Posted By: volaredon
how high of a reading should I expect on a vacuum gauge - 03/05/09 01:54 AM
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?
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?