I have been looking through some of my data logs working on another bug. I noticed my MAP readings are pretty bad at WOT. I am getting 3 - 4" of vacuum throughout the rpm range. The air intake has a huge Amsoil cone filter running into 3.5" pipe with 1 90 degree bend. Still running a MAF, 58mm throttle body, and a ported LT1 intake. Lets hear some input..

 

What do you mean by bad readings?

 

A NA 383 shouldn't move that much air. I'd verify that the TB is opening all the way as my first step.

 

TB opens all the way.

By bad I meant the vacuum reading in the manifold should be between 1 - 1.5" at WOT. My readings are 3 - 4"..

I took a look at a log I made last year just after getting the motor running - the one and only WOT run I did with the LS1 lid I had previous. Vacuum readings were 1 - 2". So the air intake piping/filter is my restriction. I am going to try a K&N to see if the Amsoil filter is the issue.

Can't fit a LS1 lid with the stand up radiator I put in over the winter. I didn't think I'd lose that much with the intake.

 

Well I tried a K&N filter with no change. After that I installed 4" elbow, this helped a little but I am still seeing 2.5 - 3" of vacuum. I ordered a cowl hood so I can fit a LS1 lid back on the motor.