Before I got a new head put on the car. My vacuum read 20-21 pounds mercury. Or -20 to -21. After I got the new head it reads -18 at idle and at operating temps. Currently its only got GMs2. Stock everything except cat back.

When I was at -20 I had full bolt on gm 2.

Is it possible I have an unhealthy engine now with the new head on? Could the hosing be causing this issue? Car feels slower than before. But I saw close to 14~ pounds of boost on wot. Its not the same as before I feel it pull.

 

Is it an lsj head? Ported? Double check your hoses. Make sure nothing is worn out.

But the "general rule" is 18-21"

 

I believe it is. Dealer put it on. Bolts right up. I used the aero force and I'm actually at -17.1 to -17.6. Imma replace all hoses that deal with vacuum on the car. Any major hose I should worry for that has direct correlation to my concern ?

 

Here's a nice read on vacuum readings:

Tips on Reading Gauges: Vacuum Gauges

 

Make sure the one coming off the top of the manifold is good. It's right In front of the fuel rail. Also make sure your intake seals up fine, and the tb

 

ideally it should stay at -20, and i noticed when my air conditioning is on it goes up a bit to like -19, -18

 

Elevation plays into this as well.

Just like when trying to compare boost numbers you can only give a range.

You can't say it "should" stay at -20, because a perfectly healthy car might be at -18 but at a higher elevation (just giving an example fyi, not intended to be a jab against u man). Also, you are correct about the a/c. I notice the same thing.

My car is usually around -16, but I have aftermarket cams, which also plays into idle vacuum. Too many variables. That's why I posted that link. It's a nice read.

 

I started going off by my interceptor. On idle. 750 rpm average. I get 17.3 to 17.6 inches vacuum.

 

That's fine man.

 

Perfectly normal.

 

That's with the ac off. Before the new head it was 20-21. Ac off.

 

When did you take those readings?

Same location, elevation, temp as the new ones?

 

Yeah my driveway. Only diff is the heat from outside.

Unless this heat wave plays a roll in it, I'll find out in a few months how it is.

 

Air density can def alter readings.

Regardless, you are still in the acceptable range of good vacuum and a healthy engine.

 

OK. That's all I kinda need to know.
This way I can start to mod it again. Was hopping to go turbo but it may be on hold. Gonna push my blower for time being. Love the power curve

 

I was getting so offended until you told me it wasn't a jab

 

Yes sir!!