Quote:
Originally posted by FlossinPrimera
Ok. now I've gone crosseyed. . .
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Ok, here's the good oil.
The earlier engines have the high ports (where the intake runners attach to the head), and the throttle body and plenum chamber (which is what you call the funky cover) is mounted underneath the intake manifold. That is, on the high port engines, the intake manifold runners curve UPWARDS from the throttle body/plenum, and into the cylinder head intake ports.
The later low port engines have the throttle body and plenum chamber mounted on top of the intake manifold (like in the P11 pic) so that the runners curve DOWNWARDS from the throttle body/plenum chamber and into the cylinder head intake ports.
IIRC, the reason they changed the position of the intake ports in the cylinder head was because, in the newer low port engine, they could avoid having so much of the intake valve guide protruding into the intake port. This was only of limited success because the low port position meant that the intake flow had to turn 90degrees to enter the cylinder. The older high port cylinder heads allowed the intake flow to approach the intake valve at a 45degree angle.
Clear as mud??