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Pettis Performance 598ci Big-Block - Big, Wild, & Nasty Part two
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The short-block was built to endure rpm and a fury of nitrous induced horsepower. Last month, we showed how a Dart Big M block was filled with a Kellogg crankshaft (4.500-inch stroke), JE custom pistons (13.6:1 compression), and GRP rods. The Dart Big M block is made of iron, providing stability to keep the cylinder bores from moving around and that means better ring seal. It was modified with 4.600-inch bores and Pettis moved the lifter bores in order to straighten the pushrod angle and prevent them from intruding on the intake port. The pistons went through a barrage of modifications from tension tests with its rings and modified domes for the valve layout of these heads. The short-block and ultimately the entire long-block were assembled and disassembled several times as Pettis checked every moving part for proper clearances and fitment. On the dyno, the Pettis 598ci didn't disappoint as it spun all the way up to 8,800 rpm without any trouble at all. The heads, intake, and valvetrain performed admirably and the final numbers are a stout 1,120 hp at 8,000 rpm. On the torque side, Pettis began the power sampling at 6,500 rpm so the only peak torque number he has is 810 lb-ft at the bottom of the pull (6,500 rpm). Peak torque probably occurs closer to 6,200 but since the engine will never run that low there is no reason to test its power output there. Pettis dissected the dyno results, "I look at the average in a 1,200 or 1,300 rpm spread, which is the optimum range of the motor with the torque converter. This engine made 1,102 average from 7,200 to 8,500." He continued, "it doesn't fall off and will run real hard on track." Pettis did explain that this engine could have much more power if they set it up for naturally aspirated trim. But nitrous oxide injection is in the future for this beast. "It makes great power despite only having 13.6:1 compression and the pistons sitting 0.040-inch below the deck," he stated. The piston location below deck is not good for quench as it slows down the burn-rate of the fuel, which is good for use with nitrous but bad for making power in naturally aspirated trim. Au naturel engines require the fuel to burn quickly to make power. Another noteworthy item is that this engine was run on VP Fuel N20 gasoline, which Pettis says makes 35-40 hp less than VP C14 or Q16. "We were dialing it in for nitrous, so we dyno with the fuel that we run on the track to eliminate a variable," he explained. All this talk of nitrous oxide might have you wondering about what was plumbed into this manifold. "We installed two Edelbrock E3 direct-port nozzle systems in the runners and then added a third stage of nitrous with our Punisher plenum system," commented Steve Johnson of Induction Solutions, a nitrous specialty company located in Brooksville, Florida. Johnson also flowed all three nitrous systems before shipping the intake back to Pettis Performance. The main purpose of flowing the system is to meter the pounds/hour for both the nitrous and fuel. Induction Solutions also monitors the nitrous pressure, fuel pressure, and solenoid amperage draw to make sure things are operating properly. According to Johnson, it gives them an idea of where the systems are with the nitrous/fuel ratios and gives the team a baseline. Manufacturers give a one-size-fits-all tune-up with jet sizes and fuel pressure. The flow testing establishes an application tune-up for that particular system.  "We are checking the piston-to-valve...  "We are checking the piston-to-valve clearance with all of the valvetrain installed. We put a dial indicator on the retainer and roll the engine over to 10 degrees before TDC for the exhaust and 10 degrees after TDC for the intake, zero the dial indicator, and open the valve with the wrench. You can then see how many thousandths until the limit. The most accurate way to check the clearance is by using all the springs and the pushrods. By mocking up the engine this way we can maximize the piston dome design when we final cut the valve pockets." said Pettis. A checker spring won't deflect the valvetrain realistically resulting in inaccurate measurements; this is done during the engine mock-up phase.  Pettis checks the roller tip...  Pettis checks the roller tip as it moves across the valve. They use a spring height mic and perform this task on the bench. It simulates peak-lift, mid-lift, and zero-lift. Pettis uses this technique rather than just eyeballing it because he can assign a numerical value to the valve tip movement and plot out the most desirable sweep pattern. The head was machined to get the proper height rather than relying on shims to move the base around. Eliminating the shims helps with valvetrain stability.  The pushrod holes had to be...  The pushrod holes had to be enlarged and moved over to accommodate the relocated lifter bores; long pivot length rocker system; and large 1/2-inch diameter pushrods.  Here is a finished look at...  Here is a finished look at the Manton pushrod coming through the head and the Jesel rocker arm resting on top of it.  One of the first specs that...  One of the first specs that Pettis measures on any engine build is to verify the camshaft lobes. It is critical that he verifies the camshaft because of the many measurements and adjustments that are made to the heads, valvetrain, and pistons. Each adjustment is based on the camshaft specs and if those are wrong, it will be a lot of wasted time and effort. The only specs Pettis admitted to were 0.950/0.900-inch lift; the duration was over 280 degrees and 310 degrees, intake and exhaust respectively at 0.050-inch lift. The lobe separation was also wider than 116 degrees. Comp Cams is responsible for cutting the custom profile.  A Buxton billet spring compressor...  A Buxton billet spring compressor measures the valvespring pressure. Our Comp valvesprings showed 425 lbs. on the seat and 1,100 lbs. open. To put that into perspective, the typical mild street hydraulic roller is 140 lbs. on the seat and 350 lbs. open. The heavy springs are needed to control the valvetrain at 8,800 rpm. Pettis also accurately checks coil-bind height, which can be more important than actual pressures. Thanks to Spintron testing, the racing community now knows that it is typically better to set the springs closer to coil-bind. The old belief to set them further away has shown spring surge and vibration issues at higher rpm levels. These springs were set up 0.060-inch from coil-bind.  Ferrea 2.350-inch intake valves...  Ferrea 2.350-inch intake valves and 1.900-inch exhaust valves were used. Here a ball bearing was attached to each valve and is part of Pettis' methodical way of measuring piston-to-valve clearances.  The intake rocker arms are...  The intake rocker arms are Jesel 1.85:1 ratio and the exhaust uses a Jesel 1.8:1 ratio. The tie-bar lifters are also from Jesel and Pettis used Manton 1/2-inch 0.188-inch wall thick pushrods with hardened steel ends. The rocker arms have longer pivot lengths than normal for less sweep on the top of the valve, a trick that helps control the valvetrain stability at high rpm levels. The Jesel rockers also use a roller-bearing tip to help reduce friction.  The pushrod angles were straightened...  The pushrod angles were straightened out as much possible to help this engine rev quickly and to 8,800 rpm without any incidents. It is impossible to get them completely straight without going to very exotic components but every little bit helps. Another benefit of moving the lifters over in the block is that the pushrods are moved away from the intake ports, allowing the use of 1/2-inch pushrods without the pushrod hole intruding on the intake port.
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