The factory small-block is...
The factory small-block is not in danger of extinction, but when was the last time you found a good 400 block laying around the junkyard?
We are rapidly approaching the day most car crafters thought would never arrive. It's not about to rain frogs, nor are we set to see pigs flying through restricted airspace. But the scary day is coming when it will become difficult to find a decent, iron small-block Chevy. And Dart is ready. In preparation, Dart has created a more affordable, 4.00- and 4.125-inch-bore cast-iron block called the Special High Performance (SHP) block. It costs around $1,450.00, but for that price, it offers some excellent engineering changes that make it far superior to a production block, especially the original 400ci Chevy.
Let's face it, our horsepower world is changing. Not too many years ago, a heavily modified small-block 355 that made 400 hp at the crank was considered stout. Today, you can buy a Cadillac Escalade with 403 SAE horsepower from 6.2 liters. So now, 400 hp is stock horsepower. With this power escalation, you have to make 500 hp just to keep ahead of an Escalade on the street. The easiest way to make power is with more inches, so the old standby 400ci first-generation small-block Chevy looks better and better.
This is Dart's new SHP small-block...
This is Dart's new SHP small-block Chevy block. While at first glance it may not appear to be much different from a production block, there have been dramatic improvements made to this classic design to bring it up to contemporary engine design standards.
But here's the problem. First, the 400 was only produced between 1970 and 1980 and used in sedans and trucks in two-bolt main configuration. The four-bolt main blocks were only built for a much shorter time. Zip ahead 30 years and few of these blocks are still around, and the ones that are still serviceable have issues. As one Mouse motor wag recently said, "It's not a question of if those steam holes will crack; it's more a question of when." The steam holes he refers to are the small vents in the deck surface located between the cylinders in production 400 blocks. After adding up the cost of finding and fitting a suitable two-bolt main block into four-bolt caps capable of withstanding 500 to 600 hp and then wondering if the block will survive a few seasons of abuse on the street and dragstrip, it begins to make sense to consider starting with a brand-new block. We've done the math, and while it's slightly cheaper to resurrect a 400 block compared with the cost of the Dart, the real question is how long the original block will last under the stress of 500 to 600 hp.
Does this mean all new small-block Chevys should be built using an SHP block? Dart would certainly enjoy that position, but the reality is there are still hundreds of thousands of production 350 blocks in existence that would make excellent candidates for mild street use, including the later model, one-piece rear main seal/roller cam blocks. But for a higher-end Gen I small-block buildup--especially if you're considering some kind of serious supercharger or turbo application with double-digit boost--the only real answer is an aftermarket block. Dart rates this block up to 600 hp, but we think this is probably conservative and that it could easily manage a 700hp effort. If your plans take you beyond that level, you should just drop the additional coin for a Dart Little M.
So what about the specifics? We thought you'd never ask. Much of the engineering that makes this block so attractive is what you can't see from the outside. We persuaded Dart to cut one up so we could peek inside. Going one step further, Dart also put the bandsaw to a junked production 400 block so we could compare the SHP with a 35-year-old production casting. We'd also like to thank former CC editor Rick Voegelin for his help with this story. He's the one with all the cast-iron dust on his hands. If you've never ventured deep into the bowels of a small-block Chevy, put on your miner's hard hat as we go drillin' for cast-iron gold.