Piston-deck height

Deck height is defined as the distance between the top edge of the piston crown (with the piston at TDC) to the edge of the cylinder liner. The closer the edge of the piston crown is to the edge of the cylinder the high the compression ratio will be.

So if you have pistons that are 10.5:1 and they are 0.010″ below the edge of the cylinder and you are able to reduce the deck height by 0.010″ then the actual compression ratio of the cylinder will be increased.

The reduction of the piston deck height can be accomplished in several ways. Machining the cylinder block is the most common method.

A word of caution you must know exactly the minimum valve to piston clearance that is required. this varies in different engine designs. To increase the piston to valve clearance usually the valve relief pockets on the piston’s crown are enlarged or the height of the piston at TDC must be lowered in the cylinder.

Oversize Valves

Some tuners believe that larger size valves enhance Hi-RPM power at the expense of Low-RPM power. This has proven to be false due to the results of dyno tests and theory. Larger valves enhance Hi and Low RPM.

When a valve is closed it has no size whatsoever for a cylinder’s ability to induce air flow. A valve that is opened, 0.015”, appears to the cylinder as a small valve. Only when the valve reaches 25% of its total lift point does the cylinder actually experience anything near the true size of the valve. If a cylinder was stuffed with valves as big as possible to create a greater movement of the air/ fuel mixture and exhaust gasses and the larger valves proved to be excessive (too large), the solution of the problem would be to reduce the valve’s lift, besides reducing the air flow it would also reduce the wear and friction on the valve train. In the real world, the criterias for the intake and exhaust system for making peak HP and torque at a given engine RPM is the cross section area of the intake and exhaust ports, not the size of the valves.

The real advantage of using oversize valves is that, for a specific rate of the valve’s opening, an oversize valve will give a greater breathing area to the cylinder quicker. This is equal to as a smaller valve opened at higher rate of acceleration. Any time there is a higher acceleration rate in the valve train, more stress is created.

As long as valve shrouding is not a factor then the largest possible valve in a cylinder head will allow the engine to develop power over the widest RPM range, not just increase the flow at high lift rate. If a dyno test of a engine with a cylinder head that has oversize valves reveals a loss in low RPM power it is because the engines camshaft has to much overlap.

For carbureted normally aspirated Suzuki engines in the 9.5 to 12:1 compression ratio range the exhaust flow needs to be 75 percent of the intake flow. Overall when the compression ratio of an engine increases, in order to obtain the maximum results an exhaust valve can be made smaller in relation to the intake valve. This is due to the power developing earlier in the expansion cycle of a cylinder in high-compression engine, thus allowing the exhaust valve to be opened sooner and longer without any problems. A small exhaust valve will create the opportunity to use a larger intake valve.



If you read my previous post about ‘AIR DENSITY’ in this thread then it will be easy to understand the advantages Nitrogen has over Air, for those who haven’t, I would recommend to do so.

The first advantage of Nitogen is for it’s use in your tires, by doing so you will eliminated tire pressure build up, this is a really important factor in order to maintain a tire’s performance criteria. The Racing Displines of Road Racing or Drag Racing require consistency of a tire performance and the use of Nitrogen will give you that advantage.

In Drag Racing when using an ‘Airshifter’, the use of Nitrogen will add the the unit’s reliability ( No Water contained in Nitrogen) and you will find that the shifter activation responce time is faster.

Longer exhaust duration

Most stock camshafts from production 4 cylinder engines manufactured today are ground with the longer exhaust lobe duration,or that they are ground with shorter intake durations. This can be viewed that either the Exhaust Ports or Exhaust Pipe system is somewhat restrictive, and needs assistance, or that the intake system is very efficient and cam timing can be trimmed back without a sacrifice in power, in order to maximize throttle response and cruising efficiency. There is no absolute correct viewpoint in a stock engine running at conservative RPM levels, for the sake of overall efficiency, fuel economy and a quiet smooth running engine, this staggering of intake and exhaust duration is quite common and appropriate.

High Performance is another thing entirely. Change one factor, such as the exhaust system installing headers and larger pipes and the need for that longer exhaust lobe has been eliminated. Now add to this change a different carb system and camshaft and you have really changed the equation. But, why is it that so many racers & cam grinders insist on running a cam with longer exhaust duration regardless of what equipment is used? The answer is habit, many have been somewhat successful in doing it this way and will never change unless forced by circumstances.

The best result comes when we realize that an engine is basically an air pump. Air is pumped in and out and there are problems when one side or the other is restricted. Balance and flow is our objective, unless you are NOT trying to make more horsepower!

Most experienced Tuners run a single pattern cam, equal on intake and exhaust duration. This type of designed cam always make more torque.

Intake & Exhaust Port Surface Finish

As long as the intake port surface finish is fine enough so that the highest protrusions are not above the air /fuel mixture boundary layer thickness, then improvements on the finish will have little effect on air / fuel mixture flow . A rougher finish is actually an advantage. Do not over polish an intake port because of its wet fuel flow capability.

A polished exhaust port will increase the exhaust gas flow and will reduce the potential for carbon to build up on the exhaust port surface.

In conclusion 97% of a performance gain from porting a cylinder head is from the shape of the ports and only 3% is from a polished finish.

Induction System Volumetric Efficiency

here are two real world effects that determine how much fuel/air charge can get into the cylinder. The first is that air is compressible, the second is the dynamics (acceleration/deceleration) of the air. The compressibility of the air becomes a factor when the air enters the intake port around the intake valve. The intake port/valve forms a constriction, like the throat of a nozzle. Because air is compressible, it can only be pushed through a constriction so fast. Regardless of how much pressure you apply, the maximum velocity possible through the throat of a nozzle is a velocity equal to the speed of sound .

The same effect happens at the intake valve. The ratio of the typical velocity to the intake sonic velocity is called the inlet Mach index. From the science of fluid mechanics the controlling velocity in a compressible flow system is usually the intake valve opening. For a given cylinder and valve design, the inlet Mach index is proportional to the piston speed, and that the fuel/air charge flows in faster when the piston moves down faster. Of course, at some point the constriction of the valve opening starts to limit this. When the inlet Mach index exceeds 0.5 (intake velocity equal to half the speed of sound), the volumetric efficiency falls rapidly with increasing speed. Therefore, enginest are typically designed so that the inlet Mach index does not exceed 0.5 at the highest rated speed.

The effect of this constriction shows up as a pressure drop through the intake valve. Why don’t we just open the intake valve further? Because when the valve is lifted a distance equal to 1/4 of its diameter, the area of a cylinder around the valve (that the fuel/air charge passes through, not the engine cylinder) is equal to the area of the valve face and intake port, ignoring the valve stem. Mathematically, the area of the cylinder is (2 r)(d/4). Since d = 2r, this evaluates to r2, which is the area of the intake port, the amount of additional flow through the intake port increases very slowly as the lift of the valve increases beyond 1/4 of the valve diameter.

Because of the dynamics of the fuel/air charge, the intake valve normally closes at some time after the piston passes bottom dead center. As the piston moves down, it draws the fuel/air charge into the cylinder. This movement builds up momentum in the intake manifold. When the piston reaches bottom dead center, the fuel/air charge is still flowing into the cylinder as a result of this residual momentum. Thus, at the speed desired for maximum torque, the intake valve closing is timed to correspond with the velocity of the fuel/air charge through the intake port dropping to zero. This closing will occur at some time after the piston has started the compression stroke, and will result in the maximum amount of fuel/air charge being drawn into the cylinder. This maximizes the volumetric efficiency, and maximizes the torque delivered to the crankshaft, ignoring friction effects. The angle of the crankshaft at the time the intake valve closes is called the intake valve closing angle.

So what effects does this later valve closing have at other speeds? At low speeds, the momentum built up in the intake manifold will be small, such that part of the fuel/air charge will be pushed back into the intake manifold as the piston starts up prior to the intake valve closing. At speeds above the speed for maximum torque, the constriction of intake valve opening will cause a pressure loss which will reduce the amount of fuel/air charge entering the cylinder. In either case, the amount of fuel/air charge in the cylinder is reduced, and thus the torque is reduced.

The design of the intake manifold also affects the amount of momentum built up in the flow of the fuel/air charge. The momentum of the fuel/air charge is the sum of the effect of standing waves built up from previous intake strokes keep in mind that any tube will have a resonant frequency and effect the transient wave caused by the current intake stroke. While the standing waves contribute to the overall effect, there are no sudden changes in the volumetric efficiency when the RPM of the engine is an even multiple of the natural frequency of the intake manifold.

Long, skinny intake manifold pipes give high volumetric efficiencies at low piston speeds because high momentum lots of velocity is built up in the pipe during the intake stroke. At high piston speeds, the small diameter of the intake pipe causes a constriction and the volumetric efficiency falls. Fat intake pipes show a maximum volumetric efficiency at intermediate piston speeds. However, at high piston speeds, the larger mass of the fuel/air charge in the fat intake pipe is slow to accelerate, and thus the volumetric efficiency falls off.

As the manifold pipes get shorter, the maximum gain in volumetric efficiency over having no intake manifold at all decreases. However, the gain you do get with shorter intake pipe happens over a greater range of piston speeds. Basically, it comes down to the intake manifold pipe should be designed according to the engine requirements. If you need high torque at slow piston speeds, use long skinny intake pipes. For high torque at intermediate piston speeds, use long fat intake pipes. For high torque over a wide range of piston speeds (i.e. a flat torque curve), use shorter intake pipes.

Ignition components

Inductive Discharge Coils – Ignition spark for motorcycle is accomplished by the iginiton coil, coils have 2 sets of windings, a primary and a secondary. A typical coil will have around 250 turns of wire on the primary and about 25,000 on the secondary for a ratio of 100 to 1. The secondary section often uses an iron core to increase its inductance. Coil resistance on the primary will be from .3 to .5 ohms usually and on the secondary, between 5000 and 12,000 ohms. The inductance and resistance of the coil will determine how quickly a coil can be charged and discharged.

A transistor is used to switch the current flow off and on in the primary coil. When the transistor is switched on, current rapidly builds from 0 to a maximum value determined by the coil inductance and resistance. This current flow induces a magnetic field within the primary. When the current is turned off, this magnetic field collapses which cuts the windings of the secondary coil and induces a high voltage surge.

Output voltage is determined by the rate of field collapse and the windings ratio between primary and secondary. Because the path to ground for the current involves the spark gap, initial resistance is extremely high. This allows the voltage to build to a high value until it gets high enough to jump the plug gap. The difference must be high enough to first ionize the gas between the electrodes. The ionized gas creates a conductive path for the current to flow, at this point the arc jumps and current flow is established.

If only 10,000 volts are required to jump a plug gap under a given condition, that will be the maximum delivered. It is also important to note that the spark duration is determined by coil inductance and total resistance of the circuit, plus spark plug gap. Most inductive discharge systems have a spark duration of between 1 and 2 milliseconds.

When cylinder pressure increases, the voltage required to jump the plug gap increases. The second problem on high performance engines with high rev limits, is that there is less time to charge the coil with increasing rpm, high rpm and high output puts greater demands on the ignition system.

Coil Charge Time and Saturation – The time it takes to charge the coil or bring the current to maximum in the primary windings is called charge time. Input voltage and coil resistance are the main parameters relating to charge time, when the current has reached its maximum value in the primary, it is said to be fully saturated.

If current is applied longer than the time needed to fully saturate the primary, energy is wasted and there is nothing to be gained. If the current is cut off before saturation is achieved, the maximum spark energy available will be reduced.

Coils require charge times of between 2.1 and 6 milliseconds. Obviously, a coil requiring 6 milliseconds to saturate would be unsuitable on a high revving engine as there is not 6 milliseconds available to charge it between discharges at high rpm. For this reason, most racing coils have low primary resistances between .3 and .7 ohms and are fully saturated in less than 3 milliseconds permiting full coil output at very high rpms.

Capacitive Discharge Ignition – On very high output engines, an inductive discharge coil is inadequate to supply spark at high rpm and high cylinder pressures. A CD ignition or CDI is used to reduce charge times. The MSD system is very popular worldwide.

In normal inductive discharge coils, only 12-14 volts is available from the battery to charge the primary. The CDI charges capacitors to store a high voltage kick to fire to the primary side, putting between 30 and 500 volts onto the primary windings which reduces the charge time substantially. A coil that would take 3 milliseconds to become fully saturated with 12 volts is now fully saturated in less than 1 with a CDI. The same engine now will be able to turn twice the RPM and experience a major increase in cylinder pressure before encountering misfire.

Some CDIs also include a multispark function where more than 1 spark is generated after the first spark. This improves ignition probability besides the high rpm coil saturation advantages and a greater resistance to plug fouling.

Ignition Wires (Spark Leads) – The purpose of the ignition wires is to conduct the maximum coil output energy to the spark plugs with a minimum amount of radiated electromagnetic interference (EMI) and radio frequency interference (RFI). There are 3 basic types of conductors used in racing applications: carbon string, solid and spiral wound. Most production engines come equipped with carbon string. The solid core types are used exclusively for racing, mainly with carbureted or non-computer controlled engines because they offer no EMI or RFI suppression. They generally have a low resistance stainless steel conductor. These types are rapidly losing favor, even in racing circles.

The carbon string type is the most common and work just fine in racing applications. The conductor is usually a carbon impregnated fiberglass multistrand. Suppression qualities are fine with resistances in the 5K to 10K ohms per foot. They are cheap and reliable for 2 to 5 years usually, then they may start to break down and should be replaced. High voltage racing ignitions will likely hasten their demise. Dynatech makes low priced wire set which works well in performance applications.

Ignition Wires (Spark Leads) – The spiral wound type is probably the best type for any application. The better brands offer excellent suppression, relatively low resistance and don’t really wear out. Construction quality and choice of material vary widely between brands. NGK makes low priced wire sets which work well in performance applications.

Some amount of resistance is required along with proper construction to achieve high suppression levels. Resistance is also important to avoid damaging some types of coils and amplifiers due to flyback and coil harmonics. Beware of wires claiming to have very low resistance. These CANNOT have good suppression qualities.

Beware of any ignition wires claiming to increase hp. Ignition wires CANNOT increase hp. As long as the wires that you have are allowing the spark to jump the gap properly, installing a set of $200 wires is strictly a waste of money.

Lately, some truly “magic” wires have come onto the market claiming to not only increase power but also to shorten the spark duration from milliseconds to nanoseconds. As previously mentioned, spark duration is determined primarily by coil inductance and coil resistance so these wires CANNOT shorten the spark duration by the amount claimed. The wire resistance has a minimal effect on discharge time because of the high voltage involved. A very short duration spark is in fact detrimental to ignition because of lower probability.

These same wires claim to increase flame front propagation rates and the ability to ignite over-rich fuel mixtures for more power. Once ignited, the mixture undergoes a flagregation process and that the progression rate of the flame front is totally independent of the spark. As previously mentioned most gasolines will not ignite nor burn at air fuel ratios richer than 10 to 1, period, and that maximum power is actually achieved at around 12 / 13 to 1 AFR so the claim also has no basis in fact.

These wires use a braided metal shield over the main conductor which is grounded to the chassis. This arrangement offers poor suppression because it does not cover the entire conductor. Any energy leaking out of the main conductor by induction is actually wasted to ground and will not make it to the spark plug. These wires also have very low resistance which as mentioned can have a detrimental effect on coils and ignition amplifiers due to severe flyback effects which are normally damped by circuit resistance.

Other claims for these wires include current flows of up to 1000 amps. The current flow in the ignition circuit is determined by the coil construction and drive circuits, not by the ignition wires. Most ignition systems are current limited to between 5 and 15 amps. The most powerful race systems rarely exceed 30 amps. To flow current at 1000 amps, you would require #0 welding cable for the ignition system!

Spark Plugs – The final part in the ignition system is the spark plug itself. The average plug consists of steel shell which threads into the cylinder head, a ceramic insulator, an iron or copper core leading to a nickel or platinum center electrode and a ground electrode of similar material. The spark jumps between the center and ground electrode. Certain special application plugs may have multiple ground electrodes. Different heat ranges are available depending on application. For constant high power applications, a colder than stock plug is usually selected to keep internal temperatures within limits.

Again, many “trick” plugs come onto the market from time to time expounding the virtues of their incredible new design, usually offering more hp of course. Split electrode plugs are a waste of money because the spark will only jump to one of the electrodes at a time in any case.

You will find that most reputable engine builders for racing use standard NGK, Bosch or Champion plugs with a standard electrode setup. A properly selected, standard plug will easily last 25,000 miles of hard use in most engines. A platinum tipped plug will easily last twice as long on most engines. There is no rocket science here, modern spark plugs coupled to modern ignition systems in a modern engine are extremely cheap and reliable, even on race engines, a $2, off the shelf, NGK plug will work just fine.

Ignition / combustion criteria

Some people think that when a spark plug fires, the fuel/air mixture explodes instantaneously, driving the piston down. If this really happened, engines would last only a few minutes before they literally explode.

Looking at the dynamics involved from the moment that the intake valve is fully open. With the piston moving down the bore, cylinder volume increases, cylinder pressure decreases, allowing the higher pressure in the intake tract to push the fuel/air mixture into the cylinder. As the piston starts back up and the intake valve closes, cylinder volume decreases and cylinder pressure increases.

When the crankshaft reaches about 30 degrees before top dead center (TDC), the spark jumps the gap between the spark plug electrode. The purpose of the spark is to raise the temperature of a very small portion of the fuel/air mixture above its ignition temperature. This is the point where true combustion begins. As the reaction starts, the mixture directly adjacent to the spark plug is also ignited and the process progresses out from the spark plug in a roughly spherical shape.

At about 20 degrees before top dead center (BTDC), the rate of heat release causes the cylinder pressure to rise above the compression line which is what the cylinder pressure would be at a given piston position without ignition. Notice that it has taken 10 degrees of crank rotation to generate this pressure level. This is known as the ignition-delay period.

The rate of pressure rise is a function of the rate of energy release vs. the rate of change of combustion space. The rate of energy release is directly related to the flame propagation rate and the area of reacting surface. The flame speed is dependant on fuel/air ratio, charge density, charge homogeny, fuel characteristics, charge turbulence and reaction with inert gasses and the combustion chamber, cylinder walls and piston.

No two combustion cycles progress at the same rate or uniform rate. Some start slow and end slow, some start slow and end fast, some start fast and slow down. Generally, only the ones that end too fast will lead to detonation / knocking / pinging as the rapid pressure rise may happen too soon with the cylinder volume still decreasing or not increasing fast enough. Usually, not all cylinders will detonate / knock / ping at the same time or on the same cycle because of this.

By the time the crank is at about 5 degrees after top dead center (ATDC), the cylinder pressure is about double that of the compression line. From this point to roughly 15 degrees after top dead center (ATDC) the combustion process is fast due to the increasing area of inflamed mixture and the high rate of energy release. The peak cylinder pressure (PCP) occurs between 10 and 20 degrees after top dead center (ATDC) on most engines and the combustion process is complete by 20 to 25 degrees after top dead center (ATDC). The peak temperature within the combustion gasses will reach somewhere around 5000 degrees Fahrenheit and pressures may be anywhere from 300 to 2500psi depending on the engine.

Obviously it is very important to have the crankpin at an advantageous angle before maximum cylinder pressure is achieved in order that maximum force is applied through the piston and rod to the crankshaft. If the mixture was ignited too early, much of the force would simply try to compress the piston, rod and crank without performing any useful work. In a worst case scenario, the cylinder pressure would be rapidly rising before the piston reached top dead center (TDC) which would have the cylinder volume decreasing at the same time. This will often result in detonation/knock/ ping which is counterproductive to maximum power and engine life.

Detonation, knock or pinging is defined as a form of combustion which involves too rapid a rate of energy release producing excessive temperatures and pressures, adversely affecting the conversion of chemical energy into useful work. Detonation usually involves ignition and literal explosion of the end gases, these are the gases not in contact with the initial spark or the progressing flame front.

If peak cylinder pressure (PCP) is achieved too late, again, less work would be performed. Most of the useful work is done in the first 100 degrees of crank rotation. Most combustion must be done with the piston in close proximity to the chamber so that the minimum amount of heat (energy) is lost and the maximum amount of energy is delivered to the crankshaft.

Extra shift detent spring

EXTRA SHIFT DETENT SPRING: “There Is Enough Tension In Drag Racing”

I just read a thread about adding an additional dentent spring in your GS / EFE Transmission. This is an acceptable modification for a stock activated shift linkage.

A lot of my hands on mechanical knowledge has been gained thru many decades of working as a R&D Engineer for various Automobile and Motoccyle Maufactuers such as G.M. Toyota, Isuzu, Suzuki, Yamaha, Kawasaki and H-nda. An advantage of working for these Companies is that I would spend a lot of time with a large variety of data acquisition instruments. Fortunately I was able to use and apply many of these instruments to my EFE Drag Bike.

Many of our OSS members are well aware of the fact that Drag Races are won or lossed by a thousand of a second. I have had the opportunity to do A -B -A testing methods using test instruments that are capable of taking measurements in miliseconds, comparing the use of a single or double detent springs with a MRE Pro-Airshifter.

The results of the tests (confirmed repeatability) is that a bike utilizing an MRE Pro-Airshifter will engauge a gear faster with a single spring as compared to using a double spring.

You can consider the above information as another “SSR Race Trick” donated to the OSS site. I still have several more when it comes to Suzuki transmissions that will remain propriety information.

“May The Shift Be With You”

Exhaust System Efficiency

Part of getting a large fuel/air charge into the cylinder (volumetric efficiency) has to do with getting the combustion products of the previous cycle out of the cylinder. At first thought, it would seem that simply making the exhaust valve bigger would help get the combustion products out. As it turns out, the exhaust valve can be as small as 50% the size of the intake valve without affecting the volumetric efficiency over the usual range of inlet Mach speed. Normally the exhaust valves are at least 60% the size of the intake valve. This effect may arise because the combustion products are “pushed” out of the exhaust port by the piston, while the fuel/air charge is “sucked” in the intake port, pushed only by the manifold pressure.

To enhance the removal of the combustion gasses, the intake valve is opened prior to the end of the exhaust stroke. Since both valves are open at this point, this is referred to as valve overlap. If the pressure in the intake manifold is greater than the pressure in the exhaust manifold, the in rushing fuel/air charge will help scavenge the remaining combustion products in the cylinder as the piston reaches top dead center by pushing them out the exhaust port. While some of the fuel/air charge may go out the exhaust port, an engine tuner tries to design the timing such that the exhaust valve closes just as the last of the combustion gasses leave the exhaust port. An additional benefit of valve overlap is that the intake valve is essentially fully open at the start of the intake stroke, thus reducing the pressure loss through the intake port during the intake stroke. The angle that the crankshaft turns between the intake valve opening and the exhaust valve closing is called the valve overlap angle.

Of course, scavenging does not occur at all speeds. At low speeds, the throttle valve reduces the pressure in the intake manifold, such that the intake manifold pressure is less than the exhaust manifold pressure. In this case, a small portion of the combustion products enter the intake manifold, to be pulled back into the cylinder on the intake stroke. Additionally, the combustion gasess in the space above the piston at top dead center are not scavenged. Even so, at low power settings this is not a problem.

CONCLUSION- In general, we have seen that the torque, and thus the horsepower produced by an engine depends on the amount of air that can be pumped through the engine. The more fuel/air charge drawn into the cylinder, the higher the volumetric efficiency. The higher the volumetric efficiency, the higher the torque. The biggest factor affecting the volumetric efficiency is the valve timing, specifically the valve overlap angle and the intake valve closing angle. Volumetric efficiency can also be improved by the intake manifold design. Since the camshaft used determines the valve timing, changing the camshaft will change the shape of the torque curve, and thus the horsepower curve.