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craigerz
 
Join Date: Feb 2008
Location: 15 miles no. of Salt Lake City
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Porsche Crest Pop off valve needed on 930?

I know a pop off valve is almost mandatory on a regular CIS inj. car due to backfiring, yet I have heard about '0' concerning 930's w/ the same injection...
Am I missing something here? Is it needed, or just a good idea, or a waste of time... Thanks in advance for your input, Craig
Old 04-27-2008, 04:26 PM
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wcc wcc is offline
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A search may be needed here. I asked the same question a while ago.

The bottom line, and what I was told, was that a pop off valve on a 930 isn't required because of the intercooler.

Basically, the bottom line is the pop-off valve and back fire issues don't apply to the 930.
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Old 04-27-2008, 06:36 PM
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...not needed on a 930
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Old 04-27-2008, 07:13 PM
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It's been said the intake is too long to cause any problems.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

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Old 05-02-2008, 12:12 PM
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It's "needed" but you have a technical problem in that it must be spring backloaded above whatever boost you are running or you got a monster big air leak!! So not practical. Would take a whole new POP valve. Almost a wategate in the intake!!!

Vacuum and a small spring keeps ithe POP valve closed in the NA cars. Turbo with that POP valve and it'd blow open at 1psi and your motor will quit --- no air....
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Old 05-06-2008, 06:24 AM
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It's not needed on 930. SC has backfire problem due to very short intake tract. 930 has intake plumbing that is at least 6 times longer. If backfire was to propagate from engine to airbox it would need to go trough intercooler capilaries, then backwards trough turbo-impeller, then trough lot's of plumbing, then trough CIS barndoor and first then it would come to filter box, which is made of metal and much bigger than SC box made of plastic.


So no, 930 doesn't need a pop off valve and never will. Not in theory and not in practice.
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Old 05-06-2008, 06:45 AM
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Quote:
Originally Posted by NathanUK View Post
It's been said the intake is too long to cause any problems.
Yep.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 05-07-2008, 11:51 AM
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Also, the air flow through the venturi and sensor plate is the opposite direction and downward on a 930 compared to a normally aspirated motor, and there is a large rubber stop to cushion the plate if there is a big backfire upwards.

There's also no plastic air box, the housing below the sensor plate is thick cast aluminum with spring loaded screws holding it together, and a metal air cleaner housing above and upstream of the sensor plate.
Old 05-07-2008, 12:02 PM
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