Getting the engine project ready for the ECC this Sat and I have a vacuum gauge
that I thought might be useful hooked up. I have it connected to the vacuum port on the throttle valve but could easily connect it to the smaller port on top of the intake air distributor. What readings would I see on the gauge? Would it make any difference if it was connected to the intake phlenum instead of the throttle?
Click to view attachment
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If it is before the throttle body, you will not see much of anything. Connect it to the plenum for the best reading.

Depending on you cam timing, you will see anywhere from 6-20Hg or 3-10psi(-)

My engine runs at 19Hg when warm at idle.

I use a Vac gauge on the L-Jet. It's hooked up directly to the plenum. Reading are gonna vary, but note the reading when itched motor is running good. My Vac runs about 15. A higher rpms it increases...

Then, if you experience performance issues check to see whether the Vac reading is different. Changes in the reading will suggest a leak in one of the hoses going to the plenum- definitely true for L-Jets, not sure about D-Jet

I diagnose engine problems primarily by checking the fuel pressure gauge and Vac gauge.

Most people don't know you can set almost perfect timing with a vacuum gauge. At idle, adjust distributor until you reach maximum vacuum...

Once setup, depends on altitude. I have a vacuum gauge which in Flagstaff ran 10+; at sea level in Santa Clara runs 15+; at 980+ feet Grants Pass ???.

I use to have information on troubleshooting and probable causes based on different readings from the vacuum gauge. Built in and taken from the old brake booster of the 3.2 engine (brakes are non assisted and require a heavy foot).

Yes, this is still one of the best ways for tuning and troubleshooting.

Steve

Valuable diagnostic tool. Read the directions that came with thee gauge. You will be able to tell lots of stuff about the condition of your engine. a vacuum reading generally in the range of 15-21 should be good as long as the needle is steady and not pulsing wildly or dropping off intermittently. High lift long duration cams with give you a tick but it will still be consistent. It's caused by a reverse pulse in the intake during overlap.

Whoops, it was a swap meet purchase so no instructions. Thanks to all for the very valuable info. Keep it comin'!

Here is a helpful link.

http://www.secondchancegarage.com/public/186.cfm

Cool little gauge face display with explanations.

An interenting article.