Boost drop at higher rpms?

[04dreamcobra]

I have a built block in my 04 Cobra with a Gen 1 Whipple 2.3. We did comp XE-R cams, comp valve springs. It puts out about 19 psi in the low end and after about 4500 rpm, it drops to about 16-17. Any thoughts why?
Also, with the same pulley set up: before the build held at 19 psi.
After the build(installed cams, headers, jlt high boost, supporting goodies and cut outs. still held at 19 psi. Am i wrong for thinking i should have dropped some psi? explain you answers. lol.

Build: MMR 4.6 built block, Gen 1 whipple 2.3, comp XE-R 106460 cams, comp valve springs, Mac LT's lethal X,E-cut outs with option of mangnaflow cat back, return style fuel system with twin 400's, 60 lb injectors, other small items. ask if you want more details.
Whole car has 50,000 miles. blower has a little less than 25K.
Thanks for the help!

Side note... i tried to search for threads already about this, but the search wont work for some reason. Maybe because im on a work computer.

 

[Bigggy]

Usually when boost drop more and more going higher rpms, you might have belt slippage.

 

[highcompression]

Belt slippage or could be a "heating" issue ? Log IAT2's ...... Put a Gates green stripe or a Gatorback on there and check back with us, we'll go from there ..........

 

[333arod333]

I had this problem when tuning. I ended up getting a new belt tensioner and a belt that was about an inch or so shorter. You break off the tab on the tensioner so it can go back further. Fixed the problem perfectly.

If you order the tensioner make sure it is the right one. I bought one from Rock Auto and it was the wrong one, they have a problem with their catalog. If you get one from there just get the one for the lightning.