The plan for this build could be said to be only one rung from the bottom as far as available budget. But knowing what simple block mods could be done resulted not only in the saving of several hundred dollars but also some zero-cost power moves worth close to 20 hp.
The importance of having good cylinder heads is closely followed by the necessity to have a dynamically well-spec’d valvetrain. To be truly effective, the valvetrain must make the most of the intake valve’s flow capability. This, in turn, means you must diligently seek to maximize both intake valve acceleration and total valve lift. Now if this sounds easy, let me make this clear right away: That will not be the case unless you really work at it. The big problem here is the very substantial mass of the valvetrain itself, and this magnifies any negative issues a valvetrain can have. When you get to the discussions on heads and valvetrain, you begin to appreciate the value of this book as you learn about speed moves that you certainly won’t find in any other book on performance big-block Chevys.
Other Shortcomings
I have often heard that one of the faults of the Chevy big-block is that it can have more cubes than available cylinder heads can support. That situation may be so, but to look at it as a fault is indeed faulty logic in itself. Let me explain. Assuming the goal is to get power from the engine by any means (as opposed to power per cube), then at a fundamental level, the power achieved from an engine is only a function of the air it consumes. In simple terms, you can have either a 600-ci engine running 5,000 rpm or a 300-inch engine running 10,000 rpm.
When aircraft used piston engines, it was very clear early on in the development of such engines that the best power for a given overall size and weight of engine was to be had from the biggest displacement possible not the most RPM possible. In other words, bigger inches at lower RPM resulted in the best weight-to-power ratio. That also suited the engine’s application because propeller speed needed to be limited so that the blade tips did not go supersonic. So the big inches of the big-blocks are to your advantage. That is why I talk about heads and valvetrain in relation to moves, many less than obvious, that you can make to best utilize the cubes your big-block has to offer.
The valvetrain starts within the block. Knowing what can be done here can save you more than $100 if you are planning a short-cammed build. Not only that, but the torque output can increase along with that cash saving.
Choosing the best port size for the job is a critical part of a successful build. Adopting common wisdom can often severely impact low-speed torque while delivering no additional output at the top end.
Which is better, a roller cam or flat tappet? The answer you most often get is “a roller every time if you can afford it.” Unfortunately that is not possible when the budget is tight.
A Chevy big-block’s short deck height limits rod length, and as a result, it makes for a short rod/stroke ratio. You must constantly keep this in mind when attempting to spec out the best parts combination.
The short rod/stroke ratio of the big-block is another area of concern that is frequently discussed. The rod/stroke ratio is the center-to-center rod dimension divided by the crank stroke. It is common practice to use a stroker crank in a big-block, but even a stock-stroke 454 with a stock rod does not fair too well in terms of what it has versus what the engine may like. The stock rod/stroke ratio for a 454 works out to 1.576:1 (6.185 ÷ 4). This is on the short side for sure. To see by how much, let’s consider, say, the rod stroke ratio of a successful high-output Chevy small-block. Where power per cube, due to displacement rules is called for, the most favored rod/stroke ratio is in the range of 1.7:1 to 2:1. In other words, a much longer rod in relation to the stroke.
So what are the disadvantages of a short rod? The answer here is that if you take friction out of the picture: virtually none. Unfortunately, friction is ever present and carries with it a considerable negative impact. Studying the geometry, the shorter the rod the greater the rod’s angularity, causing the gas pressure to push the piston into the cylinder wall with greater force. My thoughts here are that this is something we are stuck with, so there is no point in fixating on it other than to look for ways to make the best of it. Fortunately, there is a ray of sunshine here. Knowing how best to deal with a short rod/stroke ratio is a substantial step forward and thus a distinct advantage over someone not so informed. In fact if what is said later in the book is absorbed you can actually shrink that short rod problem to near zero.
Delivering Results
So what is it worth to fix big-block shortcomings? To put it another way, What sort of power increase can you expect by parting company with the price of this book? Because I work on these engines almost exclusively, and most of the work I do is in the area of research and development, I can be relatively specific here. It is fair to say that probably better than 98 percent of the time someone who acts upon the information delivered here achieves a minimum of 50 extra hp, with an average of something around 75 to 100 hp.
Indeed, in many cases, target power levels are achieved at considerably less cost than would have otherwise been the case. How do I know this? Simple, I get plenty of calls for advice from pro engine shops asking if I have any moves that may show more power without a cost increase; as the shop down the road is beating their numbers for less money and getting their customers as a result.
Cam timing is critical. It’s entirely possible to lose 10 to 20 hp because you don’t know which factors you may have built into your engine. These can dictate a different cam advance than the cam manufacturer’s cam spec sheet.
Because of the short rod/stroke ratio, compression can be one of your closest allies. Be sure you have all the relevant facts because it can make a much bigger difference than with many other engines.
There are at least 20 hp locked up in simple block mods that cost only time. You need to ingrain it firmly in your mind that a max-performance big-block requires many cubic inches. That means nothing smaller