Building The Ultimate Ultra Street Engine Part 2: Cylinder Heads

Welcome back to the adventure of diverting our children’s college funds into something infinitely cooler! Jokes aside, our Ultra Street project has been a journey, as we transition a former grudge car into the righteous realm of Ultra Street racing. I’d be lying if I said it was an easy trek, as one man’s safety is another’s deathtrap. However, with our chassis and cage fixed in our first installment, it’s time to continue with our engine build.

Ultra Street is an extremely competitive class with each car merely tenths away from each other. To remain competitive takes more than just money; it takes clear-cut knowledge and the proper tools to produce a winning engine combination. No one has more knowledge and time in the small-block Ford world than Jon Bennett. Thankfully, our driver and car owner has spent many race days at the dragstrip with him, making the segue to getting an engine built a tad bit easier. 

The Foundation

In Part 1 of our ultimate Ultra Street engine build, we discussed the short block. We employed a cast aluminum solid Carroll Shelby Engine Company block to establish a robust foundation for the engine. The block underwent machining before being fitted with a Callies Magnum crankshaft, Calico Coatings bearings, GRP connecting rods, Diamond Pistons, and Total Seal piston rings. Once Bennett completed the bottom end, it was time to add the top end with a set of heads that could deliver both performance and reliability to last throughout the season, and hopefully beyond.

All Hands On Deck

Unbeknownst to us, aluminum blocks typically have longer thread depths than a steel block. Our Shelby engine block was no exception. Instead of using off-the-shelf bolts to secure our heads, Bennett opted for custom-made head studs. “Almost every aluminum block manufacturer uses different thread depths, including billet and cast blocks. It is imperative to check these depths and order studs accordingly,” Bennett explains. “The longer aluminum studs give more threads than the conventional steel block.”

FlatOut copper head gaskets were used to seal the gap between the block and the heads. “These gaskets are .051 inches thick and match our fire ring system in terms of press fit O-ring into the groove,” Bennett details. 

Headed For More Power

Understanding the fundamental principles of an internal combustion engine involves recognizing that the more air we can pump in, the more fuel we can burn, resulting in increased power. So, why not use the largest cylinder heads available on the market? Sounds straightforward. Well, in the words of Tom Hanks, “If it were easy, everyone would do it.” There is a science to it that involves more than just grabbing the largest off-the-shelf products. However, given that the cylinder heads are a major component of generating great power, we wanted to optimize this to the fullest.

Topping off our 400 cubic-inch displacement engine is a pair of Bennett Trick Flow Specialties High Port 265RX cylinder heads. “The Bennett 265 cylinder heads are an inline 20-degree cylinder head that packs a major punch. Through many years of ongoing development, we have ended up now with the absolute fastest inline 20-degree head out there,” Bennett declares. “We have hit 3.90’s in notime racing, four-teens in X275, 4.40’s in Ultra Street with a nitrous combination, and regularly make over 900 horsepower naturally aspirated with these heads.”

While these are no longer the raw high-port casting that came from the factory, what makes the Bennett 265 such a desirable and a race-winning head is the work that goes on behind the scenes. “The Bennett 265 cylinder heads start with a Trick Flow high-port raw casting that is CNC-machined. Intake ports, exhaust ports, combustion chambers, and pushrod tubes receive full CNC treatment,” Bennett explains. “Prior to machining oversize intake seats, high-temp exhaust seats, 5/16-inch intake and 11/32-inch exhaust guides are installed. We also delete the OEM horizontal header bolt holes allowing us to provide a unique sized exhaust port. When all this is complete it yields a 400 cfm intake port and a 300 cfm exhaust port.”

The combustion chamber found on the Bennett 265 heads is also available in different sizes, but for our build, we went with a 70 cc version. Bennett also employed a chamber cone process. “This process was originally developed for shallow valve angle heads when used with nitrous to help soften the blow of heavy nitrous on a shallow valve angle small chamber. This allowed a wider tuning window and, most importantly, protecting the engine from parts failure on nitrous,” Bennett explains. “Today, years later, you see shallow valve angle heads with very large chamber designs that allow for a very happy engine on nitrous or ultra-high boost, for that matter.”

Dry Decking And Valve Job

Since we opted for a solid block, Bennett also dry-decked the heads. “Dry decking is a process where we weld all water jacket openings on the deck of the head shut and then surface machine the head back flat. The advantage is we keep water off the head gasket, removing the chance for an external water seep/leak if the engine is rattled,” Bennett says. “We do fire ring some engines that have wet blocks and heads, but the machine specs of the ring/groove are altered to achieve a better seal on the water jackets on the head and block.

With the cylinder port work performed and the dry decking process finished, Bennett was able to start the valve job. “With a valve job, seat angle and overall design are customized to fit the customer’s combination. In this case, we used a 50-degree valve seat angle,” Bennett says. “We also adjusted the seat ring size based on the combination, as well. Seat ring size is the measurement of the valve seat at its widest opening. Seat ring size is a widely debated topic. It is one way to boost up a head flow number, but in some cases, it can make the engine lose power, especially on naturally aspirated engines.”

Bennett continues, “Seat ring is originally dictated by the valve seat cutter design, but is then hand-blended to achieve the result. A good example would be if we choose a 55-degree valve seat angle – that cutter design would yield a larger seat ring diameter based on the last angle on the cutter being, in many cases, steeper than the 50-degree cutter we used on these heads.” The final process of the head casting was to machine for and install the fire rings.

Flow Testing For Fine Tuning

“Our final flow numbers are dictated by the choice of valve size, valve job design, final seat ring size, and the design of the valve itself. These choices, though many times are a small piece of the puzzle, allow us to fine-tune every set of heads we build for the customer’s exact combination,” explains Bennett. 

While the flow bench is sometimes used as a pissing contest between engine builders, its purpose should reflect what a conventional dyno is used for: fine-tuning. Bennett is quick to explain that the flow bench should not be used as a numbers game. Instead, racers and performance enthusiasts should not ask, “What do your cylinder heads flow?” but rather inquire, “With my engine combination, how much power have you made with them or how fast have your customers been?

With that word of caution, we can’t help but be excited about the flow numbers on our new Bennett Racing 265 cylinder heads! With the heads thoroughly flow tested and a final cleaning performed, the heads were mounted on our engine block.

Valve Lift Intake CFM Exhaust CFM
.300 219 155
.400 273 204
.500 325 240
.600 365 261
.700 389 277
.800 396 284
.900 401 292
1.00 403 298

Rounding Out The Top End

With the completion of our block and cylinder head package, you can say things are starting to get pretty serious. It’s difficult for us to contain our excitement and not ask Bennett for a rush job, but art takes time and we still have a few more steps before we can install our small-block Ford engine into our Ultra Street Fox Body! Stay tuned, as our next steps will be discussing the valvetrain, timing, and all additional accessories. 


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James Elkins

Born into a household of motorsport lovers, James learned that wrenching takes priority over broken skin and damaged nerves. Passions include fixing previous owners’ mistakes, writing, and driving.
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