SR20DET: How Much Vacuum at idle? - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

BlackZenkiS14 · 10-14-2015, 03:50 PM

Hey guys, I'm trying to track down some problems with my car, and I need some comparisons, I feel like my car isnt pulling enough vacuum at idle.

I have a built S13 blacktop with S3 cams. and I get 350 mm/hg at idle. How about you guys?

Javi802 · 10-14-2015, 05:47 PM

mine runs at 20/21 inHg at idle. Which converts to 507/533 mmHg.

*e1_griego* · 10-14-2015, 06:05 PM

My car pulls ~15 inHg with S3 cams.

cotbu · 10-14-2015, 06:11 PM

I honestly think everyone quotes the 20inhg because somewhere, someone said it's what a healthy sr20 pulls at idle. Honestly vacuum without having standards and knowing a few constants makes vacuum comparing irrelevant for diagnosis.
You need to know rpm, timing and we all have different types of intercooler kits, and cams. Whoa so it's bests to say 850rpm 15dbtc and list all of the possible variables that may have an impact on vacuum, idle or boost. Like 3yr old plugs or compression on cyl4 is 90 but vacuum at 850rpm is still 20inhg

Probably not the best method to diagnosis a problem. But if you have low vacuum and weak leak down tests to boot, that should already be an indication for rebuild time.

Ummmm rebuild time!

Sent from a Highly Tuned Note 4.5!!!

BlackZenkiS14 · 10-14-2015, 06:56 PM

Shouldnt be rebuild time lol, engine only has 5000 miles on it, and made 420whp just a few months ago.

Kingtal0n · 10-14-2015, 08:56 PM

that gauge might not be exact. It is probably close, but I always double check with a second gauge if I am diagnosing.

cotbu · 10-15-2015, 08:01 AM

If the vacuum reading is not accurate then maybe boost isn't accurate either. Btw 13ihhg is pretty low!
And low vacuum isn't the end of the world, but if you think it might have something to do with your issue? By all means check it out!

Sent from a Highly Tuned Note 4.5!!!

*TheRealSy90* · 10-15-2015, 08:17 AM

Larger cams result in less vacuum. It will never have as much as it did with stock cams.

KoukiMonsta · 10-19-2015, 11:03 AM

Perform a leak down test, easy enough and can provide good info.

Stock cams, 850 RPM, 15* BTDC I pull ~20 inHg

[this motor has ~1500 miles on it]

Previous build with cams (270), less healthy/higher milage motor, were in the 15-16 region.

EDIT: I once doubted my gauge, reading 12inHg. So i hooked it up to my daily...pulled 22inHg. Then I did leakdown, verified i needed a valve job..

BlackZenkiS14 · 10-19-2015, 02:44 PM

Quote:

Originally Posted by e1_griego

My car pulls ~15 inHg with S3 cams.

I threw another gauge on the other day, and mine does 15 in/hg also. S3 cams.

10-14-2015, 03:50 PM	#1
BlackZenkiS14 Nissanaholic! Join Date: Nov 2003 Location: "St. Chuck", MO Age: 35 Posts: 2,091 Trader Rating: (15) Feedback Score: 15 reviews	SR20DET: How Much Vacuum at idle? Hey guys, I'm trying to track down some problems with my car, and I need some comparisons, I feel like my car isnt pulling enough vacuum at idle. I have a built S13 blacktop with S3 cams. and I get 350 mm/hg at idle. How about you guys? __________________ -Kyle

10-14-2015, 06:11 PM	#4
cotbu Post Whore! Join Date: Sep 2005 Location: SWFL Age: 47 Posts: 3,318 Trader Rating: (3) Feedback Score: 3 reviews	I honestly think everyone quotes the 20inhg because somewhere, someone said it's what a healthy sr20 pulls at idle. Honestly vacuum without having standards and knowing a few constants makes vacuum comparing irrelevant for diagnosis. You need to know rpm, timing and we all have different types of intercooler kits, and cams. Whoa so it's bests to say 850rpm 15dbtc and list all of the possible variables that may have an impact on vacuum, idle or boost. Like 3yr old plugs or compression on cyl4 is 90 but vacuum at 850rpm is still 20inhg Probably not the best method to diagnosis a problem. But if you have low vacuum and weak leak down tests to boot, that should already be an indication for rebuild time. Ummmm rebuild time! Sent from a Highly Tuned Note 4.5!!! __________________ LoverTechnologies "Half Broken Things!"

10-14-2015, 06:56 PM	#5
BlackZenkiS14 Nissanaholic! Join Date: Nov 2003 Location: "St. Chuck", MO Age: 35 Posts: 2,091 Trader Rating: (15) Feedback Score: 15 reviews	Shouldnt be rebuild time lol, engine only has 5000 miles on it, and made 420whp just a few months ago. __________________ -Kyle

10-15-2015, 08:01 AM	#7
cotbu Post Whore! Join Date: Sep 2005 Location: SWFL Age: 47 Posts: 3,318 Trader Rating: (3) Feedback Score: 3 reviews	If the vacuum reading is not accurate then maybe boost isn't accurate either. Btw 13ihhg is pretty low! And low vacuum isn't the end of the world, but if you think it might have something to do with your issue? By all means check it out! Sent from a Highly Tuned Note 4.5!!! __________________ LoverTechnologies "Half Broken Things!"

10-19-2015, 11:03 AM	#9
KoukiMonsta Nissanaholic! Join Date: Mar 2009 Location: NC Posts: 1,969 Trader Rating: (23) Feedback Score: 23 reviews	Perform a leak down test, easy enough and can provide good info. Stock cams, 850 RPM, 15* BTDC I pull ~20 inHg [this motor has ~1500 miles on it] Previous build with cams (270), less healthy/higher milage motor, were in the 15-16 region. EDIT: I once doubted my gauge, reading 12inHg. So i hooked it up to my daily...pulled 22inHg. Then I did leakdown, verified i needed a valve job.. __________________ @UpshiftEngineering

10-14-2015, 05:47 PM	#2
Javi802 Zilvia Junkie Join Date: Jul 2012 Location: Oklahoma Age: 29 Posts: 470 Trader Rating: (10) Feedback Score: 10 reviews	mine runs at 20/21 inHg at idle. Which converts to 507/533 mmHg.

10-14-2015, 06:05 PM	#3
e1_griego Premium Member Join Date: Sep 2004 Location: Independence, Ore. Age: 36 Posts: 2,642 Trader Rating: (24) Feedback Score: 24 reviews	My car pulls ~15 inHg with S3 cams.

10-14-2015, 08:56 PM	#6
Kingtal0n Post Whore! Join Date: Jul 2005 Location: South Florida Age: 38 Posts: 4,649 Trader Rating: (17) Feedback Score: 17 reviews	that gauge might not be exact. It is probably close, but I always double check with a second gauge if I am diagnosing.

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