Unfortunately, since parts are hard to get for everyone, it’s been a while since we last visited the shop to work on LA Thumper, our 416 cubic-inch small-block Mopar build, but it’s great to be back at it. To catch you up on what’s been done already, in December 2021, yep, it’s been that long, I showed the rundown of what we’ll be building by looking at the SCAT Enterprises rotating assembly. The next installment came in February 2022, when I discussed the basics of how to properly install the SCAT parts. After a hiatus from the shop, I got back at it in June of 2022, when I finally got to install the Lunati camshaft and Milodon gear drive. Now, it is time to install the top-end.

LA Thumper gets its name from the premise of the build to be a reliable small-block with a healthy dose of compression. Since the lower half will be able to create some serious squeeze, we need to be sure it can inhale and exhale as much air as possible. That means a serious pair of cylinder heads is required. Unlike a decade ago, there are now several great choices in aluminum cylinder heads for Mopar engines.

Our 416 cubic-inch small-block Mopar build is getting closer to having the fires lit.

If you are looking for a great cylinder head for your daily driver, there are a myriad of aluminum heads for that application. Do you need a race-only cylinder head that works best when really spinning  RPM into the stratosphere? You can find them. But what about an engine like LA Thumper? This is going to be an engine that will see more street duty than drag racing, but still be able to scream when need be. To handle our breathing chores, I reached out to the folks at Trick Flow Specialties, as my research told me that the PowerPort 190 cylinder heads for our 416 small-block Mopar (P/N: TFS-61417802-C00) would be perfect for this application.

Although the heads are CNC ported, if you need every last bit of flow possible, there is still a little meat left for gasket matching.

Ingredients To A Great Small-Block Mopar Cylinder Head

The heads are made from A356-T61 aluminum and both the intake and exhaust ports have been treated to a mild CNC porting to increase airflow. In fact, in a bench test, we found 300.1 cfm at .600-inch valve lift through the intake and 216.6 cfm at .600-inch lift through the exhaust. For a small block Mopar head, that is substantial.

Since Mopar engines use a shaft-mounted rocker arm system, the cast stands are stronger than the OE design and will accept any rocker arm system that bolts in place like the OE parts. When it comes to pushrod holes, the angle at which Mopar installs their lifters is 57 degrees from vertical. This is vastly different than that of a Ford or Chevy small-block with a 23-degree angle. So, to accommodate hefty pushrods, larger diameter pushrod holes have been incorporated to accommodate up to 3/8-inch pieces.

Oiling the top end of a small-block LA-series Mopar is accomplished through the rocker arm shafts, not the pushrods like a Magnum-series small-block. Typically, a reduced-shoulder bolt is required at the stand that has the oil passage to the shaft. With The Trick Flow heads, a machined area is cut into the stand to allow oil flow without the need for a special bolt. While this alleviates the need for a special bolt in this location, Trick Flow does recommend using the recommended Trick Flow rocker shaft studs.

Also, bronze-alloy valve guides, ductile-iron valve seats, and multi-angle valve-seat facing further increase performance and durability. Assembled cylinder heads include premium 11/32-inch stainless steel valves, Trick Flow by PAC Racing valve springs, and steel valve stem locks. You do have a choice of either chromoly or titanium retainers. The heads are designed to fit all non-emissions 318, 340, and 360 engines built between 1967 and 2003. Astute Mopar fans might think that is a typo, but it’s not. These heads fit both LA and Magnum-series engines.

When selecting the heads for our 416 small-block Mopar, one thing I did need to take into consideration was the cylinder head’s small 60cc combustion chamber. While the heart-shaped design is great for burning fuel, our Icon pistons stick out of the block .065-inch. With a flat cylinder head and a small combustion chamber, the math doesn’t work out when using a traditional .040-inch thick composite gasket.

To get the required clearance and keep the compression ratio down to what I consider an acceptable 11.5:1, I need a head gasket that is thicker than what comes in a traditional rebuild kit. I needed an MLS gasket that was .086-inch thick. When considering an MLS gasket, one name quickly comes to mind, Cometic Gaskets.

When installing the rocker shaft assemblies, make sure the oil holes for the rocker arms are facing down (at the bottom of the shaft). If the holes are facing up, the oil won’t exit the shaft and lube the rocker arms until the shafts are full of oil.

Sealing The Squeeze

Unlike a traditional, composite head gasket that uses a compressible material, MLS head gaskets utilize layers of embossed steel to create the gasket. Most MLS gaskets are comprised of between three and five layers of steel, with the embossing being localized around key points like cylinder bores and oil and water ports. The top and bottom layers of the gasket surface are treated to a thin coating of Viton (a flouroelastomer-based material that is heat-resistant up to 482 degrees). Viton is designed to meet the demands of a variety of harsh sealing environments, load conditions, and surface finishes. That said, an MLS gasket does require a certain surface finish in order to seal. Surface roughness (Ra) is a calculation of the average roughness of a surface profile. Since no surface is perfectly smooth, Ra is the mathematical average of the peaks and valleys measured across a surface, and is usually expressed in micro-inches (µin).

Most aftermarket MLS gaskets prefer surface finishes with an Ra of around 50 µin. Smoother is always better, and if you can get the finish down to the low teens or even single digits, great. But for most applications, a surface finish in the 20 to 30 µin range is more than smooth enough for a performance MLS gasket.

According to Jeff Evers, automotive product line manager at Cometic, “Cometic doesn’t rate head gaskets for horsepower or boost levels due to variations from build to build. Things such as head and deck thickness, fasteners, and surface finish all play a part in how much horsepower they can handle. With that said, our standard MLS head gasket is our biggest seller and can handle what most customers can throw at it. We generally offer these in .027 to .140-inch thicknesses with many options in between.”

Keeping LA Thumper Looking As Good As It (Hopefully) Runs

I do not know of any brushable paint system that gives the smoothness and shine the KBS Coatings Motor Coater did. The first step is to Klean the block, then hit it with Rust Blast, Rust sealer and then and then brush on the paint. Making an engine look good is just as important as how it runs. Let’s face it, if it looks like a thrown-together mess, it will always be considered as such. This brush-on paint is done in stages and creates a lasting paint covering that will hopefully look great for years to come.

Singling Out The Proper Plane

With the heads chosen, we next needed to decide on an intake. When deciding between a single-or dual-plane intake manifold, several factors need to be considered. First, the way the engine will be used. If you’re building an engine designed for daily driving, then a dual-plane intake is your better choice. When building a race-only engine that will spend most of its time in the high-RPM range, then a single-plane intake is the wise option. However, when building a serious street/strip engine like LA Thumper, the choice can be blurred.

For instance, the car will mainly see street duty, which means a dual-plane intake would be the best option. LA Thumper will not be spinning higher than 7,000 rpm, so again, a dual-plane intake would suffice. However, since we will be running what some consider a high compression ratio and do want to realize as much horsepower as possible, a single-plane intake was selected.

When installing a roller camshaft in an LA-series small block, the lifter must be installed before the heads or you ain’t getting them in there.

While this small-block Mopar will be used in a “street car” there are certain aspects of the car that require consideration when choosing the manifold. For instance, although the intended RPM range ends at 6,500, the car can afford to lose some torque down low in the Rs as it is light, uses fairly steep gears, and relies on a four-speed for gear changes. For these reasons, I have decided to use a single-plane manifold. And since Trick Flow heads are part of the plan, I decided to give the Trick Flow Track Heat intake a try.

When the short block was assembled, the pistons stuck .065-inch out of the hole. A traditional composite gasket with a crush thickness of .040-inch was not going to work. A Cometic MLS Gasket that has a thickness of .086-inch was needed. This thickness gives us .021-inch of quench area.

The Track Heat intake is perfect for engines making peak power within the 3,000 to 7,000 rpm range. This manifold utilizes a divorced-plenum construction, meaning the runners keep the plenum separated from the rest of the intake. It also features overly thick bosses for adding nitrous nozzles, which is a future possibility. There is also extra material around the ports to allow custom port work if you want to maximize the intakes power-making potential. I will say that gasket matching requires minimal effort as the ports are very close to being spot on.

These manifolds work with all 4150-style square bore carburetors. The carb mounting pad height is 5.125 inches. If you plan to put a small-block Mopar engine with a Track Heat intake in an A-body car, you need to keep in mind, the height of this intake could cause hood clearance issues in some cars depending on the air cleaner used. We’ll cross that bridge when we get to that situation.

Rock On

For rocker arms, I actually had a set of used COMP Cams’ Ultra Pro Magnum pieces from a previous build, so I decided to use them. With the heads securely attached to the block and the rocker system bolted in place, I then needed to figure out the length of pushrods I needed. I have a set of adjustable pushrods to help with this, and after some adjusting and measuring, I was able to zero in on a set of Trick Flow pushrods with a length of 7.150 inches. Although the heads do have larger pushrod holes that could accommodate a 3/8-inch pushrod, I still utilized a 5/16-inch rod with a .080-inch wall-thickness.

With the top-end secured, I am another step closer to getting this small-block Mopar together and ready for the dyno. It’s been a long process getting the engine to this point, but check back next time as we button up the engine and get ready to make some noise.