Pettis Performance 598ci Big-Block - Big, Wild, & Nasty Part two
Our Pettis 598ci Cranks Out 1,120 hp-Without Nitrous!
From the June, 2010 issue of Chevy High Performance
By Michael Galimi
Photography by Henry De Los Santos
Last month we embarked on a mission to build a big, wild, and nasty big-block engine to compete in the West Coast radial tire ranks. It is a class reserved for rowdy engine combinations stuffed under the hoods of ordinary stock-suspension equipped cars that roll on 275/60-15 drag radials in the back. Fierce competition has pushed this heads-up eliminator into the 7-second zone forcing our editor, Henry De Los Santos, and his racing partner, Artis Houston, to step up their game. The plan was to build a 598ci engine that fits with the 3,300-pound minimum vehicle weight they are shooting for, which takes into account the Hogan's sheetmetal intake and the conventional-style Edelbrock Victor 24-degree cylinder heads.
The LA-based group of racers showed up on the doorstep of Pettis Performance (Hesperia, California), where Jason Pettis and his capable staff filled in the details and built a powerful combination. The ever-determined race shop sought 1,100 hp and 8,800 rpm from this engine in order for the team to contend for the title. Pettis' goals for this engine combination were quite lofty, especially since the cylinder heads weren't of the Pro Stock origin like a set of Big Chief or other unconventional race-style heads. The Edelbrock Victor/Musi CNC 24-degree cylinder heads are considered a conventional set of heads, but they have race-style features like generous valve sizing and healthy port size and flow.
Pettis Performance mocked...
Pettis Performance mocked up the engine several times and made many modifications before its final assembly and engine dyno testing. Up front, the Jesel front drive distributor and beltdrive system are essential for timing accuracy and quick cam timing adjustments. The oil pan of choice is a Moroso unit with their external wet-sump setup.
Pettis only had to make a few modifications to the out-of-the-box heads. "All we did was add a larger intake valve and increase the cross section of the intake ports. Edelbrock did a great job out of the box," he said. "We did increase the runner volume of the exhaust ports due to the nitrous. The reason for that is a nitrous motor has a larger exhaust gas volume than a naturally aspirated engine because of all the extra fuel. The exhaust gas is also hotter, so there has to be more volume to allow it to expand. Another reason for the port volume is that the bigger motor requires bigger ports to achieve the rpm levels we were shooting for."
The goal with this massive 598ci bullet was 8,800 rpm, a lofty one but that rpm range was needed in order to keep up with the quick blower and turbo combinations that are taking over the Wild Street category. You could hear the enthusiasm in Pettis' voice, "I was impressed with how this combination worked with the cubes and it went right to 8,800 rpm. With the correct intake and cam, these heads would work great even on a 632! Sure, a Big Chief or other spread-port head would outperform it, but this is a 24-degree head."
It takes more than a great set of cylinder heads to turn serious rpm and make over 1,100 hp on the dyno. Pettis explained, "the intake has to have enough runner cross section and plenum volume to support the 598ci." Hogan Intakes built a custom sheetmetal intake based on the target hp range of this bullet. It wears two Holley HP series 1050 Dominator carburetors that were dialed in on the engine dyno. The cam is top-secret but Pettis did admit to lift numbers of 0.950-inch for the intake and 0.900-inch lift on the exhaust lobes. "The valvetrain is the biggest key for a high-rpm combo, the 4.500-inch stroke isn't that big of a deal," commented Pettis. The team relies on Jesel rocker arms and lifters as well as super-thick Manton pushrods. Valvetrain stability can be directed back to the small details, one of the biggest is the way the Pettis Performance shop sets it all up on the heads. Pettis spent some time working the heads and the rocker stands to his liking, namely to ensure a solid foundation. The Jesel rocker arms are also longer and feature a roller-bearing wheel tip.
A BHJ cutting tool was used...
A BHJ cutting tool was used to add an O-ring in the block and a receiver groove in the head. Pettis said he prefers to add the ring in the block because if the head ever needs to be repaired it is one less modification required. The deck rarely gets re-cut over time, which is why he prefers to have the O-ring in there. A 0.041-inch thick ring is used to help seal the heads to the block.
The Edelbrock Victor/Musi...
The Edelbrock Victor/Musi CNC 24-degree heads were inspected and modified for this application. Pettis Performance opened the intake ports slightly, performed a valve job, added larger intake valves, and modified the exhaust ports. Overall, Pettis was very impressed with these cylinder heads and its capabilities.
Edelbrock sent the heads with...
Edelbrock sent the heads with a CNC port job and Pettis added Ferrea 2.350-inch intake valves and 1.900-inch exhaust valves. The combustion chamber checks into the party at 114 cc.
Hogan's Racing Manifolds builds...
Hogan's Racing Manifolds builds each sheetmetal manifold as a custom piece. For ours, we downloaded a template, which asks for very specific dimensions, including cubic inches, deck height, chassis weight, compression, along with whether it's an EFI or carbureted application. Once completed, we submit the information and were very pleased with the quick turnaround time.
The heads received a 50-degree...
The heads received a 50-degree seat and as Pettis explained, the steeper valve seats improves flow on some heads, with the Edelbrock Victor 24-degree being one of them. Seats are cut on a Newen GII CNC machine using custom cutters designed by Pettis with CAD software furnished by Newen. The cutter is labeled with a serial number that is recorded on the engine blueprint sheet.
Valvetrain stability is one...
Valvetrain stability is one of the key elements that Pettis performs on these racing engines. An often overlooked part of valvetrain stability is how the rocker stands fit on the cylinder heads. The shop custom fits the stands to each head to ensure proper fit and clearance.
Pettis welded the intake and...
Pettis welded the intake and exhaust rocker stands together to form a stronger foundation. The stands also needed to be milled down and adjusted for the ultimate fitment. Pettis commented that these are built to fit wide applications and he just custom fits them to what each engine requires.
You see where the stand now...
You see where the stand now has a step cut into its base to clear the top of the head bolt. It's small details like this that has put Pettis Performance on top, churning out record-breaking and championship-winning powerplants for dozens of racers in serious heads-up organizations.
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.
On track, the '71 Nova is a beast as the team eclipsed its best time with a 7.82 at 183 mph this past fall at the Street Car Super Nationals. Houston's career best e.t. was even sweeter due to the fact that it was accomplished with a few baby hits of nitrous. "That was with all three systems but they were small and we have a lot more left in it. As the chassis continues to get sorted with the torque converter dialed-in, we can start adding more nitrous. There isn't a whole lot of nitrous going through that thing yet," said Johnson. He went on to say that if the team can get the Nova more efficient through the 60-foot times, then they could run 7.60s on the 275 drag radials. The big, wild, and nasty 598ci is ready for all challengers.
What is it
Pettis Performance-built 598ci big-block
What it made
1,120 hp on motor with three units to go
On nitrous, this big-block powered our '71 Nova to 7-second e.t.'s at well over 180 mph
Check out chevyhiperformance.com for bonus content on this story, including full dyno details.
Pettis marks the intake rocker...
Pettis marks the intake rocker arms with blue paint while the exhaust arms are marked with red. It helps the engine assembler identify the components-especially if making the repairs at the dragstrip late at night.
SCE Titan copper head gaskets...
SCE Titan copper head gaskets were used to seal the heads to the block. The red marks on the gasket are a special coating to help seal various coolant and oil passages. These gaskets are designed to go on dry, meaning no special spray coatings or any crazy sealing tricks. Pettis prefers copper head gaskets for nitrous-equipped engines to the popular MLS-style gaskets.
Induction Solutions plumbed...
Induction Solutions plumbed the twin Edelbrock E3 direct-port nitrous systems as well as a third stage, its Punisher plenum nitrous system. Steve Johnson flow tested the system and consults on the tuning adjustments.