So, what does that tell me? Is it good or not?

 

If the idle is at 750 rpm...that is really good.

Patrick

 

Yeah, between 750-800 rpm

 

mines around -470 mmhg on the PFC, gauge shows a little more than 17. Is your gauge off any when the car is off? I'll bump up my idle to 800 with the PFC and see what vacuum I pull then, it should be more.

Tim Benton

 

Mine shows about 450-500 mmHg at idle 850 rpms. That is on a stock motor with no mods and 66,000 miles.

 

Mine`s at 15 -16 at 800rpm.. is that good ?

 

According to Mazda shop manual {what the dealer use} if I remember correctly anything above 14 is good on stock motor not ported.

 

Im boosting 10lbs and i pull 15 vaccum...at around 1000 idle..?

 

it's usually a good sign to pull 15-16 at idle (750ish)...but porting ..airpump and other mods can change the vac. Nothing replaced a compression test...

I for instance pull 490 on the PFC sometimes 510...sometimes 450...
depending on I dont know what...car always pull hard and strong

 

Well at 1000rpm i have like 19-20 around that ..

 

Also it depends what your mods are. Air flow mods (intake, IC and exhaust) will drop the idle vacuum down. With intake, IC, DP,MP,CB, i see about 13 psi at 740 idle. Runs like a champ.
~Tom

 

My car was just ported and at around 800 rpm i'm pulling like 17 or 18lbs of vacuum.

 

Probably not a very aggressive port. My street ported motor has always pulled 14-15inHg@750rpm from the beginning.

 

I have a ported motor as well and I pull ~15 @ 800 rpm.. at first I was concerned that I was getting low vacuum, but since im ported and have some intake and exhaust mods, i think it is normal?

 

I also think that atmospheric pressure will affect your readings to some slight degree.

Not that I care....but an engine at idle produces a vacuum. Not pressure. So, any idle vacuum reading is just that (Vacuum being messured as Inches of Mercury (HG). Not PSI (pounds per square inch).

James

 

Altitude affects the idle vacuum, too. With that, RPM, gauge accuracy, porting, mods, etc., I don't think it is very useful for comparing between cars. If you notice a distinct drop in idle vaccum, that might tell you something about your engine. Or if it starts jumping around a lot, that might tell you something as well. But comparing car to car doesn't tell you much, in my opinion.

-Max

 

im pulling 19-20 on vaccum.....but i idle around 1k-1150. What does that tell me? I also have a intake and CB

 

you know you bumped a thread over a year old...

dont you ?

 

i pull around 17-19 at idle @ 1100~ rpm, and have full open exhaust and a street port...

 

Wow, post whoring from the past!!!!!

James

 

vacuum at idle = lazy person's excuse for not running a compression check

in other words, meaningless

 

480 to 510 mm Mercury from the Power FC Commander display @ 750 rpm idle. Converting to inches Mercury that's 19 to 20 inches Mercury. FWIW my Autometer shows 17 inches Mercury. I tend to believe the Power FC readout over the Autometer, at least for accuracy's sake.

 

15-16 at 1100-1200 idle.....why's my car so different from everyones? its a new reman, ~3000 miles.

btw, my idle NEVER goes below 1000

 

The only really significant information here is that some people need to adjust their idle...

 

ok... this is a dumb question... so dont flame me guys...

What's the vacuum tell us anyways?? is it how healthy the engine is??