500HP Small-Blocks
Ronald Brooks, via CarCraft.com: I find it interesting in your online article about 500hp engine combos that run on pump gas that there are no real small-block (5.7L or smaller engines) in it. Why is that? It can't be done? It should be easy to make 500 hp when you're toting 383 or more cubic inches. Why not ramp up the difficulty a little? What about 500-plus horsepower on pump gas with small-cubic-inch engines with no power adder at all?
Jeff Smith: Great question, Ronald. Making 500 hp has never been easier, even with a small-block. But there are compromises that must be made when you're talking about smaller-displacement engines that we'll assume are still going to be run on the street, since you mentioned that they should run on pump gas. The concepts are really easy, but there are some critical points that are often overlooked by enthusiasts who are interested only in peak horsepower numbers as opposed to the overall power curve. We chose the big-blocks at 500 hp because this is a relatively easy number to attain, which means you don't have to push an engine nearly as hard to achieve that number.
While making 500 hp is achievable with a small displacement, the smart street engine plan is to build it with as much displacement as possible. This is a Ken Crocie Pontiac 455 that made 516 hp at 5,300 rpm and 575 lb-ft of torque at 3,900. That's great grunt.
It's not difficult to achieve 500 hp with a smaller-cubic-inch, normally aspirated engine. Just for grins and giggles, let's simulate a 302ci, small-block Chevy. We'll start with a set of good 210cc intake port heads that flow 280 cfm on the intake side at 0.600-inch lift. Let's add a set of domed pistons (remember, we only have a 3.00-inch stroke) with an 11.5:1 static compression ratio, a huge 242/248-degree-at-0.050 mechanical roller camshaft with 0.600-inch valve lift, a large single-plane intake manifold, an 850-cfm carburetor, and large 1 71/48-inch headers with very low-restriction mufflers. We plugged all this data into our ProRacing Sim DeskTop Dyno engine simulator program and it spit out some interesting numbers. First of all, peak horsepower was an impressive 555 hp at 7,000 rpm. That seems a bit optimistic, because just last month we tested a 383ci small-block with a set of Dart 227 CNC ported heads, 10.5:1 compression, a 750-cfm carb, big single-plane intake, and a mechanical roller cam with 254/260 degrees at 0.050-inch lift, and that engine made an impressive 570 hp. That was 1.48 hp per cubic inch (hp/ci), but doing the math on the 302 comes to a far stronger 1.83 hp/ci. Granted, both engines have the same bore, and the 383's piston friction at 7,000 rpm will be much greater due to the 0.750-inch-longer stroke, but what we're getting at is that the 302 combo is probably optimistic by at least 30 hp. Still, 525 hp is certainly achievable.
While the peak horsepower was at 7,000 rpm with the 302 (and very close at 6,900 rpm with the 383), the 302 achieved a simulated peak torque of 450 lb-ft (again, perhaps optimistic by 30 lb-ft or more), but this came at 5,500 rpm. Here's where the reality of street engine operation begins to blend into the romance of 500hp engine combinations. That hopped-up 383 managed to pull around 350 lb-ft of torque at 3,000 rpm while the simulation reported almost the same torque, but a real dyno test on an engine like this would probably see closer to 300 lb-ft at 3,000 rpm. That's much less torque than a stock engine makes at this rpm, which means you'll need much more gear to make up for the lack of torque at lower engine speeds. For example, even with a lightweight Chevy II at 2,800 pounds, you're going to need a 3.73:1 or deeper gear. To optimize this motor at the dragstrip, something closer to a 4.56:1 gear with a 26-inch-tall tire will be necessary to pull 7,000 rpm at the end of the quarter-mile, assuming a trap speed of roughly 125 mph. Now what we have is much closer to a race car than a street car.
CC Quickies
How's this for attention to detail? Harley Graves had most of the fasteners on his '69 Charger ceramic-coated. It wasn't cheap to have done, but it looks nice.
Everyone's idea of what constitutes a "real" street car is different. Personally, my Olds with a 3.23:1 rear gear with a 28-inch-tall rear tire suffers from unacceptably high engine speed at 70 mph without an overdrive trans. A car with a high-strung small-block and a 4.56:1 rear gear isn't something I'd like to drive at 4,125 rpm on the freeway here in L.A. at 70 mph to keep from getting run over by everybody else driving 75 to 80 mph. But perhaps your tolerance for buzzing small-blocks on the freeway is greater than mine. That's fine as long as you're willing to put up with all that racket. As an alternative, let's look into a 550hp, big-block 496 (or better yet, a 540ci Rat) that will make that same 550hp number at a leisurely 5,800 rpm, as an example, with peak torque of roughly 630 lb-ft at 4,200 rpm. This motor would probably pull well in excess of 550 lb-ft at 3,000 rpm and as a result would not need much more than a 3.23:1 rear gear, most likely getting by just fine with a mild stall speed of 2,000 rpm with a 3.08:1 rear gear. This combination could easily run decent 11-second dragstrip times without pulling stratospheric engine speeds, which also means it would live a long time without breaking parts. This engine in a relatively heavy car would still be quick on the dragstrip and yet much more fun to drive on the street. The reason the big-block will run as quick or quicker than a tiny small-block with the same peak horsepower is because the big-block (by virtue of its large displacement) will make much more torque throughout the entire rpm band in which the engine runs down the track. If peak horsepower and vehicle weight are the same between two engines, the one with the stronger overall power curve within the rpm band where the engines run on the track will always be quicker (assuming decent traction). This is overlooked when you concentrate only on peak horsepower numbers. The Rat motor can give up a little peak horsepower if it has more torque in the middle. That extra torque in the middle will out-accelerate the smaller motor at midtrack every time. The only choice for the small-block is to run a much deeper gear to compensate for its lack of torque.
There's certainly nothing wrong with the 302 combination, and some guys prefer these little motors that spin to the moon. The problem is that high rpm requires excellent (that means expensive) valvetrain parts that tend to not be as durable, because you have to run high valvespring pressures to keep everything glued together. Then buzz the motor all the time and you can begin to see why these high-strung beasts don't make good street motors. On the other side of the coin are the big-blocks that just loaf along at low engine speeds while still offering tremendous torque. It's really not a matter of taking on a challenge, Ronald, to build a 550hp small-block as much as that a larger-displacement engine will make the power really easily and offer more streetable power at lower engine speeds so stuff doesn't break as often. And fewer broken parts is a concept everybody can agree on.