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2.7 cis upgrade

Looking for about 210-220 horsepower from a 2.7 cis 1977 911s. How much will the ssi exchangers and muffler bring alone. What is the best displacement cam upgrade for this engine, with CIS. All known reliability upgrades are done. Car is stock now.

Old 05-10-2004, 11:23 AM
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Can't be done - not with your two restraints, CIS and 2.7 displacement (okay, maybe if you bolt a turbo on it).

You need to either increase displacement, or replace the CIS system. The cams that are used with CIS (not a high-performance system) are relatively mild. The 1973 911RS engine got about 210 HP (you can probably get more by bumping the compression higher than the stock 8.5:1) with Mechanical Fuel Injection, which has individual throttle boddies, and can run a hotter camshaft without affecting the fuel injection system.

This is all explained in my Engine Rebuild book (http://www.101projects.com).

The 1974 911 & 911S engines used the older-style heat exchangers, which are nearly identical in design to the SSIs. As such, the 911S engine was rated at 175 HP min. I would suspect that a 2.7 CIS running SSIs would put out about 175.

Now, you can upgrade to some higher compression JE pistons, and run a 964 cam in your engine, but I doubt that you would get 210 out of it. See this tech article by Noah for more info:

http://www.pelicanparts.com/techarticles/911_engine_rebuild/911_engine_rebuild2.htm

Hope this helps,

Wayne
Old 05-10-2004, 12:32 PM
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The Webcam 20/21's are about as radical as you'll be able to get with the CIS and they may still only get you close to 200 HP. Their duration is between an MFI'd E and S, but they have a really wide lob angle to keep the overlap to only 8 degrees (versus the 964's 9 degrees). But you'll need new pistons to boost the static CR (given the long duration of the cams) and not have the valves hit the pistons. In the end you may still find that the CIS system limits your airflow so that you'll never get to 200 no matter what you do to the engine. It's also not clear how drivable that engine would be. There's a whole bunch of details that you'd need to work out.

It's an interesting configuration that people often ask about (since the CIS 2.7's are pretty cheap right now), but no one has really worked out how to make it work.
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Last edited by jluetjen; 05-10-2004 at 01:11 PM..
Old 05-10-2004, 01:09 PM
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Quote:
Originally Posted by Wayne 962 View Post
Can't be done - not with your two restraints, CIS and 2.7 displacement (okay, maybe if you bolt a turbo on it).

You need to either increase displacement, or replace the CIS system. The cams that are used with CIS (not a high-performance system) are relatively mild. The 1973 911RS engine got about 210 HP (you can probably get more by bumping the compression higher than the stock 8.5:1) with Mechanical Fuel Injection, which has individual throttle boddies, and can run a hotter camshaft without affecting the fuel injection system.

This is all explained in my Engine Rebuild book (Do-it-Yourself Project Books for Porsche, BMW, and MINI | Water-cooled and Air-Cooled Porsche Books | E30 and E36 3-Series BMW Books).

The 1974 911 & 911S engines used the older-style heat exchangers, which are nearly identical in design to the SSIs. As such, the 911S engine was rated at 175 HP min. I would suspect that a 2.7 CIS running SSIs would put out about 175.

Now, you can upgrade to some higher compression JE pistons, and run a 964 cam in your engine, but I doubt that you would get 210 out of it. See this tech article by Noah for more info:

http://www.pelicanparts.com/techarticles/911_engine_rebuild/911_engine_rebuild2.htm

Hope this helps,

Wayne
Hi Wayne, the author on the article you reference says

"...I dyno'd the car on a Dynojet and achieved 203 rear-wheel horsepower and 176 pound-feet of torque-all without doing anything to the CIS. Figuring 15-20 percent drivetrain power loss, this engine produces in the ballpark of 230-240 horsepower..."

Is that realistic ?

Also, what does he mean when he says that "...my car had been outfitted with a 2.7 fuel distributor, which surely robbed my engine of at least a few ponies"

My car is a 1975 2.7, what is wrong with that fuel distributor?

Many thanks in advance.
Old 06-28-2020, 09:09 PM
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Old 06-30-2020, 08:01 PM
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Nius - Wayne was describing a Carrera 3.0, not a 2.7. With 9.8:1 compression pistons those rear wheel HP numbers are believable, especially if a really good exhaust system with no muffler is used.

Won't happen on a 2.7.
Old 07-07-2020, 09:16 PM
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Thanks Walt.
Are there any articles or publications where I can get a better understanding of the 2.7 CIS engine ?
I'm in the process of changing the stock exhausts to the SSI ones. The cam and the new pistons will have to wait for the time being.
Thanks for the help.
Old 07-12-2020, 12:59 AM
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Mein Herr:
There is probably more literature on the CIS than you may want to read. A good start would be Bosch publications. Your 2.7's CIS is a bit less complicated than later ones, which simplifies things. Bosch had a pamphlet describing how it worked, what can be adjusted, and had one of those tree diagrams for finding (and thus fixing) faults. You can find and download a couple of these easily enough.

Volume III of the factory workshop manual also has a good discussion of CIS, how it works, how to adjust it.

CIS can be fairly simple to keep working as it should. For engine efficiency, be it power, fuel mileage, or passing government inspections you need a way of checking the air/fuel mixture. Nowadays, air fuel gauges are less expensive, I think, than CO/HC testers. You adjust this with the 3mm Allen wrench you've seen mentioned. And there are techniques you can use to get pretty close without the instrumentation.

For that matter, you can take a car to a shop with the right stuff, and have them adjust the air fuel mixture. Quick and simple usually.

For the general condition of the system you need the gauge and plumbing (shown in the Bosch literature and elsewhere) to check system pressure and cold and warm control pressures, as well as how long pressure stays in the system after you shut the engine off (this has to do with hot start issues which can arise). Not expensive, and the warmup regulator isn't hard to adjust.

Adding an SSI isn't really going to change things too much other than to give you a bit more power. It is basically the exhaust Porsche used on the '74. You may not have to do anything to adjust to having the SSI. The factory workshop manual gives the specifications by WUR part number, both Porsche (which I think isn't on the unit) and Bosch (which is on a plate on the WUR). If it makes the engine run a little lean, no problem fixing that with the 3mm tool.

There are a couple of suggestions on where to look earlier in this discussion. A guy named Jim Williams has a website with "CIS Primer" on it (someone else is keeping up this site for Jim). You can find that, and go from there. Put "CIS" into the search engine here on Pelican, an wade through the results looking for ones with a whole lot of replies.
Old 07-12-2020, 04:43 PM
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CIS References

Brian Bodart (Pelican RarlyL8) has taken over for Jim Williams in keeping CIS Primer for the 911.

Thanks Brian for keeping this data alive and for the work you did on my SC CIS.

Rennlist also has a good Bosch Workshop Manual Porsche K-Jetronic

Old 07-12-2020, 07:25 PM
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