CIS Question
 

Hi,

I have a 1977 911 S Targa with a 2.7 and CIS, I am planning on replacing the 2.7 with a 3.0 and I was wondering if the CIS from my 2.7 can be used with the 3.0?

Just to clarify, the 3.0 I am purchasing is a short block and I will be adding pistons/cylinders and heads and I am planning on running CIS but not sure if need to purchase/source a different CIS system or can I transplant my 2.7 CIS?

Kevin

I think people a lot more knowledgeable than me (which isn't saying much, necessarily) will ask "why" - probably why not EFI?

It sounds like you're going to a lot of trouble building the engine - do you just want an easy to trouble shoot system with lots of reference materials? My understanding is that a lot of the CIS components changed in 1978 when they went from the 2.7 to 3.0. I think the earlier, non-lamba 3.0 CIS would probably be the closest thing to your 2.7 CIS, so my assumption (purely an assumption) has been it was to account for the additional displacement. Those come up fairly regularly, and I think you can typically have the WUR and fuel distributor refurbished for around $1000 total or less, and probably a couple hundred more to have new lines installed on the factory fittings. If you're already spending several thousand on an engine, it might be much less frustrating in the long run to source a 78-79 3.0 CIS system and have it rebuilt. People do have great experiences with EFI and I think there are some folks on the board that offer some relatively plug and play kits.

No experiences on this. But you have to know - despite that the CIS of the 2.7 looks pretty equal to the CIS of the 3.0 / SC engines - there are plenty of differences. Any CIS system is fitted to the particular engine/car. And not only the CIS parts are different, but also some of the 'hardware', like the intake pipes... I guess to get an overview make your own research and compare all part numbers from engine and CIS between them to see which parts can be reused and which parts needed to be replaced. Do not underestimate the effort...probably it's better / cheaper /faster to get an 3.0 engine as much as complete incl. CIS...

Question: Why do you want to replace the 2.7? Is it toast?
Do you know that Porsche started in 2023 manufacturing the Mg crankcases again for the 2.7 engines? Guess this would be not that costly as a 'new' used engine (where you never know about its state) and it would have the advantage of keeping the car as much as original, which will be keep and raise its value because so many 2.7 have been 'upgraded' in the past and are no more being original...

Also a good info souce is the workshop manual for the CIS models with more details about their differences...

https://www.scribd.com/document/469896521/Porsche-911-Workshop-Manual-pdf

Thomas

My initial thoughts were to use an RHD ITB but after some discussion with William Knight, he recommended that it wouldn't be a waste to go ITB without upgrading the crank, connecting rods and other stuff.

I'm just looking for a nice bump over my 2.7 and with William's recommendation to use the M1 Cam, that is what I think i'll get.

Yes, my 2.7 had a leakdown test which indicated that two of the six pistons were leaking at the rings and as such requires a full rebuild.

Rather than dealing with the magnesium case, I thought about getting a 3.0 instead.

I also called Porsche Classic Canada about the new 2.7 Mag Case but was quoted $16K canadian :eek::eek:

Intake runner port sizes are different for the 2.7 CIS among other things. Better to just look for a 3.0 CIS system of which there are 2 variants , small 80-83 and big port 78-79. Which one do you have ?

I thought I saw a full CIS set up with out the block
For sale locally. Might be better to just plug that in
Instead. I'll try to find it.

It does make sense that the port sizes would be different and i'd need a 3.0 CIS instead.

Or u use a 3.0 from 80 to 83 US build, which comes with small ports as well.