Monthly Archives: June 2015

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.