Sr20det Low vacuum at idle..pondering - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

SoguRacing · 03-11-2009, 12:41 AM

ok guys so I had my engine rebuilt a few months back due to 2 spun rod bearings during tuning. Anyways long story short, My engine was rebuilt where it was tuned and I recently did a vacuum test and the reading was 12inHg. I know that normal reading range between 17-21inHg. So, My question is..What do I do or go about this problem? A reading that LOW would indicate either an intake manifold leak or late valve timing. So again..How would I go about the process or figuring out how to resolve this situation? Keep in mind that I haven't modified anything since the rebuild. Stock rebuild with hks step 1 256 cams...very mild and shouldn't cause low vacuum. There isn't enough valve overlap at idle. Any Ideas? Should I take off the valve cover and see if the timing marks line up???

slider2828 · 03-11-2009, 09:29 AM

I haven't done a vacuum test, but on my boost controller it only stays at about -7psi or so.... I have 264HKS Step1s.... But yah my vacuum is low too, but I think it could be piston design and ring seals and maybe head gasket.... BUt I am just thinking...

clark · 03-11-2009, 09:40 AM

have you noticed a change in gas mileage?

i don't know if you saw this, but i googled "low vacuum at idle"

http://www.international-auto.com/fi...uum-gauges.cfm

looks like a good resource. they mention that high performance cams will lower your vacuum. plus when you did your rebuild, did you use a thicker head gasket? which would cause lower compression.

smelly240 · 03-11-2009, 09:43 AM

-7in/hg is pretty low for having step 1 264s/

Is your boost controller giving you it in metric?

slider2828 · 03-11-2009, 09:43 AM

For me no... not really, depends hahaha!!!

If I step on it, I might get like 12 MPG lol.... But I was cruising to LA and back and I got like 22MPG. But I get like crazy torque and hp.... so eh depends how you drive. But normally, no not a decrease in MPG, maybe a little, 1 to 2 miles tops if driving civilized.

slider2828 · 03-11-2009, 09:45 AM

What is metric? lol.... its in PSI.... did conversion and that is 14.3 in/hg

SoguRacing · 03-11-2009, 01:27 PM

i do have a thicker headgasket. 1.1mm compared to the stock .8mm. I wouldn't think that would actually cause the vacuum to drop so significantly. by the way, the cams are hks step 1 256 not 264.

slider2828 · 03-11-2009, 01:55 PM

Yah it should not that bad..... Leak down test might tell you something and also do a piping tester... See if you have any leaks.

Muad-Dib · 05-30-2010, 12:57 PM

any news about the solution?

03-11-2009, 12:41 AM	#1
SoguRacing Post Whore! Join Date: Nov 2007 Location: (714) Age: 39 Posts: 2,967 Trader Rating: (23) Rides Gallery: SoguRacing Feedback Score: 23 reviews	Sr20det Low vacuum at idle..pondering ok guys so I had my engine rebuilt a few months back due to 2 spun rod bearings during tuning. Anyways long story short, My engine was rebuilt where it was tuned and I recently did a vacuum test and the reading was 12inHg. I know that normal reading range between 17-21inHg. So, My question is..What do I do or go about this problem? A reading that LOW would indicate either an intake manifold leak or late valve timing. So again..How would I go about the process or figuring out how to resolve this situation? Keep in mind that I haven't modified anything since the rebuild. Stock rebuild with hks step 1 256 cams...very mild and shouldn't cause low vacuum. There isn't enough valve overlap at idle. Any Ideas? Should I take off the valve cover and see if the timing marks line up??? __________________ Pre Tune Checkup! Compression,LeakDown,Vacuum Test $80. Cams Install: $180

03-11-2009, 09:29 AM	#2
slider2828 Post Whore! Join Date: Oct 2004 Location: San Francisco, CA Posts: 6,040 Trader Rating: (13) Feedback Score: 13 reviews	I haven't done a vacuum test, but on my boost controller it only stays at about -7psi or so.... I have 264HKS Step1s.... But yah my vacuum is low too, but I think it could be piston design and ring seals and maybe head gasket.... BUt I am just thinking... __________________ Turn and Burn!

03-11-2009, 09:43 AM	#4
smelly240 Nissanaholic! Join Date: Oct 2006 Location: Philaburbia Age: 47 Posts: 2,137 Trader Rating: (4) Feedback Score: 4 reviews	-7in/hg is pretty low for having step 1 264s/ Is your boost controller giving you it in metric? __________________ HREs on a S13 - check, 6262 - check, Girlfriend.... - nope

03-11-2009, 09:43 AM	#5
slider2828 Post Whore! Join Date: Oct 2004 Location: San Francisco, CA Posts: 6,040 Trader Rating: (13) Feedback Score: 13 reviews	For me no... not really, depends hahaha!!! If I step on it, I might get like 12 MPG lol.... But I was cruising to LA and back and I got like 22MPG. But I get like crazy torque and hp.... so eh depends how you drive. But normally, no not a decrease in MPG, maybe a little, 1 to 2 miles tops if driving civilized. __________________ Turn and Burn!

03-11-2009, 09:45 AM	#6
slider2828 Post Whore! Join Date: Oct 2004 Location: San Francisco, CA Posts: 6,040 Trader Rating: (13) Feedback Score: 13 reviews	What is metric? lol.... its in PSI.... did conversion and that is 14.3 in/hg __________________ Turn and Burn!

03-11-2009, 09:40 AM	#3
clark Zilvia FREAK! Join Date: Mar 2008 Location: new york Posts: 1,035 Trader Rating: (1) Feedback Score: 1 reviews	have you noticed a change in gas mileage? i don't know if you saw this, but i googled "low vacuum at idle" http://www.international-auto.com/fi...uum-gauges.cfm looks like a good resource. they mention that high performance cams will lower your vacuum. plus when you did your rebuild, did you use a thicker head gasket? which would cause lower compression.

03-11-2009, 01:27 PM	#7
SoguRacing Post Whore! Join Date: Nov 2007 Location: (714) Age: 39 Posts: 2,967 Trader Rating: (23) Rides Gallery: SoguRacing Feedback Score: 23 reviews	i do have a thicker headgasket. 1.1mm compared to the stock .8mm. I wouldn't think that would actually cause the vacuum to drop so significantly. by the way, the cams are hks step 1 256 not 264. __________________ Pre Tune Checkup! Compression,LeakDown,Vacuum Test $80. Cams Install: $180

03-11-2009, 01:55 PM	#8
slider2828 Post Whore! Join Date: Oct 2004 Location: San Francisco, CA Posts: 6,040 Trader Rating: (13) Feedback Score: 13 reviews	Yah it should not that bad..... Leak down test might tell you something and also do a piping tester... See if you have any leaks. __________________ Turn and Burn!

05-30-2010, 12:57 PM	#9
Muad-Dib Join Date: Nov 2007 Location: france Age: 41 Posts: 2 Trader Rating: (0) Feedback Score: 0 reviews	any news about the solution?