Playing The Stock Market: Going Cheap With A Stock Block Is A Gamble

It’s a temptation that’s nearly as old as that lady and the apple — the bad decision. You’re putting a parts list together for your next engine build, but you’ve got a buddy who has an old block sitting in the corner he will sell you cheap. You could save a bit of cash versus buying a new aftermarket block. But what is the true cost of cheap (or even free)? Sometimes, bringing a used stock block back up to spec is a lot more costly than you expect — especially if performance after the build is complete isn’t up to snuff.

So we’re taking a real-world look at the cost of rehabbing a used engine block that may have powered a work truck or family wagon in its previous life versus purchasing a new aftermarket block designed specifically for high-performance applications.

From Junkyard To Racetrack

“There’s a lot more to it than just grabbing up an old stock block and building a competition engine out of it,” explains Jami Stoen, owner of Stoen Racing Engines in Medford, MN. “First of all, if we are talking about racing, we’re almost always talking about a Chevrolet small-block. That’s still by far the most common engine being built. Those blocks are so old now, that you’ve usually got to go through 10 to find one that’s either not cracked or just worn out. And by worn out, I mean hasn’t been rebuilt and machined so many times that the cylinder bores aren’t maxed out or just otherwise to its maximum limits.”

Stoen specializes in Dirt Modifieds, Street Stocks, and even Late Models, and his engines find Victory Lane just about every weekend across the central US. So he knows what he’s talking about. And here’s what he had to say when we asked him to add up the real-world costs.

Jami Stoen of Stoen Racing Engines has been incredibly successful building race engines not only for top-flight professional racers, but also grassroots-level race teams where the budgets are limited and every penny has to count. Here he is putting the finishing touches on a USMTS Dirt Modified engine utilizing a World Products Motown II block. Interestingly, even though he might be able to save a few bucks up front, Stoen says he hasn’t built a race engine with a stock block in years. Even though the up-front costs may be higher, he says the value with a quality aftermarket block, both in terms of reliability and performance, is simply better.

“Around here, lately for a Chevrolet small-block, you are looking at $200 to $300 for a decent core. And there’s no guarantee that it will be good. Then, typically, it will run you about $150 to clean and magnaflux it (which is a crack-checking procedure). And hopefully, at that point, you don’t find anything  that requires you to throw that block away and start over.”

That’s the basic cost just to get started. Just because an engine was running when it was purchased, doesn’t mean the block is good to go for a performance build. We’ve seen situations where the block had the beginnings of a crack but the engine was still functional in its stock, low-horsepower form. However, it would quickly fail in a performance build if left alone.

Using A Stock Block Isn’t Always Cheap

“So if you find a block that’s still good,” Stoen continues, “if you plan to make any power at all, you are going to need to put splayed-bolt main caps on it. [The machine work to install four-bolt main] caps is going to run you a considerable amount of money. I haven’t done them in forever, but I bet it’s going to be up around a thousand bucks. There are a lot of steps involved if you are going to do it right, and in a machine shop, time is money. And from there forward, you’re still dealing with a stock block,” he adds.

“You are horsepower-limited before it’s going to break. If you are starting with a 350 block, you can make 500 or so reliably, but a lot of racers are trying to make more than that these days. And if you use a 400 block, if you make any power at all, you’re going to split a cylinder.”

One quick note before we continue. For these examples, we’ll be referring specifically to the venerable Chevrolet small-block, as you may have already noticed. We can’t cover every type of engine here, or else this story would get lost in the weeds. But whether your build is a Ford Windsor or an LS, the basics will be much the same.

One of the big advantages of an aftermarket block designed specifically for performance, like this Motown II block, is the cylinder walls are thicker than stock, allowing for bigger bores while still maintaining excellent cylinder bore strength. Also, notice the oil galleries running through the lifter valley. This promises equal oil pressure between both banks of lifters and also easy adjustment of restrictors to dial in the flow of oil to the valvetrain.

Buy Once, Cry Once

While gathering information, we also spoke with Lance Stillwell on the topic. Stillwell has the unique perspective of being an independent race engine builder for decades at his shop, Motorsports Unlimited out of Terre Haute, IN, but he’s also recently signed on as the Director of Operations at World Products — so he’s seen it from both sides.

Stillwell says that in the right situation, a stock block can be a good choice, but to rehab a used stock block to make it work in a performance application, the juice often just isn’t worth the squeeze. “If you brought a stock block to my shop right now for machining work and we just do the standard stuff. That would be line honing the mains, clearance for stroke, bore it, hone the bores with a toque plate in place, all the good stuff. That would be $1,250 out of my shop to get that done, and I think that’s a pretty competitive price. That is also if everything else is good and we don’t have to make any repairs or do anything else.”

Since we’re talking to Stillwell, let’s use one of his aftermarket blocks for comparison. As this went to press, a World Products Motown II cast-iron small-block with four-bolt nodular-iron main caps is going for right at $3,100. They arrive mostly machined, but not completely, and you likely will spend another $500 to $1,000 (depending on your specifics) to get the block honed. Depending on the build, you may also want to have the block decked and possibly get the cylinders bored to a larger size. But the block is designed from the get-go to handle absolutely huge power levels without breaking a sweat and has many features, such as priority main oiling and extra-large water jackets for improved cooling, that you just can’t get in an OEM block.

Squeezing a lot of stroke into a stock block can also be a difficult task. You must cut clearance into the block for the extra swing of the crankshaft throws and connecting rods, all the while praying you don’t cut into water. Not an issue with a well-designed aftermarket performance block which can usually accept a 4.00-inch stroke (a full half-inch longer than stock) with no issues.

So the aftermarket block is likely going to be more expensive in terms of up-front costs (if you don’t wind up with a cracked stock block and have to start over), but Stillwell points out that the differences in lifespan can be significantly greater. “These days, if you are able to find a stock block, it’s likely to have already been rebuilt at least once,” he says. “So the cylinders are probably already oversized. If you have to bore it again to clean up the cylinders, you are likely getting pretty close to 0.040 or 0.060 of an inch oversize, and there’s no more life left in it. With a new aftermarket block like the Motown II, there’s a lot of life in it. If you don’t blow it up, it’s going to last through several sets of pistons, and likely even a few crankshafts and sets of rods. I mean it’s going to be with you a long time, so it’s an investment.”

Stillwell continues, “Plus, I know that with the Motown II block there’s plenty of cylinder wall thickness there. It’s designed so you can open it up for big pistons and lots of displacement and still have plenty of strength to run boost. But that wall strength is still awfully important, even if you are running naturally aspirated. Up where we are, we have a lot of truck pullers and mud boggers. I’ve seen guys try to make do with a Chevy 400 block, but those things just won’t hold up. So they will use hard block to try to stiffen up the bottom end.”

“But when they get in the mud bog or wherever, they will have the motor redlined but the truck won’t be moving. The only air getting through the radiator is whatever the fan can pull through. And with hard block, you just can’t get the cylinder wall to get out of the way fast enough for the piston to grow. So you’ve either got to put way too much piston-to-wall clearance into it from the get-go — and then it never runs quite right — or you run the risk of galling a piston. It’s a lose/lose situation,” explains Stillwell.

Lance Stillwell built performance engines for years as the owner of Motorsports Unlimited before signing on as the Director of Operations for World Products. These days he’s spending his time making sure World Products’ blocks provide as many competitive advantages to race engine builders as possible.

Precision And Accuracy Matter

One surprising point that many may not consider at first when it comes to building an engine is how a more precisely cast and machined aftermarket block may actually help the engine run better. This specifically works with respect to the valvetrain. Any misalignment in the lifter bores — either from core shift or imperfect machine work — will change the angle at which the lifters interact with the cam lobes and can potentially affect the valve timing events. And after you’ve spent so much time and energy trying to determine the perfect cam grind to maximize power, that’s the last thing you want.

Besides the lifter bore alignment, the cam bore centerline can also cause issues. And unfortunately, that’s a check that few machine shops actually do. Line honing the main caps is a common task in machine shops to ensure the correct crankshaft centerline, but honing the cam bores is much rarer.

Here’s another option you don’t get using a stock block. This Motown II block not only has a raised cam position (notice how the cam bore is cut off-center in the boss), but it also allows a larger diameter cam protected by roller bearings. A larger diameter camshaft helps make power because it reduces cam twist during high-RPM rips to keep the valve timing more stable.

That’s mostly because a cam-bore misalignment is easy to catch — it’s hard to slide the cam into place and even if it goes it is tough to spin. But it is actually the parallelism between the camshaft and crankshaft centerlines that can also cause problems. If they aren’t right, it’s going to cause issues that can be quite difficult to diagnose.

“If the camshaft centerline is off, if it runs uphill or down or a bit left or right — which is what they call sway — I feel that contributes a lot to early failure of flat tappet lifters,” Stilwell says. “That proper alignment to the lifter bores is critical, and if you have sway, it’s going to change from front to back. Also, if you have a cam that’s lower in the front than it is in the back, that cam is always trying to shove itself right out of the timing cover.

“But those checks you need to do with a stock block to bring it up to the same spec as a well-made aftermarket block like the Motown II just keep stacking up,” he adds. “You just about can’t machine a stock block affordably to honestly blueprint it to the same level as new blocks you can buy from World Products or some other guys. When you can pick up a junkyard block for 500 bucks, it may seem like a pretty good deal. But when you’re broken in the pits, or the engine just never seems to run quite right and you can never figure it out, you realize the bargain isn’t quite so good after all.”

The main caps should be a big consideration with any engine build. If you are making any sort of power, four-bolt main caps are practically a must. A two-bolt main block can be converted to four-bolt mains, but the results often aren’t as good as you might think. That’s because the webbing in the block isn’t thick enough to maintain its proper strength once the two additional bolt holes are drilled into it. That’s one of the reasons why an aftermarket block is usually a little bit heavier than an OEM block. It is designed to be able to handle tons of power with plenty of thickness through the webbing and beefy splayed-bolt main caps which would split an OEM block in two after just a few nights of racing.

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