I thought for a long time about how to share the information on the different iterations of Wildcat cylinder heads. I decided to adopt a timeline approach for the cylinder head development as recounted to me by Wildcat himself.
Wildcat Engineering was founded by Ian Richardson, formerly an official McLaren CanAm racing driver and Le Mans GT40 reserve driver. Ian was one of the race engine builders for the 1960s Ford Le Mans winning GT40 race cars. During his racing career Ian had always admired the little Buick (Rover) aluminium V8 engine, but thought someone should do something about the restrictive cylinder head design. After all, the Buick 215 (Rover V8 3.5-litre) was designed in the late 50s.
As nobody did ‘do something’, in 1994 Ian started creating his own performance cylinder heads. Around 1995, word got out that Ian was manufacturing these prototypes for the Rover V8 and he was approached by club racer Simon Allaway looking to step up the performance of his own Rover V8 powered Lotus Esprit silhouette race car.
When Ian was happy with his cylinder head castings, he showed a pair to Simon (an aeronautic engineer) and John Felsted (a historic race car technician). Together they decided to build a Rover race engine with a pair of prototype Wildcat cylinder heads. Over the next few months, the three of them developed and built a 5-litre all steel bottom end engine with the very first pair of Wildcat cylinder heads. These heads featured enlarged and straightened ports, a new combustion chamber shape and adjustable roller rockers. In addition, the valves were the biggest seen at that time – 47.75mm & 40.64mm (1.88″ & 1.60″). Ian achieved this by repositioning the valves wider apart and on the cylinder bore centreline.
The top illustration shows the ports in the Wildcat cylinder head compared to the ports in the modified Rover cylinder head underneath
While the 5-litre engine was being built for Simon’s Lotus, Ian received a visit from Charles Morgan of the Morgan Motor Company seeking assistance with the factory FIA Morgan GTR-8 race programme. This was a usual occurrence, as according to Ian “In the world of racing things never stand still; they’re always changing, looking for that next bit of performance”. Graham Nash of NCK Racing had a proven reputation based on the race engines he had built, including the renowned TVR Tuscan Challenge Rover 4.5-litre units. Jointly Ian and Graham were contracted by Morgan to build a 5-litre race engine with Ian’s second pair of castings which he went on to modify further. This pair of castings featured relocated inlet pushrod holes with even bigger ports and valves – 49.28mm & 40.13mm (1.94″ & 1.58″). The Morgan engine also featured bespoke Jesel offset rocker gear, a hybrid injection system based on Hilborn and EFi fuel injection components, plus the engine block was modified to accommodate the fitment of a mechanical roller camshaft and the associated roller lifters. This was the first Rover V8 engine to have a roller camshaft. The engine was raced in 1995 and 1996 in the Morgan GTR-8 GT2 race car and it outperformed the previous Rover V8 race engine by some margin.
Now back to the engine for the Lotus race car. Simon, John and Ian complete the build and in 1997, the engine ready to dyno at Aldon Automotive with the following results:
400 hp @ 7000 rpm & 330 lbs-ft @ 6000 rpm
For comparison purposes, a 1997 TVR Griffith 5-litre Rover V8 typically makes 270 hp & 300 lbs-ft.
And a further comparison, Autocar & Motor Magazine (20.09.89) tested a TVR Tuscan Challenge Rover V8 4.5 litre race engine with the following results:
348 hp @ 6750 rpm and 297 lbs-ft @ 5500 rpm
(All quoted horse power and torques are measured at the flywheel)
These two sets of prototype cylinder heads formed the foundation for what we now refer to as the Wildcat Stage 1 and 2 heads.
Ian manufactured a few more pairs of the Stage 1 cylinder heads for customers before he hit a major supply issue. Kenne Bell stopped making the adjustable roller rockers that he was using for these heads.
This meant a redesign was required. Ian took this opportunity to make some other changes and these included raising the inlet ports even further, thus straightening them and reducing them in size. New valves were sourced at 46.99mm & 39.37mm (1.85″ & 1.55″). For a more reliable supply of rocker gear, Ian chose Small Block Chevy stud mounted adjustable roller rockers. The new rocker gear was more bulky, so Ian was forced to create new rocker covers. These featured a double angled top to reduce the engine installation space required and provide more space for the new rocker gear arrangement. At this stage, Ian dropped the previous WILDCAT F85X logo cast on the old rocker covers and adopted a new Wildcat script logo. Now the Stage 1 Wildcat cylinder head was established.
In 1998 Ian was approached by the Rover Group to work with Janspeed on a record breaking engine for the MGF Bonneville Land Speed Project EX255. To achieve the level of engine performance demanded by the Project, Ian refined the stage 2 heads previously used in the Morgan GTR-8 race car. Remember these heads already featured repositioned push-rod holes and to make even more room for the larger and straighter inlet ports the pushrod hole were move across by an increased amount. Now Ian added bespoke designed shaft mounted T&D roller rockers and new double angled top rocker covers, although in this case they were machined with the MG logo.
When dynoed, this engine produced at 16psi
946 hp @ 7700 rpm & 640 lbs-ft @ 7500 rpm
This development formed the basis of the Wildcat Stage 2 cylinder heads where Ian offered custom options depending on the desired application. Options included titanium valve spring retainers and valve guides positioned further apart to allow for even larger valves. Valve sizes on these heads started at 49.53mm & 40.64mm (1.95″ & 1.6″).
In Ian’s words, the Stage 1 heads were for the “fast road enthusiast and the Club racer”, while the Stage 2 were “out and out race heads”.
During the production of the Wildcat Stage 1 heads, Ian received numerous requests for a version suitable for fast road applications. With this in mind, Ian developed the HP (High Performance) heads. The ports in these cylinder heads were smaller than those found on the S1s, they came with soft valve springs and had similar valve sizes to contemporary S1 heads.
Around 2007, Ian introduced the final iteration which he referred to as the 1x cylinder head. This was a hybrid of the Stage 1 and 2 heads.
The Stage 1x cylinder heads had similar size ports to the Stage 1 heads with relocated push rod holes that provided space for a straighter inlet port path. They came with larger valves 49.28mm & 40.64mm (1.94 & 1.60″) than those fitted to the Stage 1 heads. They also had the larger diameter valve springs as fitted to the Stage 2 heads. To reduce production costs, Ian opted for bespoke shaft mounted Crane adjustable roller rockers as these were, in his words, less expensive than the T&D roller rockers on the Stage 2 heads. These were normally gold in colour.
In 2006, Ian also started using Crane adjustable roller rockers on the Stage 2 cylinder heads. These silver coloured rockers ran a polymer matrix bearing and were superior in design to those fitted to the Stage 1x heads.
In 2013, Ian retired and sold Wildcat Engineering to ACR Ltd. ACR’s Technical Director Roland Marlow has been working on rationalising the range, updating the manufacturing process and testing new port shapes.
In 2017, ACR released the CNC machined ACR Wildcat cylinder heads. The inlet and exhaust ports are smaller than the original Wildcat Stage 1 heads. The valve sizes have been increased to 49.28mm & 40.64mm (1.94″ & 1.60″).
From the flow bench figures I have seen, the ACR Wildcat cylinder heads outperform the previous Stage 1s and flow slightly less than the Stage 1x and Stage 2 heads up to 0.580″ valve lift. This is about the maximum valve lift attainable with a mechanical flat tappet camshaft.
I have come across high performing naturally aspirated engines built with Stage 2 heads with better flow figures above 0.600″ valve lift. In these cases, larger Small Block Chevy cam bearings had been fitted into one of Ian Richardson’s 4-inch bore engine blocks. The larger Chevy size camshaft journals allowed bigger lobes that generated higher valve lift in the 0.700″ range.
Now, flow data isn’t everything…
The flow data I’ve seen would suggest the performance of the S1x, S2 and ACR cylinder heads would be similar. However, in reality from my observation of the Wildcat engines (see home page for examples) the engine performance does not support this. All three heads perform well, but the S2 does better. So I wondered what was going on.
I’ve noticed in recent years that American tuning companies, including AFR, Dart and Trick Flow Specialities, offer after market cylinder heads for their domestic V8 engine tuning market with a range of port volumes for each model of cylinder head, depending on the intended use.
Perhaps the inlet port volume is an important factor in performance tuning.
Further research led me to consider the effect the inlet valve has on the behaviour of the gases flowing into the engine as it repeatedly opens and closes. As a consequence of this action, the gasses have to repeatedly accelerate and stop which generates pressure waves. This stop and start action is not replicated in the flow bench testing, meaning the pressure waves are also not present. In the real world, pressure waves can enhance power when pulsing in harmony with the engine or hinder power when working against the engine. We experience these waves as sound, such as the rumble of the engine especially at idle. Some factors that affect the pressure waves are the valve size, valve opening and closing timing, capacity of the cylinders, compression ratios and piston speed range. More importantly, I now believe the inlet port shape, cross-sectional area and volume are directly relevant because they affect the behaviour of the gases and therefore the characteristics of the pressure waves.
As the S2 heads have the largest volume inlet ports, this may answer why the most powerful Rover engines have Wildcat Stage 2 heads. Carl Hansen’s 5.8-litre, Tim Garlick’s 5.8-litre, MGF EX255 project 4.8-litre, Steve Green’s 6-litre…
I used to think that the engine was a simple air pump, but it’s a bit more complicated than that. I guess I’m still learning!
Go to the home page for more information