What do we need from you?
Please supply us with a standard Mazda MX-5/Eunos 1600cc or 1800cc cylinder head – the more ‘standard’ the better (some heads we have received in the past have already had the valve seats cut which makes it difficult/impossible for us to re-cut them). We can only work with what we are given – the better the initial parts, the better the end product !
The head should be reasonably clean, with the inlet manifold, exhaust manifold, cams/pulleys and lifters already removed, but with the cam caps replaced onto the head so as to keep them in order. If possible, please also remove the cam angle sensor, front thermostat housing and front timing mark backplate
When the customer supplied head arrives at our workshop it is completely stripped down to its component parts.
Then the head is ‘flow tested’ on our digital flow bench. Although the cylinder heads are production items there are subtle differences in the quality of them as standard. These differences are down to casting quality and valve seat alignment within the bowl area of the intake and exhaust ports. From the flow bench evaluation it is decided whether the head is deemed to be ‘no good’, then the customer will be informed and subsequent course of action can be discussed.
Clean & Check
Once the initial evaluation has taken place the Cylinder Head and its components are thoroughly cleaned using various processes. Once the parts are cleaned they can be fully inspected for faults/cracks.
An example cylinder head stripped and ready for cleaning
The following components are measured for tolerances:
- Valve guides
- Valve seats
- Valve stem diameter
- Valve stem length
- Valve margin thickness
- Valve spring free length
- Valve spring ‘out of square’
- Valve spring poundage
Only items that are ‘within tolerance’ are used and the others discarded and replaced.
Cylinder Head Reassembly
Once the above has been completed the Cylinder Head is re-assembled. Depending on whether it is destined to be a Race or Road application different processes now take over……
The valve seats are cut using three angle carbide cutters – the angles we choose are not common to a ‘three angle valve job’ but are what we have found to flow the best through our own testing.
BLiNK Motorsport have invested in top of the range valve seat cutting equipment made by Mira. The unit is a VGX-21 tool head driven by a variable speed motorised drive.
Using Carbide cutters the valve seats are cut precisely unlike grinding them with stones. Here is a brief video of an Mazda 1800 cylinder head being cut :-
The valve seat width is also checked to ensure correct valve head cooling. The valves themselves are fully cleaned to remove any carbon deposits, they are then refaced on a precision valve re-facer. This gives the valves a ‘mirror’ like seating surface ensuring good combustion chamber sealing and superior airflow.
At each stage of the above the cylinder head is subjected to flow bench testing to ensure that each step is producing the required results. Once we are satisfied that the results meet our exacting standards the inlet and exhaust valves are pre-installed and combustion chamber volumes are measured – this ensures they are within tolerance of each other and also determines the skim that the cylinder head receives.
The Mazda engine runs a very low compression ratio as standard (9.4:1) which heralds from the day that the engine was fitted as a turbo application in the Mazda 323. Racing has shown that the MX5 can run at higher compression ratio’s and still operate reliably. Today, it seems common for racers to use a ’50 thou’ head skim but this is very misleading and vague!
The standard Mazda cylinder head has production tolerances in head depth and previous use could have already seen the cylinder head being skimmed. Only by measuring the combustion chamber volume can you accurately determine what amount of material to remove from the cylinder head.
Once the volume of the combustion chambers is known we specify the amount of material to be removed to obtain a specific compression ratio.
Measuring the chamber volume to calculate compression ratio
Once all the machining operations have been carried out the cylinder head receives another clean to ensure no foreign matter remains within the component.
New valve stem Oil Seals are fitted throughout and the valves are finally fitted into the head and their pre-installed height is checked. Please note that the valves are not ‘lapped in’ as this destroys the valve face/seat profile and is not required with carbide cutters.
Head 1 When grinding and lapping, Surface A and surface B will match but take an uncontrollable form. The geometrical quality of the valve is destroyed, the qualities given by various heat treatments, machining or re-facing is lost. Most valves have some form of treatment and by grinding in this fashion, it is destroyed.
This means that the flow over the edge of the valve is interfered with losing performance and the quality of the contact between valve and seat is insufficient to secure good heat transfer between valve, seat and cylinder head. Heat is not transfer away efficiently and so builds up around the exhaust seat and along the valve in a damaging manner that causes increased wear to the engine.
All valve springs are then installed and the cylinder head is subjected to a visual Check. The cylinder head does not include camshafts or hydraulic cam lifters – these must be fitted by the customer or can be installed by ourselves at extra cost.
Road/Trackday Cylinder Head
If you’ve managed to follow up to now you will have gathered that the cylinder Heads for this application do not initially perform as well as the race heads. This is not a problem but requires more work to ensure that these products perform as well as, or if not better than a race application.
Now is probably a good time to briefly discuss what cylinder head porting is all about!
It is a common misconception that an engine is just an ‘air pump’ and the more air you can get through the engine the more power it will produce – if life was that simple cylinder head porters would be out of business overnight!
Air in itself is very heavy and therefore has ‘mass’, when it flows through a cylinder head it also has velocity. If an object has mass and velocity it has momentum. It is this momentum that needs to be increased to improve the performance of the cylinder head.
Imagine the cylinder head port as a drainpipe flowing water – the larger the drainpipe the more water it will flow but if the pressure remains the same (a normally aspirated engine fills it’s cylinders at atmospheric pressure) then the velocity of the water will slow down considerably.
The same is true of the airflow through the cylinder head – its all to easy to just ‘hog out’ lots of material from the ports and obtain impressive flow figures but the velocity of the air is so slow the performance of the engine is ruined!
The ‘energy’ within a port = 1/2 x mass x velocity². We can see that when port velocity goes up the port energy goes up far faster and when port velocity drops the port energy drops far faster.
The secret is to obtain more airflow through the port but not to increase its volume – this ensures that the cylinders are ‘rammed full of air’ and the best possible power is achieved.
The airflow profile also needs matching to the camshafts being used in the application – there is no point achieving very impressive flow figures at valve lift heights the engine will never ‘see’.
A standard MX5 inlet camshaft lifts the inlet valves to 0.309″. A well known UK based website for cylinder heads shows an MX5 cylinder head flow chart showing very impressive flow figures at 0.4″ and 0.5″ of valve lift. This flow will never be used by a Mazda camshaft and almost certainly shows the port is far to big for the application.
It is far more beneficial to improve the flow at low to mid camshaft valve lifts as this ensures increased torque and driveability. The camshaft is only at it’s maximum lift once in it’s cycle where as it ‘visits’ the lower lifts twice (opening and closing).
The Road/Trackday cylinder Heads receive the same careful attention to detail as the race heads but are ported to ensure optimum performance.
Please do not expect to receive a cylinder head that has lovely shiney Ports – this is a marketing strategy and does not improve the cylinder head’s performance. In the words of probably the most respected cylinder head porter in the world, David Vizard, “Shape is everything – surface finish is nothing!” I’m sure as a customer you don’t want to pay us for producing a ‘jewel like’ port that will not improve performance and will be hidden by either an inlet or exhaust manifold!
Please note : as per the race head, the product does not come fitted with camshafts or hydraulic lifters. These will have to be fitted by the customer at the time the Cylinder head is installed into the vehicle. The cylinder head is also supplied with a full flow bench analysis.
Disclaimer – The Road/Trackday cylinder heads do not conform to Ma5da racing regulations and are therefore not permitted. All cylinder heads we sell are marked and identifiable (and the scrutineer’s of the series know where to look for these marks!). BLiNK Motorsport accepts no responsibility for using this specification of Cylinder Head for racing purposes in the various MX5 Championships
Turn round time
Expected delivery of a BLiNK Optimized™ Cylinder Head from receipt of customer unit is 5 weeks.