Impersonating The Impersonator
Steve Schaffer, via CarCraft.com: How close to The Impersonator can I get with L98 heads, a Performer intake, and the same cam on my 406; would this require a different cam? I don't have the Vortec heads at this time. I'll be putting this in my '79 Camaro with a 700-R4 and 3.42:1 gears. How much horsepower and torque would this setup make?
Jeff Smith: The story Steve is referring to actually appeared in a sister magazine (Chevy High Performance, June '03). That engine was a 406ci small-block with Vortec iron heads, an Edelbrock Performer RPM Air Gap intake, a 750-cfm Holley double-pumper carb, and a mild Lunati hydraulic flat-tappet cam. The single-pattern cam spec'd out with 230 degrees of duration at 0.050-inch tappet lift, 0.480-inch lift, and a 109-degree lobe separation angle. The engine was also fitted with smaller 151/48-inch headers, and on Duttweiler's dyno it made an amazing 525 lb-ft of torque at 3,500 rpm, grunting out 471 lb-ft at 2,300. Horsepower was acceptable at 428 hp at 5,000. The limiting factor to more horsepower was two-fold with this engine. First, Vortec heads are exhaust-port limited, so using a camshaft with about 10-12 degrees more exhaust duration and a little more lift would have helped. Second, to accommodate this additional lift would require modifications to the heads, and probably better valvesprings as well
The combination you plan to assemble is not going to power up nearly as well. The Performer intake is not as good in terms of torque or horsepower as the RPM Air Gap. But the aluminum heads you suggest running are a bigger problem. The L98 heads are the aluminum 1.94/1.50-inch castings first used on the Tuned Port Injection (TPI) engines in the late-'80s Vettes and Camaros. While these heads look like they might perform, frankly, they're lame. Not only do they not flow nearly as well as even a stock old iron set of 76cc heads, but with a 58cc combustion chamber on a 406ci small-block with flat-top pistons, the compression will be somewhere around 11.75:1, which is way too steep even for aluminum heads.
You mentioned that Vortec heads are not in your current plans, but we suggest selling those weak L98 heads to some street-rod guy who doesn't care how much horsepower he makes as long as the heads look cool, then use that money toward a set of Vortec iron heads. Clearly this combination appeals to you, and the torque is flat impressive. You can purchase a pair of Vortec iron heads already modified with more retainer-to-seal clearance and better valvesprings (PN SD8060A) from Scoggin-Dickey Performance Center for $680 ready to bolt on. Granted, that's a bit of money, but if you are serious about making great power, you can probably find a way to come up with the dough.
As for the camshaft, we'd go with a flat-tappet hydraulic cam with specs of around 230/240 degrees at 0.050 with lift around 0.480/0.510 inch and a 110- to 112-degree lobe separation angle. The cam also needs to be a small-base-circle grind to clear stock-style connecting rods. This small base circle will also affect rocker geometry, which means you'll need at least 0.100-inch-longer pushrods, perhaps longer. Also remember that the Vortec heads use 64cc combustion chambers, so 22cc dished pistons will bring the compression to just under 10.0:1 with 0.040-inch head gaskets and a negative deck height of 0.020 inch. Tightening the piston-to-head clearance will improve quench, but this will also increase compression, making it tougher to be safe on 92- or 93-octane pump gas.
You really shouldn't run the L98 heads because of compression limitations unless the engine has dished pistons of around 23 cc-that makes the compression around 9.7:1. If you're still thinking of going with the Performer intake and the L98 aluminum heads, expect to make great torque, perhaps 440 lb-ft or so up to about 3,500 rpm. At this point, the heads will choke that 406 and you might make 335 hp if you're lucky. Throttle response right off idle will be excellent with this combination, but don't anticipate making much in the way of horsepower. The heads just don't flow any air.
Scoggin-Dickey Performance Center; Lubbock, TX; 800/456-0211; sdpc2000.com