76s backdate - cis off and carbs on
 

Ok guys , i have a euro 76s 2.7ltr that being backdated to a 74 rs / rsr . i want to remove the cis and add webbers or pmo's . now who has done the swap before and what bits are needed beyond the carbs and process please .

the search function is your friend...read and learn !

Here are a few for starters........ Just search and you will find.

http://forums.pelicanparts.com/porsche-911-technical-forum/630129-backdate-question-rs-rear-fenders.html

http://forums.pelicanparts.com/porsche-911-technical-forum/247099-update-c4-rsr-project.html

http://forums.pelicanparts.com/porsche-911-technical-forum/396207-my-1977-911-s-widebody-backdate-project.html

http://forums.pelicanparts.com/porsche-911-technical-forum/429999-78-sc-backdate-hybrid-hotrod.html

http://forums.pelicanparts.com/porsche-911-technical-forum/139484-ultimate-backdating-thread.html

All good links with bits of info , i found the how to remove the cis thread but is there a how to install the carbs and what needs changing ( electrical , fuel lines , etc...) it must have been done 100 times so a how to must be there?

Well, low pressure fuel pump and regulator.....gaskets, proper manifolds, good carbs that have butterflies that don't leak. Most people block the fuel return line.

carbs
 

PMO fuel pressure regulator Is a must, It also is a bypass fuel regulator that accommodates you with a fuel return line. It is only abt. $90 worth every penny.
Good Luck Bob.

does the main metal fuel lines in the tunnel need changing or are they fine for dia?

also coil and distrib. need changing ?

If you are going to use the CIS fuel pump you will need a pressure regulator, as suggested PMO makes a good one I have it on my 83SC with PMO carbs. Yes you can use the fuel line in the tunnel. You will need proper manifolds, linkage, air cleaners. You can use the coil as is but you really should have the distributor " set up " to run with carbs. Other than that really no additional electrical changes. You might find you'll go one heat range hotter on the spark plugs to prevent fouling it really depends on your tune. The motor will be a good runner but will run even better if/when you change pistons and cams to best utilize the carbs. Good luck.

Thanks for the good solid answers , just what i needed to know

John, my RS spec 2.7 started as a CIS engine.

I had the advantage of the engine going into an older car with the low pressure fuel pump (facet) and wiring. It's up to you if you run only one fuel line or two, but as mentioned you'll need a pressure regulator if using the CIS pump.

The heads may have the CIS/MFI injector cut-outs, there's no need to worry about having them filled in. You probably should add some extra fuel filtration (carbies hate debris of any kind). I had the distributor recurved to suit and run hotter plugs. Consider getting the PMO heat isolators that go between the heads and the manifolds - they make a difference in summer (even in NZ ;) )

I am currently doing this conversion, why do you say not to worry about the CIS injector cut outs? I have the PMO heat insulators and original Porsche manifolds and I was under the impression filling the injector cut outs was critical to prevent the possiblity of a lean condition burning your valves?

yes just advised a similar thing , who can advise here ? i have std mainfold onto cis heads with the insulator to be installed and have been advised that the insulator will bend and cause issues if unsupported ?

I've responded to John on a PM, but my experience (so far) has been positive. I have CIS heads, insulation blocks and 36mm ports. Engine is 7 years old and I haven't struck the issue... I use Hylomar to assist the seal.

Well long time getting this done , and I need a couple of further questions answered please.
I have taken off the cis which was 35mm intake sized but the heads measure 37.5mm intake ? What am I missing here

Secondly what is recommend to do with all the cis wires and plugs ? Do I just deloom back to the plug and remove all , is there any wires that need to stay or be convereted ?
What should happen to the heat sender in the cam cover , do I remove and blank off ?

If you never want to go back to CIS and you don't plan on selling the car to someone that might want to go back to CIS then go ahead and remove all the CIS wiring it will clean up the engine bay. When I did my 911SC I just neatly bundled all the wiring but at some point in time I'll remove it as I'm never going back. In regards to the port size I would say you can gently massage the carb intake manifolds with a Dremel tool to match the size of the port. You may or may not have to do the same to the insulators, I can't remember it's been a while. Good luck.SmileWavy

Did you notice the tunnel line fittings are not AN (which is what the PMO carbs, ITB's, and regulator uses) and require special adapters yet? There is a guy on here that I think makes the lines with proper fittings....

i noticed that the fuel lines have connections , should be able to convert with the pipe fitting shop here