Ok I've been trying to run down an issue if it realy is an issue of the fact that my MAP sensor readings usually fall from 95-97 when running below 5900 rpms, to about 89 to 93 above 6000 rpms. I have hunches that it could be due to the 52mm TB I have but I wouldn't think that would make that drastic of a difference with my set up.

Set up Specs: 383 w/cc306 cam, ported heads flow 272cfm @ .560in 28' of water. Of course all the other bolt ons like LT Headers, ZO6MAF, 52mm TB, port matched intake to heads, etc. Computer tuning from pcmforless and my own tweeking. I'm running about 44 degrees of advance at those rpms to get the best times with no retard being pulled by the pcm.

Again I'm leaning towards some kind of restriction in the intake system at those rpms. Course there could be something else out there I'm not thinking of. Thanks for the help folks.

 

Looks normal to me. They heads while nice, are in no way huge for a 383. And no head or intake setup will ever reach 100% efficiency, so you are making a bit more vac up top because teh motor wants more air than it can get.

 

Since you have a non-stock MAF, computer calibrations will be skewed and results could vary. There is no longer any baseline for troubleshooting or comparison.