Technical Adapting truck heads to a 331 Hemi

When I first built my Willys in the mid '60s the vision was always to imitate a gasser. Here is a photo of the first hacked together build which should have killed me (farm implement rear tires 'cause they look like slicks - and act like slicks on wet roads, a fender bracket for a brake pedal, junk yard foreign car wheel cylinders adapted to the Willys factory cable operated front brakes, etc., etc.). The photo shows the fender dump gasser headers I built. Unfortunately I didn't know much about hemis and tried to use 2" tubes on the small round ports so ended up with mashed ends in cut up flanges. Plus the take-off pipe from the collector to the glass packs under the frame didn't work for the look.

My first set of 'gasser' headers in about '67. Didn't work out.


When I did my proper build of the car in '95, I made these headers that better fit the small engine. Never was happy with the look.


I survives driving this death trap through my years at Fresno State, then tore it down and didn't get it back on the street for 20 years. When I finished it in 1995 I built this set of headers with header mount glass packs which are fine and have served well for 25 years, but I was never happy with the look; small tubes and the mufflers hid my Hydro tranny & ladder traction bars.

In recent years I became aware that truck heads are cousins of the early 331 engines with no water crossovers but a thermostat in the intake manifold. But they have those great 2" oval exhaust ports, big valves, and an added benefit over even 345 and 392 heads, no exhaust crossover in the two inner ports that messes up header performance in those engines. Negatives on the heads are they have strange bosses cast in the ends and they have sodium filled exhaust valves with huge valve stems that don't allow passenger car valves to be used. Finally, they use a water crossover under the intake manifold with tall ports that aren't compatible with passenger car intake manifolds.

exhaust ports on early 331 heads. Can't use big header pipes.


Truck heads with big 392 type exhaust ports. Yeah!!!!


Problem is truck heads use water crossover manifold heater with these tall ports. Can't use passenger car intake manifolds.


The benefits seemed to outweigh the negatives in my twisted mind so I acquired a set and started the adaptation. I consulted with Hot Heads company and they assured me the conversion was possible and provided me with all the parts I needed. They sent me new valve guides, stainless valves, valve springs, spring retainers & clips, stem seals, intake manifold and head gaskets, & sparkplug tube seals.

With everything I needed I started my conversion. The first step was to cut off those bosses on the heads. This wasn't just cosmetic, my engine has bolt-on accessories in those locations (remote water pump, A/C compressor) that interfered. They came off cleanly with a cut-off blade in a grinder.



The next modification I did was drill and tap a couple of accessory holes in the ends of one head that I need for accessories. I set up my drill press to drill these. I made a paper hole locating pattern off the drilled head. Strange that my heads have the same part number but one head was drilled, one wasn't.





Then for some strange reason Chrysler made the locator pins on engines built in later years a few hundredths inch smaller that the ones in 331 engines. They make replacement pins for conversions but I decided to drill the truck heads to fit the early pins. I found a U letter drill bit was the perfect size. Just hand drilled these. No problem.



Finally I brazed in steel plates to block the heat crossover extensions outside the intake manifold.




With all the preliminary work done, off to the head shop (not that kind of head shop). Only took them a week to do the conversion. They came back beautiful. They even removed my brazed plate and welded the crossover ports for a better fix.






After painting, I chased all the holes with a tap. A strange feature of Hemis is that valve cover and exhaust manifold bolt holes enter the water jacket. I used this thread sealant and doped up both the hole and the stud threads for a better chance of a water tight seal. X my fingers!




Heads had a few Helicoils so I for sure doped them inside.





Factory 354 head gaskets don't fit 331 engines well. The former gaskets have strange elongated push rod holes that are exposed on the smaller engine. I bored my 331 1/8" over to convert it to 354 so had to use those gaskets. I use some gasket inserts to fix it but wasn't good. The Hot Heads gaskets fix that with some round holes that work on all engines.

Stock head gaskets have holes that go to the outside of the block.

Her is the bad stock head gasket laid on top of a Hot Heads gasket. Problem solved.

 

With my new heads, I set to making a set of fender dump Gasser style headers. I use 2" mandrel bends, 3/8" flanges, and 5" x 11" truck exhaust tubing for collectors. Nothing fancy about construction.



I didn't want to do the usual takeoff pipe to glass packs under the car. That screams "this is just a poser street car". I wanted the exhaust exiting the collector, right onto the ground. I designed a muffler that fits in the 5x11 collector and it totally hidden. It is effectively a 21" glass pack. Started the engine and it works great. Really nice sound but totally legal. Unfortunately I didn't take any pictures of it while building it and it is welded into the header. Will make some sketches of it and post them later.

In the second photo above you can see I was running the stock Chrysler cartridge filter canister bolted to the firewall. I decided to convert to more practical spin on filter so built this conversion while the headers were off.


I finally have the look I have dreamed of for 50 or so years.



You might notice in these photos that I also added Chrysler Marine valve covers with the awesome valve adjuster dents. Strictly a vanity addition.

 

Just what I needed. I have a freshly rebuilt '56 331 out of a dump truck. It had only a couple of thousand miles on it when the transmission took a dump and the owner pulled it. I really don't want to rebuild it again, so I'll run it like it is for a while. I am currently running the truck two barrel manifold and carb. I have a 4 BBL manifold out of a '54 New Yorker that I want to run, and this is the ticket.

Thanks.

 

Here is how I converted a 354 4bbl manifold to fit my 331 so I can run my Holley 3bbl carb. 331 needs a manifold thermostat but 4bbl 331 manifolds are really rare.

Here is a rare 331 4bbl manifold.


Here is a stock 354 manifold. Bolts up to a 331 but carb bores are too small, has no thermostat.



I bought a large bore carb spacer and used it as a guide for a hole saw to open the ports. The factory runners are plenty large enough. Chrysler was a leader in intake manifold design in the 50s. Note I cut out the web to accommodate my 3bbl.



Here is the finished product.



I opened the front water ports on the manifold with a hole saw then brazed in stub pipe for radiator hoses.



Then I brazed together a thermostat housing with all the side ports I needed - bypass to the pump suction to heat the thermostat, heater hose takeoff.


This is what a Holley 3bbl looks like. Made for NASCAR in '64, got banned as usual. Only made a couple years. It's a 780 with cut out web. I made some inserts for smaller primaries, better streetability.