Car magazine staffers like us get to personally interact with more car nuts than anybody else in this business. On the show grounds and in the pit areas we often overhear enthusiasts bench racing and talking about how they built their own powerplants. The term "Blueprinting" seems to be thrown into the conversation quite often, but we've learned that many car fanatics don't have a full understanding of what blueprinting an engine really is. And of those who do grasp its fundamentals, truly blueprinting their engines is out of the their realm simply because the tools and equipment involved cost a ton of money. We've had the opportunity to peek over the shoulders of some of the best engine builders in the world and also watch as some downright rookies attempt their first build-up. And from these experiences we've learned ways to perform a basic blueprint for a moderate investment.
Originally we were going to call this story $100 Blueprint, thinking that you could buy all the tools you'd need for the basics from the big mail order houses like Summit, Jeg's, and Powerhouse for about a hundred bucks. Then, after researching even the bare essentials required for an average engine blueprint job, we found out how wrong we were. The good news is that for a little more than double that amount, you can blueprint your engine at home with reliable accuracy and results.
Let's get something out of the way up front. This story is not going to tell you how to blueprint a 1,000hp nitrous or turbo motor. Instead, these are simple ways that the average enthusiast assembling an engine can measure and calculate essential information for making the powerplant live in the harsh daily grind. When blueprinting an engine in its purest sense, all you're doing is making sure that all the parts fit together the way they're supposed to. In theory, a backyard blueprint, if done properly, will provide the same engine reliability that a $1,000 blueprint from a professional race shop could turn out. It will not, however, give the same accuracy, down to the smallest detail, that some professional shops could supply, but that level of accuracy is hardly needed on the street.
WHAT IS BLUEPRINTING?
Contrary to its name, blueprinting an engine has nothing to do with big rolls of paper that have strange, blue-colored drawings on them. Blueprinting an engine starts by designing it on paper first. Calculating things like compression ratio, piston pin (compression) height, displacement, and carburetor cfm requirements are all the beginnings of the true blueprinting process. From there it involves properly communicating your needs to the parts manufacturers and to your machinist and finally checking the parts, by hand, to ensure that they all meet your requirements.
Let's say you want a 420hp small-block for your daily driver. You've already got the block, crank, and connecting rods, and you need to know which pistons will give you a true 9:1 compression ratio for pump gas. You also may want to squeeze a little nitrous into it, so you'll need to use a piston/ring package that can take some abuse. And you know that you're going to drive long trips to go to car shows around your state, so it would benefit you to optimize your bearing clearances for the best oiling and power you can get. You can take the easy--and probably less reliable--route by simply purchasing some off-the-shelf parts then assembling your beast gambling that everything is the way it's supposed to be. Or you can take the time to check every component before it goes into the motor. In this story we've given you some of the critical formulas you'll need to calculate your requirements. We've also referenced actual build specifications for things like bearing clearance based on real-world testing and performance.
MEASUREMENTS BY FEEL
Your fingers and hands are the best measuring tools you will ever own. If you've had the chance to use a micrometer and tried to measure an accurately machined part, you'd know that by simply turning the micrometer's spindle just a bit harder you can change your readings. That's why they make micrometers with ratcheting spindles that are supposed to produce accurate, repeatable measurements no matter who's turning the screw. But micrometers are still tough to use, and good ones are very expensive, so we like the good old dial caliper instead. While you'd never see a Winston Cup engine shop using something like a simple dial caliper to measure pistons, we're here to tell you that it's okay, provided you're not trying to build a 750hp small-block that can run wide open for 500 miles. If you want to go out and buy a good-quality micrometer set, you should also buy a set of standards to check the micrometers against and a simple set of accurate plug gauges to "calibrate" your feel. By using tools like plug gauges, which are precisely machined pieces of steel in specific ranges, you can practice your "feel" for the proper readings. A small plug gauge set will cost about $100 and will go a long way in helping you learn how to feel if the measurements you're making are correct.
BLUEPRINTING ON THE CHEAP
This story will give you the basics of what blueprinting an engine is. If you practice with these low-buck tools and techniques, it will help any engine you build last longer, and you'll get results within about +/- 0.001-inch. We can't stress enough how important "feel" is to the entire process. And using your brain more than your bank account is always helpful. Backyard blueprinting for the masses is what we're trying to teach here.