Porsche-O-Phile

Does anyone have a schematic or some kind of sketch showing the routing of the air and vaccum hose routings around the intake for an '86 951? I specifically need to know which hoses go to the idle stabilizer, venturi, intake, j-boot, and intercooler pipe. My diagrams don't show these. Thanks!

Sam Lin

These are for an updated car, which I'd advise you do if possible, it simplifies things a lot, but hopefully they help you in either case.

Edit: Thanks to whoever made that diagram, I've long forgotten where I got it from.

Sam

Porsche-O-Phile

Thanks that's pretty good. Is that the one from the Lindsey vaccum hoses? I had one of 'em but I used the hoses on my n/a car and chucked the diagram because at the time I didn't have a 951. . .

Only question is where in the system is the venturi? I might do the update at some point but right now I'm just trying to troubleshoot and I need to know where everything is to make sure I have it right. What prompted this is (1) the car won't idle correctly, (2) there is a hose (attaches to intercooler pipe across from diverter valve) that is split down the side, so I plugged it off for now - the dealer can't find this hose in their diagrams to order a new one. I think the other end goes to the venturi but I'm not sure. (3) the two hoses that connect to the intake from underneath it are likewise quite old and I suspect are either leaking or about to start any time. I want to make sure I know where the heck they go so I order the correct stuff. Paragon already screwed this up twice trying to explain on the phone which hoses I needed and sending the wrong ones. I kept what they sent, figuring if one is bad they're probably all about to go bad and it's worth replacing 'em, but it isn't exactly helping me solve the immediate problem.

Photos would be useful also if anybody's got 'em with the intake on and the intake off showing how things are connected underneath. Thanks.

Ben Z.

OZ951 made the diagram, I altered it (crappily). Here's the best jpeg I can make from the original bitmap:



The y-shaped deal under the intake manifold is the venturi. Mine was just held in place my the tubing, not sure if that's how it's supposed to be. Everything in Oz's diagram is pretty much right on.

Oz- did you ever get any royalties from lindsey?

Porsche-O-Phile

Perfect. Much thanks. That has the "missing" information I'm trying to pin down. I'll rip into it tonight after the WS game. Thanks again.

Porsche-O-Phile

OK someone tell me if I understand this correctly - the manifold has likely lower pressure in it than at the intervcooler pipe, which is in front of the throttle plate. When the throttle plate is closed or partially closed, the air "backs up" in front of it due to the restriction causing a higher pressure there than exists after the throttle plate.

As such, there is a flow created from the intercooler pipe (via the black line) to the "y" connector with the curved elbow (I'm guessing this is the venturi), to the idle stabilizer to the manifold. In a venturi, pressure is lowest at the midpoint, so the flow mentioned above creates a "suction" on the red line coming off of the curved elbow to the "Y" piece to the manifold.

So how exactly do these various pieces regulate idle? It seems that the "loop" described above would actually be ineffective in an idle surge which would create an increase in manifold pressure and decrease in pressure gradient between the intercooler pipe and manifold via the idle stabilizer. How's it work?

PorscheDoc

Vacuum Line Writeup

Its about a meg, so it takes a second to open.

Sam Lin

The stabilizer lets more or less air in to simulate throttle opening to regulate idle - it is controlled electronically through DME, not by any pressure difference before/after TB.

Sam

OZ951

Hey Ben, No there have been no royalties or favours from anyone including Lindsey racing, when I first found out they were including it with the kits they were selling, I emailed Dave Lindsey about it, he claimed he did not know where the diagram came from. I don't know if he subsequently put an acknowledgement on it.

When Travis at Rennbay included the link on his web page he was quick to acknowledge the source (well after I mentioned it to him anyway).

Travis - sflraver

If something looks interesting enough to post and I don't know where it came from exactly I just put "Posted on Rennlist" at the head. Someone usually claims it and asks to be kept anonymous or to have their name at the top.