Beneath the head of the intake...
Beneath the head of the intake valve, AFR designed a wing to promote swirl as the air/fuel mixture enters the chamber. Once trapped and Compressed, the efficient chamber design helped the little engine harness the burning fuel without wasting energy. This AFR design feature is one we'll also revisit for the 408ci we're building for Project Talladega, our '75 Laguna.
We were able to adjust cam timing with our Comp Cams beltdrive. Not nearly as expensive as you might think, this was an extremely valuable tuning tool. We were able to move our cam as much as 8 degrees advanced before the power output started to decline. We ended up backing up the cam to 7 degrees, and it was probably a good choice as there were witness marks on each of the pistons from the intake valves kissing them! Probably the most common time in a tight-tolerance race engine's life to expire is at the top end of the track or dyno pull, just as the throttle is slammed shut and the engine decelerates rapidly. This creates a scenario where the rpm is still peaked, but instead of the piston being under load from compression or exhaust as it approaches TDC, the load is suddenly removed and the piston is allowed to travel farther towards the cylinder head and with a greater G-force, due to the lack of opposing pressure. Most timing chains have more slack than a beltdrive, allowing the cam to advance during this deceleration. This "extra" advance, coupled with the piston being closer to the head, greatly increases the chances of a piston-to-intake-valve collision, with disastrous results. Lightweight pistons and the Comp Cams beltdrive likely prevented a catastrophic ending to our engine in testing.
With every jet and cam timing change, we maximized our ignition timing as well. Small-stroke engines like our 337 prefer a good amount of lead, and ours was happiest with 38 degrees. The ICE 10-amp setup was overkill for our pump-gas guzzler, but like ICE owner Michael Konstandinou says, "The worst that can happen is you won't lose any power. The best that can happen is that you'll gain some."
Tuning didn't end with changes to the cam, carb, and spark. We spent a good amount of time running our combination through a software program called Pipemax. It's a great simulator of engine dynamics, and we were able to use the information it gave us to build a set of headers and collectors tuned for the engine and rpm range given. Opening our three-inch collectors into the beautiful Magnaflow mufflers produced a great sound without hurting power a bit.
A mirror image to the chamber,...
A mirror image to the chamber, the pistons show evidence that the intake guide "wing" worked as intended; however, the slight fuel tracking is an indicator that some fuel came out of suspension. A less homogonized mixture can lead to a loss in power. Only further testing without the wing will tell us for sure whether it helped or hurt. Also seen here is proof that we had advanced the cam as much as possible. Check out the self-clearanced intake valve notch!
Once the clock struck midnight in this Cinderella story, the little Chevy twisted the dials to a whopping 529 horsepower, and 481 ft-lb of torque. Had I said last December that I knew we could make that kind of power with such a short stroke, surely my nose would have grown an inch. As it was, when the Challenge had ended and we loaded up our mini-mouse, we couldn't help but happily go whee whee whee all the way home.
Comp Cams BeltDrive: The Tuner's Advantage
Lurking behind the 327's water pump and Powerbond harmonic damper is one of the least known members of the Comp Cams family. Calling up Jegs to order PN 6100 will get you this beltdrive timing set that makes assembling and tuning a high-performance engine a breeze. Beltdrives are often thought to be reserved for ultra-high-dollar endeavors, but with a price under $500, there are few reasons not to pick one up.
The main advantage of a beltdrive is adjustability. During dyno or track testing, it takes literally just a few minutes to move the camshaft a degree or two, reset the ignition timing, and make another pull or pass. In most cases, this can be done without removing the water pump or damper-way better than having to tear down the whole front of the engine to try different cam settings.
Another great advantage of the Comp beltdrive is the ease with which you can set the camshaft endplay. Flat-tappet cams use tapers ground into the cam lobes to force the cam toward the rear of the engine; however, all hydraulic and solid-roller cams are ground with no taper in the lobes, and require some method of keeping the cam from walking back and forth. Cam buttons are typically used, but they rely on flimsy timing covers that tend to flex. The Comp beltdrive uses an adapter mounted to the front of the camshaft as well as brass shims on either side of the adapter to keep the cam consistently located. End play is easily adjusted with various shims (included).
Unlike other aftermarket timing covers, we've had zero issues with oil leaks, and nobody can dispute the added bling factor a beltdrive adds. It costs a little more, but one thing I've learned in years of building engines is that it's better to spend a few dollars up front than to waste precious time and performance down the line.
Using a flat-tappet cam with...
Using a flat-tappet cam with very little duration and banging the valves open with stout 1.9-ratio rockers were instrumental in getting as much air in as soon as possible. To stabilize the valvetrain, stout 3/8-inch-diameter pushrods were employed, and have been proven to reduce valve bounce. Reducing weight on the valve side of the rockers by the use of titanium retainers and small-stem valves is critical, but is not as important on the camshaft side of the rocker, where strength and stability are king.
A NASCAR-inspired modification...
A NASCAR-inspired modification is seen here where we drilled oil squirter holes in the main oil galley, providing a direct feed of precious lube on the cam lobes. Using bronze lifter bushings assured that the bores were correctly angled, and located over their respective lobes.
A block-off plate kept Comp's...
A block-off plate kept Comp's cam almost Completely submerged in oil while running. Excess oil was drained down the main webbing walls instead of being poured on the crank.
With a small arm and ARP main...
With a small arm and ARP main studs, we felt the factory two-bolt mains would handle the torque without any problems. Not pretty, but functional; our last-minute crank scraper was sandwiched between the pan and the block and added another layer of protection from excess windage as it helped keep oil in the pan, and not whipping around.
Starting with a factory steel...
Starting with a factory steel crank, we did some reshaping with a grinder, and turned the counterweights down as well. Even after 40 years of service, the OEM piece was ground straight and true at .010 on the mains, and .020 on the rods.
Our short stroke allowed us...
Our short stroke allowed us to use a super-long rod. The flyweight 6.250-inch rods from Eagle use ARP cap screws to keep their shape under load. A set of flat-top pistons from Ross provided strength and stability, and the machine work was impeccable. Total Seal supplied a set of their gapless top rings to seal up the combustion process.
Pro-Systems has gained notoriety...
Pro-Systems has gained notoriety as one of the top carburetor builders in the world. Using a Holley 4150 design that flows 860 cfm, they assembled a carb with annular boosters that would help atomize fuel throughout the long rpm range required for the engine.
Better known for their circle-track...
Better known for their circle-track efforts, Kevco built an oil pan within the scope of the rules that included a windage screen and a lower solid tray to separate the oil at the bottom of the pan from that still flying around. That second tray does a great job of preventing air bubbles from entering the Melling M-Select pump. Notice the lack of boltholes on the passenger side of the pan. Liberal amounts of Permatex on both sides of the Fel-Pro gaskets kept the pan from leaking a single drop.
Headers built by chassis master...
Headers built by chassis master Gene Steele were stepped and fed into a merge-style collector and collector extension. Lambda sensors were used to dial in the fuel curve and timing changes. The engine made the same power with and without the 3.5-inch Magnaflow mufflers, a tribute to their power potential.
Ignition Components and Electronics,...
Ignition Components and Electronics, or ICE, provided a 10-amp ignition system designed and built with only the best parts and under the tightest tolerances. The billet distributor houses a hall-effect sensor known to be more accurate than a common magnetic pickup, and with less dependence on phasing setup.
Here we are at the Engine...
Here we are at the Engine Masters Challenge, where we're at the mercy of Matt, the DTS dyno operator. PHR contributor Steve Dulcich tries to pry tidbits of information from teammate Shannon Carnathan and the author as Competition director Wesley Roberson tallies up the preliminary score. There's plenty of time for fun before and after our dyno session, but during our time "on the pump," we have our race faces in full effect.