan shroud for the intakes today. Then I had to take everything apart to clean up the dust (that took another hour and a half - sheesh). Just as I was finishing up, the fed ex guy showed up with what became my intake screens. I am really pleased with the end result!! I am just a flywheel and a throttle linkage away from being all done - then I get to start on the chasis....

[J P Stein]

Here's something you may find interesting.
A dyno graph with back to back runs with different intake set-ups above the carbs.
The blue line is with open stacks.
The red line is with a stock 911 airbox with a bellmouth mounted instead of the snorkle and a K&N replacement filter rather than stock.
I wouldn't have believed it.

[ArtechnikA]

Here's something you may find interesting.
A dyno graph with back to back runs with different intake set-ups above the carbs.
The blue line is with open stacks.
The red line is with a stock 911 airbox with a bellmouth mounted instead of the snorkle and a K&N replacement filter rather than stock.
I wouldn't have believed it.

The discontinuity betweenn 5500 and 6000 is unfortunate. The peak numbers are really close. I need to look at things more closely but what jumps out is that the open intake is just a bit too rich for max power.

But the plenum effect is not news.

Air has a lot more mass than you think of at first, which is why wind power is so attractive... And at intake velocities (about Mach 0,5) there is significant momentum to the airstream. It's be _really_ interesting to see manometer readings comparing airbox pressure to atmosphere.

Once you get a stream of air moving into the plenum, it tends to keep moving, so even when one intake valve closes, another is opening (and this is one reason why 6's are so much smoother than 4's - you make power over about 120º of crankshaft rotation...). With 6 individual throttle bodies, the best any can expect is to gulp in from atmospheric. In a plenum, each cylinder can take advantage of the momentum generated by the previous cylinder's intake airstream momentum.

Sizing is critical, but I believe this graph is evidence that Porsche got it right.

BTW - if you compare the Inglese photographs with the others, and cross-reference 'Prepare To Win' you will be reminded that Carroll Smith observed 25 years ago that the intake stack must have a full radius on the entry, and that 'only Porsche and Ferrari' really grasped the concept.