There’s a lot of information out there for low vacuum and I can almost assure you that I have tried troubleshooting with almost every method possible and still same results with no issues found.

Heres my situation, I have a 1968 Mustang Coupe with a 302w engine with 351w heads. This is the 2nd engine I put in the car and still have 10 in hg at idle vacuum. Both engines had the edelbrock performer intake and a Holley 600 carb. No headers and dual exhaust with H pipe. Pertronix ignition (full 12volts). 6-10 degrees timing. I’ve looked for vacuum leaks everywhere from hoses to ports to seals and no leak. I even had the heads rebuilt because I thought maybe it was a valve seals or a burnt valve. I thought burnt valve because of the one thing that stands out which is the classic dollar bill test. When I put a dollar bill at the tip of the exhaust, I can see it getting sucked in. So that tells me there is some sort of reversion. Anyone have any tips or experience this?

 

so how much vac are you expecting from it?
How much vac is that cam suppose to make?

 

It’s the stock cam and should have 18-22 in hg so I’m expecting at least 18. I need at least 15 for my power brakes. I’ve even disconnected all the vacuum ports and still no change. I’ve taken the intake off 3 times.

 

when was the last time it produced an acceptable vac reading and does engine idle seem to have degraded?
Does the engine idle well?
Does it make good power?

 

Does the needle hold steady at 10inhg or does it flutter erratically?