402 Big Block Cylinder Head Swap - Head Games

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.

Sucp 1110 402 Big Block Cylinder Head Swap Head Games 004

1 We baselined the car on our Snap-on Tools Tech Center Dynojet as is—no tuning beyond making sure the plugs were fresh and clean, and the timing was at spec. We ran the car three times, with a best run of 283 rear-wheel horsepower at 4,900 rpm and 383 lb-ft of torque at 3,700 rpm. The air/fuel ratio was staying in the mid-12s through the whole run.

1 We baselined the car on our Snap-on Tools Tech Center Dynojet as is—no tuning beyond ma

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.

2 After the motor cooled off, the first order of business was simple: strip off the top of the engine, including the front accessory bracket for the alternator. Make sure to have plenty of shop rags handy during this, especially when disconnecting fuel lines to the carbs (or fuel injection if your own motor is so equipped).
2 After the motor cooled off, the first order of business was simple: strip off the top o
3 Taking the valvetrain apart is pretty straightforward. Just remove all the rocker nuts, then pull the rockers and pushrods. We used a valvetrain organizer tray to keep all the rockers in order, important for reassembly later. We pitched the old rocker nuts though and had new ones ready to replace them.
3 Taking the valvetrain apart is pretty straightforward. Just remove all the rocker nuts,
4 This car still runs cast-iron manifolds, and they needed to come out so we had plenty of room to pull the heads. While not as free-flowing as a set of headers, the factory manifolds are cast in a shorty-header-like style and aren’t as restrictive as one might think.
4 This car still runs cast-iron manifolds, and they needed to come out so we had plenty o

5 With the head bolts out, we (well, Bruce) could remove the old cast-iron monsters. We put one of these on a bathroom scale and it came out at a whopping 70-plus pounds—hence the veins popping out of Bruce’s neck as he hefts this one over the Corvette’s fender. After the heads were off, we used some of those blue, heavy-duty shop paper towels to soak up any spilled coolant from the cylinders and lifter valley.
5 With the head bolts out, we (well, Bruce) could remove the old cast-iron monsters. We p
6 The guys at Proform sent us these handy head stands (part no. 66481) to use while we checked out our new Trick Flow Specialties heads. The combustion chambers are 113 cc, the same as the factory heads, so the motor’s compression will stay the same. They come fully equipped with stainless steel valves (2.190 int./1.880 exh.), dual valvesprings, 10-degree locks and retainers, high-temp viton valvestem seals, new ARP rocker studs, and adjustable pushrod guideplates. We pulled one of the springs and checked the installed height, and while taller than what the old heads were set at, the seat pressure was within 3-4 pounds of the originals and the rate similar, perfectly compatible with the motor’s flat-tappet cam.
6 The guys at Proform sent us these handy head stands (part no. 66481) to use while we ch
7 Before installing the heads, we chased all the head bolt threads to make sure they were clean.
7 Before installing the heads, we chased all the head bolt threads to make sure they were

8 Here’s a close-up of the combustions chambers, new vs. old. The TFS heads feature a modern chamber design with more efficient flow of the flame front than the old heads, less valve shrouding, and an open chamber design.
8 Here’s a close-up of the combustions chambers, new vs. old. The TFS heads feature a mod
9 A quick view from the intake side, and you can see how the TFS intake ports offer a much straighter shot to the intake valves than the factory heads. This flow improvement alone makes for more horsepower, and the potential for future horsepower increases with cam and intake improvements.
9 A quick view from the intake side, and you can see how the TFS intake ports offer a muc
10 Proform also sent its cylinder head cc kit so we could measure the combustion chambers on both heads for comparison. Easy to use and a handy tool if you’re working with heads you don’t have the full specs on; we verified the 113cc chamber size of both heads. Watch for a future tech story on cc-ing a cylinder head for more in-depth info on the process.
10 Proform also sent its cylinder head cc kit so we could measure the combustion chambers

11 Weighing in at a much lighter 44 pounds, setting the new TFS heads in place was a lot easier on Bruce’s back. Taking weight out of a car (even one as light as a Corvette) is always a performance gain, the basic math being that for every 100 pounds you remove, the car picks up a tenth in e.t. With over 60 pounds off the front end in this case, even on the street we’ll see a difference in handling and performance.
11 Weighing in at a much lighter 44 pounds, setting the new TFS heads in place was a lot
12a To attach our new heads, Trick Flow/Summit Racing supplied us with a set of new ARP head bolts, part no. 135-3607...
12a To attach our new heads, Trick Flow/Summit Racing supplied us with a set of new ARP h
12b ...Because of the raised exhaust ports, the outer head bolts are longer than stock, so for the swap we needed new ones anyway.
12b ...Because of the raised exhaust ports, the outer head bolts are longer than stock, s

13 Because some of the head bolts are “wet”, meaning they go into the water jackets, we needed to use non-hardening thread sealer on them to prevent coolant leaks. The sealer also acts to lubricate the threads, very important when installing head bolts, especially if you’re working with an aluminum block.
13 Because some of the head bolts are “wet”, meaning they go into the water jackets, we n
14 ARP includes a tube of assembly lube with all of its head bolt kits. We used it to lube underneath the heads of our bolts where the washers go, again a must for accurate torquing of the bolts and to prevent the washers from galling into the bolts and creating stress points that could lead to premature bolt failure.
14 ARP includes a tube of assembly lube with all of its head bolt kits. We used it to lub
15a Head bolts are torqued down in three steps (four steps for just the longest bolts) for proper stretching of the bolts...
15a Head bolts are torqued down in three steps (four steps for just the longest bolts) fo

15b ...Bolts and even compression of the head gasket for effective sealing. Trick Flow includes the torque specs and sequence for these heads in its instructions.
15b ...Bolts and even compression of the head gasket for effective sealing. Trick Flow in
16 The heads come with two different rocker arm stud lengths, one for intake, the other for exhaust. Because the intake rocker stud holes go into the intake ports, TFS specifies using Teflon tape on the threads in their instructions. Miss this step and you could end up with oil in the cylinders.
16 The heads come with two different rocker arm stud lengths, one for intake, the other f
17 The heads come with adjustable pushrod guideplates to help get the rocker alignment more precise than the standard one-piece plates. Leave the adjustment bolts loose so you can adjust them after the rockers are in place, along with the rocker arm studs.
17 The heads come with adjustable pushrod guideplates to help get the rocker alignment mo

18 When installing non-stock heads, unless they’re the same height as factory, you will need longer pushrods, as TFS notes in its instructions. Our buddies at Comp Cams sent us their adjustable pushrod kit (comes with three different-length checking pushrods) so we could figure out the length necessary. Once calculated, we ordered up a set of Comp 7757 9.600-inch-length, one-piece, 3/8-diameter, heavy-wall pushrods. Since pushrod length can vary by application and block (deck height, whether a head’s been milled, etc.) it’s always best to measure pushrod length to verify you’ve got the right ones. Pushrods too long or too short can wreak havoc in the valvetrain and lead to serious engine damage like valves hitting pistons.
18 When installing non-stock heads, unless they’re the same height as factory, you will n
19 As we reassembled the valvetrain, we used a liberal amount of red assembly lube on the pushrod ends, rocker pivot balls, and rocker tips. Even on already used parts like rockers, still use this so you don’t have dry start-up issues that could damage the valvetrain.
19 As we reassembled the valvetrain, we used a liberal amount of red assembly lube on the
20 Once the valvetrain was set up and the rockers properly aligned thanks to the guideplates, the rocker studs were torqued to the spec in the instructions. Everything like this has a torque spec to follow, and it’s even more critical when dealing with aluminum heads. Don’t just crank everything down until it’s tight.
20 Once the valvetrain was set up and the rockers properly aligned thanks to the guidepla

21 With the rockers done and lifter preload set for every valve, the rest of the engine’s top end was reinstalled.
21 With the rockers done and lifter preload set for every valve, the rest of the engine’s
22 To verify timing and true top dead center (TDC) we used a Proform TDC locator so we knew the balancer’s timing mark was accurate.
22 To verify timing and true top dead center (TDC) we used a Proform TDC locator so we kn
23 Because of their increased heat dissipation, aluminum heads typically require a hotter-heat-range spark plug. Along with that, aftermarket heads like our Trick Flow units utilize a long-reach plug so the flame kernel is fully exposed, meaning better combustion and more power. TFS spec’d our heads with Autolite 3924 plugs, and you can use this number to cross-reference to other plug brands to suit your preference.
23 Because of their increased heat dissipation, aluminum heads typically require a hotter

24 For coolant, we used AMSOIL’s heavy-duty service antifreeze, which is compatible with both standard (green) and long life (orange or other colors). We also used AMSOIL’s 20W-50 racing synthetic oil, which has higher ZDP levels than regular synthetics, a must if you’ve got a flat-tappet camshaft, especially on camshaft break-in. Even on a properly broken in flat-tappet cam, it’s still good insurance to run this oil, especially in a car that doesn’t see regular driving.
24 For coolant, we used AMSOIL’s heavy-duty service antifreeze, which is compatible with
25 Back on the dyno, we ran the car up to moderate rpm to simulate a road cruise and let everything break in on the new heads just to be safe, and check for oil and coolant leaks. Off the bat, the new heads solved the overheating issue, confirming our suspicions that one of the old heads was the culprit. This was double-verified by testing the coolant for exhaust gas traces and coming up negative.
25 Back on the dyno, we ran the car up to moderate rpm to simulate a road cruise and let
26 After a decent amount of break-in miles on the street, we strapped her back down on our Dynojet. Ready to go, we nailed the throttle and were rewarded with a higher peak output of 311 hp at 5,000 rpm and higher peak torque of 344 lb-ft at 3,500 rpm. We knew the engine was running rich (which can hurt power output), and noticed that the air/fuel ratio leaned out to the high 12s, low 13s with the head swap. Since the only parts changed affecting hp numbers were the heads, we know for a fact that these heads are worth 30 hp straight up on a low-compression big-block. And with better-flowing heads capable of more lift (max lift for our heads is 0.700 inch), the number of cams we can select from in our next performance upgrade is greatly expanded.
26 After a decent amount of break-in miles on the street, we strapped her back down on ou

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