What happened to the big power numbers of the 454? The last generation big-block by GM (Vortec 454) leaves much to be desired when it comes to output. The Vortec big-block was gifted with a sequential port fuel-injection system that provided more power than its predecessor (throttle-body injection), but it still wasn't even close to the numbers found in the late-'60s and early '70s engines.
In fact, the LS6 (optional motor) that was available in 1971 was one of the highest-output 454 engines in production for its configuration. The fire-breathing Rat blew brimstone at the rate of 425 hp. Not bad for a powerplant straight off the showroom floor. The LS5 of the same year pumped out 365 hp. In 1972, all that power was lost. The LS6 was no longer available, and the LS5 only put out 270 hp.
Manufacturers are given a specified number of smog credits per year. The lineup of vehicles and quantity of vehicles manufactured consumes these credits quickly. So, you can see how making vehicles run lean and choking down the bigger engines would directly affect the company's profitability. But, that doesn't stop motorheads from seeking out ways to unleash the potential locked in the stock powerplants.
As part of the motorhead family, we at Sport Truck decided to see if we could revive some of the numbers locked away in the mystery of the Vortec big-block. We started by strapping our '96 Chevy dualie to the dyno to see how much power our Vortec engine had. After a couple pulls, the best run the Bow Tie could muster was 215 hp, and 329 lb-ft of torque.
We then pulled off the top of the engine to look inside. We found what GM had done to keep the Rat at bay: If you can't breath, you can't run. The Vortec intake pockets have a ramp that is suppose to swirl the air/fuel charge to increase velocity and provide more torque. The problem is that the ramps were rough-cast and needed some work to allow the air to move over a smooth surface instead of tumble over it. The intake runners are fairly respectable and are definitely an improvement from the "Peanut" heads found on the throttle body-injected Rat GM used before the Vortec. The runners were "as cast," of course, leaving a rough surface with mold seams in the runners, reducing airflow efficiency even further. In the exhaust runner, a large bulge that shrouds the exhaust valve stem consumes about one third of the exhaust runner, making the port restrictive. We also found that the intake valve in the Vortec head is 2.060 inches in diameter, and the exhaust is 1.72 inches, which is small for a 454ci engine.
We took the heads to Superior Automotive in Anaheim, California, to have the heads flowed and ported to improve the airflow problems. Owner and founder of Superior Automotive Joe Jill and his techs tore into the heads and told us what we needed to do to make a good strong combination. The cams in these trucks are retarded by the factory about 6 degrees. So, we got Competition Cams to remedy the problem with its Ultimately Adjustable Timing Set to dial in the cam. While we had the top pulled off the engine, we opted to convert the hydraulic flat-tappet cam to a hydraulic roller and gain a few more horses. We also ordered a mildly upgraded cam with no more duration and the same centerline, but with a little more lift to take advantage of better airflow through the heads.
Superior also opened up the airflow in our Vortec heads by installing a lager set of valves. The new Manley stainless swirl valves provide more valve surface area, which enables a larger volume of air to pass through the valve openings. The head was cut to hold a 2.190 intake valve and a 1.800 exhaust valve. Superior bolted the heads to its SuperFlow SF600 flow bench to test the stock combination. The enhanced cam we got from Comp has 0.510 lift, which is about 0.060 over the stock cam. We also got a 1.8:1 rocker to enhance the cam lift. With the 1.8 rockers, the new cam lift will actually be 0.540. This meant we needed to pay attention to the flow numbers up to 0.550 lift. The stock intake flowed 246 cfm at 0.550 lift, and the exhaust flowed 162 cfm at 0.450 lift. We flowed the exhaust at 0.550, but the air in the runner started to tumble and the flow numbers started to fall off.
After the head work was done, the flow number came up across the board. At 0.550 inch of lift, the intake flows 271 cfm and the exhaust 0.204 cfm at the same lift. With the head work done, all we needed to do was assemble and break in the engine before we strapped it down to the dyno. Check in next month to see how the big Bow Tie does on the dyno after all the mods.
1.Removal of all the accessory...
1.Removal of all the accessory brackets, the radiator, and the intake was essential in getting to the cam and heads. The Vortec intake manifold is constructed in two separate pieces. The injectors and fuel rails are mounted in the center of the manifold.
2.After the fuel rails and...
2.After the fuel rails and injectors were pulled free of the intake, the base manifold could be removed.
3.The rear (left side half)...
3.The rear (left side half) of the exhaust gaskets were obviously leaking. This was surely robbing some grunt from our Bow Tie behemoth, because of a lack of backpressure.
4.Notice the slight difference...
4.Notice the slight difference between the left and right rocker arms. The right, driver-side rockers are darker than the left, indicating the right head may have been subjected to more heat than the left. There were also large amounts of calcium around the water jacket of the right head. This is why you don't want to just put water in the cooling system. The calcium deposits obstructed the coolant's flow through the right head, which allowed that side of the engine to run hotter.
5.Wouldn't you know it? The...
5.Wouldn't you know it? The rear gasket on the right head was slightly leaking coolant. The rear cylinder was steaming off the water, allowing the calcium to build up on that side. This is what allowed the coagulation of calcium on the back water jacket, which made the engine run hotter on that side.
6.Not only was the whole cylinder...
6.Not only was the whole cylinder wet with coolant, the electrode on the spark plug was corroded with impurities. This certainly reduced the power in that cylinder.
7.The intake valve upped in...
7.The intake valve upped in size from 2.060 inches to 2.190, increasing the intake's ability to move more air.
8.Superior Automotive employs...
8.Superior Automotive employs some of the best machinery available to hold super-tight tolerances. The Serdi 100 isn't new to the automotive industry, but it's still a staple in cylinder head machining.
9.The Serdi's machine head...
9.The Serdi's machine head centers itself into the valve guide of the cylinder head with the use of a pilot that fits into the valve guide. This three-angle cutter can be adjusted to open up the head to accommodate any valve that will fit the head casting.
10.A dial indicator was used...
10.A dial indicator was used to ensure all the valve seats are cut symmetrically. This eliminated any variances in flow that would come from the seat being machined at different depths in each of the combustion chambers.
11.After the valve seat had...
11.After the valve seat had been cut, we could see a harsh edge that needed to be blended from the back side of the seat to the runner pocket.
12.The valve seat cutter was...
12.The valve seat cutter was replaced with this angle cutter to remove this harsh edge.
13.Using this cutter removes...
13.Using this cutter removes the majority of the unwanted material from the seat to the pocket. The rest of the material will be removed by hand.
14.The exhaust was increased...
14.The exhaust was increased from 1.720 to 1.800. This was where we were really going to pick up power. The intake flowed pretty well, but the exhaust was very shrouded.
15.The exhaust seat is a hardened...
15.The exhaust seat is a hardened insert that the Serdi makes quick work of, but, not without the hardened material squeaking and smoking from the heat caused by friction.
16.We could see a huge difference...
16.We could see a huge difference between the exhaust and intake seat. The exhaust sees the brunt of burning fuel and needs to be hard enough to prevent the head material from eroding. The intake gets cooled by the air/fuel charge, which makes it run much cooler.
17.The valves were installed...
17.The valves were installed into the head to ensure the valve seats are symmetrical. The installed height of the valve was noted so the proper valvespring can be ordered to provide the proper valve seat pressure.
18.The exhaust was significantly...
18.The exhaust was significantly chocked down. This is where the grinding comes into play.
19.Superior didn't just grind...
19.Superior didn't just grind away at the exhaust area to match the gasket. A straight edge was taken to the ports to uniformly attack the exhaust passage, keeping the same symmetry from one port to the other.
20.The area in the rotation...
20.The area in the rotation of a cam where the intake valve and exhaust valve are opened simultaneously is know as overlap. The reason for this is so spent fuel leaving the head will actually create a vacuum that will enhance cylinder efficiency by pulling the fuel charge into the cylinder, which is known as scavenging. Superior used a D-port on the exhaust runner to increase the efficiency of the scavenging. This helps because as the valves open and close, it's possible for the piston to pull from both the intake and exhaust. The flat area of the D-port of the exhaust will create a vortex that provides pressure in the exhaust, preventing the spent charge from being pulled back into the combustion chamber.
21.A radius gauge was used...
21.A radius gauge was used to ensure the port job was as symmetrical as possible. We mention symmetry a lot, don't we? If all of the cylinders make the same power, the engine will be well balanced, providing smooth, clean power.
22.Next, the pockets were...
22.Next, the pockets were to be massaged to increase airflow. Here, you can see the stock runner casting of the Vortec cylinder head.
23.We didn't want to open...
23.We didn't want to open the intake too much because we would run the risk of reducing the intake air velocity. The intakes flowed well to begin with for the hauler we're building. The ramp on the Vortec pocket was slightly cut down and smoothed for airflow, but the swirl design was in the port job.
24.This is the untouched exhaust...
24.This is the untouched exhaust valve pocket. You can see that the combustion chamber shrouds the valve, and the valve seat is recessed below a machine cut that restricts flow.
25.Even after the exhaust...
25.Even after the exhaust seat was cut to fit the larger valve, the valve seat area still retains the restricted machine cut from the factory.
26.A cutter was used to unshroud...
26.A cutter was used to unshroud the valve and remove the machine step in the combustion chamber. This freed up the airflow restriction around the exhaust valve, which will help increase the percentage of flow, providing us with something that's more along the lines of a good balance between exhaust and intake airflow numbers. After the port work was done, the heads flow 271 cfm at 0.550 inch on the intake and 204 cfm at 0.550 on the exhaust.