I know this has been posted ad nauseum, but I was cleaning my upper and lower intake manifolds this weekend and noticed something very strange.
First, I have an 98 EO SVT #580 something I think.
When I removed the upper to clean, I decided to take a few measurements to try and port match the upper to the lower. I noticed the uppers were all about 2-3 mm smaller than the lowers on both the short and long runner ports. I don't have the exact measurements, but the lowers were closer in size to the 99-00 measurements. I thought this was very interesting as I knew the upper was supposed to be slightly smaller than the opening of the lower, but a 2-3 mm diff. on all of the upper ports was a big suprise.
So, now I'm thinking, if the upper and lower are designed to gradually taper for more velocity into the heads, why is there such a difference between the upper and lower.
The intake air is forced through the much smaller upper, then expands at the beginning of the lower, only to be compressed again at the bottom of the lower.
How is this supposed to be efficient?
