Chevy Big Blocks - David Vizard

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Fig. 1.10. If valvespring clearance allows it, use low-cost ARP hex-head bolts instead of the 12-point items. For the record, they deliver just as much clamping load.

      I am often asked whether or not the heads should be held down with studs or bolts. The easy answer is studs. But they cost a lot more than good hex bolts (from ARP, for example). A set of studs provides a marginally better clamping load than a good set of bolts, such as ARP’s. Also, you need to consider ease of service when the engine is installed. If the engine is equipped with studs, you need to have at least 8 inches of clearance above the studs in the direction that the heads are lifted off the block. If this is not the case, you cannot remove the heads without having to take out all the studs first. This is not the case with bolts. My advice? Unless it’s an “on-the-limits” build, use ARP bolts.

      When explaining the use of a stroker crank in my previous Chevy big-block book, I spent most of the time covering what is needed with a 1/4-inch stroker and the Scat cast-steel crank, which is a budget-priced item with great power potential. Whether you choose a cast-steel or forged 1/4-inch-stroker crank for either a 454- or a 502-style block the installation is pretty simple as stroker builds go. For the most part, cutting the block for rod clearance is minimal assuming you are using the right rod for the job (covered in Chapter 2, Pistons, Connecting Rods and Crankshafts). In some cases, the block has enough clearance to allow a 1/4-inch stroker to drop right in but you should not count on it.

Fig. 1.11

       Fig. 1.11. This factory 572 is based on a tall-deck block with a 4.560-inch bore and a 4.375-inch stroke. This is a good combo from the point of view of RPM capability and rod-to-stroke ratio.

      Let’s focus on strokes of 4.375, 4.500, and 4.75 inches; that is 3/8-, 1/2-, and 3/4-inch strokers. The good news is that almost all 454 and 502 blocks accept a stroke increase of up to 4.5 inches, which is a 1/2-inch increase. If you opt for a forged crank, you should go for the longer-stroke crankshaft because the price difference between a 1/4-inch stroker and a 3/8- or 1/2-inch stroker is virtually nil. That being the case, the minimal amount of extra work for additional block clearance is worth it in terms of results.

      As of 2014, I have experience with four 454 1/2-inch-stroker test engines, bored 0.060 over, and each has delivered gratifyingly good results. In spite of having a smaller bore and thus a breathing penalty, the resulting 525-ci build does remarkably well, as long as the combination is right. The principal aspects to focus on are the heads and, most important, a cam spec that suits both the heads and the displacement.

Fig. 1.12

       Fig. 1.12. Dart’s short- and tall-deck blocks are almost certainly the most popular choice. The taller deck allows for a longer stroke that is typically worth about 40 ci over the short-deck variant.

Fig. 1.14

       Fig. 1.14. Here is a BMP aluminum tall-block. Going from cast iron to aluminum saves about 100 pounds. If big displacement is what you are looking for this particular block can accommodate 632 inches.

      Putting a 1/2-inch stroker in a 9.8-inch short-deck block means the rod has to be 6.385 inches long and that’s 1/4 inch longer than stock rods. If the rods are any longer, there is insufficient room for the ring pack. With this length of rod the piston pin height is down to 1.165 and packing a regular set of rings into much less than that for a budget-conscious build is impractical. 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

       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.

      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

       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

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