Issues Swapping a 3.0 CIS Engine into a 1971 911T?
 

I'm considering transplanting a stock 3.0 CIS (but with SSI heat exchangers and Leistritz muffler) into my 1971 911T. I've tried searching this forum as I'm sure this has been discussed before, but I'm not really coming up with any threads that address the issues involved and parts required for this swap.

Can anyone help with a summary of the issues?

Thanks,

Bob

Someone who has done the swap will offer the details but I can get things started.

To begin, you will need a new fuel tank, one from 73.5 or later, that has a swirl pot inside. The chances of finding a good used 73.5 tank are slim, but you can go with a later, larger capacity tank or even a new replacement, but it will not allow you to use your full size spare tire.

You will need a high pressure fuel pump and design a mount for it, preferably on the front beam near the tank outlets.

I'm not familiar with carb'd engines but I don't think they came with fuel accumulators as did the CIS engines. If not, you will need an accumulator also, along with a filter designed for the high pressure system. You can often find the plumbing connections for these in the For Sale section.

As far as wiring, someone else will have to chime in. Your new engine should have the engine harness and to match it to your chassis should not be difficult but you will need some new connections for the electrical devices (cold start injector, wur, aar, etc.) and maybe a few relays.

I think your original engine was carbureted. If so it would be much easier to just put carbs on your new 3.0 engine. The only changes you'd need are the proper clutch/flywheel to mate to your 901 tranny and a new ignition box to match the SC distributor. You can just retune your existing carbs.

-Andy

Go with carbs
 

I 2nd Eagledriver with the carbs. I had my 73 converted from MFI to CIS when I went to a 3.0 (a long time ago). 20 gallon tank & space saver spare too. My car spends a garage time between outings and CIS was better suited to my needs. CIS conversion was a lot of parts & changes that will be very expensive today. Lots of good threads about tuning the carbs for the new motor. Carbs look cooler anyway.:cool: You may want to save the 71 motor & 901 trans just in case you want to backdate for resale value. There is a lot of heated debate about updating to an early mech speedo 915 trans. I had my rebuilt 73 915 when I ran a stock 80 US 3.0 for moderate street use. Upgrading the trans may give you a lot more bang for the $$$ that a CIS conversion. Don't forget to install a Turbo dist rotor for the rev limiter. In ATL summer heat & humidity a front oil cooler will probably be on the short list after the motor conversion. Check out the PMB bolt-on Brembo caliper upgrade to slow it down without going broke.

Ossiblue,

I recently bought a '73 with a Euro 3.0 and it has the larger 85 ltr gas tank. I wondered why?

Why the large tank requirement?... what's a "swirl pot"?

Also... what are the acronyms... aar, wur? any other off the top?

thanks,

kj

Transplanting a 3.0 CIS into........
 

Bob,

This project has been done many times by numerous people. So it is not a novel undertaking. What you need to know is what components are essentially needed to run an SC engine. As an example, I have transplanted this 3.0 liter engine on a test stand after an engine rebuild for break-in test run.

http://forums.pelicanparts.com/uploa...1331613107.jpg

Ossiblue (Larry) has given you some of the components your '71 would need for a 3.0 liter conversion. Apparently, your 3.0 liter SC engine would need a 6-pin CDI, an auxiliary thermostat, auxiliary cooler, changing the stub axle or flange axle (trans), modifying the 14-pin connector, oil lines, etc.

Understanding the wiring diagrams for '71 and SC's would make electrical work conversion easier and faster.

Tony

I did exactly this, a row 3.0 into my 71 T. Traded carbs for the cis for simplicity and personal preference.

The only real consideration was transmission mating which wasn't a problem at all.

I didn't need to touch the tank, and a large Canton filter acts as an accumulator.

If you find you need any cis components I have 2 complete systems minus the cdi and lambda boxes. I have a cdi core, not sure it works.

Could be the tank was switched out although a larger tank was offered as an option back in 73--it was stock for the 73.5 RS.

There is no requirement for a larger tank, but it is necessary to have a swirl pot in a fuel injected engine to help prevent the return fuel, which is under high pressure, from forming a vacuum or whirlpool effect around the outlet causing a drawing in of air to the fuel pump. 73.5 tanks were the only year that had the set up for CIS and a capacity for a standard size spare. Later tanks had the swirl pot but were larger capacity and require an inflatable spare.

"Swirl pot" is explained above. Basically a structure inside the tank that directs the inflow of the returning fuel away from the outlet where the fuel is drawn out to the pump. There are pictures posted if you want to do a search to see what one looks like.

aar=auxiliary air regulator, one of the warm up devices on a CIS.

wur=warm up regulator or more properly, control pressure regulator, an essential device to control fuel pressures on all CIS engine systems.

Transmission mating experience........
 

John,

So a stock 3.0 SC engine would mate with the 71 T transmission with no modification? What early 911 transmissions (year) would not mate properly without modification to SC engines? Just curious. Thanks.

Tony

:)

The engine will mate up fine to your 71, including the clutch. 69 & earlier models had a different push type clutch that takes more pieces to make it work.

You will also need to swap the original 71 Engine Oil Cooler over to the SC motor so the Tank to Engine hoses will match. If you do not have the original 71 Cooler, I can help with an adapter pipe I make up to mate your oil tank to the later slip-on eng coolers.

If you plan a RS front oil cooler setup you may want to use 911SC lines & regulator under the rockers. Not cheap but by far the best way to go. Often they are available used here on Pelican. Of course you then must use a 30mm oil hose that goes up & over the tranny.

I can help you with any or all the Metric Oil Hoses you might need, along with any special fittings to mix & match the old (26mm) w the new (30mm).

I am doing a similar set of hoses right now for a customer, and can post photos if you like.

Len at Autosportengineering dot com

:)

I did this too.

:)

Here's a Hi-Rise set of hoses I made up for a fellow Pelican with a 71 911 needing extra rear tire clearance............

http://forums.pelicanparts.com/uploa...1332979101.jpg

He runs 245 rear tires needing lots of room, and this has worked out well.

Of course, he still has the original SC exhaust. For SSIs you either need a new and longer hose as noted above, or my new "Up n Over" hose assy being developed presently. This is routed up & over the trans, thus avoiding the clutch linkage of your early 911 tranny.

Hope this helps.

Len

:)

Don't forget the Tachometer. The '71's tach won't work with the 6 pin SC ignition unit. Don't forget with the new fuel pump you will need to add a return fuel line.

To to it right IMO a newer oil tank with larger capacity and the correct fittings is worth doing.

I'm planning on doing a 3.0 swap into my '71 as well. I'm going to use carbs and an MSD ignition. I already have a 915 and a Carrera oil tank.

:)

I am presently working on a custom 26mm fitting so that anyone who bought a set of used 911SC hard lines with cooler & engine hoses/lines can also use the 911SC return hose that probably came with the set.

I am able to re-hose this and add my custom Hose End with crimped sleeves so that it fits as the original.

Photos to come once its back from the platers.

Len at Autosportengineering dot com

:)

:)

Heres what I came up with for the Hose end at the early Oil Tank.................

http://forums.pelicanparts.com/uploa...1338299062.jpg

Its the larger M30 hose end combined with a M26x1.5 nipple & nut. This of course has to be crimped to the SC return line or whatever you choose to use. I will get this crimped and post a photo of the assembly shortly.

I also have started the "Up n Over" hose assy for the early cars. Here's what I have so far..............


http://forums.pelicanparts.com/uploa...1338300419.jpg


It the larger 30mm hose routed up & over the trans so there are no clutch linkage issues. I will make support brackets as the original early models used so all will be secure. At the other end it will end with a M30 Male supported with a bracket as used with the factory hard line for the 74 & SSI models.

More to come......Have a great Porsche day averyone.

Len

:)