Head Skimming
We offer engine head skimming, to all trade and garages. Bring the unit to us, some cases we can turn around as quick as two hours. Prices start from only £25 + VAT
.


Cylinder Heads Refaced:
Aluminium and Steel. We provide a Reliable Service

From only £25 + Vat


We can now offer helicoil service: this is a dying art, and is specialised!
We now have a large selection of sizes to fit any vehicle

so if you strip a thread on an Injector, glow plugs or bolt’s we can easy fix it! Instead of spending hundred’s replacing parts

This Service is only £50 Inc VAT per Heli Coil. Along with our Head Skimming service, we are number one in the area







Little bit of information regard this procedure
How to do so safely and effectively, by measurement and calculation.

People often quote the Compression Ratio (CR) of an engine and a higher CR is considered an essential part of 'making it go faster'. But what is the CR, why is it important and how can it be raised safely, without risking damage to the engine?

Theory.

An internal combustion engine burns fuel to produce heat and energy. Although the conventional four strokes are often labelled "Induction, Compression, EXPLOSION, Exhaust", it is not true that the third stroke includes an explosion. The third stroke is really one of 'Combustion', or burning.

A pool of petrol (gasoline) will burn. Pour some into a plastic container and throw it in that fire. It will heat up, vaporize, and raise the pressure in the container until the plastic burns through. The confined petrol will burn very quickly, forming a fireball. If you use a strong metal container, the petrol vapour will heat and compress, but the container will not melt. Eventually, if it gets hot enough and there is enough air in the container, the petrol vapour will get so hot and compressed that it will detonate. The spontaneous explosion may shatter the container, throw shrapnel about and make a loud noise. More heat, more compression and the fuel/oxygen reaction will happen more quickly and more efficiently.

Compression ratio ®

A petrol engine will run more efficiently if the fuel/air mixture can be compressed as much as possible. BUT, too much compression and it will detonate, diesel style. The shock wave can easily shatter a four stroke piston.

A diesel engine is designed to compress its' fuel until the pressure and the increased heat produced by that compression cause the fuel to detonate. As a result, diesels have the advantage of high efficiency in terms of fuel use, but the disadvantage of needing to be very strongly constructed.

If the hotter, more compressed mixture is more efficient, why are all production engines not high compression for more power? There are several answers, including emissions as the extra heat produces more oxides of nitrogen (NOx), and less reliability as the engine is under greater strain. Fuel additives, including lead, and high octane petrol are necessary to allow reliable high compression without detonation. Fuel free of lead and benzene is all we have now, so modern engines have sensors and computer chips that adjust the ignition timing, so that they can run near the detonation point without being damaged.

But we want that power! If we are willing to put up with the downside, and without electronic engine management, how can we safely make the engine compress and heat the fuel more? By knowing the Compression Ratio.

The CR is a number, that shows how much the fuel/air mixture in the cylinder is compressed before it is ignited. The simplest way to calculate it is to take the stroke of the cylinder, the maximum volume of fuel/air, and divide it by the volume of the combustion chamber into which all that volume is compressed.

CR = Stroke volume

Combustion chamber volume

But that's too simple. When the piston is at the bottom of the stoke, the total volume in the cylinder includes the combustion chamber, so we must include that in the equation:

CR = Stroke volume + Combustion chamber volume

Combustion chamber volume

Again this is too simple. The head and block are separated by gasket, which has a definite thickness, so that the hole in the gasket for the bore has a volume - Gasket Volume.

An even smaller, but significant factor is the space in the bore, above the piston and below the top of the block, when the piston is at the top of its' stroke - "In Block" Volume. This can be made zero, or even negative if the pistons protrude out of the block at the top of the stroke, but only for very specialised purposes (See "Decking the block").

Thus the volume into which the stroke volume is compressed, the Compressed volume, is made up as follows:

Compressed Volume =

Combustion Chamber Vol.+ Gasket Vol. + In Block Vol.


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