2.7 CIS engine specs

[Phil Gilsdorf]

What are the differences between the 74-75 2.7 CIS and the 2.7 mechanical injection engines? Specifically, do they have different cams? The 73 rs had 36mm intake and 35 mm exhaust valves and the 74-75 2.7 had 35mm intake/exhaust. Did all of the 74-75 models (S, Carrera) have the 35 mm intake and exhaust valves??
Thanks !

[jgparker]

Phil,

The fundimentals of both 2.7 engines are the same, but there are some very important differences. The 2.7 RS had 8.5:1 compression, just like most of the CIS 2.7 engines, but the RS had much more agressive cams (early S-cams), and pistons cut to accept these cams. You can not put S-cams in a 2.7 CIS long block due to valve clearance issues. Not all CIS engines had 35mm ports, some early ones had 32mm ports. Read Wayne's and Bruce's books. Both cover the differences and the best upgrades for a CIS engine. My opinion is the 2.7 CIS longblock is a great starting point for a great engine, but the upgrades are not cheap.

Good luck,

JP

[Phil Gilsdorf]

Thanks for replying, how much power do you think a cis based 2.7 with the stock internals could make with a set of 40IDA carbs, straight exhaust, and crank-fire ignition? In PCA club racing the 74-75 carrera's are in H stock, but you can run as a prepared car with 2 in. wider than stock wheels, big brakes, and carbs. That would put it in F stock with 9/10 in wheels, big red's and if it could make around 200 hp that car would be unstoppable.

[Henry Schmidt]

The difference between cis 2.7 and an RS 2.7 is the injection and hp. CIS had 165 and the RS had 210. The RS is basically a larger 2.4 "S". The RS engine has 911 "S" cams and MFI. MFI injection is a race bread injection that used large amounts of fuel to make HP. 6 individual throttle butterflies for good response vs the single butterfly of the CIS system. The MFI also had timed injection pulses and the CIS injection had a constant injection spray, hence CIS. Compression ratio on both engines was the same 8.5 to 1. The valve sizes were the same 46 mm intake and 40 mm exhaust. The difference was port size. 36 mm intake on the RS and 35 mm CIS. The pistons were also different. The RS has valve pockets to accommodate the large lift and duration hence overlap of cams. The CIS piston has a squish chamber dome ( half a dome) to allow the engine to function on lean fuel mixture for smog regulations. The cams on the CIS engine has a large lobe center 112 vs 98 ? degrees of the "S". Reduced intake pulses was the goal. They also had different ignition distributors. Crank, rods, 7R case, valve train, timing chain mechanism, and oil pump were all the same. In 75 the CIS engine got an oil pump upgrade, but I believe the 75 MFI engine got the same upgrade.
Basically these are the important differences.

[klaucke]

Actually, with big reds I believe the car would be quite stoppable. Sorry I had to.

[jgparker]

I think 200 HP with stock 2.7 CIS internal would be just about imposible to achieve. The consensus is not to put Webers on a stock CIS longblock, since the HP benefits would be minimal for the cost. Now, with Webers, new pistons and cams, 200HP would be a piece of cake.

I assumed you were just talking about the longbock, so I did not mention the significant differences in the induction systems between CIS and the RS. MFI is awesome, but I do enjoy my Webers. As alwasy Henry is a wealth of great info.

Good luck,

JP

[Phil Gilsdorf]

thanks guys,
I used to drive a 72 E so I know how great MFI is but I guess I thought the CIS was more restrictive than it really is. So even with the 40IDA carbs, crank-fire ignition, and open exhaust, it isn't possible to gain much more than the CIS's 167hp?

Those cams must be terrible!