Two months back we bolted a thumpin' Vortech V7 YSi centrifugal supercharger to our ZZ502 for a quickie blow-through carburetor boost test. We didn't touch the 9.6:1-compression long-block except for a Moroso oil pump and pan, but we did add an Edelbrock Victor, Jr. single-plane intake with a Demon blow-through carburetor. With no other additions except for a set of big-tube headers, the carbureted ZZ502 made exactly what Chevy claimed for the naturally aspirated version at 500 hp. Then we added the Vortech supercharger and that same stock 502 with 10 psi of boost made 822 horsepower and 786 lb-ft of torque. We were impressed.
As we mentioned in that test, we decided that the low rpm peak horsepower numbers for both the naturally aspirated and supercharged tests were a result of the weak valvesprings supplied with the 502 engine. We tested the springs and weren't surprised when the results were barely 150 pounds of load on the seat. These are very low numbers for a big-block Chevy with heavy valves. Westech's Steve Brule says his experience is that a minimum of 200 pounds of seat load is required to keep control of the valves at higher engine speeds. But rather than just change springs and add aluminum roller rockers, we decided that the cam was also too conservative and that with a little more duration and valve lift, we could really make some power with this Rat.
We looked through the Crane Cam catalog and discovered a cam that we thought would work really well. We certainly could have increased the intake duration more than the 230 degrees that we chose, but we didn't want to push the peak horsepower rpm point much past about 6,200 rpm in a naturally aspirated state because the supercharger would also conspire to do the same thing. The main reason we chose this cam was because it offered an outstanding 0.070 more intake valve lift (0.066-inch on the exhaust) with only a small duration increase. The plan was to install the new cam, degree it, check for valve-to-piston clearance so we didn't bend the valves, and stick our 502 back on the dyno and see how far up the power numbers went.
With the engine reassembled with the new Crane camshaft and valvetrain, we were excited to see what our new cam would be worth. Our initial goal for the naturally aspirated test was anything above 530 hp. So after fully warming the engine and resetting the timing to 36 degrees total, we were ready for the first pull. The 502 immediately responded to the cam change by pushing the torque up everywhere and elevating the peak horsepower on the very first run to 557 hp – adding a solid 57 hp. The peak horsepower point was still low, at only 5,600 rpm, but we had obviously improved the power and also had dramatically pumped up the torque. Looking at the previous peak torque number of 539 at 3,700 rpm, the cam swap gained 36 lb-ft at that same rpm, but the whole curve improved dramatically. Usually when we add a longer duration cam, torque below the peak usually falls off, but in this case, we gained everywhere.
We backed this test up with a second run just to make sure and were about to make a jetting change after a third run when we noticed that the power fell off. Another run saw the power drop even further. This was when we decided that something was wrong. Westech's Steve Brule has seen these kinds of issues in the past, so we pulled the Fram oil filter and cut it apart to find lots of shiny aluminum bits in the filter. We were done for the day so we removed the engine from the dyno and we took it back to the Smith shop for a post-mortem inspection. Yanking the oil pan revealed that the Number 2 main bearing had failed and bits of aluminum bearing had killed four rod bearings on either side of the failed main. We have actually seen this before on an 800-plus horsepower big-block Chevy, but didn't really expect to find this kind of problem on a brand-new 502 engine.
This set us on a mission to discover exactly what had gone wrong. We called Mahle Clevite's Bill McKnight for a quick course on engine bearings. The aluminum bearings had failed but we really didn't know why. Bill says that for roughly the last 10 years, most (if not all) current production engines now come with steel-backed aluminum rod and main bearings, called bi-metal bearings. This is in response (at least partially) to European demands that no engine bearings contain lead as a bearing material. Bill says that aluminum has a slightly lower load capacity compared to performance-oriented tri-metal bearings, but even so, aluminum is capable of handling the load. He says the problem with aluminum is that, oddly, it is very hard. Aluminum has no soft facing, which means if the main bearing journal deflects slightly under high load, the material will tend to wipe and micro-weld as opposed to buffing or wearing a softer bearing material.
01. Two months back, we realized that the stock ZZ502 cam and valvetrain was leaving a lot of power on the table. We decided to order a slightly more aggressive Crane hydraulic roller cam, lifters, springs, retainers, and rocker arms to complete the valvetrain.
02. Normally, we would just re-use the factory hydraulic roller lifters with our new cam. But big cams generate lift by reducing the base circle diameter. If the base circle is small enough, the lifter can drop low enough in the lifter bore to release the factory dog bone. This will produce disastrous results. The Crane lifters are not only longer to prevent this but are also of a very high quality with a much more robust snap ring.
03. One focus for this test was to ensure we improved valvespring pressure, so we compared the original springs to the new Crane units on our InterComp digital spring tester we got from Summit Racing. The included chart lists the spring loads, but even on the seat, the Crane springs increased load by 29 percent and 31 percent at 0.600 lift.
04. After installing the new Crane cam, we also replaced the original cam drive with a new Crane adjustable timing set. We started out by installing this straight up with no advance or retard.
05. The next step was to degree the cam to ensure that it was in properly phased. Crane calls for an intake centerline number of 107 degrees and our numbers came in at 107.5 degrees so we left it there.
06. After we degreed the camshaft, we then set the heads back on the engine with checking springs on the valves for cylinder one. Using a dial indicator, we rolled the piston through 20 degrees on either side of TDC to check for valve-to-piston clearance. By pressing down on the intake rocker, we can measure the amount of additional room between the valve open position and the piston. At its closest point, we had 0.150-inch clearance. You can use this technique when you don’t want to remove the heads for the clay method.
It's probable that this is what happened to our 502 engine. In this case, we think that the bearings began to fail back with the blower test. The multiple 820-plus horsepower runs excessively loaded the Number 2 main and very quickly it began tearing material from the bearing and sending it through the rest of the engine, scoring the crank and sending aluminum chips all through the engine. This is not a condemnation of the stock 502/502 engine. Instead, it's an opportunity to illustrate that the stock, aluminum bearing inserts used in these production engines have a power limit that appears to be somewhere in the 750 to perhaps 800 hp area for big-block Chevys. At the 500- to 600hp naturally aspirated level, Bill says that the stock aluminum bearings would probably work just fine. One advantage to these bearings is that because they are harder, they tend to last much longer.
Based on our experience, it would appear that if you have plans to follow our lead to build a similar supercharged 502, it would be wise to assume that new performance rod and main bearings would be one of the first things you would want to change before bolting on the supercharger or perhaps an aggressive nitrous system. So what makes performance bearings like the Clevite 77 performance bearings capable of handling this additional load? McKnight says that performance bearings like the Clevite TriMetal bearings use a steel backing inlaid with a combination of copper and lead with a very soft electroplated lead tin alloy overlay. This softer bearing material is more than capable of very high load capacity yet it offers the ability to easily embed foreign materials and also to be self-sacrificing should the crank occasionally push through the oil film. Because the bearing material is softer, it wears as opposed to micro-welding and tearing apart.
Other advantages to using high-performance bearings is that Clevite and others offer larger chamfers and narrower bearings to clear larger crank fillets that improve strength. Plus, Clevite also offers coated bearings for situations where that little added protection is also desired. For our rebuild of the 502, we will be going with the Clevite HK series bearings, which are the coated versions of the classic H performance bearings. These bearings will provide the protection we need since it appears that this engine could easily be pushing 950 hp or more in the near future.
While our bearing issues prevented us from getting to the supercharger portion of our test, we learned quite a bit about bearings and hopefully we've also saved a few other 502 engines from a similar fate. While aluminum bi-metal bearings are plenty good for production engine power levels, when it comes to making big power, it's clear to us that a better bearing will be able to handle the load imposed by 850 to 900-plus horsepower. But let's not forget that despite our setback, we still made an honest 557 horsepower with our cam change and we might have been able to push past 560 hp with a little more fine tuning. Editor De Los Santos is already considering just bumping this whole package up to 540 inches with a long-stroke crank, rod, and piston package. If that happens, it's obvious that the power will expand as well. We might just be looking at a blow-through big-block at 1,000 hp. Stay tuned, it's gonna get fun!
07. Setting up the new Crane springs required reducing the installed height by 0.100 inch. We added Crane spring seats that were 0.050 inch thick, placing them on top of the existing shims and then we also added Crane locks that located the retainer 0.050-inch lower on the valve stem. With these new parts, we created our required 1.900-inch installed height.
08. When we installed the taller Crane lifters, this required shorter pushrods. To determine the proper length, we set the lobe on the base circle and used an adjustable pushrod to position the rocker arm so that it contacts the valve tip roughly one-third off from center. We marked the end of the valve tip with a black Sharpie and then wiggled the rocker to leave a witness mark. Increasing pushrod length moves the mark outboard and vice versa.
09. With the engine assembled and back on the dyno, we used an 850-cfm Mighty Demon carburetor for the naturally aspirated runs. Unfortunately, we never got a chance to tune the engine because on the third pull, disaster struck.
10. Once we discovered the engine was ailing, we pulled it apart and this is what we discovered. It appears that Number 2 main was the first to suffer and the aluminum shavings quickly scored the rods on either side. The block was not damaged but will require new cam bearings and a thorough cleaning.
11. The original equipment aluminum bearing is on the left. On the right is a big-block Speed-Pro performance tri-metal bearing. Note that it may appear corroded but these bearings are not flash-coated. Performance tri-metal bearings have good load capacity but are soft enough to accommodate load spikes that destroyed the harder aluminum bearing.
12. This graph makes it easy to see that our cam swap improved power throughout the entire test curve from 3,000 to 6,000 rpm. Perhaps the biggest difference in power is at 6,000 rpm. While 6,000 rpm is past peak power, this would be where you would shift. The new cam makes 88 more horsepower here. You will feel that in the seat of your pants.
|Cam Spec Chart|
|Camshaft||Duration at 0.050 (degrees)||Valve Lift (inches)||Lobe Separation (degrees)|
|Stock 502 hyd. roller, Intake||224||0.527||110|
|Crane hyd. roller, Intake||230||0.598||112|
|Valvespring Spec Chart|
|Valvespring||Load at Installed Height||Load at 0.600 Lift||Spring Rate|
|Stock 502 Spring||155 lbs. at 1.900||380 lbs. at 0.600 lift||375 lbs/in|
|Crane 96878 Dual||200 lbs. at 1.900||500 lbs. at 0.600 lift||475 lbs/in|
|RPM||TQ1||HP1||TQ2||HP2||TQ Diff||HP Diff|
|Chev. Perf. 502 engine, base kit||12496963||Summit Racing||$8,009.97|
|Crane hyd. roller cam, Gen VI BBC||168761||Summit Racing||490|
|Crane hyd. roller lifters, long travel||26535-16||Summit Racing||696|
|Crane valvesprings, dual||96878-16||Summit Racing||164.8|
|Crane titanium retainers, 7 degree||99659-16||Summit Racing||355.2|
|Crane locks, 7 degree||99094-1||Summit Racing||32.4|
|Crane locks, 7 degree -0.050 install ht.||99088-1||Summit Racing||40|
|Crane spring seat locators||99465-16||Summit Racing||72|
|Crane Pro Billet timing set||16977-1||Summit Racing||196|
|Crane Gold Race rockers, 1.7:1||13750-16||Summit Racing||381|
|Crane pushrods, Intake, pr. (8 req.)||95785-2||Summit Racing||22.4|
|Crane pushrods, Exhaust, pr. (8 req.)||95806-2||Summit Racing||22.4|
|Edelbrock Victor, Jr. intake||2904||Summit Racing||279.97|
|Mighty Demon 850-cfm carburetor||5563010GC||Summit Racing||634.95|
|Moroso oil pan||20411||Summit Racing||275.97|
|Moroso oil pump and pickup||22175||Summit Racing||103.97|
|Moroso oil pump driveshaft||22080||Summit Racing||15.97|
|Autolite spark plugs, N.A.||AR3932||Summit Racing||4.97 (ea.)|
|ARP intake bolts||135-2001||Summit Racing||27.01|
|Lucas 10w30 Muscle car oil, 5 qt.||10679-1||Summit Racing||25.97|