Need advice: Machining 74 CIS cam to 964 spec

[Patronus]

I understand that 964 cams will add extra power to my '74 2.7S with CIS. It will be very difficult for me to get hold of 964 cams, so I want to know whether my existing cam can be machined to 964 spec.

If the answer is yes, do I have to 'copy' the cam profile from a pair of 964 cams, or is the exact specs of the 964 cam available somewhere so that an engineer can work from that?

Thanks
Martin

[dd74]

Hey Noah:

Can the work you did on your engine apply to a 2.7 CIS with much the same success? Secondly, did you do any other preparation to the motor, i.e. building up the bottom end, head work - stuff like that. And last, how do you think your mods done on a 2.7 CIS compare to the overall horsepower of a 2.7 MFI? What would the differences in torque and responsiveness be?

Thanks.

[82SC]

yo noah...

well as you know I have a set of used 964 cams in my garage...can I use used rockers with used camshaft?

MJ

[speeder]

MJ, Not unless rockers came w/ cam and you get them all in same position. They "wear-in" together. Actually you can do anything you want, but results may or may not be OK, ie. keeping valve clearances constant, etc.

I have not read any reports of 964 cams in a 2.7, but I can definitely say that 964(or bigger 20/21's), do not require any "building up" of bottom-end on a 3.0 like Noah's, these cases can handle a LOT more HP than we are talking here.

[dd74]

Speeder and/or anyone

Okay on the no building up on the bottom end for the 3.0. So do you think it'd be the same for a 2.7? I mean, aside from size, 2.7 vs. 3.0, and a .5 bump in compression, and of course the aluminum block as opposed to magnesium, what's the big difference between the motors. Please give me an excuse not to spend 10gs on an 2.7 MFI.

Thanks

[speeder]

dd74, What is the car you would be putting this engine in? There are many different options on motor swaps/ rebuilds for a lot less than $10G's, especially if motor you have now can be sold for something- what is car/motor you have now and condition of both? Then I and others could advise you better on smart-money way to go.

[marcesq]

Andial sells a 2.7 to 2.9 conversion that is a straight bolt on operation. So it follows that the mag block can handle Noah's modifications (pistons, cams, etc.) as long as the block is time certed.

Good luck.

[Jim Smolka]

To regrind the Cam to 964 specs, Elgin Cams in CA did a set of 3.2 cams for about $250.

[dd74]

Speeder:

I have a bone stock 74 911. A Bursch exhaust system is the only addition. It's fairly quick per the LA/San Fernando Valley congestion I force it through. That congestion, however, may merit an oil cooler soon. With that said, the engine is strong, does not smoke at all, and borders around 210 degrees heat-wise, maybe a little higher. I wanted to get my air/fuel mixture checked because I switched exhaust systems, and the guy who checked it out was amazed at the efficiency of the engine. He said it ran as clean as a catalytic converter engine, which it isn't, thank goodness. If it was, I don't think the motor would have lasted this long.

I don't plan to track this car. I'm interested only in something with a good amount of speed, but not outrageous. Also, bang for buck would be good. I'm looking for about 220 or 230 hp; or at least something comparable to an RS MFI motor, but with CIS still in place. Any mods would be done during a rebuild. That's the one thing I plan. But bang for buck has its importance.

Any suggestions? Anyone?

Thanks

[dd74]

Marcesq:

Thanks for the tip. I didn't see the 2.7 to 2.9 conversion on their website. I'll give them a call, unless you have more information about it.

[dd74]

Noah: I read your article and it was terrifically inspiring. Great work, and well written too.

Question: how do you think such mods would compare to a 3.6 conversion, horsepower wise and money wise? Oh, and one more question: what about the venerable MFI engine? More horsepower than 210? Would such mods, in your opinion, make about the same or more horsepower as an MFI 2.7? By the way, did you swap out your clutch for a Sachs unit, or something like that? Do you reccommend this, or will a stock clutch work?

Thanks.

[Wayne 962]

It's almost not a fair comparison, the 2.7 CIS and the 2.7 MFI motors - they are almost entirely different.

They have different pistons, fuel injection, and camshafts - just about the displacement is the same.

Noah is right, compression on the 2.7RS is about 8.5:1, and it runs the standard 'S' cams (the RS engine used 'S' cams). The power comes from the MFI, the pistons and the cams. Don't forget this is only about 30-40 HP above CIS (175 for a stock 911S CIS engine).

If you're going to go with an MFI route, then use custom pistons from JE, with a higher compression spec than the stock RS pistons, and reuse your old cylinders (Nikasil only). Then use the 2.7L RS-spec pump and 'S' cams. If you bump the compression up past about 10:1, then twin plug it with an HPX crankfire system.

Of course, performing all of these mods on a 2.7L mag case will require the full set of mods to the case. Building this motor would probably cost about $15K when you get done with everything:

- $3K for rebuilt injection
- $1K for the new pistons
- $2.5K for the twin plug ignition system and mods
- $8K for the basic rebuild

-Wayne

[Vipergrün]

Noah,

I recently read your article on the CIS improvements as well

What compression JE pistons did you end up with? What Octane would one need to use the 9.5 or 9.8's? If the exhaust, cam and piston upgrades are cumulative in performance, I'd get about 45-50 HP using the 9.5:1 pistons. Is that correct assuming 15 for SSi's, 10 for cam and 20 for 9.3:1 -> 9.5:1 piston upgrade?

Looks like I may be in for a rebuild of my 3.0 SC motor and these options look really nice! Are you able to pass smog with a cat?

Does enything special need to be done to the stock cylinders if they are within spec?

Wow! I'd love to get 200HP at the wheels of my SC!

cheers
-Brad
80SC

[dd74]

Thanks for the advice and clarification about MFI and CIS engine stuff. Thanks to Wayne, too.

Now here's the next question: anyone out there know a good shop where I can get my 2.7 rebuilt? And approximate prices, too of that rebuild?

I live in the So. Cal area, but don't feel like going as far south as Orange County, unless it involves free admission to Disneyland.

Thanks all.