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My Car's Pulling 20 Vacuum at Idle

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Old 02-17-02 | 07:08 PM
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My Car's Pulling 20 Vacuum at Idle

So, what does that tell me? Is it good or not?
Old 02-17-02 | 07:10 PM
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If the idle is at 750 rpm...that is really good.

Patrick
Old 02-17-02 | 07:15 PM
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Yeah, between 750-800 rpm
Old 02-17-02 | 07:37 PM
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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
Old 02-17-02 | 07:41 PM
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Mine shows about 450-500 mmHg at idle 850 rpms. That is on a stock motor with no mods and 66,000 miles.
Old 02-17-02 | 07:47 PM
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Mine`s at 15 -16 at 800rpm.. is that good ?
Old 02-17-02 | 07:59 PM
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According to Mazda shop manual {what the dealer use} if I remember correctly anything above 14 is good on stock motor not ported.
Old 02-17-02 | 08:01 PM
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Im boosting 10lbs and i pull 15 vaccum...at around 1000 idle..?
Old 02-17-02 | 08:02 PM
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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
Old 02-17-02 | 08:28 PM
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Well at 1000rpm i have like 19-20 around that ..
Old 02-18-02 | 09:20 AM
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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
Old 02-18-02 | 09:52 AM
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My car was just ported and at around 800 rpm i'm pulling like 17 or 18lbs of vacuum.
Old 02-18-02 | 10:06 AM
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Probably not a very aggressive port. My street ported motor has always pulled 14-15inHg@750rpm from the beginning.
Old 02-18-02 | 12:54 PM
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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?
Old 02-21-03 | 06:46 AM
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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
Old 02-21-03 | 06:53 AM
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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
Old 02-21-03 | 07:41 AM
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im pulling 19-20 on vaccum.....but i idle around 1k-1150. What does that tell me? I also have a intake and CB
Old 02-21-03 | 12:42 PM
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you know you bumped a thread over a year old...

dont you ?
Old 02-21-03 | 12:49 PM
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i pull around 17-19 at idle @ 1100~ rpm, and have full open exhaust and a street port...
Old 02-21-03 | 04:40 PM
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Wow, post whoring from the past!!!!!

James
Old 02-21-03 | 05:48 PM
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vacuum at idle = lazy person's excuse for not running a compression check

in other words, meaningless
Old 02-21-03 | 10:15 PM
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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.
Old 02-22-03 | 01:01 AM
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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
Old 02-22-03 | 08:06 AM
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The only really significant information here is that some people need to adjust their idle...
Old 02-22-03 | 08:36 AM
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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??



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