So, I added a vacuum guage this week. Yikes.
Start - 19inhg
warm idle - 20inhg(occasional random drop to 19.75inhg)
idle in gear - 16-18inhg(needle is a blur)
40mph - 17inhg(flat terrain, side wind same for below)
45mph - 16inhg
60mph - 14inhg
70mph - 12inhg
Coast - 22inhg maximum.
jump across intersection - 6inhg(primaries only... I think)

I was surprised how much pull it took to hit 70mph. I believe my cruising speed just dropped. Do these number look normal?

 

That occasional drop at idle is caused by a carb that is not quite adjusted right. From the looks of everything I would venture to guess they are a bit low. Sounds like a good carb and general tune is in order.

 

The internet is your best freind and is loaded with information. I am surpised your vacuum gauge didnt come with some sort of illustrated guide. You can do alot of tuning and diagnosing as well as monitor your engine behavior with a vacuum gauge and increase fuel mileage driving to achieve maximum vacuum. Check out this site for a good over view of what a vacuum gauge can do for you.




http://www.centuryperformance.com/vacuum.asp

 

I'm wondering if the transmission isn't to blame. It's running 210 on the highway. Building heat requires energy. Add in that the vacuum results are a little low, indicating the engine is working harder than necessary, and it's an interesting coincidence. Unless there's a dexron/mercon rebuild kit in the tranny and the extra friction of the Type F is to blame? Though I thought it would just shift harshly, which it does not.

Good link socketman.

Low, though Steady Reading = Late timing, low compression, sticking throttle valve, carb or manifold vacuum leak
timing... advanced if anything, compression is stock which is low, idle is repeatable so probably not sticking, vacuum leak... I can check the plugs for a lean cylinder.

 

maybe find a freind with a similar vehicle ,put a guage on it and do some driving. damn i havent had a vacuum gauge on anything in a long time ,i cant remember what the hell i saw.Remeber too that a pickup is about as aerodynamic as a brick and the faster you go the more power its goin to take. Check these 2 sites , one has typical (cd) drag coefficients for different vehicles and the second is a calculator for hp loss. Compare a small car to a truck, we need double the power to go the same speed. Remember when calculating your frontal area it includes the portion below the bumper. measure the width and the height from ground to top of windshield. Hence the craptastic mileage we get. I get 10-11 mpg, 12 inches at idle lol truck weighs 4850 with little or no fuel.

maybe i will do a test just for a laugh on my truck at highway speed.


To be continued





http://www.bgsoflex.com/airdragchart.html



http://www.gtechprosupport.com/support/AeroDragCalc.htm