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Chevy Nova: Ask Anything

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Jeff Smith: You have a stack of good questions, so let’s get started. To begin with, the classic car-crafter approach with engines is to start with what you have. The limitation with a 396 block is its small bore diameter at 4.094. Even the 0.030-over 402 barely pushes the bore to 4.125. The stock 396 engine stroke is 3.76 inches, so adding a 4.00-inch stroke to the oversize 4.125-inch bore delivers 427 ci. The 434ci effort you mentioned is attained by stretching the bore to 4.155. While the bore increase helps, the question comes down to increasing inches with a stroker crank assembly to push it up to 427 or 434 inches. But at the same time, it might be easier (and cheaper) to find a usable stock 454 short-block and start there. Staffer John McGann just came back from a local boneyard hunt where he found three complete 454 engines for $399 each. If you bought just the short-block, you might get it for $350 or less but then need to invest $600 to $800 in machine work and $400 in pistons and rings, after which you’d have a larger-displacement engine for the same price as the stroker 396 package and would still have to invest in machine work. The advantage of the 454 block is its larger 4.250-inch bore and stock 4.00-inch stroke crank. Punch the bore another 0.060 and you have 467 inches while retaining the stock crank and rods. I found a 0.060-over Sealed Power hypereutectic piston in the Summit catalog for $355 with an 11 cc dome that would make 9:1 compression. Milling the 118cc heads down to 110 cc would bump the compression to 9.5:1, which is about the limit on pump gas with a mild cam.

Part of the problem with choosing the smaller-bore 396—even after boring it to 4.155 inches—is that the large, open-chamber 049 heads hurt the compression, even if you go with a 4.00-inch crank. With the stock 118cc chamber, you’re looking at 8.4:1 compression, which limits power and only works if you want to run 87-octane fuel. Milling the heads to 110 cc will push the compression up to 8.96:1. This assumes an 11cc domed piston, a 0.015-inch deck, and a 0.042-inch-thick head gasket. The whole idea behind the 454 is not only the added torque and cubic inches but also the hidden value of the larger bore that will help even those oval-port heads to breathe better. Over the years, you might recall that I’ve done several oval- versus rectangle-port big-block head comparisons. The oval-port heads always win. A fair number would be an average of 12 to 15 lb-ft of torque and 10 to 14 hp increase with the oval ports, especially with a smaller-displacement engine like a 454. If you go the 454 route, remember that it’s an externally balanced engine, while the 396/402/ 427 engines are all internally balanced.

From what I’ve found, there is very little difference between the 049 and 781 casting-number heads. If you go the smaller bore route, I suggest you retain the stock 2.06/1.72-inch valve sizes since the larger valves will deliver a minimal power improvement considering the investment. If you decide to go the bigger-bore 454 route, I would recommend bumping the valve sizes up to original 2.19/1.88 dimensions on the rectangle-port heads. More than likely, the stock valves will be worn anyway, so this is a great reason to upgrade. Also, you have the opportunity to use smaller, 11⁄32-inch (0.3415-inch-diameter) stem valves that save weight over the stock 3⁄8 (0.3715-inch) stems. This requires different guides, but the price of replacing them with smaller ones should be the same. The larger-intake valves require grinding the seats larger, which is a benefit on older heads where the valve seat has likely seen prior work. The larger diameter moves the short-side radius location, which improves the midlift flow on these stock heads. All of this will help midrange torque and throttle response. As the least expensive aluminum head will cost roughly $1,400, you should be able to rebuild the stock oval-port heads with high-quality valves and good machine work for less than $800. Not only that, but the heads on a 467ci Rat would make excellent torque. So unless the benefit of the lighter-weight aluminum heads is important—along with their wow factor—you might stick with the iron oval ports. There would be few good reasons to put an expensive set of aluminum heads on the smaller-displacement stroker 396, as the flow advantage would be limited with the smaller-bore engine.

As for a camshaft, I like your idea of going to a hydraulic roller. This is where you will spend some money, but I think this is also where the return on the investment (dollar per horsepower or dollar per lb-ft of torque) really pays off. On the big-block, oval-port cylinder head test we did back in the Mar. ’08 issue (“Big-Block Cylinder Head Test”), we chose a Comp XR276HR cam for our 496ci engine. That cam delivered fantastic torque, making as much as 626 lb-ft of torque at 3,900 rpm. Assuming you go along with our 454 suggestion, a slightly smaller cam might be beneficial, since our engine was 50 ci larger. I’d suggest the XR270HR cam with 218/224 degrees of duration at 0.050 tappet lift. This cam still delivers the same 0.510-inch lift as the larger XR276 cam on the intake side, but the shorter duration will make more usable torque in the midrange for your smaller engine. I’d suggest a set of 1.7:1 roller rockers and the same valvespring used on our dyno test—the 933-16 Comp hydraulic roller spring worked very well controlling those heavy big-block valves. Combine all this with an Edelbrock Performer RPM intake and a 750-cfm Holley carb, and you will have a muscular street 454 that could easily make 530 to perhaps 550 lb-ft of torque. That’s what you’ll feel in the seat of your pants when you stomp the throttle. The oval ports should also make enough steam to push your 454 to between 475 and 500 hp. Those are good numbers for a stock iron-headed budget Rat. Hit it, maestro!

More Info

Comp Cams; Memphis, TN; 800/999-0853; Compcams.com

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