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402 Big Block Cylinder Head Swap - Head Games

We swap the cylinder heads on a 402 big-block and pick up big power

By , Photography by The Author

Flow. For an engine, it's the key to getting maximum possible output from your internal combustion horsepower-maker. Without it, your engine, whether it be a small- or big-block, is nothing more than a wheezing mass of iron and steel gasping to be put out of its misery. Think of it this way: Run 10 minutes on a treadmill normally, then run another 10 minutes with someone's hand around your throat squeezing mildly. Notice the difference? Restrictive heads do the same thing to your engine.

A good friend of ours was having trouble with his '65 Corvette. The 402 big-block he'd installed years ago was having some overheating problems, which were tracked down to exhaust gas in the cooling system, meaning there was a crack in one of the heads, probably an exhaust valve seat.

This provided us with an excellent opportunity to show what swapping to a set of modern, better flowing heads could do to an otherwise unchanged engine. At the same time, we could ditch the massive, cast-iron, disco-era monsters for a pair of 21st-century aluminum units.

It wasn't that long ago that guys with street-oriented Rat motors had one, maybe two choices for a set of aluminum heads. Notice how we said street, not the expensive race-oriented heads that were cost prohibitive for most. Usually the only option was finding a set of vintage L88/L89/ZL1 factory heads, and even then the cost was enough to build a whole cast-iron performance Rat.

Well, now it's 2011. No, we don't have flying cars, people living on the moon, or any explanation whatsoever for what GM was thinking with the Optispark ignition. But what we do have are honest, great-flowing, performance aluminum heads that'll fit any budget, even that of a frugal big-block owner.

For this test, we weren't going to change anything except the heads. Why? For the guy on a budget, you take everything in steps. Setting aside our subject motor's overheating problem, if you're out to improve your engine's performance without tearing into the short-block, the first place to start is the heads. They're the foundation for your induction system. Even the cheapest budget head on the market today is likely tons better than the factory stuff from 40 to 50 years ago.

Like you wouldn't build the frame of your house before the foundation, you wouldn't get a camshaft first before buying heads. By upgrading just the heads first, we stay within a reasonable budget and allow ourselves a wider range of roller camshafts, both hydraulic and mechanical, to choose from for our next major performance upgrade, including increased lift thanks to the 0.700-inch max lift capacity of the new heads.

For a set of heads that would be street- and pump-gas friendly, we looked at the various catalogs and decided to go with a set of Trick Flow Specialties' PowerOval 280 oval-port aluminum heads, part no. TFS-41310001. These heads feature 113cc combustion chambers, 280cc intake runners, and 137cc exhaust ports raised 0.300 inch to optimize outbound flow and scavenging. While the exhaust ports are raised, the intake ports are in the stock big-block location, so any standard big-block intake will bolt right up. Retail price for these heads is $924.98 (equipped) a piece through Summit Racing. Follow along as we baseline our test engine using our Snap-on Tech Center's Dynojet chassis dyno, swap in our new heads, then strap the Sting Ray back onto the rollers and see what kind of improvements we've gotten.

SOURCES
Trick Flow Specialties
1248 Southeast Avenue
Tallmadge
OH  44278
330-630-1555
www.trickflow.com
AMSOIL
925 Tower Ave.
Superior
WI  54880
800-777-8491
www.amsoil.com
Comp Cams
3406 Democrat Road
Memphis
TN  38118
800-999-0853
www.compcams.com
Proform Parts
Roseville
MI
800-521-1005
www.proformparts.com
Automotive Racing Products
1863 Eastman Ave
Ventura
CA  93003
800-826-3045
www.arp-bolts.com
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