How much vacuum will my engine produce (gauge selection)?

[robroy]

Good evening!

I'm trying to choose gauges for #50 (I've been looking at them for months), and one thing that varies between gauges is the amount of vacuum they're designed to indicate.

For example, the Autometer "Phantom" vacuum gauge reads from 0 to 30 in Hg. But I've seen other gauges that read a wider range of vacuum levels.

What's a typical range of vacuum levels I can expect from my new engine?

For those who aren't familiar with the engine, here's the thread that covers it:

http://www.fordification.com/forum/view ... =3&t=34516

Thanks for the great advice!
Robroy

[averagef250]

30 is about the limit of vacuum isn't it? You should be fine with that.

At idle you likely won't see more than 15 with an engine like yours and the most vacuum you'll see is on light or no throttle downshift.

A vacuum gauge is not so critical as to what the measurement is as to what it's doing. If vacuum flutters or jumps around you have issues to address. It is helpful for economical cruising as well though, not that it's a concern for your truck though.

[DuckRyder]

I agree, 30 is plenty.

18-20 has always been considered "normal" for a stock engine is very good conditon. An engine with a larger cam probably won't do that.

[robroy]

Good morning Dustin and Robert! Thanks for replying!

30 is about the limit of vacuum isn't it?

Do you mean the limit of what most gauges will indicate or the limit of what a car engine will produce? Or both?

A vacuum gauge is not so critical as to what the measurement is as to what it's doing. If vacuum flutters or jumps around you have issues to address. It is helpful for economical cruising as well though, not that it's a concern for your truck though.

I see! That makes sense--thanks for explaining that. And as for economical cruising, odd as it sounds, I'm sure times will come up when I'll much prefer getting 6 MPG to getting 4 MPG, so I'll use it for that also. Maybe times like that won't come up though.

I agree, 30 is plenty.

18-20 has always been considered "normal" for a stock engine is very good conditon. An engine with a larger cam probably won't do that.

Perfect, thanks Robert!

Thanks again for the replies.

Robroy

[montana_hiboy]

A healthy stock engine at sea level should pull in about 20"-21" of vacuum @idle, a lopey cam will reduce that to about 15"-16" of vacuum.

[robroy]

Hey Jim, thanks for replying! It sounds like the 30" gauge is good then (no need to measure more vacuum than that).

Thanks again,
Robroy

[cmoore]

I have a "Pontiac" vacuum gauge on my 360 that reads about 18-20 hg's at idle. The gauge maxes at 24, with between 24 and 15-ish showing "economy", and below that is listed in the "power" range on the gauge.

[montana_hiboy]

Hey Jim, thanks for replying! It sounds like the 30" gauge is good then (no need to measure more vacuum than that).

Thanks again,
Robroy

I should have added, as Dustin previously stated, the actual reading isn't of utmost importance, whether it be 17" or 21" you want a rock steady needle at idle, a fluctuating needle is indicative of underlying problems, a vacuum guage is a great diagnostic tool and an excellent indicator as to the health of your engine.