
TECH
TALK

STEP 1 - "BLOCK PREPARATION"
STEP 2-"ROTATING ASSEMBLY
STEP
3 - "HEADS & CAMSHAFTS"
STEP 4 -
"SUPERCHARGERS"

BUILDING A MINI ROD PULLING ENGINE
SUPERCHARGERS
THE MORE AIR AN ENGINE BREATHES THE MORE
POWER IT WILL MAKE
When a pulling engine is supercharged, it makes a
tremendous amount more horsepower than a naturally aspirated engine. The
reason it makes more power is that the supercharger takes in 14.7 pounds of
atmospheric pressure, this pressure goes through the rotors and then is
literally pumped into the engine. An engine can only breath so much air
when it is naturally aspirated, by pumping air into the engine through the use
of a blower you are providing the engine with more air than it is suppose to
breath, which creates your boost pressure. The more boost pressure the
blower makes the more power the engine will have. The amount of boost can be altered by these
factors:
ENGINE SIZE, CAMSHAFT SPECIFICATIONS, PULLEY SIZE
AND BLOWER SIZE
Whether you buy a blower or build one for your
puller, there are of course a couple of options for choosing a blower other than
its size. A Street style blower has no seals in it. This means when
the rotors interlock with each other, there is a leading and trailing clearance,
as well as the clearance at the top and bottom of the blower case, therefore
nothing touches or rubs. This style of blower is lower maintenance
supercharger because it doesn't wear and will last longer. The
disadvantage to this style is that since there are clearances the boost pressure
will leak past the clearances which isn't as efficient.
A competition blower uses Nylatron and Teflon
strips to seal the clearances. It is a good idea to have the rotors and
case hard coat anodized. This makes the blower have harder surfaces and
will slow down the rate of wear caused by the rubbing of the seals. A
competition blower will have a distinct whistle sound to it, when the seals are
fresh and tight this sound is enhanced. To seal the rotors to the blower
case Nylatron is used in most cases. The Nylatron (black) strip is slid
through the dove tail groove in the rotor. The rotors are then put into
the lathe to outside diameter machine the diameter of the rotor to fit the
case. The outside finished diameter size is slightly larger than the case
which causes interference. The Teflon (white) strips are slid in the
rotors to help seal rotor to rotor clearances. When a competition blower
has new strips you should not be able to turn the blower rotors by hand and
should stay this way for 4 - 5 pulls. By then it will have loosened to
where you can turn it by hand. What has happened it those runs is that the
interference that was left when the rotors were machined has now worn
away. The strips still provide a tight seal to fill the clearances and
will remain sealed for quite a few passes. Some Professional Drag Racers
will change the strips in their blowers every two passes to ensure that they
have a fresh, tight blower for maximum power. A tight blower requires more
maintenance but it will make more power because it is more efficient, creating
more boost.
If you are not using an aftermarket blower, there
are a few things to do to make a blower compatible for a pulling engine.
In the case of some of our Top Alcohol Mini Rods a 671 blower is used on a 350
small block Chevy. The endplates of the 671 Supercharger are not near as
strong as aftermarket ones and the bearings in the endplates are stronger as
opposed to the original 671 bearings. Clearances should be checked when
building a blower for tractor pulling. The blower turns much faster when
put on a 350 engine for pulling than it ever did on the GM Detroit Diesel.
Clearances when new endplates are installed will be closer to what is
needed. The bottom of the blower should have a very tight clearance (rotor
to case) and the top should have a larger clearance. This is because the
boost pressure of the engine forces the rotors up in the case, so a little more
room at the top is required. The drive mechanism is different than the
diesel. For tractor pulling it involves a billet snout which drives the
drive rotor. This is the mechanism that the blower pulley is attached
to. The crankshaft drives this pulley through the use of a toothed belt.
STEP 3 - CYLINDER HEADS
& CAMSHAFTS
CYLINDER HEADS
The most important component on a natural
aspirated engine for making power is the cylinder heads. That coupled with
the right camshaft allows the engine to breath more air. The more air an
engine will breath the more power it will make. The critical part of the
head is the port size and shape. The shape of the port determines how the
air and fuel travel through and the trick is to make this as easy as
possible.
Stock heads have very sloppy port shapes because
when they are made in production for cars and trucks, it's to costly to detail
the port shapes. When stock heads are ported properly, they can increase
horsepower. Shape of port is very important to improve the head. On
a stock head, shape is primarily the biggest improvement over size. If the
size of the head ports are larger they will flow more air. Unfortunately
size cannot be increased much on a stock head because the casting is thin.
In a small block there are several casting numbers, but what we are looking for
usually is small chamber heads. These heads were used primarily on the
corvette engine and are becoming very hard to find. One popular
combination is to use 305 heads on a 350 engine to increase compression.
There has been some success with this but it presents a problem.
Most of the time larger valves are installed in 305 heads, this way the
compression is higher and the bigger valves provide more flow in the port like a
350 head. However, the way a 305 chamber is designed, when the larger
valves are installed, the chamber shrouds around the valve opening and reduces
flow into the chamber. Stock heads are a good choice in street rodding,
but for a racing application aftermarket heads should be seriously
considered.
AFTERMARKET HEADS
If your serious about making power, aftermarket
is the way to go. Aftermarket heads have been designed to solve all the
problems with stock heads. They have thicker decks for higher ability to
plane, they have small chambers, the ports are much larger than stock and are
shaped very well. They measure the intake port size by its cc volume.
Heads can be purchased from 205 - 230 cc's and even higher. Of course with
aftermarket heads, stainless steel valves are a good choice. They are not
only stronger than stock valves, but they flow much better because of their
shape. Cast iron heads are cheaper and have less of a chance of having
head gasket problems because the heat expansion rate is closer to the
block. Aluminum heads can be purchased for a lot more money, but they have
some advantages over cast iron heads. Aluminum heads can be repaired a
little easier if there is any breakage and they save a lot of weight.
Your
budget plays the biggest role on the type of heads you select. In most
cases, the price of new cast heads are not much more compared with what you would pay for
stock small chamber heads with the porting and machining required to make the
head flow well.
CAMSHAFT
The camshaft is one of the most important items
to controlling horsepower at a desired RPM. The camshaft is totally
dependant upon the application of the engine. The selection of camshaft
also depends on what RPM you want the engine to run at, the kind of induction
system being used, quality of the cylinder heads and the strength in the bottom
end of the engine.
The RPM is an important factor that depends on a
combination of carburetion, intake and cylinder heads. These items must all work together to have a successful engine.
For example in a natural aspirated small block Chevy pulling engine, If
you use a single plane manifold designed for up to 7500
RPM operation with a Holley 750 CFM carburetor or equivalent, this
induction system would be considered a good system for pulling in limited
modified. The cylinder
heads are the most important for power, so assuming they are aftermarket with
high flow rates, high power can be made.
With this combination in mind a certain camshaft
can be selected. The lift of the cam depends on the head port
design. With a stock head, the lift can't be too high because the valve
and port doesn't flow good at high lift. If you are trying to run the
engine high on RPM with stock or reworked stock heads, lower lift and a lot of
duration would be necessary because of the poor port flow rate. The
duration, meaning the amount of rotation of the crankshaft when the valve is open
is greater to allow more air to flow through the stock ports at a high
RPM. If the heads flow better than stock the amount of duration required
is less at the same RPM of operation.
There has been many street rodders that use stock
heads and decide to use the biggest cam in the catalogue. This makes the engine
idle very lumpy and sounds very impressive. When the engine revs up the
lift could be too high for a stock port and flow can actually decrease causing
extreme lack of power. Of course as mentioned before if the bottom end is
not built strong, high RPM from intake, heads and camshaft can destroy possibly
the whole engine. OUCH!
In a blower application, the induction system is
totally different. When air and fuel are pressurized into the cylinders a
different cam must be considered. Usually a high lobe centre is a good
choice. This retards the intake duration which allows better cylinder
filling and reduces static compression (cylinder pressure) because a blower
engine has such high pressures to begin with. Another thing is high lift
and duration. As previously discussed, the engine is breathing 2 - 3 times
the amount of air it normally would (depending on the boost). This makes a
larger cam a necessity because all this extra air and fuel must flow through the
engine.
ROLLER CAMSHAFTS
Roller camshafts sound very attractive when
talking about them, but they do have their disadvantages. Roller cams have
a wheel that rides on the cam which reduces friction. It also allows
faster ramps on the cam. This makes the cam appear as a rounder
lobe. Faster ramps open and close the valves at a much faster rate.
This allows the valve lift to be open at a larger lift for more of its
duration. This means more power in most cases. One disadvantage of a
roller cam is it takes more power to drive the cam. The reason is that a
roller cam requires much more spring pressure to keep the lifter on the
cam. This adds more stress to the entire valve train, so you have to make
sure there are very good parts that make up the valve train. Maintenance
is higher for this very reason. A rev kit can be installed to reduce the
stress on the valve train. It consists of extra springs in the lifter
valley to add pressure on the lifters only. This allows less pressure on
the valve springs and makes it easier on everything. Roller cams allow
much more lift as the engine requires it because the roller geometry can be much
more aggressive then a flat tappet. If the engine doesn't require extreme
lift a flat tappet will work fine and be much cheaper in price.
This is a just scratching the surface, the
subject of heads and camshafts expands much more deeply but hopefully this will
provide some general information for those who are curious.
STEP 2 - "ROTATING ASSEMBLY
The rotating assembly is the next set of parts to
consider when building a performance pulling engine. This is one of the
most important decisions because the rotating assembly is subject to the most
abuse.
CRANKSHAFT
The most important part of the rotating assembly
is the crankshaft. There are many different types on the market but some
of them can be intimidating (especially the price of them). When selecting
a crankshaft it directly relates to the application. In a carbureted
engine that produces 400 HP or less, a stock cast iron crank is more than
adequate. A great deal of people think that just because the engine
"has a cam in it" that they need a forged steel crank. Forged
steel cranks are much more expensive and are not always necessary. If the
crankshaft is going to be "stroked" by means of offset grinding the
crankpins which reduces the diameter, then a forged steel crank is highly
recommended.
In a blown application a forged steel crank is
the only choice. An OEM GM steel crank will live in a mild blown
application, but it is considered a risky choice. If the blower produces
16 lbs of boost and up (running on alcohol), a 4340 steel crank is the premier
choice. This is assuming this is for a Small Block Chevy but for a
big block, the GM steel crank will take a lot more abuse. There are many
4340 steel cranks on the market and they range from $1000.00 to $2500.00 CDN.
It would depend on how much boost is created to determine which crank to
use. Whichever crank is chosen it is mandatory to have a big block
diameter snout on the front. A Small Block Chevy snout is only 1 1/4"
diameter and is not strong enough to drive a supercharger. Bearing
supports that support the front pulley are available but the snout can still
twist off from the sheer torque. When the snout does twist off it usually
breaks behind the cam drive which throws the cam timing out of sequence with the
pistons.
As a result, valves and pushrods will be bent. If you're lucky, this will
be the only damage.
How do you get a big block snout? You can
special order a crank made with a big snout but this will put the cost of the
crank closer to $2500.00 CDN. The other alternative is to get your local
crankshaft specialist to weld the snout and then turn it to size.

The keyways would then have to be milled after
grinding. The next thing to overcome is the timing chain sprocket or gear
drive gear must be enlarged in diameter and re-keyed. A big block crank
hub can now be used. The front cover needs to be bored out to accommodate
a larger seal.
Periodically the crankshaft should be magnifluxed
to check for cracks. Cracks develop in the radius of the journals and can
lead to disaster. Cracks usually start on the journal and if the crank is
continued to be used, the cracks will grow all around the journal until the
journal separates from the web. Ouch!
Crankshaft journals should be free of scratches
and marks otherwise undersize grinding is necessary. Most crankshafts can
be ground .010 - .020 or .030 inches.
CONNECTING RODS
Another very important part to the rotating
assembly are the connecting rods. For engines 350 HP and under, stock OEM
steel rods are adequate. The RPM must be kept below 6000. It is
highly recommended to use aftermarket hardened bolts for the rods. ARP are
the most popular. This requires the rods to be resized on the big end to
ensure the big end bore is the correct diameter for the correct bearing interference.
The rods should be magnifluxed to ensure there are no cracks. Cracks can
occur on the beam of the rod or where the holes are for the rod bolts.
These are the most common places. These rods can be shotpeened to
increase strength but if all these procedures are done, the budget spent could
add up to the cost of an aftermarket set of rods.
The premier choice is aftermarket rods.
There are several rods on the market and range widely in price just like the
crankshafts. In a naturally aspirated application, a good quality steel
rod will allow higher RPM's and still be as safe as the engine can be. If
your going to spend the money, a set of "H" beam rods with 7/16"
bolts are very strong. Now your pulling engine can turn up to 8000 RPM and
should be reliable.
Another advantage that aftermarket rods have is
that they usually come bushed on the pin end. This allows the wrist pin to
be full floating. When RPM's reach over 6000, the floating pin is a good
choice. Refurbished stock rods still use the press pin system which only
allows the pin to rotate in the piston pin boss. Quite often the pin
starts to seize in the pin boss and it results in piston damage. Stock
rods can be bushed but it reduces the strength on the small end of the rod and
again as mentioned earlier, the cost of refurbishing a stock rod completely will
cost almost as much as aftermarket rods.
In a blown application, it is highly recommended
to use aluminum rods. The reason for using aluminum rods is not because
they are lighter, (in fact by the time you add more material to the rods to make
them strong enough they can be almost as heavy as a steel rod) aluminum rods are
used because they are softer than steel. That makes them act like a shock
absorber every time the piston is forced down. This gives longer
crankshaft and bearing life. There is one disadvantage, aluminum rods will
only last so many runs. Every time the rod compresses and absorbs the
shock of combustion, it work hardens the rod and the rod becomes more
brittle. A rod will only take so many cycles and then it will break. How
often to change them depends on how hard your running the engine (RPM, blower
boost, etc.). On average in a blower tractor application, they should be changed
about every 70 passes. People have tried to run aluminum rods in stock car
and street engines and they end up breaking. Even though the power of the stock car
and street engines are less, these rods go through many more cycles.
PISTONS
In a natural engine, cast aluminum pistons are an
OK piston to use. The Hypereutecic pistons are the minimum pistons
required. For a Limited Modified engine you are looking for as much
compression as you can get. There are Hypereutecic pistons available with
a big dome, it usually combines with a small chamber head (64 cc). It is
quite simple to get 12 1/2 to 13 to 1 compression with this combination.
For the serious competitor, a forged piston is the best choice. With forged racing pistons they
machine the domes closer to the shape of the head so compression can be
higher. They usually have deep valve relief pockets so higher lift and
duration cams can be used. The last advantage is that they are much
stronger allowing for higher RPM's.
In a blown application, a forged piston is the
only way to go. There is much more force and pressure on the piston so its
a good idea to run the strongest. The compression ratio should be less
than the previous engine discussed. The supercharger increases the
compression ratio as it creates boost. Usually 10 - 11 to 1 is high
enough. This is an easy combination to achieve in a Small Block
Chevy. With a 64 cc chamber head and a flat top piston, it will be
close to 10 to 1. A slight dome on the piston will raise it to 11 to
1. It depends on the engine builders preference. The cylinder
pressure is tremendous in a blown engine. If the engine produces 14.7 PSI of
boost, this is twice the pressure of the atmosphere. This means the
compression ratio is 20 to 1 in a statically 10 to 1 engine. This is only
theory because the blower produces heat which expands the air causing more
pressure. So there is a inefficiency which would make it less than twice
as much but it gives you an idea of the potential pressure that can be
created. Some extremely built supercharged engines can create boost up to
48 PSI. These engines can be found running for example in the NTPA TWD class. This high cylinder pressure is what makes a blown engine much
louder than a natural engine.
PISTON RINGS
A molly piston ring works very well in almost all
racing applications. The end gap should be carefully checked on every
ring. Usually file fit rings are the most common choice which allows you
to file the ring to fit each bore accurately. In a blown engine or any
alcohol engine, it is wise to choose a zero gap ring. This helps to keep
the oil from contamination from alcohol. It also helps the rings seal with
more efficiency.
ASSEMBLY
Assembly is a whole different chapter but when
doing so make sure the bearing
clearances are checked carefully!!! And don't forget to get the assembly
balanced. You don't want the engine to shake apart!
All of the suggestions are only a guide and may
change according to the engine builders preference. This is only scratching the surface when it comes
to the rotating assembly. There are endless options and opinions on ways
to build the engine.

Looks like a mess but this is a rotating assembly
ready to be installed in a blown Small Block Chevy

STEP 1 - "BLOCK PREPARATION"
Every engine building project starts with one of
the most important parts, the block. Most block prepping procedures are
similar, but we will concentrate on the most popular engine, that being the
small block Chevy.
The first thing we need to know is the
application. Carbureted gas (naturally aspirated) or blown alcohol.
When that has been decided then we need to determine whether the cylinders are
in fair shape. For a small block, the cylinders can be bored out as much
as .060" safely. It would be preferred to bore out to .030" that
way if the engine is hurt it can still be freshened to .060".
However, if the cylinders are not in good shape and it requires .060" to
clean it up then that is a sign that it is on its last life.
The next thing to consider is the main bearing
caps. For most naturally aspirated applications, the stock 4 bolt main
caps are more than adequate. For a blown alcohol application it is highly
recommended to install billet splayed main caps. They have angled outside
bolts that thread into the pan rail part of the block which is much
stronger. Since the bolts are angled it helps prevent cap walk. If
the stock caps are going to be used, the bore needs to be measured. Most
of the time, the block right from GM has accurate bores and doesn't require any
line honing, but it is always good to check.
Now it is time to look at the deck surface.
In a naturally aspirated combination we usually are looking for "O"
deck. This means the surface is to be ground down to its true blueprinted
dimension. On a small block Chevy the deck height is 9.000 inches.
This is from the crank centre line to the deck surface. Small block
Chevy's are usually 9.025 - 9.030 right from GM, so there is material to
machine. A "O" deck block will make the quench area of the
piston dead flush with the deck at top dead centre. This will set your
quench clearance (or piston to head). Assuming steel rods are used, this
is a good approach for a natural engine. The head gasket thickness will
determine the piston to head clearance. A Fel pro gasket is approximately
.040" thick which is adequate for a natural engine. In a blown
application we require copper head gaskets with stainless steel O-rings.
Due to the increased cylinder pressure this method has a greater sealing
ability. There are many different thickness of copper gaskets on the
market. The thickness of gasket chosen depends on how much the block has
been decked, because those two items determine the quench clearance (or piston
to head). In a blown application decking the block to "0" is not
always the ideal thing. Usually in an aluminum rod Super Charged engine,
you are looking for at least 0.065" clearance. There are two ways of
O-ringing a block, using receiver grooves and not
using receiver grooves. Receiver grooves are machined on the opposite deck
that the O-rings are placed. If O-rings are in the block, the head will
have the receiver grooves. Receiver grooves and O-rings are the best
method for sealing a chamber and is only necessary in extreme blown or nitrous
applications. In a non receiver groove application the O-rings are
usually machined in the block and the head remains flat.

Cylinder boring is the next procedure and it is
always better to bore the block before you hone. The boring bar will
ensure that the cylinders remain straight. Some production engine shops
just rough hone with roughing stones, but doing it that way doesn't allow for
control over the position of the cylinder. There are a few extra
procedures for a blown engine. The first is putting hard block water
jacket filler in the water jackets. This gives the cylinder walls more
support under extreme cylinder pressures. The second thing is to clear the
pan rails for more connecting rod clearance. Its usually done in a
standard vertical milling machine. Aluminum rods are most common in a
blown application and they require clearance because they are much larger than
most steel rods. They need 1/8" clearance or larger.

This is a general overlook on block
prepping. There are different methods and opinions on these procedures but
most of those mentioned are necessary to build a performance pulling engine.
