Go ahead and laugh; everyone does. That deep groove in the head that looks like it was done with some big guy's thumb in the mold is the intake manifold. Welcome to the 1930's by way of 1963.
But "performance" of another kind was the goal of this engine, and within it's design criteria, it is quite good, and the more I stare at it, the more secrets are revealed.
Most Rambler Americans with this engine had a single venturi Holley carburetor. In my particular car 65mph at 2200rpm, the engine is pumping 106cfm, assuming 85%ve. Given that as a goal, you can stop laughing.
One surprising thing about this engine is that it has perfect fuel distribution. Check out these plugs, #1 is on the left, #6 on the right:
The engine is short, but the intake valves are on the end (the port order is I EE II EE II EE I), about the same distance, #1 intake to #6, as the current 232/258 (which has terrible distribution). But look carefully at the laughable trough -- there's a wedge right at the paired 2-3, 4-5 intakes. This pinches the flow enough to distribute evenly.
I am about to do some measurements with this, below -- but more hilarity -- check out the optional intake charge heater; a brass pipe that not only fills a good third of the plenum, but blocks at least half the area of the carb base:
It's not clear which engines got this option, or why. Most of the 1-bbl cover plates have bosses for the heater, but are not drilled. Blocking the carb hole (all of an inch and a quarter) probably causes a lot of turbulence -- keep in mind that total flow number at highway speeds! -- and the fuel charge temperature would be quite warm and stable.Fuel charge temperature
Discussions on the AMC-list about the applications for the above heated intake trough got me to question some assumptions about what goes on in intake runners. Underlying it I guess was the question, "Why bother to heat the intake space of a in-head plenum? It's already hot in there!" Knowing that Nash would probably not have wasted their time unless it had some value (though this was the era of Studebaker and Chrysler's left-handed-lugnut nonsense) I thought the only way to figure this out was to (gasp) measure something. So I did exactly that.
The temperature probe is a K-type thermocouple, commonly found on mid-end multi-meters. It's very low mass and fast-acting. I drilled out a street elbow that provided suck to the overdrive switch, thusly. I tapped it #8-32 so I can plug it with a screwn when I'm done. The seal is just a small piece of neoprene with a pricked hole, held to the top with bailing wire. Took all of 30 minutes, including lashing the DVM itself to the cowl intake and wiper arm.
The results were genuinely interesting. Ambient temperature was 70 (10am)- 75F (11am), so assume that the intake air is that temp or slightly higher. This car has a cold air intake in the grille, it's not getting under-hood air. 180-degree thermostat (no other available for this car) and it was fully warmed up to start. I drove for one hour on the freeway, south to Irvine, so though it was later in the morning (warmer) it was closer to the ocean (cooler) so the net increase was small (shown below).
|state||intake temp (F)||engine RPM|
|car off, one minute||195||n/a|
|hard accelleration, 30 mph to 60 mph||98||n/a|
|steady cruise, speeds 20 - 50 mph||135 - 140||n/a|
|steady cruise, 55 mph||130||1850|
|steady cruise, 60 mph||120 - 122||2050|
|steady cruise, 70 mph||100||2400|
|after arrive irvine (60 minutes)|
|off one minute||215||n/a|
Anyways, at full throttle the temperature is 30 degrees over ambient, and 95 degrees below coolant! Interestingly, charge temperature was basically proportional to throttle plate opening, straight up. Open cool closed hot.
Back to the heated intake -- clearly here in Los Angeles it's worthless. But if ambient is 0F, the intake charge would (probably) not get over 30F, even with the engine fully hot. Presumably the brass heater pipe brings this up a lot. Nash designed nice motors. I'm not gonna test this, I'm done here.