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Table of Contents
1. Budget
2. Old Vs New
3. Small
Block Vs Big Block
4.
Two bolt Vs Four bolt Vs Splayed
5. Buying a used
block
1. Budget
Its only appropriate to start with the budget. A good rule of thumb is
each horsepower will cost you $10 (example if you want 500 HP, expect to
pay $5000 dollars for your engine). Of course if you can reuse existing
parts and buy other parts used you save significantly. Do not cut too many
corners, if you do you will pay more in the end.
2. Old Vs New
If you are building an engine for your street car, you can easily find a
seasoned block for your project. There are many places you can find great
deals on the Internet. Example
www.rpmcat.com,
www.hemmings.com,
www.carsandparts.com,
www.motorsportsmarketplace.com, and
www.flag2flag.com.
If you are building for serious competition, you should consider buying a
brand new block
3. Small Block Vs Big Block
Small blocks commonly make between 300 and 500 horsepower, and even up to
750 horsepower naturally aspirated. If you add turbos or nitrous, the 1000
hp mark is possible but will seriously test the integrity of the engine
casting even when using an aftermarket block. If you want to make a
reliable 750 to 1000 horsepower engine your money will be better spent on
a big block.
4. Two bolt Vs Four bolt Vs
Splayed
Two bolt main blocks are more common and easier to come by. Many will even
argue they are stronger than their four bolt counterparts because they
take less material out of the web of the engine block. A two bolt also
gives you the option later of installing 4 bolt caps or splayed main caps
-- the strongest combination possible. Keep in mind there are significant
machine shop labor costs using this option.
If you plan to exceed 400 HP with a small block or 600 HP with a big
block, you should use a four bolt block.
If you plan to exceed 500 HP with a small block or 800 HP with a big
block, buy a two bolt main block and have splayed caps installed.
Be careful with certain 4-bolt blocks before you buy them, especially the
400 small block Chevy. It is very common for these blocks to be cracked in
the web area near the mains.
5. Buying a used block
Use extreme caution when purchasing an engine block at a swap meet or thru
the classifieds. Invest in a set of calipers before giving your hard
earned cash for a block.
Measure the cylinder bore. You ideally want a virgin block that has never
previously been bored. A seller knowingly or unknowingly will often tell
you the block has never been bored when it reality it has already been
bored 0.030 or more. You can safely go to 0.040 on the 350 Chevy, and
0.030 on the 400 Chevy, and 0.060 for the 454 Chevy for street use. Any
further boring beyond this you will need to fill the block at the bottom
of the cylinders to keep the block strengths.
Of course if you fill, the cooling system will still be able to keep the
cylinder heads cool, but the ability of the water to remove engine oil
heat at the bottom of the cylinders is lost forever and you have a 'race
only' block.
Inspect the block for cracks in the cylinder walls, around the freeze
plugs, near the main caps, and especially in the lifter valley if the
engine used a roller cam. If a block is too greasy to perform these visual
checks, look at the grease very closely. If there is any milky color,
there will be a good chance of a crack somewhere in the lifter valley or
the engine has a warped deck and lost the head gasket seal. Make sure
there is no evidence of a spun bearing in the mains (heated and rough
bearing seating surface). A block can be repaired from this type of
damage, but the cost for repair is very high and you should start with a
different block.
Again, do not lay down your hard earned cash until you have measured and
thoroughly inspected everything yourself
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