Here's the scenario: You're looking to make big power, so you're looking to build a big-block. Sure, you can make plenty of ponies with a small-block, but it's hard to match the brute force provided by sheer cubic inches. When the first "Mystery Motor"-powered Chevrolet won the 1963 Daytona 500, an undeniable big-block mystique was created. More than 40 years later, that aura of all-out performance is as strong as ever. So you want a big-block. You know how much money you have, and you want to get as much performance as possible for your dough. What are your options? Is the 454 still a viable performer, or is bigger--as in 496 or 540--always better?
That's the question we first set out to answer: 454 versus 496 versus 540? We planned to look at the power potential and price of this trio. Our exploration of the big-block world, however, quickly led us in a slightly different direction. There are plenty of 454-powered vehicles still making the scene, but they're becoming the exception rather than the rule when it comes to performance builds. Stroker rotating assemblies, we learned, cost nearly the same as a stock setup, making them more cost effective. If it costs the same to build a 496 or a 506, then why not do it and make more power while you're at it?
The "bigger is better" ethos doesn't stop there. For many builders, especially those beginning from scratch, the increasingly affordable price of aftermarket blocks makes 540 ci the displacement starting point. "People want the biggest and baddest engine they can get," we were told, and whether they buy it all at once in crate form or in pieces over time, that's what the aftermarket is giving them. Whereas 500 hp was once a respectable number, 600 seems to be the new minimum.
In fairly simple mathematical terms, the quest for more displacement is logical. More displacement means more power, but you knew that, right? In general, a properly tuned production automotive engine produces 1.0-1.5 hp per cubic inch. Where a particular engine falls depends on many factors, so we'll use 1.3 hp per cubic inch as a middle figure. That means a 454 can support almost 600 hp (454 x 1.3 = 590.2). Indeed, many do. Using the same multiplier, a 496 can support 645 hp. And remember, the price difference between the two is minute. We're sure you see where this is heading. So we ask, how much does it cost to build a 454 that can support 600 hp, as opposed to the cost of a 540, which can support more that 700 hp?
Exploring the Big Country
By way of examining this issue, we set out to take a big-block cross section of sorts. We talked to a number of engine builders and parts suppliers, and we pretty much asked the same questions: What's your best bang-for-the-buck package? What are people actually buying? And, perhaps most importantly, we asked our industry sources for the bottom line, in other words, "What is the price of power?"
Of course, we also wanted to get an idea of what kind of power various big-blocks actually make, so we rifled the dyno-pull files at Westech for a few examples. It may not be exactly scientific, but it is grist for the mill. Let the bench racing begin.
If we learned anything from our Rat-motor reconnaissance, it's that big-block Chevy heads ain't cheap. Some may cost only a few hundred dollars more (apiece) than their small-block counterparts, but many cost half as much again--or more. Anecdotal testimony came from our expert sources, almost all of whom sell plenty of short-blocks to customers who already have cylinder heads. With this in mind, we sought the voice--or rather voices--of experience, namely our friend Steve Brul of Westech Performance and our new friend, Harold Bettis of SuperFlow Technologies. Here's what our experts had to say.
CHP: All right, guys, what's your take on the oval-port versus rectangular port deal?
Steve Brul: The current thinking is that the oval shape is better than a rectangular port, as shown in current Pro Stock technology.
Harold Bettis: An oval-port head leaves fewer opportunities for eddies and irregularities of flow in the corners, because there are no corners.
CHP: So oval ports are better?
SB: Generally, with traditional-style oval-and rectangular-port heads, the smallest port with the highest flow volume is best.
HB: Yes, proper flow numbers are more important than size. Think of the air as a concentration of energy. If that concentration is high, it's easier to get air into the cylinders and harder to get it out (reversion).
CHP: So how does that relate to port shape?
SB: You should refer to oval and rectangular ports as a function of size, not of shape.
HB: At power levels over 550 hp, a rectangular port is the normal trend. When the volume changes to meet this level, it's easier to get the needed flow from a rectangular-port head.
SB:HB: Remember, an engine does most of its work and spends most of its time at part throttle, and it needs to be happy there. Higher average power, under the curve, is what makes it go down the road. And the guy who gets on the torque curve first wins.
CHP: Do people tend to use heads that are too large?
HB: People build engines to make max power, then drive them at part throttle. Force is not the issue; air speed is. Given that, it's better to be slightly small (when it comes to port size) as opposed to slightly large.
CHP: So, is there any kind of formula for determining what size head to use?
SB: The better head is dependent on application, rpm range, and size. Obviously, a 7,000-rpm 572 isn't going to want the same head as a 5,500-rpm 454. Sizing a cylinder head comes down to a lot of previous data. That being said, a reasonable power potential on a high-quality street engine is 2 hp per cfm.
HB: If you measure the intake flow of the complete air tract, with restrictions, and multiply that number by 0.26, you'll get a number that represents power per cylinder. So 400 cfm times 0.26 equals 104, which times 8 cylinders equals 832 hp.
CHP: Any parting words?
HB: The way to go about creating an engine is to determine the goals and objectives, make a plan, and set a budget. If one gets out of kilter, then you have to readjust.