2.7S carb conversion newb question

[rich]

This is really about saving a wrecked but rest free factory 914-6.

I'm new to the 911 engine. I was able to purchase a 1973 2.7S engine with CIS. I would just keep the CIS as I am familiar with how to tune and repair it. I have done a couple 928 euro spec "S" builds but I'm installing the engine in a factory 914-6. The original engine is long gone.

Believe me if I could keep the CIS I would. I like it but In order to use the CIS I have to cut the engine lid latch off and move it. the plenum interferes with the latch and I don't want to modify the car in any way so I want to change to carbs.

On to the questions already...

I have a set of factory cabs from a 1972 2.4 911. I thought I read someplace there is an issue with lining up the intake manifolds from the CIS setup to carb manifolds.

Is this true? If so what gaskets aid in matching up this issue?

Second: Can I re-jet these carbs for the 2.7S? What jets are recommended as a base line?

Third: Can I use the F.I. cams? I assume these are low lift long duration for low intake pulse.

Fourth and final: If I MUST change cams is there a low cost solution for a sporty set of cams?

[rich]

Originally Posted by rich

This is really about saving a wrecked but rest free factory 914-6.

I'm new to the 911 engine. I was able to purchase a 1973 2.7S engine with CIS. I would just keep the CIS as I am familiar with how to tune and repair it. I have done a couple 928 euro spec "S" builds but I'm installing the engine in a factory 914-6. The original engine is long gone.

Believe me if I could keep the CIS I would. I like it but In order to use the CIS I have to cut the engine lid latch off and move it. the plenum interferes with the latch and I don't want to modify the car in any way so I want to change to carbs.

On to the questions already...

I have a set of factory cabs from a 1972 2.4 911. I thought I read someplace there is an issue with lining up the intake manifolds from the CIS setup to carb manifolds.

Is this true? If so what gaskets aid in matching up this issue?

Second: Can I re-jet these carbs for the 2.7S? What jets are recommended as a base line?

Third: Can I use the F.I. cams? I assume these are low lift long duration for low intake pulse.

Fourth and final: If I MUST change cams is there a low cost solution for a sporty set of cams?

[jkh2cpu]

1. You really need different manifolds. I'm putting the
webers from my old 2.4 on my 2.7, and I got new manifolds
from PMO / Oil Analysis. The manifolds from my 2.4 are
not large enough to cover the intake ports on my 2.7 heads.
A notch in the heads for I guess the CIS injectors spoils the
mix. My 2.4 manifolds are 32 mm where the manifold meets
the head.

2. I cannot tell you much about the jetting, but you will
want 32 or 34 mm venturies. I'm conservative (about motors)
and went with the 32s. Bigger isn't always better ;-)

3,4. You need CIS cams. I'm going to spring for the 'SC'
grind from WebCam.

HTH.

John.

[rich]

Great info. I'll look into the PMO intakes and pull the carb apart to see that's in them. I'm not there yet as I have a chassis to restore first.

Thank again!

[al lkosmal]

A good baseline Weber setup for 2.7 CIS:

32mm Main Venturi
135 mains
F26 emulsion tubes
180 correction
55 idle

regards,al

[rich]

That's what I was looking for Al! When I pull the carbs apart I can check to see what's in them and what I need to base line them. You have been very helpful! Thank you!

[911pcar]

Lots of Weber info in the archives. E.g.


Cam choices are limited by configuration of the piston crowns. Since yours are CIS pistons, more aggressive cams can't be used due to insufficient valve clearance.

Sherwood

[Jack Stands]

Swapping out the Pistons and cams really make the 2.7 come alive. The stock CIS pistons and cylinders are compromised for smoothing pulses to the CIS plate. My RS piston and Weber carbed 914-6 conversion puts out 199.5 HP at the wheels, so it's more than enough to have fun and a nice choice if you go that route.

Perhaps you could remove the engine latch and use the CIS. It could always be reinstalled if originality was an issue. Alternatively, could you heat and reform the air box to allow it to clear the engine lid latch? Without swapping ut cams, you might be a bit disappointed in the carbed engine.

[rich]

Jack,

Do you think the HP will drop with carbs?

I really like the CIS just don't want to cut off the latch to use it. I was told I may be able to lower the front of the engine a couple inches and the plenum will clear.

My Alien was a 16 valve 4.7L M28/11 euro spec "S". I have the heads, cams and CIS on a 5.0 32 valve short block. Yee Haaa!

[Jack Stands]

If the carbs are set up correctly, the HP will be similar but the mileage will definitely go down. My 2.7 is jetted a bit more aggressively, but I have S cams and the RS pistons and cylinders.

If nothing else, the Webers certainly look nice!