I have a 350 with Vortec heads, XE274 cam retarded 4 deg, Rhoads lifters, Hooker SuperComp headers, and a Performer intake.

Now at 5000 RPM WOT Vacuum goes to 1 in. and by 6000 it's at 2. I thought it was the carb so I switched from a Q-Jet 750 to a Q-Jet 800. Same thing. Switched to a Holley 650 DP and the same thing.

I know the performer is designed for idle-5500 but could it cause such a problem?

 

Yes.

That's why they say it's "designed for" 0-5500 RPM. It's all done once the RPMs get up to that point.

Basically you have a cam/heads/exhaust vs. intake mismatch to the extreme.

 

Would adding a 1/2 inch open spacer help the problem? What if I cut down the divider 3/4 of an inch? Or is my only solution to go with the Performer RPM?

 

Look at the port cross-section. I think you'll realize right away that dinking around with the stuff at the base of the carb won't change the basic situation very much.

The RPM would actually be an excellent match for the rest of your combo.

 

the performer is almost as bad as your stock intake was.

you might as well get the Vic Jr for vortecs... heh

 

Thanks for the help. My main concern is that I have a Q-Jet and a Holley Q-Jet replacement and those don't work on a Performer RPM. I also have a 700 DP and a Holley VS 750 but I'm afraid gas mileage would take a significant dip. I'm going to mess with the Performer a lil more and see what I can get out of it.

 

http://store.summitracing.com/partde...art=EDL%2D7104

 

It's not for Vortec heads though.

 

EDIT: nm

 

Oh yeah... duh...