Word on european intake manifold and Holley four barrel?

[yellowbullet]

I just purchased another '74 3.0CS with a 3.3L swap. The previous owner installed a European intake manifold (same as the one being sold on the forum) and a Holley 350cfm four barrel carb. Is this intake set-up any good? Should I revert back to stock? Thanks in advance.

 

[TodB]

carbs

Interesting set up. How does it run?

If you decide to revert back to stock, there are a set of Zeniths and manifolds currently listed on Ebay that look to be in decent shape.

 

[61porsche]

M30 with Holley

Yep. Several E3 guys converted. It's written up on thier website- Senior Six as well as suggested tuning. 350 would be a little small, but with Holleys you can change a lot to suit the application. How's it run? Good kick in of the secondary barrels?

For some time in Europe, mid- late 70's, a single, four barrel manifold was available from BMW. Solex, I think.

 

[MMercury]

I just purchased another '74 3.0CS with a 3.3L swap. The previous owner installed a European intake manifold (same as the one being sold on the forum) and a Holley 350cfm four barrel carb. Is this intake set-up any good?

Much depends upon your intended use for the vehicle.

The single four barrel is simpler, it obviates the need to synchronize the two stock Zeniths, and it is probably lighter in weight too. Much can also be said about the flexibility of the Holley, yet each system is full of compromises.

Setting aside the fact that each manifold runner in the 4 bbl. setup is a different length, there is also the issue of maximum airflow. This latter point is meaningless if this is for a reliable garage queen and significant only if you are attempting to squeeze maximum performance out of the engine.

I do not recall the flow rates of the Zenith carbs, but - if you accept the premise that the 38/38 Weber has a “fairly” comparable flow rate and you abide by metric mechanic’s published measurements, the ‘38 will flow 295 cfm. If you double that, the dual carbs will outflow the single four barrel carb by roughly 240 cfm.

As mentioned before, if you rarely push things with the current setup, you will likely never know the difference between the two fuel delivery systems. Moreover, your pictures indicate a very clean installation, so there is good cause for leaving things as they are - especially if you are satisfied with performance and fuel economy. :wink:

Your conversion is described here: http://www.seniorsix.org/faq/2_4bblconv.html

The author makes clear that this may not be the optimal setup.

"Getting fuel into the Big Six motor, ranked from best to worst:

* timed / multi-point fuel injection with optimization capabilities ' Motronic
* multi-point fuel injection: L-Jet, D-jet
* triple sidedraft carburetors (3 x 2 barrels)
* twin carburetors (Weber 32/36's)
* single four barrel (Solex 4A1, Holley, Quadrajet)

Put simply, it's always better to have a dedicated source of metered and timed fuel for each individual cylinder. Depending how you drive and your budget, you can be happy with one of the lesser alternatives. I chose a four barrel carburetor versus the others and I am satisfied.



Disadvantages of the Big Six four barrel manifold

Fuel distribution
None of the intake runners on the Big Six four barrel manifold are the same length, shape, and even their inside diameter varies slightly (different volume). Cylinders attached to a common plenum scavenge mixture from each other. What is unused fuel mixture doing floating around unused in the first place? This clearly affects fuel distribution, power, and drivability:
* All six of the intake charges vary slightly from one another. Air/fuel mixture velocity is different in each intake runner because of the differing plenum volumes and the varying signals present at the jets. Cylinders closest to the carburetor will get richer mixtures than those which are further away.
* Air/fuel mixture from the carburetors gets bounced around and lost on its way to the intake ports because of the greater amount of common area in the manifold and the intake pulses from the cylinders.

In contrast, examine at a Big Six with fuel injection or triple carburetors with six independent runners. Those systems have six identical intake runners, both in length and diameter. In these intake systems, the air drawn into the engine may come from a common source but the fuel is introduced downstream, at the intake of each cylinder. The further our design moves away from six balanced intakes and individual fuel meters the worse off we are."