Now comes the fun part. You sweated over selecting the parts, built the rotating assembly, and bolted the heads and intake in place. Now you get to fire that jewel and see what kind of power it makes. Most enthusiasts never test their engines until it’s in the car. But since we can’t plug each reader behind the wheel of a 10-second street car, the next best thing we can do is at least test some engines and put some numbers on paper that will illustrate the kind of power we’re talking about.
This chapter will deliver a broad range of different engines from a mild street 383 and 406 to hard-core, thumper engines that run on race gas and will probably never see the street.We’ve also rated these engines in terms of horsepower- per-cubic-inch and torque-percubic- inch, but these numbers can be deceiving. Generally speaking, as displacement increases, engine efficiency in terms of power per cubic-inch decreases, since internal friction, especially for long stroke engines, has a tendency to cost horsepower. The advantage is that the added displacement still manages to make serous horsepower.
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There are a couple engines in this chapter that are serious, high-RPM engines. It may be tempting to move in that direction because of the impressive horsepower that these engines make. As we mentioned in Chapter 2, this siren song of horsepower can be misleading. The reality check that should accompany these numbers are items like how the engine you plan to build will be used. If you just want to run with your pals and impress the drive-in crowd, then a high torque engine will deliver on the fun factor without costing big dollars down the road in terms of maintenance.
The high-horsepower engines require race gas to keep the engine out of detonation and usually also demand serious valvespring pressure necessary to control the mechanical roller camshaft at high RPM. While you can certainly run these engines on the street, a few thousand miles will also abuse those springs, eventually leading to valvespring breakage, roller-lifter wear, bent pushrods, and an overall abuse of the valvetrain. If you went further by opting for a set of 0.043-inch gas-ported rings, you can expect to have them live about 2,500 miles before cylinder leakage past the rings becomes a big problem. Frankly, we don’t see the fun in replacing rings every 3,000 miles, unless you like spending your weekends swapping engines and replacing rings. Leave that to the Top Fuel guys.
If we had to choose a few favorites out of this bunch of engines, there are three that deserve a little additional cov-erage. We’ll take them in ascending order with the mildest first — the very streetable 406 in Test 1. This engine would be a ton of fun in a first or second generation Camaro, Chevelle, or even a pickup.With 470 ft-lb of torque at 2,400 rpm, there’s only one engine in this assemblage that makes more torque and that’s the much larger 454ci small-block. For its size, this engine makes amazing torque, which is what pushes you firmly back in the seat when you jump on the throttle. This engine has excellent throttle characteristics due to its relatively short cam, dual-plane intake, and reasonably- sized carburetor. Because of its strong torque, you would not need to put a deep gear behind this engine. In fact, anything deeper than a 3.73 gear would probably slow the car down in the quarter mile. This is one of those engines where you allow the torque to do the work for you.
The second engine has to be Test 4’s 383. This is a understated compromise between horsepower and torque with an excellent set of heads and a decently sized camshaft. Peak horsepower is under 6,000 rpm, which makes things easier on the valvetrain, while peak toque is 506 ft-lb at a slightly elevated 4,900 rpm. This is due to the short-runner Super Victor intake manifold that pushes the torque peak up. With a dual plane intake, this engine would lose some peak horsepower but gain torque that would help accelerate a medium weight street machine somewhat quicker because of the torque increase, even with the reduced horsepower. This is a difficult concept for many street machiners to grasp since horsepower has been the gospel for so long. There’s sufficient power in this small block to push a 3,500-pound street car with good traction well into the 11s. The beauty is that this engine could perform that kind of service all day long with relatively no maintenance, using pump gas. Pretty impressive for a “small” mouse motor!
Our third selection has to be the biggest engine in the bunch, the World Products 454ci mega-mouse. What’s not to love about this engine? It makes as astounding 610 hp at 6,400 rpm with a massive 584 ft-lb of torque at a reasonable 4,500 rpm. The test only started at 4,000 rpmand it’s cranking 559 ft-lb even at this low RPM. This engine is probably capable of 500 ft-lb even at under 3,000 rpm, which is awesome torque. But then, it should be for a 454ci engine! The interesting thing with this engine is the amazing power it makes with some relatively small 220cc heads. This pumps the velocity way up with these heads and must be the reason for its incredible power. There are few 454ci rat motors that we’ve seen that come anywhere close to this kind of power, even with oval port heads. What this points to is the concept that even 260cc oval port rat heads are too big for a 454ci rat motor and that with the right flow potential, it’s possible to make better power with a rat motor with very small heads — a concept that is not very popular with most rat motor fans!
This brings up an interesting question concerning the relative size of even small-block heads. If you look back at our first selection of the 406 that makes 525 ft-lb of torque, this is an engine with downright tiny intake ports of only 170ccs. Many might claim that these heads are way too small for decent power. That may be true, but what if you could increase airflow with a similar set of heads by really working on the bowl area and perhaps increasing valve size while working towards a smallest cross-sectional area only slightly larger than these stock Vortec heads. This would increase mixture velocity while keeping things strong enough in the flow department to deliver enough air to make respectable horsepower. This is an interesting concept that deserves more attention and more dyno testing. If a 454ci small block can make 610 hp from a set of 220cc intake port heads along with outstanding torque, perhaps there is some paradigm shifts that need to occur with respect to smaller displacement small blocks as well. If nothing else, this should spark some rather interesting debate for the next engine-building bench racing session when someone says, “I’m thinking of building a small block Chevy…”
One last point that is important to note is that the following combinations are proven to make the power as indicated by the dyno curves. These power curves can be duplicated only if the entire engine package is duplicated. The crucial point here is that all the parts must be duplicated. Deviate from any component, even a carburetor, and the power will probably change. Substitute a different cylinder head, intake manifold, or camshaft, and we can guarantee that the power will not be the same. If you have significant experience in building engines, then you may decide to deviate from these combinations and perhaps even improve the power. But if this is your first foray into the world of small-block performance and much of the information presented in this book is new, then we’d suggest choosing a combination and duplicating it.
Having presented this, we should also mention that these combinations are not the only ones that can make good power. One of the intriguing aspects of performance engine building is that there are dozens, if not hundreds, of ways to get where you want to go. For each combination presented here, there are easily four or five others that could make similar or even more power. Just keep in mind that if you deviate from what we’ve presented here, that the power could very well be different.
Written by Graham Hansen and Posted with Permission of CarTechBooks