Not all vacuum gauges are created equal.... and neither are the parts our cars were made with. Make sure you use a good quality vacuum gauge. Usually the ones made by professional tool companies are more accurate (i.e. Mac, Snap On, Matco). This stands true with compression testing equipment.
A liitle story.........
I remember going crazy once when the cam doctors 1st came out. I was cam doctoring everything to see what was what. Wheather it was a factory cam or a performance cam to see if they were ground properly. Had a normally aspirated Buick come in at the Dealership I was a tune up tech at with a huge pinging problem. Cust says it's always done that since it was new. Was around an 84-85 Buick Regal 3.8 Carburated deal. No matter what... this thing would ping like a S.O.B. on light throttle. Egr worked fine, diaphram lifted all the way while driving under load, no excess carbon on the pistons, Egr port was clear, emissions were fine (not too lean), no cooling system or head coolant circulation problems, timing spot on and the advance was working properly. But no matter what I did... this thing pinged bad.
Checked the compression and it was around 200 psi. All the other Buick N/A cars I tested were around 175 psi or so with the throttle wide open, all the plugs out and a battery charger on the battery to get good cranking speed. Sold the customer on a camshaft. Sent the car to one of my line mechanic/buddies and pulled the timing cover. We installed a degree wheel and checked to see where the intake lobe centerline was.... it was around 101-102 degrees. A stock Buick cam is usually around 108-109. This was the problem. Cam was ground wrong. A phone call to my buddy John Erson (Sig Ersons nephew) confirmed this. John told me that when his uncle did runs for GM or any other manufacturer, they could be off by 4-6% and they'd consider that "acceptable". Ever wonder why if you test drove 10 cars of the same make/model/combo, but 1 or 2 of the cars just ran really snappy?? Well... there you go. This is why the guys that build the NASCAR motors or work for say Warren Johnson get paid the big bucks. Because everything in their motors are perfect.
So the moral to this story is..... even if you have a stock Buick GN.... you can have different vacuum readings from car to car (provided all other things are the same.... no vac leaks, etc) depending on if the cam was ground properly and it's intake lobe centerlines and int to exh lobe centerlines are correct.
Wells......
Not sure what you mean by Mopars not reacting well to larger cams?? We've never had problems with these motors as long as the "correct" cam is installed. Very much like Buicks require certain things (i.e. retarded intake lobe centerlines/late cylinder filling to reduce dynamic compression-detonation and wider int/exh lobe centers to promote turbo spool/scavenging of the exhaust). In line valve Mopars in a N/A actually do quite well with tight lobe center cams and long duration/lifts. Hemi's respond well to wide lobe centers because of the massive cantedness of the valve positions and their large chambers.
