philip77o

Hi, I'm sorry to make a new thread each day, I'm in the middle of doing venturi delete and some other stuff and I'm trying to understand how everything works.

I've manage to figure out 95% of the vacuum routing and when I read the vacuum diagram I know where everyting is going. So far I've found a couple of loose hose clamps and it is obvious that it was the cause of my bouncing iddle. The wastegate hose was a little loose on the cycling valve nozzle as well as the iddle control valve output hose.

But there are 2 things that I can't figure out, the first is that small vacuum line that goes out from the brake booster line, there's a black n blue check valve, then a factory T fitting, one side goes to the vacuum reservoir in the battery compartment, and the other side is an orange factory vacuum line that goes into the fire wall... what is that line ? Another light blue line is geting out of the firewall and it has been blanked by the PO, I think it's A/C related... (A/C has been delete by PO)

The other thing I don't understand is how MBC works ? My car has a custom chip set, probably Steve R chips, with a factory banjo bolt (empty banjo bolt?), stock wastegate. There's a homemade MBC on the wastegate line
(on the section before cycling valve) I didnt test it yet. Does it need to be fully close for max boost ? or fully open ? It doesnt looks very accurate, the valve is wether fully open or closed.

Again I'm sorry to pop out a thread every day, I do a lot of research but I can't find everything that I want to know.

mahoney944

The blue and black valve is a valve that blocks off your heator core vac system during boost, but allows it to be open in vaccum pressure. lindsey racing shows a good reprsentation of how everything goes in this picture. Also on a single port setup the more pressure you send to your wastgate the sooner it opens and the further it opens, this causes low boost. Mind you that this image shows a duel port wastegate setup, and a stock wg is a single port. so ignore the duel port if your using the stock wastgate

philip77o

Thanks, a saw this diagram

Does the heater core valve is under the dash ? I have an 86 951, I've seen a couple of picture from other engine bays but mine isnt like that, I don't have anything between the engine and firewall, the red factory vacuum line is going thru the firewall... the blue one is blanked... (I'm not reffering to the diagram's colors, the vacuum line is orange/red...

ender928

Can someone identify what I have circled in Black with the three green hoses? First time Turbo owner still learning.

markl951

That would be the cycling valve.
Get yourself a copy of the parts manual...
http://www.porsche.com/all/media/pdf...88_KATALOG.pdf

ender928

Figured it out yesterday afternoon and ordered from 944online. Thank you for the PDF!

Nice to see a fellow rennlister in Seattle I should have my 951 out here mid June hopefully meet you in person sometime.

markl951

When making performance mods, the cycling valve is typically one of the first things that gets deleted. If you want to keep your car completely stock then you'll want to have it installed.

I'll be out at Pacific Raceways this weekend racing the NA car.