CIS for 2.2L T Engine

Bob Ashlock · 06-24-2011, 09:51 AM

Something I have been considering for a while. I have a 1970 2.2L 911T engine with Webers installed in my '66 912. Is it possible to install a CIS system on this engine? (for example, from a '74 2.7L) Studying photos, it appears the injectors are fairly high up in the manifolds, but I can't tell if the heads still may need a recess in the intake ports. Will my stock "T" cams work OK, or is there too much overlap for the CIS system to work properly? Any other issues?

moneymanager · 06-24-2011, 01:28 PM

I think the cams would be marginal on even a T. Take a look at the cam timing differences between the basic 74 Porsche and the 72 or 73 (non CIS) T. But more to the point, why would you want to substitute the clunky, no-throttle-response CIS system for some great Webers?

Bob Ashlock · 05:33 PM

Thanks for the response, I was considering the CIS system simply for better fuel economy and improved emissions. I'm curious if anybody has actually ever tried using the CIS system on a 2.2L T engine and whether it worked satisfactorily. I have spent a considerable amount of time tweaking my Webers. They idle reasonably well, have no flat spots and make good power, but I'm always looking for improvements. It's true these carbs are great for making power, but they do have their limitations in terms of fine tuning for a perfect mix under all conditions. I have an AFR gauge continuously monitoring so its easy to see the behavior of the carbs.

moneymanager · 06-24-2011, 07:07 PM

Others will chime in but I wouldn't call CIS an improvement, especially the early versions. Over the years a lot of bells and whistles were nailed onto the original design in an effort to make an acceptable product. THis yielded a device at least as complicated as a Weber with little ability to fine tune it, middling performance, but decent for the era emissions. With the advantage of history, i'd give it a C+.
Switching to CIS and changing out your cams so the car will run decently will cost at least $5k, and likely more when you get into all the "while I'm in there..."s...in return I'll bet you save $100 a year in gasoline.
If I were thinking about the changes you are seeking, I'd be looking at some sort of modern injection system for better performance, emissions, and economy.

Bob Ashlock · 06-24-2011, 08:03 PM

Good points you make about the continuous add-ons and improvements to the CIS system. I once owned a '74 911S with CIS and (at that time) I felt it was a great system and a major improvement over carburetors. But of course that recollection is 30 years old now! Anyway, the only way I would attempt this is if I could bolt it on without changing the cams. Knowing now that is necessary, then your point is well-made that there would be so much "while I'm in there" work that the whole thing would be a ridiculous experiment!

Walt Fricke · 06-24-2011, 08:49 PM

Bob

You can pick up a CIS fairly cheaply, and convert it to Megasquirt or one of the low buck DIY electronic fuel injection systems. That can be made to give you better fuel economy and still use your cams.

However, you are correct - the CIS heads have grooves up at the port to accept the low mounted injectors. For EFI you'd be using different injectors, not as long, but I think you would still find that you are getting shrouding from the port wall.

It would be a bold man who decided to install these grooves in the heads while they were still on the motor (or even still in the car). You might be better off finding a set of 2.7 heads for this purpose, should you decide to go that far.

Lots of enthusiastic home brew EFI guys out there to mentor you.

moneymanager · 06-25-2011, 06:45 AM

Good to have Walt chime in here. He taught me most of what I know about the CIS as I tried to tame a 73.5 a while back and, as usual, his advice is spot on.

Walt Fricke · 06-25-2011, 09:13 PM

I was going to mention the 73.5, but hesitated because my knowledge of its quirks pales compared with Jim's. So I don't know if there would be any advantage to it as an intake system. Aren't the injectors actually in the heads, or in collars which are inserted into the heads, and not in the manifolds? That would make them bad candidates.

Another option would be to purchase manifolds and EFI throttle bodies. I think you are into ~$2,000 for that hardware even before you buy injectors and make up an ECU. So there would be cost tradeoffs all up and down the line here.

If I remember correctly, I think you can buy injectors to use with Holley 4 barrel carbs, but I've not heard of any way to do such a thing with Webers.

So this sounds like a paper project to delight a first year engineering professor making up a project question: how to get value for your results, since it seems you can't just plop the CIS manifold onto the existing heads.

Rough guess - maybe you could pick up a decent 3.0 for less than the cost of any of the hypothesized conversions? Need a different fuel pump, and a fuel return line, and some other stuff, but otherwise pretty much a plug-in.

Bob Ashlock · 06-25-2011, 09:21 PM

Yep, I agree that kind of money could be much better spent in a number of ways. I am grateful for the guidance. The curiosity I had about the basic practicality and whether anyone had ever done this is satisfied. It doesn't sound at all reasonable.

moneymanager · 06-26-2011, 06:43 AM

IIRC, the 73.5 heads contain "collars" which carry the injectors. The injectors themselves are not like those on the 74 and later cars. That would make these even poorer candidates as Walt suggests.

Bobboloo · Bobboloo's Garage

The cheapest way to do this conversion is to buy a CIS engine and swap it. You should be able to buy a motor cheaper than the cost of converting your motor. Then you can sell the 2.2 longblock, carbs and fan assembly seperately. You might even come out ahead an the deal.

Jay Laifman · 06-27-2011, 02:53 PM

Well, I always like to pop up on CIS things - mostly since I love my 73.5 CIS 911, which I've driven regularly for over 25 years now. Just as smooth and drivable as ever. Yeah, some guys will tell you that it can't be modified to increase the hp. Sure. But, sometimes some things just don't need any changes - including the car Pete Zimmerman wrote as Porsche's first "10."

I wonder what ratio of miles 2.4 CIS cars are getting compared to MFI cars.

Anyway, lots of other reasons why you can't put a CIS on top of the other block. Note that the CIS pistons are special too. They have a dished area to control the spray from the injector. I think the cam had to be reduced both because the engine was more efficient and to avoid hitting that special piston.

I think there are plenty of CIS engines that come up from time to time from those guys who want that hotter engine. So, you should be able to pick one up for a good price. The '74 2.7 S CIS engine is particularly nice. Don't know how frequently they come up. But, as you go that direction, there is always a 3.0 CIS engine to drop in there, with its even more robust bottom end.

Jay