Just wondering since mine seems to be very damn low. I have a BNR stage 2 with some fuel mods and basic bolt-ons and I was wondering if its a good sign that its pulling very low.

 

stock ports? 18-20" HG I think is good.

 

What about past 20" Hg? Yup stock ports.

 

Next to impossible to get anything significantly over 20inHg of vacuum AT IDLE (750RPM spec + or - 50RPM as per Mazda) unless the gauge is wrong.

What are you seeing???


-Ted

 

Its a DEFI boost gauge thats pulling near 25. I idle around 750 most of the time. What could be wrong that is giving me such low vacuum? Its a good boost gauge and it matched a VDO gauge for positive boost, not sure about vacuum since the VDO gauge didn't have vac readings.

 

that isn't low vacum... it's high vac. the higher the better.

is your gauge in " s ??.... might be in something else

 

Well I mean like low on the gauge. Its a DEFI D-gauge, which is PSI for above 0 and below is in "Hg

 

i dont know who is pulling 18-20 vac...

i have done a lot of reading and asked a lot of people and on brand new sotck motors from mazda they pull between 16-17 vac and that is strong.....

if you hold the rpms at a steady 1500 pms you pull aobut 18 vac and at 2000 rpms holding steady you get about 19 vac...

that is from what i have researched..

 

wow my car is crap, at 900 rpm i pull 12 vac. at 1500 rpm i pull 15 vac.

 

I've seen it.
I've seen a lot of 18inHg motors, but these are very new motors or recently rebuilt.
I've seen a motor pull 19inHg, but that was a very expensive rebuild with practically all brand new internals (new housings, etc.).

One loose hose and the idle vacuum takes a ****.
The motor has to be TIGHT.
All intake and hoses have to be TIGHT.


-Ted

 

I'll get someone elses gauge to make sure, but this DEFI one is of pretty good quality and it matched the VDO one. Is there anything that could be causing such a high vacuum? Mismatched lines or something?

 

at like 450rpm's i pull 12-14hg vaccum. At 750-1000rpm I pull 20hg.

 

As a general rule, 17-22 is good for all cars. (at idle)


Ted, I agree with you that everything has to be sealed up really well, Mine pulls a strong 20 at 750 rpm though.

 

So anyone know an answer to my question?

 

is this for 2n gen motors or 3rd gen motors... because what you are saying is different than what teh guys in the 3rd gen forum say..


i made a post because i was paranoid about my motor... its a new crate motor from mazda with 8k on it already.. at idle (750 rpms) it pulls 16 vac sometimes 15.9 but usually 16... when the rpms are held steady at 1500 i pull 18 vac and at 2000 rpms i pull 19 vac...

i was paranoicd because of reading so may posts on here the motors idles fine and runs very smoothly at all times...
yet you 2n gen guys are pulling 18 -20 vac no problem.... is it because you guys are running a tight clearanced rebuilt motor?

 

my engine pulls ~16inches at a 750-800rpm idle. it is also medium streetported. it also makes 120psi of compression on both rotors.

 

That is correct.

You can't do this on a ported motor either.
Porting usually adversely affects idle vacuum.


-Ted

 

yes. large streetported motors should pull between 13-15 inches of vac at idle.

medium streetports 14-17

stock ports 17-20

 

so is there a difference between the 2nd gen and 3rd gen motors and how they pull vacuum?


most of the 3rd gen guys with new motors from mazda pull 16 vac.. but 2nd gen guys pulling 18-20 vac...

 

Mines ported pretty good and I pull about 16inHg at idle of 900rpms.

 

I just bought my 7 two days ago, and I'm curious how to check my vaccuum?

Will the brake booster suffice?

 

I'm asking the question for a 2nd gen with a decently low milage engine (under 20k). I'm just trying to figure out what could be giving me these high vac readings if the boost gauge is dead on?

 

i'd say the people pulling 20in of vacuum probably have either a 9.4:1 s4 or 9.7:1 NA motor.

 

I pull between 18 and 20 @ 1000-1200 rpm idle.

street port 9.7:1 NA motor.

the most significant factors are new rotor housings & seals, and tight clearancing on the side seals to the corner seal.

 

Dude there is NOTHING wrong with high vac. It means your engine is sealed up extremely tight and is running really well. Why are you worried about it?

-Joe