In a current project on EngineLabs, editor Greg Acosta is pushing his stock block beyond accepted horsepower limits with a supercharger. Dubbed the “Retro 5.0” since it’s a ’90s-vintage engine with a modern twist, he is maintaining the stock displacement in order to maximize the stock block’s rigidity and strength. We only hope the “twist” is not an actual event inside the block.
For years, internet forums and 5.0 enthusiasts have espoused that SBF blocks will split if you push them past the 500-horsepower mark. We’ve previously written about that limit and its validity, and feel there is enough credible testing to at least attempt to exceed that mark with an OEM block.
Myths aside, the 8.2-inch deck 302 block is getting harder to come by in good condition. Things like core shift and the thin-wall castings inherent in these blocks mean that any oversized bore is sketchy for certain applications. A block bored .060-inch over may not allow for enough material between the cylinders and thus be more prone to cracking. Bolt on a power adder such as a supercharger or turbo, and the likelihood of cracking increases exponentially.
I think it’s a combination of things causing failures [with the OE block],” — Jack McInnis, World Products
“They’re grey-iron, typical production castings, which are nowhere near as strong. And then the webs are thinner; they’re thin-wall castings all-around by design. In the front web, a big oil passage goes horizontally across. That thins out the front web between the mains and the cam. I think that area is frequently where [cracking] starts. And then it just propagates right through the whole thing.”
As a result of so many having issues with stock blocks, aftermarket blocks have carved a nice niche in the market. They may cost more upfront, but the insurance they provide in thicker-wall castings and reinforced webbing can be well-worth the money for some builders. World Products Man O’ War block is one of the better aftermarket SBF blocks available, but it is also one of the most expensive (retailing for close to $3,500).
The Man O’ War, a name reminiscent of one of the greatest racehorses of the 20th century, is strengthened with a nickel-iron alloy that can withstand 40,000 psi. The webbing between the bearings is also reinforced with more material than stock. And they’ve also added priority-main oiling, so the bearings get plenty of lubrication.
“Our higher-nickel iron is class 40, whereas the stock blocks are class 30,” says McInnis. “Another thing that was always a complaint with Ford racers with those blocks [Boss 302] is that they did not extend the bores at the bottom. We did. So with a long stroke [without extended cylinders], you’ll pull the pistons out of the bottom of the hole, which allows the piston to rock.”
McInnis says piston rock is harder on rings and lands and ultimately on the entire rotating assembly. “There’s an extra half an inch at the bottom of our cylinders. So it’s not a lot, but it makes a big difference.”
World Products also casts in extra clearance for the Man O’ War, so you can run several stroker combinations without machining anything. “On the 9.500-inch-deck blocks — the 351 style — they have cast-in clearance for up to a 4-1/4-inch-stroke crank, which is considerable. You will not likely have to do any machining depending on your components. And if you do, it’s going to be very minimal.”
McInnis adds that the high-nickel iron content is not as hard as compacted graphite iron (CGI), but it’s roughly double the hardness of a stock block, so it may take a few more minutes to grind (if any grinding is necessary). “It’s not like CGI, where it’s going to take an extra hour.”
With the increase in torsional strength due to higher nickel content, the splayed four-bolt main bearings, and increased wall-thickness, McInnis says they have customers who are pushing the boundaries of the Man O’ War to the limit.
“We’ve got a guy in Australia, a customer who’s got a stock chassis; it’s a Falcon/Fairmont, I believe. He’s running 57 psi of boost and holding it together. He’s got multiple records down there.” McInnis acknowledges it is an extreme build and that it takes a lot of knowledge to pull it off without destroying many parts.”
The racer’s name is Frank Marchese with Dandy Racing Engines. He has blown up just about every block on the market with his SBF twin-turbocharged 427-ci build. A World Products engineer saw photos of Marchese’s exploits down under and called him to offer some assistance with a cast iron engine block that could handle roughly 3,000 horsepower. A 2019 dyno run with his Windsor block and 40 psi of boost produced 2,800 horsepower at the rear wheels. In 2022, he has pushed the power level even further with a reported 3,500 horsepower.
According to McInnis, the Man O’ War beats out the other aftermarket blocks due to its high-strength casting. He adds that the block is good insurance for any project that may be built up later. There’s plenty of margin for safety with the World Products block.
McInnis adds that common wisdom says the stock block’s power limit is around 450 to 500 horsepower. Some people may get away with more without a problem, but then others may have issues with less than that. It is a crap shoot.
Another area that helps the Man O’ War hold everything together is the upgraded main caps.
“They have a deep, stepped register and ring dowels. And because they are splayed with four bolts, they’re not going to chatter, which can be another cause for a failure with the stock block.”
While many install a main girdle on a stock block to keep the bottom end from moving around, it is still a band-aid solution. “When those caps start moving around, it can affect the clearance with the main bearings.”
With the stock block, McInnis suggests that you may be able to get away with some short bursts of power, but lean on it too hard, and it’s a time bomb.
With priority main oiling, there’s less chance of starving the bearings for lubrication because you feed the main bearings first. It has large passages, so you get a lot of oil supply to the mains, and then it feeds the top end because there’s an excess amount of oil getting into the top end anyway,” McInnis explains.
There are also provisions for oil restrictors on the Man O’ War, but McInnis says that’s another topic. “Who needs them, and who doesn’t? There’s always a lot of controversy about that. Generally, with hydraulic lifters, you don’t want to restrict them. So we usually refer home builders to make those decisions with their engine builder.”
Another problem with the stock blocks is that most have already been rebuilt multiple times over the years. Many blocks are unsuitable for further rebuilds as they have been bored to the limit (or more) and there’s not much clearance left.
“So if you run it for a couple of years and then decide you want more juice out of it, you’ll need to upgrade other components to make more horsepower,” McInnis notes. “We’ve seen people put a high-volume pump in and starve for oil. With all of the oil going to the top end, it doesn’t drain back fast enough into the pan, and you end up starving for oil. That has been another issue with the stock blocks.”
There seems to be a strong case for upgrading your SBF to an aftermarket block due to all of the potential pitfalls with the OE blocks. But not all aftermarket blocks are the same.
Be sure to look at the block specifications carefully and know what you plan to use your application for in the future. Are you going to run it on a drag strip or race track? Will you be naturally aspirated or running extra pressure? It may be worth the investment before you blow-up other expensive parts in the process.