The MKl Zephyr was first to get a Raymond Mays conversion for the grand price of 75pounds. These were available from Raymond Mays and partners LTD of Bourne. The basis of the conversion was the replacement of the single down draft carb by 3-side draft SU type H4 carburettors. The MKl Head itself had the ports opened up and polished as well as the combustion chambers reworked. Then the head face was machined from 6.8/1 to 7.6/1 compression. Everything else in the rocker gear was standard Ford except for the edition of extra valve springs inside the originals to raise rpm.

Fuel consumption at 60mph was 20.8 mpg.

Acceleration from 0-60 mph was improved from the standard 20.2seconds to 16.3 seconds.

For the Mkll Zephyr and Zodiac 6's, the head made and marketed by Rubery Owen and Co., LTD of Bourne, (designed and developed by the technical associates of Raymond Mays) was made of an aluminium alloy known as DTD 424, the same material as used by Jaguar as used on the XK series.

By design of the combustion chamber, the compression ratio was raised from 7.8:1 to 8.75:1 with an option of 9.2:1, which added an extra 5 BHP. A standard Zephyr made 86 HP and kitted out with the RM heads standard compression (8.75:1), made 127hp. Inlet ports were at a 45-degree angle with the valves at a decreased angle of 4 degrees to the perpendicular, made for a very free flowing set up. The intake manifold is also made of an alloy casting and mounted twin SU's which were available in 2 sizes (2H4 one and half inch or 2H6 one and three quarter inch) which could also raise the HP to 138 at 5,000 rpm. The exhaust comprised of 2 separate cast iron manifolds, each collecting from three ports. These had hot spots for intake heating. The valves were oversize (inlets 1.65 in, exhaust 1.29 in) which were highly durable and heat resistant silicon chrome alloy. A single valve spring per valve was retained. Tubular pushrods replaced the standard solid ones to save weight and increase the rev range. The standard camshaft was used usually with a full race cam that offered an extra 18hp available. Weber carbs (duel choke) were another option, ultimately expected to peak at 160bhp. The alloy head is itself 28 pounds lighter than the cast iron one but with manifolds and carbs etc works out per the original set up.

The top speed for a Zephyr with this conversion went from the standard 86 mph to 103mph and acceleration from 0-60 was down to 10.3 sec's from 17.9 seconds.

Rubery Owen claimed the conversion with the larger carburettors give the same Mpg as the standard Zephyr and is actually improved with the smaller twin inch and one half carbs.

Price from Britain for the standard kit at that time was $400 American and an installing charge of $35 was available. These prices are in dollars because market research was being done in the US as well.

The RM head supplied for the Zephyr/Zodiac MKlll was also a 6 port alloy model that was similar to the Mkll model except it was commonly ordered with three SU's or 3 twin choke Webers. The compression ratio was around 10 – 1 compared to the standard 8.3 –1. The exhaust manifold resembled the Mkll one in cast iron, however, by this stage testing had shown the benefit of tuned-length headers.

On a Zodiac MKlll sporting the super Formance stage 5 racing conversion, the car made 222 BHP. However, the car was also fitted with a Van Rooyen track cam shaft with 10.6 mm lift as well as (raised again) 10.5:1 compression, the motor was balanced and fitted with a lightened flywheel and overall the motor was bored out from 2553CC to 2708CC.

Top speed was raised to 110.4mph at 6.200rpm (142.6! with overdrive)

The standard quarter mile was covered in 14.95 seconds vs the standard Zodiacs 20.1 (Executive) 0-60 factory was 15.2 cut down to 7.6 with the stage 5 conversion.

Raymond May heads are no longer available brand-new however, they still come up occasionally before being quickly snapped up. Because of the age of these heads now, a good idea would be a pressure test etc to check the condition of the head as alloy suffers from corrosion, that usual cast iron doesn't. However, most heads were recognised for what they were and looked after.