Another factor that looks a little bleak for a performance build is the rod/stroke ratio that, at 1.42:1, is really short. However, if you keep this in mind and work to minimize all the factors that can make a short rod/stroke ratio a liability, the final result can be more than acceptable.
With longer strokes in a short-deck block it becomes very important to minimize piston/bore friction, so bore prep and piston/ring selection become critical factors. I realize that sounds a little scary, but if these factors are taken care of, the end result is an engine with great performance potential, especially for the street. If you use a taller-deck block, the engine’s geometry becomes significantly more favorable.
Before deciding to go with a tall-deck block, you need to determine whether a tall-block engine will fit into your chassis. Sure, any chassis can be ultimately made to accept any engine, but the hassle and expense may be more than you can afford or want to deal with. With that caution in mind, let’s talk tall-blocks.
It appears that other than some Chevrolet Performance Parts Bow Tie blocks the biggest displacement production 10.2-inch tall-deck blocks that General Motors made were 427s. Fortunately, these had a 4.25-inch bore and on occasions could be rebored 0.100 over even though 0.060 was a more common limit. Off-the-shelf Scat 6.7-inch rods or Callies 6.8-inch rods can be installed in these blocks. With these units, the rod/stroke ratio increases to 1.60:1 for a 4.25 stroke or 1.51:1 for a 4.5 stroke.
If you find a tall-deck production block and you verify through sonic testing that it is useable, by all means use it. But if you can afford an aftermarket block, a whole new world of big inches opens up. How big? Try the topside of 710 ci while still utilizing production-style heads.
Fig. 1.15. This short-deck aluminum block was the basis of a build that used Brodix heads, intake, and block for a 565 fuel-injected build, which was intended for a Corvette for the 2013 SEMA show. Mark Dalquist of Throttle’s Performance built this engine. I helped with the dyno testing and can vouch for the output, which was ultimately just a few horses shy of 900.
Aftermarket Blocks for Big Inches
Some exotic blocks are available for big-inch builds. The spreading of the cylinder bore centers is the most influential dimension of these exotic blocks, and it directly affects the displacement potential. Stock bore centers are 4.840 inches but some manufacturers are spreading the bores to 5 inches or even as much as 5.3, thus allowing larger bores. This can make for displacements in the region of 900 ci.
I don’t want to get into repitched bore-spacing blocks in any great detail here as it is out of the scope of this book. Basically, four sources produce standard bore-spacing iron blocks. In alphabetical order, they are: Blueprint, Dart, GM Bow Tie, and World Products. If it’s an aluminum block you are after, Bill Mitchell Products (BMP), Brodix, or Dart are the available options. But be aware that they are about twice the price.
Fig. 1.16. This short-deck aluminum block was the basis of a build that used Brodix heads, intake, and block for a 565 fuel-injected build, which was intended for a Corvette for the 2013 SEMA show. Mark Dalquist of Throttle’s Performance built this engine. I helped with the dyno testing and can vouch for the output, which was ultimately just a few horses shy of 900.
By a margin of about 8 to 10 percent, Blueprint has the least expensive block, yet it’s all American made and is of American high quality. As I write this chapter, I am about to start building a tall-deck 652-inch. This block is available at 9.8 and 10.2 inches deck height and can be had with bores up to 4.6 inches.
Dart has the greatest range of blocks in terms of heights and bore-size capability; most of my aftermarket block experience is with their blocks. However, I do feel it is worth mentioning that Dart has a 4.9-inch bore spacing variant of the block that accepts heads closely patterning regular bore spacing heads.
Brodix and Pro-Filer offer heads to suit 4.9 bore spacing blocks. These heads differ from others because the chambers are slightly repositioned and some head bolts are repositioned. Other than that, they look much like heads for a regular 4.840-pitch block. These blocks are available with deck heights up to 11.1 inches, and they accept strokes up to 5.5 inches. With a maximum bore of 4.7 inches and a 5.5-inch stroke, a short-block assembly of 763 inches can be built without undue hassle.
With the right heads, an “all engine” build can produce right around the 1,400-hp mark with torque in excess of 1,180 ft-lbs. So far the biggest Dart block build I have been involved with was a 712-inch unit that made 1,098 ft-lbs and 1,346 hp on nonoxygenated 116-octane race gas. I built this engine with Terry Walters at TWPE. There is no doubt in my mind that oxygenated fuel would have added about 40 hp.
Maximizing Bore Size
The entry-level Sportsman blocks from Blueprint, Dart, and World Products represent a good return on investment in either 9.8 or 10.2 tall-deck configurations. The cylinder walls on these blocks are much thicker than stock. Often, the bore limit is 4.6 inches, but a sonic tester can often find a block that can go significantly bigger. I have gone to as much as 4.67 inches with a Dart block and have had no subsequent problems. A 4.5 stroke in a short-deck block produces 616 ci. If engine bay space accommodates the block, the tall-deck version of this block can, with a 4.75-inch stroke and a 6.7-inch rod, go to 652 ci, and that many inches has some serious torque and horsepower potential.
My last word on Dart blocks here is that you should visit their website and check out all the variants they offer. However, don’t let the name “Sportsman” in any way make you think you are buying an “also ran” member of the Dart performance line-up.
GM Performance Blocks
I have used GM’s one-piece-seal tall-deck block for a 572 (4.375-inch stroke) and a 588 (4.5-inch stroke). Both instances used a 4.56-inch bore; they were street/strip pump-gas builds and produced very satisfying results. In round numbers, these were 850 ft-lbs and 904 hp for the 588 and 828 ft-lbs and 883 hp for the 572. That was with some super-ported 24-degree heads and a 10.8:1 CR. You should be aware of these Bow Tie blocks. They are available in short- and tall-deck versions, and most can bore to 4.6 inches. Compared to stock blocks, the Bow Tie blocks have revised oil passages and much stronger upgraded mains caps.
World Products Blocks
World Products has gone through some big changes during 2011–2012. First, the production of blocks has been split. The “trade only” parts manufacturer/distributor PBM of Louisville, Kentucky, manufactures the iron Merlin blocks. BMP, formally World Products, exclusively produces the World aluminum blocks. What does this mean? Trade customers, such as pro engine and big speed shop outlets, buy from PBM. As a retail buyer, you can purchase your Merlin block either from an engine shop, a speed shop, or directly from BMP. Regardless, you should go to the BMP site to review the lineup of blocks, details, and prices.
The iron Merlin blocks have gone through a series of important updates. Without the need for any additional clearance, the short-deck block is good for 582 ci and the tall-deck, 632. With a little grinding for additional rod clearance some extra stroke increases these figures by about 12 ci. I have not used the latest block but I used the previous version for a street/strip nitrous build that made more than 1,500 hp. That was some years back and the block is still in one piece.
