Raymond
Mays Cylinder Head
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 carburetors. 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 carburetors 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 Weber’s. 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 recognized for what they were and looked after.
Aquaplane
are currently looking into re-manufacturing their version of the alloy head for
the Ford MKl – lll cars and can be contacted by people who are seriously
interested at info@vintagecarparts.co.uk