Good question, JB. Yes, the 55-56 heads are supposed to have a lot better intake port.
These are aftermarket heads from Hot Heads Research and Racing. This is what they say about them on their website:
"The best heads ever made for the early Chrysler Hemi, period. We started with a clean slate when we CAD-designed these water-jacketed aluminum heads for '51 - '59 Chrysler 331, 354, and 392 blocks. Using the latest in casting technology, our heads are cast from 356-T6 aluminum, with an extra thick 5/8 inch deck and combustion chamber, all with machining operations done on a CNC machine. We started with the favorable 1955 factory raised intake port design, improved it, and added a better-flowing rectangular exhaust port to increase flow. Hardened seats are installed for use with unleaded fuel, with intakes at 2.0625 (2 1/16) and exhausts at 1.80 inch, with bronze guides installed for 11/32 inch valve stems. We enlarged the pushrod holes to allow for larger diameter pushrods, and machined the spark plug tube seals into the head, and eliminated the heat riser to the intake manifold. Heads are 100 percent leak tested for quality control."

So far, I'm very happy with them except for the leak. But that is always a risk when you port.

Good deal. Better ports and less weight.

Jeff made a fun, time lapse video of the gear swap. The whole job in 38 seconds:

https://youtu.be/OgPHw3CgeTg

The 1955 Chrysler 331 C.I."300" heads where the hot set up back in the day do to them having harden seats in them that you could knock out and put bigger valves in then the easiest
Both the 1955 and 1956 Chrysler Hemi heads had better port angles than the 392 motors had due to Chrysler changing the 392 port angles to reduce the total height of the motors with the new lower sleeker looking 1957 and up body styles called the "Forward" look, tail fins and all

The 392 had a taller deck also. On the 392 heads, they extended the length of the intake ports and angled them down, so the low deck 331-354 intakes would still fit. And like Cabs says, keep it from getting too tall.
To run 331 - 354 heads on a 392 block, you need spacers between the intake and the heads. The Hot Heads do not need a spacer, it is designed in to fit a 392.

Now that it’s a tested piece, and you know it won’t fill the pan with a coffee milkshake...... any plans to put it back on the dyno?

Hopefully this winter I'll get it into the Dyno with 8 02 sensors and really get it optimized. Probably try the dual quad again too. Just to see what I'm giving up with the X3. Maybe test major changes in lash to see if it might like a bigger or smaller can. Any suggestions on what to experiment with?

Interesting that you mention the 8 O2 sensors.mon yellow bullet there is a thread in the Uratchco section taking about using O2's on every cylinder. It may be in the Pro Stock Tech thread.

Anyway, I've never done any testing with 8 O2's but some say it makes the tune up hard to get, because you never get it right (I'm not saying it well but I'm trying to say it induces errors in tuning...that doesn't even sound correct) and it makes it difficult to tune from that data.


Hope I said that so it doesn't sound like a 3rd grader typed it.

Joel, since the basic configuration of the motor is already established........ I would think the biggest influence on power output will be in the induction system.

I don’t know if Hot Heads offers a race-ish oriented 2 x 4 manifold, but if they do, that might be something to explore if the set up you have seems lacking.

Of course, a properly set up Hilborn stack injection on alcohol would work pretty well on that combo too 😎

I have had one motor dyno tested with 8 O2 sensors, the dyno operator insisted on installing the bung in my race car headers.
It was a 544 C.I.B1 motor with the cast B1 single plane intake that ended up making a little over 900 HP on race gas.
The O2 sensors showed that the intake had uneven distribution but what can you do with that information to fix that problem
I will use those headers when I dyno tune my own B1 motor with a tunnel ram intake and dual Dominator carbs.

That's kind of what the thread on yellow bullet was going with 8 O2's. It showed how bad distribution can be (and most likely is for most endings that are sorted out to the max) and IIRC the real issue was trying to clean up that distribution.

Some EFI systems can do per cylinder air fuel corrections when running 8 02 sensors.

This is an interesting video, watch the Trims as the RPM comes up, they are all over the place until the RPMs get up. In those trims 100% is no correction.

Now after going through all that how much power is it worth?

https://youtu.be/6kQGp-fHuFc

If you are running EFI with sequential port injection and coil on plug or near plug ignition, OEM and I'm sure a lot of aftermarket ECMs can give you that data already with one sensor in each bank.

The computers are fast enough now that it can tell which exhaust gas pulse belongs to which cylinder.

Kevin

With the 8 carb X3, it is a cross ram with a separate left and right plenum. Each 2 bbl carb sits right over the top of a port. I'm not sure, but it would seem that the a/f ratio of each cylinder would be most affected by the carb that is above that cylinders port. The carbs have aftermarket adjustable main jets, with a needle valve extending partly into each jet. So the point of the 8 O2 sensor test would be to equalize the a/f ratio of each cylinder, then dial in the most powerful overall ratio. THen when tuning for weather changes, turn each needle exactly the same. In this pic you can see the needle valves.

Your correct on your assumptions
Jet and tune each carb for that cylinder

Great pictures and writeup so far! Absolutely love your coupe.

Don't have much to add but if you don't want 8 O2's you can install EGT's in all 8 cylinders and get an idea of distribution that way.

My friend Jay who has a Dyno in his barn is planning to set up for 8 02 sensors anyway. So I might as well take advantage of it.

Wow, so you have some external main circuit adjustments you can do, that is pretty cool!

I was trying to remember which of the really early three bolt two barrel carbs like your using flowed the most air, Holley, Bendix, Stromberg Carlson, model 97 or model 84, the later 4 bolt GM Rochesters or which one?

Bad340, I figured with 16 mainjets, I needed an easy way to make adjustments!

Cab, these are the largest holley 94's that they made with a 1-1/16" venturi. They are not nearly as common as the smaller ones. Finding 8 good cores was a challenge.
We flowed them as well as the 4 bolt Rochester 2 bbls. Testing wwas done at 20.4" (1.5" Mercury - 4 barrel standard) and 28". Here are some pics of the Rochester: