Engine Tuning

April 11, 2013 By Mike Lee
Last updated on July 27, 2015

Engine Tuning For Your Internal Desires 
Ok so you’ve put all the bolt on performance extras such as a performance air filter, sports exhaust and other bits and pieces. But it still doesn’t do it for you. This tuning article will describe the many ways to tune your engine. I’m not an engine builder and therefore will not be going into detail about how to carry out the modifications, but will describe the options and what they entail. Get expert advice for your application.


DOHC Engine Tuning Ferrari V12 Engine

Engine tuning comes in various stages that can be done individually. However it’s advisable to have them carried out all at the same time to enhance each of the changes made. Do them in the wrong order, combination or incorrectly and you could end up wasting your money and worse still, end up with a car that performs worse than before the changes were made. Remember this old saying, bigger isn’t always better.

Making these engine tuning changes is quite a specialist job (when done correctly) and is ideal for those looking to take their car on the track or building a kit car or hot rod etc. We would leave these modifications to an engine tuning specialist (machine shop) to guarantee a good solid reliable engine build up. Many machine shops have all the equipment to make sure that you end up with a good job done.

As we always say, keep in mind what your car is going to be used for, if it’s a road car then you may not need to do much if any of the following engine tuning modifications, don’t get carried away.

Also to note is that modern engines with modern electronics/engine management systems will require the appropriate changes to them (if indeed they can be made at all?).

Engine Basics

An engine is basically a large air pump, the fuel is either injected directly into the cylinder or brought in with the air, which is drawn into the engine through the inlet valve by the vacuum created as the piston is pushed down the cylinder (and of course sometimes forced, turbocharger and supercharger). As the piston rises, the air and fuel is compressed then ignited by the spark from the spark plug, combustion then takes place. Then the piston is forced back down again, rises again and releases the gas through the outlet valve and exhaust system. It then starts all over again. Note that the piston travels up and down the cylinder twice for one complete cycle.

Engine Tuning Options

Cylinder Heads
Cylinder Head
Gas Flow – The flow of air traveling through the cylinder head will slow down and become turbulent if it encounters any non smooth areas of the cylinder ports/channels or bends. By smoothing out these areas you reduce this turbulence allowing the air to continue at a less turbulent and higher speed. Note: that many cylinder heads have what is known as a swirl and tumble design, this aids in the flow of air (a reason why an engine tuning machine shop should carry out the work).

Port Matching – Matching the inlet and outlet ports of the exhaust manifold and intake manifold will help increase the smooth flow of air and reduce turbulence through the engine.

Changes can improve either the torque or maximum bhp. It can also increase or decrease fuel consumption, but it is very likely to reduce one while improving the other. It’s important to point out that not all cylinder heads will respond well to porting, seek expert advice. A good engine tuning machine shop will be able to carry out a bench flow test for your cylinder head to measure the improvements and make the necessary changes.

Again these jobs are really an engine tuning specialist job and should be done correctly to avoid messing things up and causing any imbalances.

Aftermarket Cylinder Head
Aftermarket Cylinder Heads – I’m not going to say a lot about these. All the works done for you and you can get matched camshafts and intakes, lots to choose from, but can be expensive though.

Tip: Find a better head, many engines are improved upon by the manufacturers over a period of time or from model to model. It may well be a good idea to find a later and improved cylinder head that can be bolted (maybe with a little work) directly to your engine block.

Re Bore – This increases the capacity of the engine. The engine capacity is usually quoted in either litres (2 litres, 1.8 litres, 4.0 litres etc) or CC (cubic centimetres), so 2 litres will become 2000cc and so forth. American cars use to be quoted in CU or CI (Cubic Inches). See conversion calculators. Note: that most cars will have a rounding up or down of their CC’s to get their litre capacity. And of course your overall capacity for each cylinder is divided by the number of cylinders (2 litres on a 4 cylinder engine = 0.50 litres per cylinder, as does 4 litres on a V8 = 0.50 litres per cylinder).

Re-boring consists of drilling the cylinder bores to a wider dimension, which in turn will require new larger diameter pistons. Final machining of the cylinder heads may also need to be carried out for correct compression ratios. The Re-boring process is a precision job that requires the correct equipment and calculations.

Tip – many different size engines use the same block, why not see if a larger capacity block that is the same as yours is available first.

Stroker Kit
Stroker Kits – Some companies sell stroker kits (very popular with the American domestic (V8) crowd. These kits generally consist of the crankshaft, conrods, pistons, piston rings and bearings. They alter the stroke length and therefore the engine capacity. Generally have more torque increases over re-boring with equal capacity, but creates more piston wear due to increase piston travel.

Pistons Types

There are 2 main types of pistons:
Dished Piston
Dished Cast Piston
Cast Pistons – These are gravity die cast from aluminium alloy containing silicon. Used by most manufacturers.

3 main cast piston types –
Hypoeutectic: Aluminium alloy with 9%-12% silicon
Eutectic: Aluminium alloy with 11%-13% silicon
Hypereutectic: Aluminium alloy with 12.7%-18% silicon

Forged Piston
Forged Pistons – Made from a solid piece of aluminium alloy with a little silicon, heated and gradually pressed into shape. Generally expensive and used by high power cars.

Flat Top Piston
Flat Top Piston

There are also domed, dished and of course flat piston designs, all have different effects on compression ratios and supposedly different effects on the burn rate. Dished pistons will give extra room for valve clearance.

High compression pistons increase the compression ratio and low compression pistons reduce the compression ratio.

By raising the compression ratio (to a certain limit), you can create a more rapid burning of the fuel and hence more power. However they also create a lot more pressure which creates more heat and this pressure also works against the pistons, making them work harder. Going too high with the compression ratio can cause knock (detonation), which can damage the engine.

Turbocharged cars generally require a lower compression ratio, as all this extra heat from the turbo mixed with the volatility of regular petrol can cause engine knocking. All depending on any other mods you have made to your engine however.

Head Gasket
Incidentally you can raise and lower the compression ratio by altering the head gasket height and skimming the cylinder head will also raise the compression ratio. While we have mentioned gaskets, you’ll benefit from fitting a performance gasket for extra protection against any additional pressures caused by tuning.

Performance Camshafts

A very popular engine tuning modification, along with cylinder head work, the camshaft has lobes shaped like a pear, which controls the opening and closing of the valves for the inlet and outlet ports. The shape of the lobe also controls the duration and timing of this opening and closing.

Single Overhead Cam (SOHC): Have lobes that control both the intake and exhaust valves.

Double Overhead Cam
Double Overhead Cam (DOHC): These have a camshaft that controls the intake and another camshaft that controls the exhaust side.

A performance camshaft increases the duration (in degrees) of the valves opening (valve lift), and closing while the camshaft lobe shape determines this. By increasing the duration, you allow time for more air and fuel to be drawn into the engine. Performance cams come in different stages of performance:

Piper Cam
Performance Cam

Mild Road Cams – Can be used on most any car and will improve throttle response, power and maybe fuel economy.

Fast Road Cams – For those looking for more. Ideal for a fast road car or for a little fun on the track. Good power increase higher up, ok economy, slightly lumpy idle. More lift and duration.

Competition Cams – More for cars needing high end power (racing). Rough idle, bad economy and low speed driving. Wears out quickly.

Beware that the fast road and competition cams will decrease low end torque due to valve overlap and make slow speed driving difficult.

Of course there are now variable valve cam engines (well actually they have been around a few years now).

Performance Valves

Your valves allow the air in and out of the engine. The camshaft controls the duration that the valves are open for and the lifters control how far they open. You can have the intake ports and valves polished to remove any rough edges and burrs to increase the air flow. A common job to be carried out is the 3 angle valve job, with 3 gradual angles cut into the valves. It’s also important that the valves sit nicely back in their seat and seal properly.

You can also increase the amount of air flow by widening the inlet ports and fitting larger valves (big valve job). Make sure there are no clearance issues when fitting larger valves.

16V Engine
16V Engine

Many cars increase the air entering a cylinder by adding more valves – 16v, 20v, 24v, 32v etc. This is a better option, as increasing the port size will decrease the air flow speed at low rpms and likely harm peak torque, having more valves gets around this.

Valve Springs
Also consider a set of performance valve springs to help get those springs back up and to ensure you don’t end up with spring failure, unless you want to suffer engine damage.

Tip: some engines have interchangeable cylinder heads, so you maybe able to get a 16v head on an 8v block. But be aware that there may be some work involved in the swap.

Engine Balancing (Blueprinting)

Blueprinting is something over looked by many when it comes to engine tuning. But did you know that many of the cars, either first tested, released to the press/journalists have blueprinted engines, unlike their massed produced followings. Blueprinting entails the balancing of the engine components. The machine shop will take the crankshaft, pistons, conrods, bearings and flywheel and rotate them in their balancing machine, adding or taking away material to balance the components. Sometimes lighter components can be used to reduce the rotating and moving mass as well.

Blueprinting can improve your factory mass produced engines performance, power, economy and life by reducing vibration, stress points, rough running and weight reduction on some components. It will also raise your rev limit by doing so.

Thermo Fan For Classic/Kit Cars
While you’re at it, why not consider an electric fan (thermo). Kenlowe being the most well known maker. Fit these fans to do away with the power and fuel robbing belt driven fans.

Some Engine Tuning Advice

  • Consider what you really want/need, as always adding performance and carrying out engine tuning is a compromise between costs, reliability and power gains
  • Get expert advice before forking out any money
  • If you decide to have any internal work done, get all you want done at the same time. The engines out and stripped, so it may as well be done at that time, it will be cheaper. Oh and let an engine tuning expert do it. The tolerances for errors can be strict, unless you are just wanting to practise to learn yourself
  • Tidy up while the engines out: replace gaskets, cylinder head bolts, inspect all around (better still get the experts to do it). Weak areas will show up when looking for extra power, don’t get caught out
  • Run in time: Take an easy, if you have work done, run in the engine as per the engine builders advice
  • Change the oil regularly
  • Find a better engine and swap it in, it may be easier and cheaper than carrying out the individual engine tuning mods! Either a better used engine or crate motor – your choice?