rb20det vacuum and boost lines
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Powered Bya Skyline
- Posts: 53
- Joined: Mon Dec 06, 2010 1:30 pm
- Car: 1991 nissan 240sx hatch (ka24de, daily)
1990 nissan 240sx hatch (rb20det, drift car)
rb20det vacuum and boost lines
does anyone have a diagram of vacuum and boost lines of where they go and connect to? i have some type of vacuum leak and i am currently at 12in of mercury.. any ideas? my plain was to just check over everything but i figured the best beat would be to try and get a diagram of lines
Re: rb20det vacuum and boost lines
there are only 5 vacuum ports on an rb20 intake manifold:
1 front - dedicated to fpr.
2 tb side - factory bypass valve and carbon canister evac.
2 rear - small is factory boost gauge, large brake booster.
There is a hidden vac nipple under the tb which most people miss, it is for the carbon canister...do not use this as a manifold reference. Cap this.
PCV hoses are prone to cracking as well as the idle/coldstart hoses...try not to remove these if you can as they are old and frail.
Improper base timing will also cause low vac conditions, rpm on a modified tach (or consult) should be ~650 hot and timing set to 15*.
1 front - dedicated to fpr.
2 tb side - factory bypass valve and carbon canister evac.
2 rear - small is factory boost gauge, large brake booster.
There is a hidden vac nipple under the tb which most people miss, it is for the carbon canister...do not use this as a manifold reference. Cap this.
PCV hoses are prone to cracking as well as the idle/coldstart hoses...try not to remove these if you can as they are old and frail.
Improper base timing will also cause low vac conditions, rpm on a modified tach (or consult) should be ~650 hot and timing set to 15*.
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Powered Bya Skyline
- Posts: 53
- Joined: Mon Dec 06, 2010 1:30 pm
- Car: 1991 nissan 240sx hatch (ka24de, daily)
1990 nissan 240sx hatch (rb20det, drift car)
Re: rb20det vacuum and boost lines
anther quick question.. how much is the stock tach for a ka off compared to a rb? does that amount change the higher the rpms raise?
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RustspecS13
- Posts: 928
- Joined: Sat Sep 08, 2007 5:30 pm
- Car: '74 260z and '88 300zx turbo
Re: rb20det vacuum and boost lines
its 1.5x faster. Since theres 2 more cylinders it reads 6 fires instead of 4. Its pretty funny watching it hit over 10K on a 4cyl tach. Really messes with the passengers 
~Alex
~Alex
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Powered Bya Skyline
- Posts: 53
- Joined: Mon Dec 06, 2010 1:30 pm
- Car: 1991 nissan 240sx hatch (ka24de, daily)
1990 nissan 240sx hatch (rb20det, drift car)
Re: rb20det vacuum and boost lines
i think that might be some of my problem for my high idle lol.. that gives me an idea.. thanks for the thought rustspec..
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ST240
- Posts: 575
- Joined: Sun Aug 04, 2002 11:45 am
- Car: RB30DET Nissan S13
'01 Nissan Pathfinder - Location: Edmonton, Canada
Re: rb20det vacuum and boost lines
I've adjusted my stock DOHC tach via the pot on the back and its pretty close to what consult reads. Maybe off by up to 200 or so RPM but it works.
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Powered Bya Skyline
- Posts: 53
- Joined: Mon Dec 06, 2010 1:30 pm
- Car: 1991 nissan 240sx hatch (ka24de, daily)
1990 nissan 240sx hatch (rb20det, drift car)
Re: rb20det vacuum and boost lines
carl, on the base timing, which line should the pulley (crank) be set on for the correct timing? the car runs perfect besides the idle and the low vacuum concern. i did block off the small nipple under the throttle and that helped the vacuum go to around 14 15 in. of mercury. sorry for the newb question, first rb and still learning.. cant go wrong with asking questions. any and all input is appreciated. oh one more thing. would only a turbo elbow for an exhaust affect idle?