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Charlienofun Charlienofun is offline
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Join Date: Oct 2007
Posts: 60
Originally Posted by JFairman View Post
Early 911 turbo's had a second saucer shaped throttle body bypass valve that looks alot like a deceleration valve without the 3rd small accuating intake manifold vacuum line going to it.

It was mounted back behind the auxiliary air slide cold start valve and you can't really see it with the factory aircleaner in place.

I've never seen one other than occasional pictures and I don't know what opens it so i can only guess air pressure in the intercooler when you let off the throttle quickly opens it letting air bypass the throttle body during upshifts and initial deceleration.
Probably an emissions and anti turbo compressor surge device.

They got rid of it by 1986 when the turbo came back to US dealers with more emission controls.
Now that I think about it I believe I have seen this in a picture posted on here but thought that was only on the early cars mines an 87.

So if that thing exist my '87 actually has three devices to alleviate compressor surge when the throttle quickly closes.

1: the pop off valve (Blow off valve)
2: the decel valve thats bolted to the back of the "pop off valve"
3: the one were talking about

I'm going to take her all apart during the holiday so I should be able to figure it out once and for all. I wonder if the car ended up with an earlier intercooler than it originally came with and whats why I have the two ports on the stock unit. I have been running the B&B intercooler for a few years it certainly does not have and 2nd outlet in that spot just the one for the idle valve.

'87 930
Old 12-11-2009, 02:45 PM
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