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From Tame OE Block To High Performance Monster
By Jim Walbolt
The race engine is only as good as its weakest part. There are many ways to build a great high performance engine, but one key is essential: each and every part of that engine must work together to build the "best" power. In this case, "best" power means that the engine does exactly what the driver, regardless of racing type, wants it to do when he wants it to do it. It also helps a driver’s winning percentage if the engine makes it to the end of the race. Remember that old saying, "To finish first, first you have to finish."
The basic foundation of a high performance engine, or any engine for that matter, is the block. The difference between an OEM block and a "race" block, however, is that the tolerances allowed in OEM applications just won’t do for high performance applications. It is not uncommon for bore locations to be as much as .030˝ off in OEM blocks. For high performance blocks, the bore must be square with the centerline of the main journals, and again, OEM blocks are always off. Aftermarket blocks are generally much closer and won’t require as much work to get them where they need to be.
Another thing to keep in mind when preparing a block for high performance is that the more symmetrical the block is and the closer it is to the proper specifications (bore centerlines in the proper location, decks square to the crank centerline, etc.), the easier the rest of the building job will go.
Besides the bore centerlines and alignment fore and aft, the cylinder banks in an OEM V8 will also be off a couple of degrees. A V8 block that should be at 90° may be found to be at 87° or 88°. These are some of the little things that make the difference between a good high performance engine and a great high performance engine. As bad as the OEM blocks may be, no matter the manufacturer, the aftermarket replacement blocks, whether iron or aluminum, are usually always very good. Still, checking everything must be part of your process.
When a customer brings you a block, there are several steps you need to take to turn it into a great foundation for high performance. Of course, different applications will have different needs. For instance, a high performance street motor won’t need to be as perfect as an all-out drag motor. The application and performance level your customer is seeking will determine the amount of work the block will require.
For this article, we’ll assume that we are building an all-out race motor – but remember, not all motors will require each of these steps. We’re assuming that we’ll be working with an iron block, but most of these steps would also apply to aluminum blocks. Also, because there are literally hundreds of different applications, we won’t get into specifics, but will try to cover all the basics.
Unless you’re familiar with the block and have worked on it before and know that it’s in good shape, your first step should be to clean and Magnaflux. You sure don’t want to get through half of the machining work and find a crack. Unfortunately, you will generally be unable to find cracks in the cylinders even with Magnafluxing, so you’ll need to "eyeball" them carefully. As you gain experience with different blocks, you will get a feel for where to look for specific problems with each particular brand.
Although not required in all cases, the block may also need to have the cylinder walls sonic tested. Some blocks, such as an old FE 427 Ford block, and some of the later small blocks, are known to have thin cylinder walls. With most blocks, if it’s an all out race motor, or it’s going to be bored very big, they should be sonic tested to be sure there is enough material to give you a sound starting point.
If you are starting with a stock block, most likely you will be installing aftermarket main caps. If it’s a two-bolt block you will probably be installing splayed, four-bolt caps in the middle while retaining the stock end caps. In other applications, you may be replacing all the caps. When installing nearly all aftermarket caps, you will also need to align bore them.
It’s a good idea to always align bore to near finish size, say within .004˝ to .007˝ then hone to finish size. It is also a good idea to measure each bore and cut the caps so that they are all the same when you bore them. You don’t want them to all be a different size when you begin to align bore them.
In most cases, you will be using steel aftermarket caps, even in aluminum blocks, but one trick that builders of Chrysler big blocks have found is using aluminum caps. The crankshaft and bearings in these blocks seem to hold up better with the aluminum caps than with steel. Also, for a mild supercharged motor, you can probably get away with a two- or four-bolt block, but for any high powered "blown" application you should advise the customer to start with an aftermarket replacement block with cross-bolted mains. Blowers put a tremendous strain on an engine’s bottom end.
A good reason for doing your align bore/hone first is because some shop equipment uses fixtures that use the main bore as the block mounting point. Such a setup also makes it much easier to check for a square deck and cylinder location and alignment. One such machine to accomplish this is a boring mill, but it also gives you the option of performing many other tasks without moving the block from station-to-station.
Once you have the align bore/hone done, you can bore the block according to the customer’s wishes. You need to keep everything as symmetrical and as standard as possible. The more identical each cylinder is, the better the engine will be.
When boring a block, even though your customer may want it as big as it can go, you are much better off to leave a little room to work with. You should always leave a little cleanup room to be able to freshen the motor after the season or to repair a cylinder in case a burnt piston gouges it out a little. Remember, even though your customer said he wanted that block as big as it could be, he won’t be happy if he has to throw the block away after burning a piston the first night out. You’re the expert. Sometimes you need to remind your customers of that.
Among the most common blocks you’ll see are Chevrolets. A big block Chevy has the capability to be bored at least a hundred over and, of course, a lot of your customers will want that big bore. You will need to watch how deep you bore the block in those cases. You will be boring into the upper side of the main web, and if you bore down too far, you’ll nip the oil galley that comes in from the outside and goes to the cam bearings. In that case, you’ll have an oil leak that you may not notice until your customer starts it up and has no oil pressure. An expensive repair job will then be needed.
Your final bore size, of course, will depend on the piston you will be using. Piston type, alloy and manufacturer will all determine proper clearance in the bore. A high performance engine will always require more clearance than stock. Different alloys will grow at different rates and the higher the performance of the engine, the higher the heat it will generate, thereby needing additional clearance. Your piston manufacturer should be able to help you here. One note: all clearances – rod side clearances, bearing clearances, etc. – in a high performance engine will need to be increased.
Bore finish will depend on the application of the engine and also the type of rings you will be using. Different ring materials require different finishes. Your ring manufacturer should be able to help you in this department.
Once you have the cylinders squared up, you can turn your attention to the deck. It is critical for the deck height to be the same across every square inch of surface. A slightly higher deck at one cylinder can make a big difference in the performance of the engine. In fact, a quarter-point difference in compression from one cylinder to another can add up to a full point difference.
If it’s a V8, you need to do your best to make both banks the same deck height. Once again, however, the lower the expected performance of the particular engine, the more you can get away with. With an all-out high performance engine, zero tolerance should be the rule.
When decking an iron block, you always need to remember to remove the dowel pins that locate the heads. On an aluminum block, you must remove the sleeves to properly deck the block. Many shops have been known to deck an aluminum block with the sleeves in and they end up with a nice smooth surface with no protrusions at all, but a problem soon develops after the engine is run in competition a few times. The sleeves tend to work themselves down into the block, and the next thing you know, you’ve burnt a head gasket and probably torched the head and block at the same time.
If you do find yourself decking an aluminum block (after the sleeves are removed, of course) you will also need to re-cut the counter bores that the top of the sleeves fit into. The sleeves must protrude above the deck. On a small block, the protrusion should be about .002˝. On a big block, the protrusion should be .004˝ - .005˝. Without that protrusion, the sleeve will work its way below the deck, and once again, you will lose a head gasket and torch a head.
Once the block is decked and the sleeves are reinstalled where applicable, you can groove the deck for O-rings if you will be running a dry block and using copper gaskets (often the case with drag motors or tractor pulling motors that will run dry without any coolant).
Although a copper gasket can be used with a wet block, it’s not the best choice, as you will eventually get some water seepage. Gaskets are so good today that if you are running a wet block, you should use a composite gasket. If you want the combustion sealing properties of an O-ringed block with copper gasket, there are several manufacturers that have what are called "ring lock" gaskets. These might just be the alternative you are looking for.
However, if you insist on using copper gaskets and an O-ringed block, there are just a few things you need to know to get a quality job. Once again, those four little words are critical: "proper cylinder bore spacing." Hopefully, your bore spacing is perfect and you can cut your grooves in the block in the standard position for the combustion chamber and the receiving groove in the heads. Of course, the receiving groove in the heads is cut after the block is grooved.
The common wire size for O-ringing a block is .041˝ stainless steel aviation tie wire. This is a good size to use because if you lost a head gasket in the motor, and it burnt the block and groove at the same time, you can save the groove by going up to .052˝ wire and you would only need to do that one cylinder.
When cutting the groove in the block, you will cut it to a depth of 66 percent of the diameter of the wire and a width of .002˝ less than the diameter of the wire. One note of caution, be sure your cutting bit is sharp because a dull bit will generally cut a wider than expected groove. It’s a good idea to do one cylinder, then check it for proper fit.
The wire can be tapped into the groove using a brass drift. You should square up one end of the wire before working it into the groove. Once you work the wire all the way around, you can nip the wire off with a pair of cutters and butt it up against the other end of the wire. It’s a good idea to leave a slight gap between the wire.
It isn’t necessary to angle fit them so they are flush, because the copper gasket will fill any imperfections. This would only make them tough or nearly impossible to remove if needed. It is also a good idea to line the wire ends up with a known point, such as a head bolt hole, so that you always know where the end is should the time come to remove them.
That’s about it for the basics. Of course if you O-ringed the block, you will also need to cut receiver grooves in the heads. That should be a piece of cake because you have all of your bore spacings correct, the cylinder alignment is perfect and the deck is square to the centerline of the main bores. There are other, more advanced operations we can do to a block such as coolant control in a wet block, oil control and installing "Hard Block" block filler into a dry block, or short filling with "Hard Block" in a wet block.
We could also discuss sleeve replacement and damaged sleeve removal, main saddle repair and block repairs, which perhaps we’ll do in another column. If you have questions, suggestions or disagree with something you’ve read here, please contact us by snail mail or e-mail. This column is for you, and we welcome your involvement.
I would like to thank Jeff Fowler and shop foreman Robin Elliott of Fowler Engines of Columbus, OH, for taking time out of their busy schedule to help us with this column. Fowler Engines is one of the premier performance engine builders in the Midwest, particularly well known for their "blown" alcohol motors.
Jim Walbolt, a professional writer and photographer covering motorsports activities, is from Luckey, OH. You may e-mail Jim at firstname.lastname@example.org