CNC engineered gas flowed cylinder heads

Frequently Asked Questions

What does “Exchange” mean ?

The question we are asked most. Exchange costs are simple and is standard practice for many automotive parts based on used parts. If you order a head from us, we normally require your existing cylinder head in exchange. We charge the exchange fee in addition to the cost of the new head. When we receive your old head and it is checked and accepted, we credit your credit card with the exchange fee. This also means your engine is not out of action while heads are sent to and from CNCHeads. If you don’t have a head to exchange we charge the exchange fee in addition to the head price.

Example :

  • Cost of head £600.
  • Exchange cost £350
  • You Pay £950
  • When we receive your old head and it is accepted we refund £350 to your credit card.

There are several options here :

1. Outright purchase. You pay the cost of the head work plus the exchange. This is often preferable for international orders (avoiding postage costs) or where your existing head is damaged.

2. Straight exchange. Deliver your head before we begin work and avoid the exchange cost.

3. Pay the exchange cost. We can begin work straight away and will refund the exchange cost when we receive and have inspected your head.

4. We machine your cylinder head. If you wish, you can avoid the exchange costs by allowing us to work on your head or by delivering the head before we start work. Work will take several days as up to 12 hours of machining is required and the head will need to be inserted in to our machining schedule. Our 3 CNC machines run 24 hours a day so we will do our best to reuturn your head as soon as possible.
What warranty is available on our heads ?

A 12 month warranty is available with certain reasonable conditions. See our TERMS AND CONDITIONS .

What are the benefits of a gas flowed cylinder head ?

A gas flowed cylinder head improves the flow of air and fuel in to the engine making it more efficient and making more power and torque. All modifications (turbo, supercharging, electronic, fuel injection, exhaust etc will all be enhanced by a gas flowed head. If you plan a series of modifications you are well advised to do the head first to reap the full benefit from other modifications. See lots more detail HERE

Can you supply a standard head ?

Yes, we supply standard reconditioned cylinder heads too. It would be easy to simply fit a used cylinder head to your car from the scrap yard. But if you want to restore the performance and economy your engine once had, it is best to fit a new or reconditioned head. The cylinder heads we supply have undergone a rigorous re-manufacture process which bring specially selected heads back to as near new condition as it is possible to do at a reasonable price. We stand by our heads too. Each head comes with a 12 month no quibble guarantee.

Can a CNCheads gas flowed cylinder head be used on a road car ?

Yes. We aim at top race standard because racers demand the best possible head but there is no reason why you cannot use our head on a road car. Many of our customers are road car enthusiasts. What ever the state of tune of your car, a gas flowed cylinder head will improve performance.

Will I get more power from a standard engine without further modifications ?

One of our heads won’t turn a standard engine in to a fire breathing monster by itself and we make no predictions on power for a standard engine because the condition and state of tune is unknown, but there are excellent benefits to be had.

Typically you will see:

  • Better power & torque
  • Turbo lag is reduced greatly with faster spool up. More power in low to mid range. Superb top end.
  • No visual change in the engine bay
  • No risk of overheating
  • Improved fuel consumption
  • Fewer Gear changes
  • Better throttle response
  • Reliable performance
  • Any modifications you do make will be enhanced by the gas flowed head.
  • Excellent value for money in terms of cost/bhp and fuel savings.

Can you recommend modifications for my engine which will work with a CNCheads cylinder head ?

Yes – CNCheads are part of RIC WOOD MOTORSPORT – one of the UK’s leading race engine and performance car specialists. We specialise in racing and performance engines. We are fully equipped with a 1000BHP dyno cell and 4 wheel drive rolling road. We have over 20 years of building cars and engines for road and track. Whatever your requirements or budget we can advise and help.

Why are some heads measured at 10″ of pressure and some at 25″ ?

10″ was a European standard which we used and is suitable for Smaller European engines (as opposed to big US V8’s). We have recently updated our flowbench to one which is capable of 25″ or 28″ pressure. 25″ is the pressure achieved by a normally aspirated engine and will therefore simulate the swirl and tumble effects you can expect which can affect flow. Our power predictions for both pressures are accurate as mathematical predictions (from our Port Flow Analyzer software) and most heads have been verified by an actual engine build and test on our in house Dyno.

Do you add material to the port (such as resins) ?

No. We dont because we are aiming at many race series which do not allow this technique. We recognise this a legitimate technique for many engines (especially gas flowed cylinder heads for motorcycle engines) but we have not (yet) adopted this technique for our heads. As such they remain eligible for many race series.

How do I know you haven’t just made these flow figures up ?


We don’t run the data through a spreadsheet or anything else which would allow us to manipulate the figues you see. The flow figures come directly from the software used with the flowbench. The Graphs and other data we show are paper print outs direct from the Port Flow Analyzer software. We simply scan the printout and insert in to the website to show we don’t mess with the figures we see on the flow bench. It’s easy for us to do and it shows we hide nothing.

How do I know the head you sell has the flow you claim ?

We compare our finished heads to the original final prototype on the same flowbench. We do this as part of our quality control process. We see less than 1% difference. Our flow results are consistent between heads and between cylinders in the head. This is only possible with CNC engineering. We are totally sure about the flow of the heads we sell which is why we publish the figures and why many gas flow firms don’t.

How do I know the horsepower figures you claim are achieveable ?

Once flow figures are measured on the flow bench and the data is captured via the Port Flow Analyzer software, it is possible to calculate horsepower by adding known parameters such as number of cylinders, camshaft profile, lift details, valve size etc. It is also possible to specify a custom camshaft profile and we can use this data to manufacture a custom camshaft if required. The claimed horsepower is derved by an algorithm using the parameters to derive a predicted horsepower and torque at a known RPM. Obviusly we know we need to go further than this.

We have verified the BHP predictions many times through full engine builds and testing on our dyno. We have full faith in the predictions. It is also something which you won’t see on any other gas flow engineering firm. But we stand by it because we can prove it.

Horsepower using a turbo or Supercharger is more difficult to calculate as boost pressure is variable electronically and by the client (unlike atmospheric pressure in Stockport where the baramoter always predicts rain and is usually right).

All of the heads we supply have been either tested in our dyno cell or via our rolling road when fitted to a car. We are 100% confident about our power claims for engines of a known state of tune and condition.

If you put our head on a knackered old engine though, it’s unlikely to match the results we see on one of our engine builds. Our heads work wonders not miracles !

Do you guarantee the power you claim ?

Yes – but only on engines we build and tune. This is a fair condition. Our claims are verified but we cannot predict BHP on engines we haven’t seen. Engines must be of known condition and state of tune. The only way we can be sure of this is by having full control over the engine build.

I can get the same power increase from a re-chip for less money .

You can achieve a lot with electronic tuning especially with Turbo and Turbo diesel engines. (We are a Superchips/Unichips/DTA dealer so we know what we are saying here)

But the performance improvements are always limited by the standard head. Electronic tuning might give you 20% with a standard head. A similar state of tune with one of our heads might give you 40% or more. If you have a normally aspirated engine, it may be quite difficult to get really good improvements without a gas flowed cylinder head. If you anticipate doing a series of changes (say, new camshaft, electronics, exhaust, new carbs or even turbo or supercharging), it would be wise to look at the head first as it will improve the benefits gained from all the other modifications you are planning.