In our ongoing coverage of Ivan Korda’s Project Boring 4-Valve Cobra engine, we’ve made a lot of progress with this budget-friendly road-racing build. While Ivan and his team are working feverishly on the chassis of his 2001 Mustang Cobra, Exigent Solutions is nearing the completion of the 2004 Mach 1 engine. Todd Warren of Apocalypse Performance has spec’d out the combination to be a 400-plus horsepower (at the wheels) powerplant, with an emphasis on a strong midrange suitable for road racing and autocross.

 

In Part 2, we got the top end sorted out and the camshafts set up, so it’s now time (no pun intended!) to move on to the front of the engine — setting the timing and sorting out the intake. So far, the key takeaways have been adding lightweight components to the rotating assembly with custom pistons that included valve reliefs and a cast crank that reduced our rotating mass by 12 pounds. 

The cylinder heads were pretty straightforward, as we used mainly shelf parts from Ferrea and Todd Warren-spec’d cams from COMP Cams. Then we just touched up the heads and did a standard three-angle valve job. All of the machine work was provided by our friends at Exigent Solutions in Cincinnati, Ohio. 

Timing Is Everything

As we focus on our timing setup and the front of the engine for the Cobra C-Head 4-Valve, engine builder Todd Warren got a camshaft Ford Performance drive kit (P/N: M-6004-A464) from American Muscle. That covered most of the timing components we needed for the 4.6-liter engine, including the tensioner arms, chain guides, front cover gaskets and front main seal, primary and secondary timing chains, primary and secondary timing chain tensioners, camshaft sprockets, spacers, bolts and washers, crankshaft sprocket, and the crank position trigger wheel.

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Our engine builder insisted that we go with upgraded billet timing chain guides that are bored out to accept a larger tensioning pin because the spring loads will be higher and for longer durations than any stock application. On the left, you can see the comparison between a stock and the upgraded tensioning pin. On the right are the billet chain guides.

Warren insisted that we upgrade the chain guides and passenger-side tensioner because of some deficiencies with the stock parts for the loads we’ll be putting on the engine. So we got a kit from Wonder Racing that included billet chain guides, guide pins, and a tensioner spacer. The guides are machined from a solid block of 6061 aluminum and have a pinhole for a factory-sized 0.318-inch guide pin. They can also be honed to fit upgraded guide pins, which we did.

The billet chain guides and larger guide pins are used because the stock pieces can break under higher RPM, greater spring loads when using aftermarket springs, and higher lift cams. We also like to use them with a two-step limiter and when more time will be spent on the rev limiter. — Todd Warren

According to Warren, tensioner spacers prevent the tensioners from compressing under high loads. “Without spacers, the tensioners can compress, which can compromise your cam timing.”  The spacers also reduce the extreme load changes seen by both the primary and secondary chains and reduces the chance of chain failure. Warren chose to go with a sturdier passenger-side secondary tensioner from Cobra Engineering because he didn’t think the stock tensioner could handle the high spring loads and RPM of the upgraded 4-valve engine.

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We upgraded to some stronger parts for the secondary tensioner because Warren didn't think the stock tensioner could handle the high spring loads and RPM of the upgraded 4-valve engine.

The stock chain tensioner is designed to allow the [passenger side] intake camshaft to retard the timing under higher spring loads and at higher RPM. — Todd Warren

“The exhaust camshaft drives the intake camshaft, and the stock tensioner is designed in a way that the tension side of the chain pulls across its plunger rather than in a fixed position,” explains Warren, adding that the new Cobra Engineering part flips the tensioner upside down and provides a solid, fixed base on which the secondary chain can pull the intake cam.

Continuing with the front-side upgrades under the timing cover, Warren chose to go with a Melling 3-valve oil pump because it would provide the increased oiling we needed. “We used the bigger volume Melling pump because it has a larger diameter gerotor that provides a higher volume of oil. The 2-valve and 4-valve pumps can’t put out the oil volume of this higher capacity Melling pump.”

Moving On To The Top End

After the front of the engine was buttoned up, we were ready to move on to the top of the engine and discuss what our trusty engine builder chose for the intake, injectors, throttle body, and headers. 

We chose to go with 440cc/min (42 lb/hr) Deatschwerks fuel injectors because the fuel needs wouldn’t be that demanding for this naturally-aspirated application. Instead, we focused on the airflow coming into and out of the engine. The Deatschwerks injectors are all dynamically flow-matched on state-of-the-art injector testing equipment. They also come with detailed calibration data for whatever EFI system you are using, to ensure that they are ready to go, out of the box. 

One of the most significant modifications of the top end came from a custom runner intake manifold from Matt Hayes at Never Enuff Performance Racing, who works with Warren on many projects. Warren says he used to make the short-runner intakes himself but, now he works closely with Hayes to modify the factory intake manifolds for his customers. 

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With a custom-made 10-inch runner from NEP Racing, we are able to achieve more average power up to 7,400 rpm.  Anything above that, and you're going to need a higher 8,000 rpm shift point, so you’d want to go with a six-inch intake runner.

“There are probably 20 hours into modifying an intake manifold,” explains Warren. “You have to cut the intake apart and then there’s a ton of fabricating and welding, and a lot of smoothing out that needs to happen. The beauty of this intake is it doesn’t kill low- and mid-range power like a 6-inch runner. It gives you more power from 5,000 rpm and up. The stock intake kills power at 6,300 rpm, but this one will allow peak power to be made up around 6,600 rpm and it does not fall off out to 7,000-plus rpm. On the stock intake, after peak power is produced the power drops substantially… Torque and horsepower take a nosedive.”

“With the 10-inch runner, it produces more average power, if you’re going up to 7,200 to 7,400 rpm. Anything above that you’re going to have an 8,000 rpm shift point, so you’d want to go with a six-inch intake runner. But that short of a runner destroys power below 4,500 rpm. Since this is going to be a road racing car, you can’t destroy your mid-range power.” 

We got a bit of a bump in power from an Accufab twin-60mm throttle body and paired it with a stock 2003-’04 MAF sensor, which results in a 10-horsepower gain, according to Warren. The cold air intake was sourced from JLT, which comes with a 4-1/4-inch I.D. intake tube made of roto-molded plastic to resist engine heat and keep the intake air charge nice and cool. And the ABS molded-plastic heat shield blocks engine heat at low speed and idle.

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We chose a twin 60mm throttle body from Accufab for a gain of about 10-horsepower, and the JLT cold air intake tube keeps the incoming air-charge cool to help accomplish those gains.

Getting The Gasses Out

Warren was pretty specific about which exhaust header tube diameter he wanted to use. So we chose 1-3/4-inch-primary headers from American Racing Headers because they are a good compromise between the 1-5/8-inch and 1-7/8-inch offerings. “The 1-5/8-inch primaries make great low- and mid-range horsepower and torque,” Warren notes. “The 1-7/8-inch primary tube headers provide outstanding high-RPM output, but come with some noticeable losses in the low- and mid-range areas of the powerband.”

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We chose 1-3/4 inch primary tube headers from American Racing because it was the best compromise between 1-7/8 and 1-5/8 options that would give us good mid-range but not drop off like the others. But it still left about 10-horsepower on the table.

While the 1-3/4-inch-primary headers leave a little on the table in terms of low-RPM power, compared to the 1-5/8-inch tubes, they produce more power than the 1-7/8-inch headers in that area. What tipped the scale for the 1-3/4-inch headers is they offer more power from 3,500 rpm and up compared to the 1-5/8-inch headers. However, according to Warren, the 1-3/4-inch primaries are probably down about 10 peak horsepower compared to the 1-7/8-inch headers. 

Since the car’s intended use is road racing, it will spend a lot of time between 3,000 and 6,500 rpm. So the 1-3/4-inch headers were the obvious choice. — Todd Warren

“If this were a 3,000-pound drag car with 4.56 gears, it would have gotten the 1-7/8-inch headers… then again, it also would have received cams with more duration, so the peak output would have been much greater.”

Stay tuned for part four of the Project Boring 4-Valve, where we will wrap up the build and see how it performs on the dyno!