Cis (911 T, S)

[Dr. injection]

Greetings

I have a complete 22 page workshop manual for the CIS in 911 t, s and 924 wich is dated 78'. With test sheets (all pressure settings) One thing notable it has the specs for both (140hp versions) the mechanical injected 911 T(USA version) and the 911 T with CIS showing exactly the same hp/torque, however the cams and valve control timings and compression (also the piston tops are different in shape, made for the CIS; 8,0:1 vs 7,5:1 on the mech) differs. Inlet cam height and base circle radius is 1.513in. vs 1.425in. on the mech.
Exhaust h. & b. circle radius is 1472in. vs 1.393in. on the mech.
Valve timing with 0.040 in. valve clearance *CA: Exhaust opens before lower BTC (first being CIS the latter MFI): 30* vs 42*
Exhaust closed before lower BTC: 10* vs 4*
Inlet opens before upper BTC: 0* vs 16*
Inlet closed before lower BTC: 32* vs 30*
Inlet valve lift at overlap BTC and 0.004 in. valve clearance: 0.035 - 0.043in VS 0.0094 - 0.110in.
Valve springs remain the same length at 1.378 +- 0.012in.

Result with changing injection system to CIS, increasing compression and altering piston tops is that the CIS engine dont have a sharp dropping torque curve like the mechanical has, however the MFI engine has a smoother hp top curve. The fuel consumption is about the same but if you drive normally not pedal to the metal, the CIS uses less fuel below 4500rpm, but after that the CIS curve rises fast .Where the mech one peaks at 260 (grams/HPh) 6600rpm. the CIS stops at 283.

It all sounds like we all know from before, the metering plate acts as air brake, needs more fuel at high rpm, higher compression to work like the MFI even tho the mfi uses drive from the engine to operate. (up to 10hp effect loss on big engines wich becomes evident on fuel consumption under 4500 rpm) No wonder air mass sensors on expensive injection systems is the best of choice when going for max turbo boost or scrapping the CIS for webers if your running an normally aspirated engine. But as previously stated do this only if your planning on installing higher lift cams (over 911 s duration/lift dont work with CIS) or the result will be marginal. But, if you own a 2.7 CIS with a really good stainless exhaust/headers, S/RS cams (pushes the CIS to its limits) and throw on some big bore webers correctly adjusted should make for much better throttle response and hp.

If your working on your 911 and need CIS pressure values in models 78 and before reply and i will assist.

[MotoSook]

Doc, can I have a copy of that manual? WHo published it?

[jluetjen]

What are the cam specs for the 2.7S-CIS?

[Dr. injection]

The specs for the 74 911 S 2.7 CIS; cams 143/144, intake valve is open .40-.54m/m at TDC overlap (.016-.021")

Intake opens at 6 ATDC
Intake Closes at 50 ABDC
Exhaust opens at 24 BBDC
Exhaust closes at 2 ATDC