"Update" Cold Start Valve for 911 CIS car?

[Jay Laifman]

In working through issues on my 1973.5 CIS 911, I see that there were some developments in connection with the gas lines, and the cold start valve.

In particular, the hose from the distributor to the cold start valve was a rubber hose for a 73.5 and 74 to some point. The CSV had a hose connector for the early ones, then a banjo fitting for the later ones - and the rubber line was changed to plastic. Seeing as how gas fires from rubber hoses that break is a big danger for 911s, and that the factory improved this, is there any reason to do this or not do this for my 73? I have all the parts to do it.

I note there were three ways the factory did this. On my 73.5, the CSV hose had its own port.

Sometime around 1974, there was still a rubber hose and the same CSV, but no longer a port. So it had a special banjo fitting with two ports, one for the inlet, one for the CSV (these are not pictures of my car)


Sometime after that, the rubber hose from the plastic gas line to the cold start valve was changed to a polyamide hard plastic tube. And the CSV was changed to a banjo fitting.




One thing I also noticed is that in 1974, Porsche added a flange to the CSV. At first the flange was just that, and the port off of it was blocked off. But then in later years, that port is actually used. I wonder if there is a reason to add that at this time too. If there is any benefit to getting the CSV to not be as deep into the air box.
https://www.youtube.com/watch?v=Nc-lJjwmovQ

Anyone have any thoughts on making the CSV hose into a pipe, and whether the CSV flange is valuable?

[E Sully]

It's an interesting question. Changing to the Poly line would seem like a good move due to the fuel pressure. I don't know why Bosch didn't do it originally since they found it necessary for the other high pressure lines.
The spacer flange leaves a few questions. There are 2 parts, the one used first is closed, but with a later part number 911 110 264 01. The functional one used later but with an earlier number 911 110 264 00. It's strange to have a piece made for a hose, but not functional. Was Porsche working to eliminate the hand throttle sooner but held it up a while till they got it right, so made the piece for an additional air line but closed off?
I don't think using the flange without adding the AAV, AAR, etc would make a difference, and even then it seems you would want the spider pipe set up to be effective. With the 73.5 CIS you are a bit limited, as it is not available with the spider. The other replacement air boxes with spider seem to be one for '74-77 & '80-83, and the one for the large inlet '78-79. Spider only works with working adapter and AAR AAV.

[Jay Laifman]

I had assumed the spacer was to pull the CSV nozzle out of the flow of air coming down from the intake. But now that I see the spider all "in the way," it makes the nozzle seem like nothing. So it seems that if I want the poly line, I can just use the newer CSV and mount it directly like the 73.5 CSV.

The CSV line is also narrowed from the main line going from the gas filter to the fuel distributor. As I recall from physics, the amount of pressure is still the same in the smaller line. But what I don't recall, is if that smaller line with the same pressure has less surface area so less risk of breach?

[eastbay]

Just re plumb with ethanol safe barrier fuel line. That's what I did on my 74.

Heck, the old lines lasted 30 some years with no leaks.

I've owned cars with either the rubber CIS lines or the Poly lines and I see no advantage to the Poly. Well, unless you like a whole lot of effort to swap over.

Kind of like making the effort to swap to the SC style metal injector lines, why?

[Schulisco]

Concerning the change from rubber/poly lines to steel lines I can suspect that this was related to the fuel pulsations by the fuel pump, still touchable when engine is running, the fuel accumulator flattens them, but obviously not enough. They also increased the volume of the FA over time also on other cars. Some people claim that surging engines could be cured with the steel lines. Porsche transferred experiences from the 930 to the 911..Also they will last much longer. Don't forget that a correct pressure is key on a CIS...
E.g. the fuel lines on other CIS cars like an Audi 4000CS / Audi 90 Type 81 from 1985 has steel braided fuel lines...I suppose that it's related to heat stress as they're mounted on top of the engine and above the exhaust manifold and secondly due to the fuel pulsations.

I have no secured information on the CSV flange if it matters to mount the CSV with or without the flange. What I know is that Porsche struggled on blown airboxes when starting the engine. Porsche claimed the CSV as the culprit because the fuel sprayed did not distributed evenly on every intake runner. Instead the fuel enriched those intake runners first sucking the air which leads to backfires and blown airboxes. Therefote Porsche introduced the spider. Probably the flange was introduced before the spider to manage a better distribution of the fuel before they introduced the spider. Also the air line coming from AAR and intake boot helps mistifying the fuel.

Thomas