Category Archives: Engine Tuning

You can optimize the short-side turn of a cylinder’s intake port by expanding the sides of the port. This is necessary in order to address both of the aspects in order to make the turn more effectively and to compensate for the valve guide boss and valve stem which uses some of the available cross sectional area. A well streamlined valve guide boss can enhance results especially swirl rather than hinder it. Expanding the cylinder head walls helps to accomplish the filling of a cylinder when the port and valve is feeding a pair of intake valves in a multi-valve head.

When cylinder head modifications are limited to removing metal dealing with the short-side turn means making the most of whatever is already there. Most production heads have a more abrupt turn than is necessary due to the result of machining the valve throat below the seat. Rounding this off is the best possible solution to what can be done to improve the form of the short-side turn, once the smoothing out of the contours in the valve throat have been completed.

The best way to get the air to move to the back of the valve is to slow it down so that it can make that turn, expanding the intake port’s wall area creates a significant change. When the port is progressively widened and the intake port’s roof is raised in the turn area the slowing of the air just before it reaches the valve can create some substantial HP and Torque gains.

The majority of the air wants to flow in the top half of the intake port, so that area should be favored when removing metal. The increase in cross-sectional area in the valve’s throat area will also create an improvement by converting some of the high velocity into pressure energy, thus intensifying the air / fuel mixture charge into the cylinder.

Even when the exhaust valve is at relatively low lift, the exhaust gasses can exit the exhaust valve’s seat area at super sonic speeds, during this phase the exhaust gasses responds more to the opening area of the exhaust valve rather than the shape of the exhaust port.

As the exhaust valve’s lift increases, the exhaust gas velocity drops to subsonic, and now the shape of the exhaust port becomes the overall factor towards creating high flow. It is also worth noting that for a given size, an exhaust port flows better than an intake port. This is due to the fact that as the exhaust passes from the cylinder into the exhaust port, the flow becomes more organized, which is just the opposite of what takes place at the intake valve.

Another condition that helps the exhaust gasses reach a higher flow efficiency is due to the exhaust valve is typically lifted higher in proportion to its diameter than the intake valve, thus creating the situation that the valve head spends more time out of the influence of the exhaust valve seat.

If an exhaust port has a steep up draft angle and a large short side turn, then the exhaust port begins to resemble a venture like nozzle and a pressure recovery will occur after the gases have passed through the port’s minor diameter. If an exhaust port has a reasonable up draft angle and a short side turn, it will work well for evacuating the cylinder’s exhaust gasses.

Due to the way the exhaust works, a good exhaust port must have an efficient approach to and from the actual exhaust valve seat, otherwise there will be no effectiveness no matter how good the rest of the exhaust port is.

For a general rule, the minor diameter right under the valve seat needs to be 85% to 88% of the exhaust valve’s diameter. Additionally the outward taper from the minor diameter needs to be about 4 to 6 degrees. When the port area gets to be equal to the exhaust valve, for most purposes, it is as large as it needs to be. Also you must make sure there are no low flow spots in the port, as these areas will amplify the low-speed losses seen with Hi-performance camshafts.

Cylinder Heads (3 or 5 Angle Valve Seats)

The greatest flow restriction in any engine is the cylinder head. Having the air / fuel mixture to efficiently pass through this restriction will increase an engines HP and Torque.

The Intake and Exhaust Valves are part of the cylinder ports, and when they are closed their ability to flow is zero. This means until they have opened to a very large opening, the valves are the main restriction to the engine’s cylinder head’s airflow.

Even when the valve is at a large lift, it still presents a difficult path for the air to travel on its way into or out of the cylinder. The priority is to make the valve capable of passing as much air as possible, whatever the lift is. To do this both the valve size and the valve’s seat must be considered.

Although it may be the last operation during a porting job, the valve’s seat design is the most important priority toward effectively filling the cylinder. It would seem that the hole under the valve head needs to be as large as possible so as to flow the most air. Before flow benches were developed, it was a common practice to make a valve seat as thin as possible in order to achieve the maximum throat diameter. Objective flow bench testing found this to be untrue. In the real world the maximum flow is always a combination of size and form around the valve before and after the seat.

Air has mass and does not like to hug a port wall around a short-side turn. With low-angle ports, the air at mid and high valve lifts do not make the transition around the short-side turn very well. As a result, most of the air goes out of the long-side turn.

This situation is even greater as the higher the valve lift becomes. As a result, the streamlining of the port on the long side needs to be addressed for low, medium and high lifts, while the valve seat approach on the short side needs only to deal with the requirements of low-lift flow.

It does not matter if it is the intake or exhaust port, the worst part of the port for air to travel is the short-side turn. If the air fails to make it around the short-side turn, there obviously won’t be much air exiting the valve in that area.

Changes in the valve’s seat angles can make the valve appear bigger than it really is and flow more air during the beginning of its opening phase.

Cylinder Block

Well looking back at this thread my expectation was to encourage additional information from other OSS members to be added to this thread, although there was some I guess my expectations were greater. That being the case this will be my last input of information in this thread for the remainder of this year.

The following information can be used for race or street engines, several Worldclass engine builders have known and have been using the technique for decades.

If you REALLY want to have cylindrical cylinder bores when it comes time to hone your cylinder block, the block needs to be at operating temperatures. Getting the block up over 120f degrees is a good temperture to hone it, but if you can get it to 150f degrees, it’s even better. In addtion any honing oil that you use must be of equal temperture of the cylinder block, when the cylinder block is heated and you douse cold honing oil on it and then hone it, the localized cooling is going to distort the bore.

Many times people ask me how I am able to consistantly build long term reliable high HP race engines, well M8’s this is one of my secrets.

Copper Head Gaskets.

Copper head gaskets are great for extremely high compression ratio (over 13:1), turbocharged or supercharged engines that are running lots of boost pressure (over 15 psi), or engines with nitrous oxide that add an extra 150 to 200 or more horsepower.

Due to the fact that Copper conducts heat much better than most other metals, Copper will help to stabilize a cylinder head and cylinder block temperatures. This will prevent any hot spots that can cause detonation or head warpage, and a Copper head gasket reduces the risk of the head gasket blowing out or burning through.

Copper has a 25 percent coefficient of elasticity which allows it to stretch before it will fail. if an engine starts to detonate because the air / fuel mixture leans out, or there is excessive ignition advance or too much compression and low fuel octane, a Copper head gasket will provide a margin of safety. Copper is strong and the alloys used for copper head gaskets may have a tensile strength of up to 32,000 psi, which is many times stronger than that of the materials used in conventional performance head gaskets.

Copper head gaskets are reusable for a limited number of times (3). This is a plus in situations where the heads are on and off the block between races, or frequent tear downs are required. One of the downsides of Copper head gaskets, though, is that they do not seal oil very well. A Copper head gasket must be coated with some type of sealer, and both mating surfaces must be absolutely flat and clean.

The way to anneal a Copper head gasket is that the gasket should only be heated until it is a dark red color and no more. After the Copper head gasket gasket has air cooled, the surface needs to be cleaned with a brush or abrasive pad to remove oxide from the surface. The Copper head gasket should then be cleaned with brake cleaner or a similar product and allowed to dry before it is coated with a sealer.

The sealer must be allowed to dry before the gasket is installed. Some aerosol sealers may require multiple coats for the best results. RTV silicone also works, and may be applied around oil galley openings in the cylinder head gasket, the cylinder block or cylinder head, only a thin coating should be used, and it must be allowed to set before the gasket is installed.

Copper is a soft metal and it does not provide much conformability. This is a good aspect because the gasket doesn’t crush when the head bolts are torqued down, thus the thickness of the gasket remains the same and does not change. Unfortunately a Copper head gasket does not conform very well to small indentations and surface irregularities in the cylinder head or cylinder block

If a copper head gasket is accidentally bent during removal, it can be straightened and annealed. But if the gasket has kinked, it should be replaced because a kink concentrates stress and hardens the metal. This will increase the risk of a Copper head gasket cracking. Copper head gaskets should not be cleaned by bead blasting because it will harden the metal. The same is true for hammering the metal.

On all applications using Copper head gaskets there should be annealed / softened Stainless Steel or Copper wire O-rings installed in grooves that machined into the block or cylinder head. The wire rings help concentrate loading around the cylinders to prevent combustion pressure from blowing past the gasket. These wire rings are typically .041″ in diameter, and are placed in a .039″ wide x .030″ deep groove. The wires should protrude only about .010″ above the surface of the deck, and the thickness of the gasket should be about four times the protrusion of the wires in their grooves, or about .040″. Engines that produce over three horsepower per cubic inch should also have a corresponding receiver groove machined into the head opposite the O-rings in the block for optimum sealing. The depth of the receiver grooves should be 75 percent of the O-ring protrusion and the width of the grooves should be 1.5 times that of the wire.

COMPRESSION TEST GAUGE READINGS.

Your Motorcycle will always have a higher reading on your compression tester gauge with a stock or low duration cam, due to the fact that you will be closing the intake valve earlier on the compression stroke. This longer effective compression stroke always delivers a higher gauge reading.

Installing a longer duration cam, your intake valve will close later, thus giving a lower gauge reading because of the shorter effective compression stroke. Some individuals feel that this is impossible, claiming that if it were true, why will your Motorcycle go faster with the bigger cam? The reason is that a bigger cam will have higher compression effect in the cylinder at higher engine speeds where all that additional valve timing can do you some good, but at lower speeds and especially at starter-cranking speeds, the effect will be lower.

When you increase the compression of an engine it will produce an increase in the HP and Torque output throughout an engine RPM range. If a long duration cam is installed in the engine, increasing the compression ratio at the same time has a greater advantage than these two modifications made separately at different times. By raising the compression ratio of an engine, the peak combustion pressures are increased.

Engineering studies have found that cylinder pressures are about 100 times what the compression ratio is. That means that an engine that has 10:1 compression ratio, would create 1,000 psi of peak combustion pressure. Increasing the compression ratio will increase an engines cylinder pressure and this increase in compression also increases the an engine’s thermal efficiency. Thermal efficiency is a measurement of how effectively the an engine converts heat into mechanical power.

Due to the fact that a high compression cylinder makes its power much earlier on in the power stroke there is another issue that can be taking an advantage of. That is that the early opening of the exhaust valve opening needed for high RPM output can be utilized without effecting the engine’s low RPM output.

How much HP and Torque can be gained from an increase in an engine compression ratio?

By using the chart below you can fiqure the thermal efficiency at any given compression ratio. First locate the original compression ratio listed horizontally, then locate the new compression in the first column. Where the two compression ratios intersect, that is the gain that can be expected. For instance if the compression ratio of an engine is raised from 9:1 to 12:1 the two values intersect at the box with 7.7 in it. This is the percentage increase of thermal efficiency that can be obtained from raising the compression from 9:1 to 12:1.

ORIGNIAL COMPRESSION RATIO New Compression Ratio
9:1 10:1 11:1 12:1 13:1 14:1 15:1

10:1 2.9
11:1 5.5 2.5
12:1 7.7 4.7 2.1
13:1 9.7 6.6 4.0 1.9
14:1 11.5 8.3 5.7 3.5 1.6
15:1 13.0 9.8 7.1 4.9 3.0 1.4
16:1 14.5 11.3 8.6 6.4 4.4 2.8 1.4

On normally aspirated engines at low engine rpm’s there is little ramming from intake charge velocity into the engine’s cylinder. When the piston starts to move up in the cylinder bore on the compression stroke prior to the intake closing, some of the air / fuel mixture is pushed back into the cylinder head’s intake port. This creates the situation were the volumetric efficiency and the effective displacement of the cylinder is well below 100 percent.

Raising the compression ratio one point from a low ratio has a greater effect then raising the compression ratio up from an already high ratio. This means the larger the duration and lift of a camshaft the more responsive it is to a increase in the compression ratio, especially in the lower engine rpm.

Here is some info that might be helpful for those who are interested in fine tuning their bikes camshafts.

The common range of lobe center values for SUZUKI engines is only about 10 degrees wide from about 102 to 112 degrees, a change of one degree can have considerable effect on the power delivery characteristics of a SUZUKI engine.

The effect of moving lobe centers is that by advancing the intake and retarding the exhaust, known as CLOSING UP THE CENTERS, it will increase the valve overlap and will move the power UP in the RPM range, although it will at the sacrifice LOW- RPM power. The result would be LOWER numerical values on both intake and exhaust lobe centers.

If you retard the intake and advance the exhaust, known as SPREADING THE CENTERS, valve overlap will decrease and will result in a WIDER power band while sacrificing HI – RPM power. This is indicated by HIGHER numerical values on both intake and exhaust lobe centers.If you move only one cam the results are not as predictable, traditionaly it is the INTAKE CAM that is moved to change power characteristics since small changes here seem to have a greater effect.