The key to decent engine performance is moving air in and out of the engine efficiently. O
Brandon Clark, via CarCraft.com: I recently scored a disassembled 305 engine for $50 because the dude said it was junk. I've found a couple of stroker kits for the 305, but some say 334 and some say 335. I've read this is a 400 crank in a 0.030-over 305. I know 305s had smaller bores and most aftermarket heads won't fit without some valve shrouding. If the engine is bored 0.030 over or more, how big would that make the bore, and what heads would be OK on the motor? The main reason I'm bench-building this motor is because I want something different in a sea of 350 and 383 small-blocks. However, if building a stroker 305 is a waste of money, I'd like to know now.
Jeff Smith: At least once every couple of years we review this combination. This stroker package is popular because the 305 small-block is probably the most easily accessible small-block Chevy engine on the planet. As you mentioned, you bought this motor for almost nothing-that's the lure. The 305 uses a tiny 3.736-inch bore and the same 3.48-inch stroke as the 350ci motor. While it's relatively easy to drop a 3.75-inch stroke crank in a 305 block to create a 0.030-over stroker that displaces 334 inches, it's just not a great performance decision for several reasons. If you want to build this engine just to be different, then have a great time. But if you want to build a performance engine to make good power and do all the things a performance engine will do (and why wouldn't you?), then find a good used 350-they're just as cheap-and build that instead. You'll be much happier. Here's why:
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There are only a couple of small-block Chevy engines with a smaller bore than the 305-the minuscule 262ci V-8 is one that comes to mind. In the realm of bore size, the 305 is smaller than the 283 and 307 engines (3.875 inches) and even tighter than the original '55 265ci small-block (3.750 inches). Any knowledgeable performance engine builder will tell you that larger bore diameters create better airflow out of even the weakest cylinder head because the cylinder wall is farther away from the valves. This is why when Chevy decided to build its 302 SCCA Trans-Am engine in 1967 for the Z/28, the company used a 4.00-inch-bore 327 block with a short, 3.00-inch-stroke 283 crank to create the displacement. The engineers went this route because they knew a 4.00-inch-bore engine would make more horsepower than a smaller bore engine with a longer stroke. As further proof, pay attention to any published cylinder head flow data. Most companies will actually tell you what bore size adapter they use to flow their heads. For a small-block, no one ever flows a performance head on a bore smaller than 4.00 inches. Most companies test their heads on a 400 small-block's 4.125-inch bore because the flow numbers will improve.
We talked to Tony Mamo at Air Flow Research, and going from a 4.00-inch bore to a 4.125-inch bore is worth perhaps 2 to 3 percent more airflow. Three percent will bump 240 cfm to 247 cfm without touching the cylinder head. This might also clue you in as to why wider bore spacing engines have an inherent advantage because they offer better airflow potential and bigger intake valves, as with the L92 LS engines that now sport a monstrous 2.160-inch intake valve.
Increasing the 305's 3.766-inch bore another 0.030 inch to allow slightly bigger valves is such a small bore change that it really doesn't help very much. You can't fit a 2.02-inch-diameter intake valve (which is now considered small) in even a 0.030-over 305 bore-it won't fit without hacking on the bore. Your idea is good, it just needs to keep going out to 4.030 inches, which will offer a decent bore size for good airflow. Then you can go ahead with a 3.75-inch stroke cast crank kit in a 350 block and you have a nice little 383 that will make more power not only from the larger bore size, but also the increased displacement of almost 50 ci. That alone is a great reason to build the 383 versus the 334. And if it bothers you to say it's a 383, then tell everyone it's a warmed-over 307-that'll keep 'em guessing.
CJ Strickley, Alexandria, KY: I want to try something a little different for my next small-block and came across some of Smokey Yunick's information on 180-degree cranks. I was wondering if you could shed a little more light on some of the pros and cons of using this arrangement on a street motor.
If there were an '11 Camaro Z28, this is what the engine compart
Jeff Smith: To get the skinny on this, I talked with veteran race engine builder Ryan Falconer, who has considerable experience with 180-degree crank race engines. There are several advantages to the 180-degree, or flat crankshaft, concept. This crank is called a flat crank because the rod journals are spaced 180 degrees apart as opposed to every 90 degrees in a typical production V-8 engine. In other words, all the paired rod journals are located 180 degrees apart, placing the journals in a single, flat plane. One good reason for this is it creates a stronger crankshaft, but the advantage of the design is it separates each cylinder firing to opposite sides of the engine. A typical 90-degree V-8 crank demands that one pair of neighbor cylinders on one bank fires sequentially. As an example, in the small-block Chevy with its firing order 1-8-4-3-6-5-7-2, cylinders 5 and 7 fire next to each other. In the small-block Ford (1-5-4-2-6-3-7-8), cylinders 7 and 8 are the two that fire in sequence. The 180-degree crank fires one cylinder on the left bank and then one on the right. This also allows some freedom in terms of intake tuning in regard to common-plenum intake manifolds. This 180-degree crank orientation also produces a very distinctive exhaust note, since the exhaust pulses are evenly distributed.
There are also distinct disadvantages to the flat crank concept. Falconer says that while the flat crank idea works well with short strokes, it tends to create a damaging harmonic at higher engine speeds with longer strokes. He was involved with a 5.0L V-8 engine with a 3.00-inch stroke flat crank that created such damaging harmonics with its opposed cylinder firings that the engine destroyed itself in relatively short order. So while there are several advantages, it appears that for anything with a stroke longer than 2.75 inches (which is pretty short for a street engine), this wouldn't be a good idea. Keep in mind that a 180-degree crank would also require a custom camshaft, since the firing order would be different.