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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,267
Originally Posted by 911st View Post
Yes, I was going to remove mine for the same reason. I had a 914 and removing it helped a bunch.

However, reducing rpms between shifts is not the best performance goal on a turbo. But, removing it dose make daily driving a bit more palatable. Especially if you have one that is not working very well.

Yes it may help emissions some but on a turbo it also reduces the shock the turbos can get when the throttle plate is slammed shut. Letting some air pass around the throttle plate helps to keep boost up between shifts.

The Compressor Bypass Valve also helps reduce lag and stress on the turbo.

One passes air around the throttle plate, the other around the compressor wheel. Together there is more benefit than if there is just one. Look at the size of the tubes plumbed into both.

One well respected tuner actually used to relocate the deaccel valve to make it work more better. I wish I knew what he was doing and how.

I do not know how well they do or do not work with the old style 930 set up. They have a different over-boost set up. I am used to the C2T set up which is the same as 930's with aftermarket IC's.

I understand how all of it works and when people talk about it here they are coming from different year cars which have some different parts, etc, and some folks don't actually have a 930, instead they have a 930 motor in a different 911 chassis so some of these parts are a little different again.

My car is not stock and that changes the way mine reacts again...
Previous owner was tracking the car and he put in powerhaus group B cams which make lots of power from 4500-7200 rpm and none below 4000 rpm. feels like 50 horsepower until 4000rpm and then it's 400+hp all at once.
These cams suck for street driving but thats whats in there right now. I have a set of SC330 cams and 12 rebuilt rockers but havn't installed them yet
It also has B&B headers and muffler, and I put in a garretson long neck intercooler with C2type recirculation blow off valve in the big rubber elbow. It is a Turbo XS valve to replace the bosch unit and it has a brass piston and adjustable spring tension.
The car also has a 4 month old K27HFS turbo with adjustable boost valve set at 1.1bar, and an IA modified fuel head, and Brain Leasks adjustable control pressure regulator or WUR and an rpm switch operated solenoid in the boost signal hose going to the WUR.
I have the deceleration valve in there right now hooked up between the intercooler and the intake manifold, but at this time I have the small vacuum line that operates it disconnected and plugged so it never opens and is the same as plugging the 2 bigger hoses that bypass the throttle body.

The turbo XS cast aluminum C2 type blow off valve with brass piston and adjustable spring tension is there, hooked up the normal way and working just fine.
I can put the vacuum line back on to the decleration valve in about 10 seconds, it's easy when you have the long neck intercooler (because there is no intermediate manifold under there taking up all the room) and have it fully operational again but it doesn't have any noticable effect on lag that I can tell.
Now that you have said there is a difference i'll put the vacuum line back on it and try it and see...

What I do notice and don't like is when driving around town at normal legal speeds the engine decelerates between shifts slower than
I like and I hate that... I want it to decelerate as fast as possible with that heavy stock flywheel in there so I can shift to the next gear quicker and have the revs perfectly matched.

I'm coming from light flywheel multi weber carbed cars in the past and I don't want slow engine deceleration, and there is no turbo effect on my car when driving around town so turbo lag is not an issue. I never get into any boost at all because there is none until 4500rpm with these cams.
I have to be on open road or entrance ramp to get into boost and then it's pretty intense.

I'm still experimenting with system pressures with the shims in the IA head and then trying different threshold, steady cruise and boost enrichment settings on Brian's adjustable WUR, and rpm switch points on the summit racing digital rpm switch. It takes time though and lots of test runs...

I enjoy reading your posts on 930 CIS.
Hopefully I'll get mine working the way I want it someday.
I have the LC-1 and G3 gauge installed so I can monitor AFR's.

Thanks for your cool information.
Old 06-09-2008, 11:19 PM
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