I just finished putting EQ Magnum heads on my '83 318. along with the associated 1.6:1 Magnum rockers, etc. I also put in a stock replacement 360-2 barrel cam. Melling brand. 0.410 lift on a stock LA motor, but 0.437 lift with the 1.6 Magnum rocker gear. extremely close to a COMP 252 at 1/2 the price. Performer intake, AFB #9636 625 CFM. Eddy double roller T chain set; cam installed dot to dot, at 0* adv/retard.
Motor runs dead smooth, and I can set my idle at 650 RPM, w/o a problem. (I've actually got it at 700 though) But I'm worried a bit, that I can only get a best reading of 16" on my vacuum gauge (verified with a 2nd gauge); though that reading is rock steady.
Runs great, huge difference in power, between now and when it was a completely stock, 318 2 barrel motor.
but, I had a steady 19.5" then. Is 16" to be considered "normal" for the new combo?
this cam, in a 360, gives 19-20" vacuum.

(1) will the 42 less CI, influence the reading THAT much, with a given cam???
(2) how 'bout the increased flow potential of the EQ heads, as compared to the original 318 heads(they were not the "302" ones, but standard open chamber "163"s) I'm thinking that the larger ports and valves can flow more air, so there can be less difference between atmospheric pressure vs inside-the-engine pressure(or vacuum)

Yes, this is a heavy truck, but now it moves much easier down the road, with much less gas pedal needed to do the same as before. Meaning the engine now does not have to work as hard as it used to. (or does it)
I'm definitely not after Neon type MPG (or I would not be driving a truck in the 1st place, would I) BUT I want what I had before, at least; if not a bit better. I had an '81 W 150 with a TQ on a 318, that surprised alot of people in that department, so I'm using that truck as my "bench mark". (though that engine was 100% OEM stock)
Lower vac readings, usually mean thirstier engines, from what I've seen in the past.. I got 12-13 MPG from this truck before the swap; driver, weather loading (or not) percentage of hwy to in town miles all being equal, think I can expect that to stay the same or maybe even increase, even?

I am going to be doing pretty much what you have done but I am going to adv the cam 2 degrees(& maybe try 4) as I have the cam bushings & I might as well experiment with them. It sounds like you are in good shape even with your idle vac being lower & I dont have an answer for that.

16 sounds like more than enough to me. if it was 13 or less id then id worry

so a reading of 16 is realistic?? I have no signs of any vac leaks and the needle is steady there but just "seems" low. What's "magical" about a reading of 13? Is that like the minimum needed to run the brake booster or something?

heck ya, thats great.

shoot, mine reads 10 in neutral and 6 in gear (but i have a much bigger cam than that)

I have not extended the vac line to see the gauge in the cab in gear or under load, but that 16" is at idle in Park.

I would drive it a bit before I worried about it. None of my 318s have had more that 16-17 inches of vac either.
Travis..

Did you try playing around with your initial timing to see if you can get some more vacuum?
Ran