There have been numerous comparisons to the engine residing under the hood of your car to the heart that beats in your chest. That would seem like a reasonable association to the majority of people in this world, however, lovers of the performance side of things know the internal combustion engine is far more complex than that simple idea.
The engine is a mixture of many things that equate to different organs in the body, all with different jobs, and cylinder heads would be considered part of an engine’s respiratory system since they help move the air into the machine. To accomplish this task with the small-block Chevy engine for our Project Evil 8.5 Ford Mustang, we picked out a set of Brodix cylinder heads that have been worked over by Chris Frank at Frankenstein Racing Heads, and outfitted with the best valvetrain parts from Manley and Jesel.
Using Frankenstein Racing Heads was a solid choice based on the shop’s reputation. For the past decade, Frank and his team have been working on heads for NHRA teams that run everything from Pro Stock to Top Fuel.
“Frankenstein is a high-end development shop that doesn’t do any production run stuff; all of our work is custom. We gear everything towards an engineering background since most of us come from the engineering side of things. We look at putting out quality over quantity with good results and a solid product,” Frank says.
We selected the Brodix symmetrical port, raised runner, cylinder head that’s capable of flowing big time air. These heads originally were designed for sprint cars, but Brodix revamped the design so they could be used as a boosted application cylinder head, and that’s now what the head is mostly used for today.
“The first thing we do is evaluate the engine program as a whole and see what power adder will be used. This particular build was going to use a blower and as much boost as possible for the class. We tried to evaluate all of the small-block heads that were available to find the best fit. The Brodix were the most efficient of the bunch, and would allow us to use port designs that would be beneficial for a supercharged application,” Chris explains.
For this build, we concentrated more on the combustion chamber design and the exhaust port design of the heads – Chris Frank
The flow the heads provide is what makes them so attractive to all racers, no matter the application, with a good wet flow pattern that allows the air and fuel to come together with great efficiency inside the combustion chamber. Brodix spent extra time with these heads in the design process to ensure that the wet flow pattern would be optimal, and that is further aided by the symmetrical port design. The symmetrical ports also allow for everything to be evenly spaced, and that helps prevent hot spots in the center of the combustion chamber like you could see on a small-block Chevy-based engine.
The intake location and port layout are two of the biggest things that made these heads the choice for a boosted project like this, according to Chris. “We really like the high intake port location, as it allows us to put the intake port really high off the deck of the head. Being able to do that makes a much better approach to the combustion chamber, because now the head can rotate down toward the combustion chamber freely in a more natural way and flow well.
“The second reason is that it’s a symmetrical port layout, so each port is equally spaced and spread apart so you don’t have any common walls. Plus, every port is the same design, so you don’t have a left or right port. Every cylinder should be just as efficient as the one next to it with this design.”
Another advantage to the heads over the other choices is that these heads use an inline valve design. This design provides all of the advantages of a canted valve setup, without the weight penalties in x275. It also allows for a more simplistic valvetrain to be used and makes the heads more cost effective overall.
All of these benefits are what helps to make the heads a solid choice for a boosted application, but the runner design is what puts them over the top. “The heads being a raised runner design really helps for a boosted application like this. This makes it so the heads have good efficiency, while the combustion chamber doesn’t become overly sensitive to timing,” Frank explains.
The heads being a raised runner design really helps for a boosted application like this – Chris Frank
All Aboard The Evil 8.5 Valvetrain
Since Evil 8.5 will be using a blower as a power adder, the valvetrain will be taking some serious abuse. For everything to function correctly, the proper hardware must be used, and that requires some upgraded parts.
“The biggest thing I feel is that you need to overbuild the valvetrain and make it as rigid as possible in a boosted application because, at the end of the day, a lightweight valvetrain doesn’t survive,” Frank says.
The CRN-coated Manley valves used on the Brodix heads measure 2.225 on the intake side and 1.615 on the exhaust side with a 11/32-inch stem thickness. These valves had to be sized a bit larger due to their application, and according to Trip Manley of Manley Performance, that’s how it should be. “With the boost, obviously you’re going to increase cylinder pressure. From a design standpoint, the valves can’t be too flimsy. You wouldn’t want to be too thin on a cross-sectional thickness, especially in the critical areas of the valves.”
To match the valves used, a set of Manley Nextek dual valve springs were added to the Brodix heads. These springs have many positive attributes that fit the build, according to Manley. “The beauty of this spring is that it’s got a really good rate, high natural frequency, and it’s light. What’s also cool about that spring is that it’s got a lot of load, and handles it in a lightweight package.”
The Nextek springs also fit what Frankenstein looks for in springs when building a boosted motor. “We’re a big believer in a lot of seat and open pressure in a boosted application, so we probably over-spring most of our boosted applications, because they’re a little more violent, and with the valvetrain, you’ve got a lot more cylinder pressure you’re opening the valve into,” Frank says.
Rocker arms on the Evil 8.5 mill are aluminum full body Jesel 1.8 ratio units. These are very stout rocker arms that don’t have a ton of material removed, so they will be strong and can take the boosted abuse. “The advantage to an aluminum rocker arm in a boosted application is that it will absorb some of the valvetrain deflection and harmonics through their dampening properties,” Frank says.
The Trend Performance 7/16-inch, .165-inch wall pushrods were a simple choice due to their size. “It’s really a simple formula for pushrods on an application like this: try to get the biggest one that will fit and use it. A lot of guys don’t realize how much deflection you get in a valvetrain, so the bigger pushrods help to negate that,” Frank explains.
The Head Porting Process And Results
A good set of racing heads have to do more than just move massive amounts of air. They must do it in an efficient way to match the rest of the engine. Taking a set of cylinder heads and just opening them up with colossal amounts of port work isn’t the best way to make optimal power. A good cylinder head shop will approach the process like a surgeon, using the mindset of making everything more efficient, and that’s exactly what Frankenstein did with our Brodix heads.
Since these heads are already designed to flow well for boosted applications, the changes required during the porting process were minimal,” as Frank points out. “We didn’t need to make any drastic changes to these heads. The big restriction on any port job is where the water is, and these heads have a pretty large water jacket. The first thing we did was X-ray the head to see where the water cores were and where the thin spots could be.”
CNC Digitizing For Port Work
The porting process is a bit more complex at Frankenstein compared to other shops, as Frank shares. “We design all the ports by hand and then solidify our designs with Computational Fluid Dynamics (CFD). Instead of using a flow bench, we use the CFD software to do all the port work. The software analyzes everything and runs a live action simulation of the head including the opening of valves and so on. It will tell us the high and low air saturation points for the ports, so we can see where the air is going and where it isn’t. We use that to help finalize the design, then it goes to the CNC machine to be digitized by the probe. The probe is taking thousands of points inside the head — we use that to program the porting for the CNC process.”
“For this build, we concentrated more on the combustion chamber design and the exhaust port design of the heads. We made sure to use a very large throat diameter for a boosted application. Paying attention to the exhaust port and the efficiency of the combustion chamber is important on a boosted application.
If the combustion chamber becomes too efficient, the motor will be extremely timing sensitive, so you won’t be able to utilize the power you make. We made sure the chamber shape was useable, that way the motor can take a higher rate of timing. After all of the work was done, the combustion chambers ended up being right around 66 cc each,” Frank says. The heads were milled to the appropriate chamber size, and slightly angle-milled.
The intake side of the Brodix heads wasn’t left totally untouched by Frankenstein. They had to take a measured approach in how they worked that orifice over to match the exhaust side. “We really paid more attention to the exhaust side of the heads, since there’s such a good port on the intake side that was appropriate for the application of the heads. We used a smaller intake valve diameter so a larger exhaust valve diameter could be used, and that allowed us to put a more aggressive exhaust port on the head. That caused us to sacrifice just a little bit on the intake port volume, so we could keep proportions proper between the two,” Frank explains.
Before the heads were shipped off to Steve Morris Engines, Frankenstein strapped them to their flow bench to see what the outcome of their handy work was. The heads were flowed on a 4.125-inch bore and at 28-inches of water. On the intake side with a 2.225-inch valve and a 50-degree seat at .900-inch of lift, the heads flowed 439 cfm of air. The exhaust side was tested with a 1.615-inch sized valve with a 55-degree seat, and at .900-inches of lift the head flowed 291 cfm of air.
“The exhaust port side of the head flowed better than we expected so that was nice to see. On the intake, the heads really performed better than we anticipated as well, so both sides really did great based on our initial calculations. In our opinion, these were phenomenal numbers for this set of heads,” Frank shares.
Making a set of heads generate acceptable levels of power for a specific application takes significant planning and thought. Chris Frank and his team at Frankenstein Racing Heads laid out and executed a strategy based on the goals of the Evil 8.5 build, the blower being used, and the class requirements.
The choices made when it came to the Brodix heads, Manley valvetrain, Jesel rocker arms, and their porting program were all carefully evaluated from the start. The end result of the tactical approach led to a set of heads that flow beautifully and will function well within the bodily ecosystem of the Evil 8.5 engine
In the next article on our Evil 8.5 engine build, we’ll take a look at the killer short block that Steve Morris Engines assembled that these heads will go on!