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Engine balancing and blueprinting go hand and han...
In racing, rules dictate much of what can be done...
Engine balancing and blueprinting go hand and han...
Engine blueprinting includes making sure the bore...
Engine Blueprinting Basics
Building an engine following set processes and procedures requires discipline
By Brendan Baker
The top professional divisions in racing today for the most part run engines that are built to comply with a very strict set of rules for each series. In NASCAR, where the engines have been roughly the same 358 cid V8 for decades, the power output has steadily increased. Engines of the same brand that are built by different teams often have vast differences. This is mainly because engine builders find different areas to focus on in order to achieve their goals.
While each engine may be virtually the same in NASCAR Sprint Cup competition, there are slight differences for each manufacturer and engine builder. And every engine builder knows a few tricks of the trade to put his engine over the top. Most people refer to building an engine to a specific set of rules or specifications as “blueprinting.”
In this process, engine builders are trying to obtain the maximum performance from a set of parameters, particularly if you are building an engine for a customer who races in a very strict class such as Daytona Prototypes. The edge your customers are seeking from you are in the small details of the build because most of what you are allowed to do has already been mapped out. How far you go into those details depends on you and how much you A) want to win, and B) can charge for it.
You also hear the term blueprinting with regard to street performance engines, and there are some misconceptions as to what some customers think a blueprinted engine is. Some people may believe that any engine that has been rebuilt by a professional engine builder is a blueprinted engine, however, that is not necessarily the case.
Without paying attention to all of the parts and tolerances being much closer than what is allowable from the factory, an engine may merely be built. It may still run very well and achieve all the goals that were set for the project, but without painstaking attention to every detail, the engine will not be fully optimized. In a street application, this may not be a problem at all, because you aren’t constrained by regulations except in the case of emissions for certain vehicles. Essentially, blueprinting is about optimization.
Engine balancing and blueprinting go hand and hand when doing a high performance build. Basically, any performance or racing engine should be balanced but also, if you are doing a thorough build, everything should be aligned and properly squared in relation to each other.
Vertical bores need to be perfectly perpendicular to horizontal bores and so on. And to take things a step further, a properly blueprinted engine should have exact tolerances that are set to the specific needs of the customer and application.
Don’t think that just because it’s a brand new part that it will be within specifications. Mass production parts have manufacturing variances. Experts say there may be big differences in the tolerances of brand new parts from manufacturers, depending on where you source them. Obviously, as most engine builders have experienced, some are better than others.
You need to have the tooling and equipment to be able to check and double check all of the machined surfaces and components to make sure they are within the specifications you have set or that are required. It takes more time to assemble and build a blueprinted engine because so much has gone into making sure everything works together and you have gotten the maximum out of the build.
Engine blueprinting is a standard procedure used by engine builders to obtain maximum power and to ensure the longest possible engine life and reliability. It also requires that engine builders be more disciplined, following a list of checks and measurements that will if done properly decrease the chance of an engine failure due to improper clearances or assembly error.
When blueprinting an engine, be sure to follow through the entire process and not skip any steps. This means hand building an engine with perfectly fit components using maximum and minimum recommended clearances. These specifications are determined by following the racing series rule book very carefully, making sure that every specification is met to allow the engine to pass a tech inspection.
If you are building a street performance engine, then the steps may be shortened a little to just the basics of align honing the cam bores and torque plating the cylinders during the honing step. However, there are many more things you could add to the list if your customer is willing to pay for it.
To begin with, you need to make sure the block and all parts are thoroughly cleaned. After you’ve cleaned the block in a hot tank or spray washer, make sure the water jackets are perfectly clean. Blueprinting experts say it is a good idea to inspect and analyze the block, especially if it’s used. All bolt holes should be cleaned, oiled and retapped if necessary. With any surface that is machined you can chamfer the bolt holes, and any casting burrs or irregularities should be removed.
V8 engine blocks should be align bored to maintain perfectly equal deck heights, keeping the crankshaft parallel to the decks. Any variation in these areas will result in irregularities in combustion chamber volume. This is critical for accuracy and precision in the blueprinting process.
After align boring, the cylinders should be bored with the main bearing caps still torqued in place. Depending on the application, you may finish hone the cylinders to their proper size using a 220-280 grit stone, being careful to produce a good cross hatch pattern using a torque plate as well. Some engine builders even bolt on the motor mounts to further simulate the distortions that will take place in order to achieve a perfectly square bore. After honing the block then take it back to the washer to remove all honing grit from the bores and also from the lower end of the block.
The crankshaft must have correct angularity of the rod throws as well as be perfectly straight. If your block is used experts suggest checking it for cracks and having the journals ground to perfect angular index. Oil holes get chamfered and bearing surfaces polished. The oil passages are then cleaned thoroughly with a good brush. Some recommendations include using fully grooved main bearings or grooving or cross drilling the crankshaft main bearing journals. These procedures are also helpful in insuring longer engine life.
If used, the connecting rods should be carefully checked for imperfections using magnetic particle inspection or other methods. All rods should be reworked so they are precisely the same length from crankshaft centerline to wrist pin centerline. Generally the length of the rods should be controlled by working to the minimum manufacturer’s clearance for piston to deck. Any burrs and irregularities should be removed from the rods, and always use new rod bolts and nuts. The rod alignment and side clearance are also critical.
The pistons should be individually and carefully fit to the respective pins. Chamfering any sharp edges on the piston reduces possibility of localized hot spots which cause pre-ignition and/or detonation. Each piston must be carefully matched for clearance with each bore. Too little clearance will result in scuffing and too much clearance reduces the effectiveness of the rings.
The compression rings should each be placed in the bore and straightened with the top of a piston to square the ring in the bore. Gaps can then be checked, with .0035 per inch of bore the minimum allowable gap according to one piston ring manufacturer. Experts say to be sure to check ring side clearance in the piston ring land with .002-.004˝ being recommended. But, again, with blueprinting, they should all be the same.
After the reciprocating components are selected and fit, the engine rotating assemblies should then be balanced. The components that are weighed and balanced include the rings, pistons, rods, bearings, crankshaft, flywheel, crankshaft damper and pulley. Some engine builders even allow for oil weight in the crankshaft when balancing. Additional weight is added to the bob weights in these cases to compensate for oil weight. Balancing the engine will give increased durability and also help it achieve maximum horsepower.
If the cylinder head is not new, it should be disassembled, cleaned and carefully inspected for cracks. If the surface is in questionable condition it is a good idea to resurface it. All holes and sharp edges should be carefully chamfered and deburred. Bolt and spark plug holes should get retapped and cleaned. The valve guides must be checked and replaced or repaired as necessary.
You should also check valve stems and replace those valves that are out of spec or not in good shape. The valve guides should be machined if necessary and seals installed. The valve job should be done according to the rule book of the particular racing series but this is also an area where good engine builders outshine the competition. A good valve job can make the difference between winning and losing.
All burrs and irregularities should be removed from the combustion chamber. After this the chambers should be checked for volume in cubic centimeters. The chambers can then be equalized by grinding to the volume of the largest chamber. When all chambers are equalized to the minimum CC’s you can then lightly surface the heads until the maximum volume is reached.
In order to check the volume of the chamber, you can use a plexiglas plate, some colored oil and a burette to get the job done. With the spark plug and valves installed the plate is placed over the combustion chamber and sealed with a light coat of lubricant. Using the burette it is then easier to measure the amount of liquid needed to fill the combustion chamber.
Valve springs should be checked for tension and installed height, and replaced or shimmed as needed. If the head has individual rocker arms on studs the stud should be threaded or pinned in its boss.
The next step is to torque main bearing and rod bolts slowly and in progressive steps to the proper tension. Some engine builders use protectors on the rod bolts to prevent crankshaft scars, and keep rotating the engine as each step in the installation of the crankshaft and pistons is taken. This will enable spotting the exact location of any misfit or mismatched parts. The use of Plastigage at this point can be helpful as a way double check clearances.
After this point you can install the timing gears and chain. Using a camshaft degree wheel will ensure perfect crankshaft to camshaft timing. Offset keys or cam gear bushings are available to allow accurate adjustment of possible timing discrepancies.
Then the heads are installed, making sure they are torqued to the proper specifications. The valve train should then be completed and checked. Experts say in cases where higher lift camshafts have been installed valve spring could bottom out or the canoe type rocker could be interfered with by its mounting stud. If this happens the spring must be changed, and the rocker arm relieved to provide the necessary clearance.
The complete blueprinting job must be performed as painstakingly and accurately as possible. There are many steps involved in the process and each application is different, this was just a general outline of what is involved. A blueprinted engine is the ultimate in performance, horsepower and durability for a given combination, and its success on the racetrack or in marketplace is what will build or maintain your reputation.