2.7 CIS Performance Upgrades

[6771911esses]

Wayne,
I am looking at purchasing a 2.7 cis to replace my 2.2T. I also have a 2.4E 72-73 with output rating close to the 2.7cis. I like the idea of fuel injection for driveability, but I would like to modify the 2.7 a bit if possible. I do not have your engine book handy (gave it to my Dad who lives abroad), so I can not reference it quickly to look at your performance mod suggestions. Could you give me some ideas on the 2.7 cis mods if any that would work with the cis injection system. I know carbs will make a world of difference, but then I am back at Webered 2.4E. Thanks in advance. I have to decide on this 2.7 tomorrow.

Cheers,

Mike

[dd74]

Since you're under a time crunch, I'll chime in for you. I'm no Wayne, and don't have his expertise, but I did at one time have a 2.7.

Make sure the 2.7 has been rebuilt, or at least acquire a comprehensive history on the engine. A plus for the 2.7 is are upgraded Carrera-style cam tensioners. If the engine does not have these, don't let their absence dissuade you. They can be done later. Just get a good history of the engine.

As for modifications, I'm under the assumption 964 or 20/21 cams may work with the 2.7 much as they do with the 3.0. You can also advance the timing, again, like the 3.0. But the big improvement (and hopefully your engine has these) is to backdate the exhaust system to the '74 or earlier style system. Equal length headers or more commonly "heat exchangers" came with the 1974-model 2.7. If you get a later model 2.7, '75-'77, you have thermal reactors attached to the exhaust system, which will destroy your engine - hands down.

The 2.7 is a great motor if sorted out. The absolute first modification you should do, more to insure its longetivity than perfomance, really, is to put heat exchangers on it - that is if it doesn't have them already. That should get a bone stock run-of-the-mill 2.7 up to about 165-175 horsepower - which is very nice for a light middle or early era 911.

Good luck with the purchase.

[Wayne 962]

Check out this article by Noah:

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

it covers some questions you have.

I would go with the 911S pistons and cams, and that would bring it up to close to 175 HP, which is close to the HP of a 3.0L. It just so happens that I have a set of 911S CIS cams for cheap (the ones used in the book) that I'm trying to get rid of (rewelded, reground by WebCam).

The CIS 2.7 engine with a few mods makes for a really fast car...

-Wayne

[RoninLB]

Maybe

- desmog
-SSI + good muffler
- CIS mix to 3.5
- investigate present ignition curve
- re-build is another story

[dd74]

Originally posted by RoninLB
Maybe

- desmog
-SSI + good muffler
- CIS mix to 3.5
- investigate present ignition curve
- re-build is another story

Agreed. Then it's probably 3.0 and higher time. Or maybe build the 2.7 into a 2.8 or 2.9. That would be fun.

[farleyd]

I was asking the same question. I plan on using Webers and headers in a somehow stock CIS longh block. Does it worth keeping the CIS induction and go 964-style cams w/9.5:1 comp. ratio pistons versus just slapping the rejetted Webers??? Four quarters for a dollar?

[dd74]

If the pistons inside the 2.7 CIS engine are like the 3.0 CIS, then installing Webers would not be completely viable, as the pistons in a CIS engine are inherent to the CIS fuel delivery. To realize the full potential of Webers, you would need to install flatter-style pistons for the Webers. The CIS pistons are more bowl shaped, I believe.

This is not to say that Webers (supposedly), wouldn't make the engine "feel" more responsive if installed on a stock CIS engine.

The most you can do with the CIS pistons intact, provided you've already backdated your exhaust, is to go with the 964 or 20/21 cams and possibly do some head work for better breathing. Anything else requires a teardown of the engine.

[farleyd]

The most you can do with the CIS pistons intact, provided you've already backdated your exhaust, is to go with the 964 or 20/21 cams and possibly do some head work for better breathing. Anything else requires a teardown of the engine.

Yes i have 914/6 headers. What would you thinnk this set-up would give in terms on HP and torque.
CIS induction, 964-specs cams and headers?
Will i have to modifiy the CIS settings?

Thanks

[dd74]

From what I understand, the true advantage of 964 and 20/21 cams are a broader torque curve. With the SC engine, the jolt of power which seems to last only 1,500 RPMs after 5,500, is circumvented via the better cam's broadness.

HP and torque numbers are up for debate. Some on this board suggest no more than 200, others have suggested (along with minor piston work, i.e. "fly-cutting") 230-240 hp. Interestingly enough, no one has recorded torque numbers; only top-end hp.

IMO the true benefit of a better CIS-appropriate cam is that it allows the engine to rev past its stock redline to about 7,000 RPM. True power is available as low as 2,000 RPM, and there is no abrupt fall off.

Mind you, all this is based on a 3.0 engine with CIS, not a 2.7. Webcam has another type of performance cam for the 2.7 CIS.

Also, I have not installed these cams on my engine. One reason is I don't think I require them. I have a 7.31 ring and pinion, and with my 3.0 in its stock form (except for SSIs and a Triad dual-out muffler) and have power from about 2,000 to 6,500 RPMs with no trail off anywhere. I think it can reach 7,000 RPMs, but why chance it?

Also keep in mind, if you do a cam change and feel like exploring the nether regions of the tachometer, I'd install better springs, valves and anything else in the heads. A piston smacking up to that stuff at 7,000 RPMs will not be a good thing.

[RoninLB]

Originally posted by farleyd
Yes i have 914/6 headers. What would you thinnk this set-up would give in terms on HP and torque.
CIS induction, 964-specs cams and headers?
Will i have to modifiy the CIS settings?

Thanks

do you have to do a smog test??

[farleyd]

do you have to do a smog test??

in a work, nope! Any suggestions on what i asked? Many thanks.

[RoninLB]

Originally posted by farleyd
Any suggestions on what i asked? Many thanks.

if the pistons don't spec you can use forged pistons with the CIS and follow Wayne's suggestion

[farleyd]

I bought the long-block already rebuilt, so i hopefully guess that they are in-specs. Not too keen on replacing them, they habe been re-ring and the heads are back on, rebuilded too. So, what would set those two options apart:
1) 911 2.7 stock CIS cams/pistons w/Webers and headers
versus
2) 911 2.7 stock CIS pistons w/964-cams w/stock CIS induction and headers.

Also was wondering if using the 964-cams with the Webers would do something.

Thanks!

[dd74]

Again, Webers and CIS pistons may not be the best combination. CIS pistons were specific to CIS induction and nothing else.

IMO I think it wouldn't be prudent to not Webers unless you install higher compression, non-CIS pistons. Notice I didn't say "higher performance" pistons. CIS pistons aren't bad for a period in time when Porsche needed to worry about fuel economy and emissions.

Andial might sell better pistons for the 2.7, but theirs is an upgrade that takes the 2.7 to 2.8 or 2.9. I'd go that direction with your Webers if you have adequate gasoline to withstand the higher compression of these engines and the potential of detonation.

As well, with better pistons and Webers, you'll be able to use a much livlier camshaft - maybe an S cam with a redline somewhere in the low 7,000 range.

That would be very fun!

[jgparker]

I'm not sure I agree. I ran Webers on my stock 2.7 before I started my rebuild project, and I thought it was a great combination. I don't have anything but 2.0, 2.2 and stock 2.7 engines to compare it to, but it had a good flat torque curve, and great low end. It was an improvement over the CIS, but not huge. I'm sure it will pail in comparison to the 2.8 HC engine I will end-up with, but it was an easy and inexpensive combination.

[6771911esses]

I would like to chime in again with another question.

Does anyone have any experience cutting the bottoms of the cylinders to increase compression? By dropping the cylinder 1mm, Anderson's book mentions a final comp. ratio of above 10:1.

I am wondering if I cut my cylinders 1/2 mm, and reuse the stock cis pistons, would that yield a better compression improvement vs. using flat top high comp. pistons? The fact that this method would retain the cis specific piston dome for better combustion with the spray pattern of the injector IMO makes a lot of sense.

My second question touches on the timing chains and how much the deck can be dropped w/o comprimising the timimg chain geometry. Where are degreed sprockets available to make up for the dropped deck?

If this is a viable method of increasing compression it would be cheaper than purchasing new pistons.

I may try this set up with a 964 cam, early exhaust if the consensus out there agrees with me on this.

Cheers,

MN

[farleyd]

jgparker, did you have to do anything else to had the engine running? Different cam timing? Advance dizz curve? Jettings? Etc?
This is less trouble solution for me, as id have to retrofit the car for CIS, means return fuel line to tank, reroute some fuel lines, add fuel accumulator, change fuel pump, etc... If Webers can do it, im in.
How did the car behave?

[jgparker]

I did not touch anything on the 2.7 long-block. I did have a distributor with an RS curve, so I used that, but otherwise, I just put the Webers and early exhaust on and ran it. The car was already set-up for the carbs, so I didn't have to do anything with the fuel pump/lines. I should have done more tweeking (jetting), but It just ran well on the first try, so I left it alone.