Choosing a fast road cam duration and cam profile

Find out about "Fast road cams (Sports camshafts)"

What is the camshaft, what does it do and how can it be modified. The camshaft is located at the top of an engine. Is is a long shaft with a series of lobes along it and it rotates relative to engine speed. The lobes push close the valves in the head and allow the engines cylinders to suck in air/fuel and expel exhaust gases.

Ultimately you want the intake valve opened as long as possible and want to delay the exhaust valve opening until the piston has started to enter the blow phase.

Timing is critical.

If the intake is not open for sufficiently long a time or the exhaust valves open early much of the power from the engine will be gone.

We describe the cam as a duration.

A 720 degree duration would not open the valves and a 1 degree duration would keep the valves closed all of the time.

Manufacturers optimise their cams for best fuel economy at around 3000 rpm and require a smooth tickover.

This caution gives the tuner a good opportunity to improve things. (A camshaft duration is based on 2 revolutions of the crank or 720 degrees.)

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The 3 power bands of cam durations.

An average family car will typically have a cam duration of 250 degrees or lower. By grinding down each side of the lobe on the cam you can decrease the duration.

As a general rule of thumb upto 265 degrees gives a good balance of extra power and maintains smooth running and is most suited to a standard engine.

Moving up to 290 degrees we have what is called a fast road cam.

This will give a noticeable increase in top end power but you will start to experience a slightly lumpy idle.

Economy will also be impaired but in most cases you will be within your cars emission standards. This is what most readers of will be aiming at.

For ultimate performance you can increase the duration to 320 degrees.

Tickover will be very erratic, the car is unlikely to pass any kind of emission check and your fuel economy will not exist!

When cams are marked "for competition use only" it will indicate that the cam is prone to excessive wear.

This wear effectively reduces the lift and sucks your power.

A competition cam is replaced at frequent intervals and is not something the average car owner wants to be doing.

Honda have a dual cam lobe which allows a profile for high rpm use and another for low engine speeds giving a much wider power band and good fuel economy.

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2 Responses to “Fast road cams (Sports camshafts)”

  1. Belthazor says:

    Quick note, changing cam duration is not as simple as this write up suggests. Bare in mind if you drive an auto you most likely will have to change the stall of your gearbox. standard cam power ranges start around 1200 to 1300 with a stall to suit. If you have a cam grind to suit say 2500 rpm then you will need to change or modify your stall converter.

  2. ahmed says:

    hi, do you supply and fit for a 1998 audi a3 1.8 non turbo?