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.