Jaguar Cylinder Heads

MAKE YOUR JAG FUN TO DRIVE!

The newly developed RG cylinder head has been specifically designed for the Jaguar connoisseur who desires truly modern performance and everyday drivability from his classic Jaguar without violating the authenticity of his vehicle. All of the original limitations have been overcome. For 4.2 liter engines, each combustion chamber is now properly centered over each bore. For all XK engines, the ports have been raised and reshaped to provide far better flow, the compression ratio and squish area are substantially increased and, if a Twin Spark model is ordered, two plugs improve power, drivability, efficiency and emissions. These features are all contained beneath the period appearance of the original head.

Each head is chill cast in a 3D printed sand mold to produce an aerospace quality component. Heads are poured as Single Spark models that can be machined to make a Twin Spark model. This means that a Single Spark model can be converted to a Twin Spark model at any time.

Performance increases of 100 hp are typical from 4.2 liter engines with stock 9:1 pistons, triple SU carbs and original cast iron headers. Even more power is made possible with Webber carbs and higher flow exhaust systems. Special CP‐Carrillo® pistons permit one to install the RG cylinder head on 3.8 liter engines while raising the compression ratio to 10:1.

 

RG Heads come with chill cast, seven bearing high performance camshafts that provide more power without affecting idle and low RPM performance. Considering that an E‐type weighs about 1,000 pounds less than a present‐day Corvette, increasing its power by 50% puts your E‐type in the same performance category. Just think what that would feel like from the driver’s seat!

People commonly ask why we did not design a four valve cylinder head. Our Answer: If the original valve angle is maintained, which is critical to maintaining the aesthetics of the original head, a four valve combustion chamber would be even larger than the original hemispherical one. Many attempts were made to make four valve designs for classic era engines – all of which failed. Even if this obstacle were not the case, the XK engine’s extra‐long stroke limits high RPM operation, which prohibits it from enjoying a substantial benefit from a four valve design.

3.8 CYLINDER
HEAD

JAGUAR XK6 3.8 LITER CYLINDER HEAD UPGRADE KIT:

This kit is designed to unleash all of the potential from a 3.8 Jaguar XK6 engine for street performance driving. The 3.8 liter XK engines require higher domes on their pistons to achieve a given compression ratio as compared to the 4.2 liter engines. This makes them prime candidates for Twin Spark ignition because the higher dome acts as an obstruction to the flame front during combustion. Although RG CAN build the 3.8 liter head as a Single Spark model, we don’t recommend it because it is especially prone to pinging at 10:1 compression. Bear in mind that the highest compression that Jaguar offered was only 8.7:1 that they called, “9:1”.

Adding Twin Spark ignition reduces spark advance by 9 degrees allowing higher compression ratios when running on street grade fuel with a much reduced risk of pinging. CP-Carrillo® has developed a custom piston that adapts the RG cylinder head to the 3.8 liter bore spacing. This piston is universal to all bores – irrespective of bore offset. Power increases of 100hp have been documented during dyno testing over the stock 3.8 liter engine with S.U. carburetion and cast iron exhaust manifolds. More performance is possible with other configurations using popular induction and exhaust components.

  • A fully assembled RG Twin Spark Performance cylinder head
  • A set of forged CP‐Carrillo® 10:1 compression pistons
  • A complete Twin Spark Ignition System
  • Optional CP‐Carrillo® forged connecting rod set
HP UPGRADE

+100 hp

 

4.2 CYLINDER
HEAD

JAGUAR XK6 4.2 LITER CYLINDER HEAD:

The RG 4.2 liter cylinder head can be built as a Single Spark or Twin Spark model. For those who want to maintain the original appearance of their engine compartments, RG can build your head with only six spark plugs. This will eliminate the added expense of the Twin Spark ignition system. A Single Spark head can be upgraded to a Twin Spark by machining the 2nd set of plug wells at a later date. A Single Spark head will require 9 degrees more spark advance, which may present pinging issues when used with moderate or low grade fuels due to the increase in compression ratio from 8.7:1 (what Jaguar called “9:1”) to 10:1. There will also be a slight loss in power, fuel consumption, drivability and emissions as compared with the Twin Spark configuration.

The Twin Spark model of the RG 4.2 liter cylinder head is designed to unleash all of the potential from a 4.2 Jaguar XK6 engine for street performance driving. Adding Twin Spark ignition reduces spark advance by 9 degrees allowing higher compression ratios when running on street grade fuel. Power increases of over 100hp have been documented during dyno testing with S.U. carburetion and cast iron exhaust manifolds. More performance is possible with other configurations using popular induction and exhaust components. Click Here to see actual dyno test results on our blueprinted 4.2 liter engine.

  • A fully assembled RG Single or Twin Spark Street Performance cylinder head
  • An optional complete Twin Spark Ignition System
  • An optional CP‐Carrillo® high performance connecting rods & pistons
  • Optional CP‐Carrillo® high performance pistons
SINGLE SPARK HP

+100 hp

 
 

4.7 CYLINDER
HEAD

JAGUAR XK6 4.7 LITER CYLINDER HEAD UPGRADE KIT:

Because of a rod ratio of 1.85:1, the XK6 engine stands to benefit greatly from “stroking” – a practice of increasing the rod journal offset on the crankshaft to increase torque and displacement. This practice is, however, constrained by a maximum safe piston speed that is reached at an offset, which yields a 4.7 liter displacement. A Stroked 4.7 liter XK engine will exhibit enormous gains in low and midrange torque, but will not rev as high as lower displacement XK engines. RG has built a special model of its head to meet the unusual demands of this engine’s configuration. This head has larger valves and ports to increase low RPM flow. The RG 4.7 liter cylinder head can be built as a Single Spark or Twin Spark product. For those who want to maintain the original appearance of their engine compartments, RG can build your head with only six spark plugs. This will eliminate the added expense of the Twin Spark ignition system. A Single Spark head can be upgraded to a Twin Spark by machining the 2nd set of plug wells at a later date. A Single Spark head will however require 9 degrees more spark advance, which may present pinging issues when used with moderate or low grade fuels due to the increase in compression ratio from 8.7:1 (what Jaguar called “9:1”) to 10:1. This engine’s configuration is the least prone to pinging due to the reduction in piston dome height. There will also be a slight loss in power, fuel consumption, drivability and emissions as compared with the Twin Spark model.

The Twin Spark model of the RG 4.7 liter cylinder head is designed to unleash all of the potential from a Jaguar XK6 engine for street performance driving. Adding Twin Spark ignition reduces spark advance by 9 degrees allowing higher compression ratios when running on street grade fuel. Power increases of over 140hp can be expected over the stock 4.2 liter engine with S.U. carburetion and cast iron exhaust manifolds. Other configurations, using popular induction and exhaust components, yield even more performance.

  • A fully assembled RG Single or Twin Spark 4.7 Street Performance cylinder head
  • An optional complete Twin Spark Ignition System
  • 4.7 Stroker Kit:
  • Forged 4.7 liter CP-Carrillo rod & piston set (10:1 compression when used with RG 4.7 head)
  • 4.7 low mass “Stroker” steel crankshaft
HP UPGRADE

+140 hp

 
 

OTHER RELATED ACCESSORY PARTS


JAGUAR XK6 RACING HEAD CASTING:

For those who wish to configure their own XK cylinder head for special purpose racing, RG offers raw cylinder head castings, which are machined to provide the basics for assembly. This permits one to develop custom porting configurations and to use custom valves. RG also sells camshaft blanks that can be custom ground to any profile. The RG cylinder head can support valve lift up to 0.600”.


RG 7 BEARING CAM COVERS:

RG’s cylinder heads have three more cam bearings than the stock Jaguar head. RG offers cam covers that utilize all of the cam studs on the RG head. These are designed to replace the Series I style cam covers that were polished aluminum. Utilizing all studs spreads the load over more points reducing point loads that cause cracking and also making oil sealing much improved. These are designed to replace the Series I style cam covers that were polished aluminum. Utilizing all studs spreads the load over more points reducing point loads that cause cracking and also making oil sealing much improved.


TUBULAR HEADER OPTIONS:

Tubular headers improve the engine’s breathing by confining each cylinder’s exhaust gasses to a singular tube that actually sucks the air out of the engine. RG offers tubular headers because the exhaust ports on its heads are slightly higher than the original Jaguar head and because their shape is different. Although you can use a factory cast iron manifolds or an aftermarket headers with the RG cylinder head, those will not be an exact match in terms of flange opening shape or performance. The RG exhaust components are tested with the RG cylinder head to optimize the torque curve for street driven cars. RG offers two tubular header options, a “Long Tube Header” (LTH) and an “Equal Length Header” (ELH).

  • Long Tube Header – This header follows the original Jaguar exhaust manifold layout where each primary tube is routed at 90 degrees from the outlet to fit between the frame rails and the engine block. These headers have primary tubes that vary in length from 19” – 21”, which is much longer than the primary lengths on the cast iron manifolds. These headers have intermediate pipes that connect each collector to one of the silencer inlets. These pipes are fitted with “bungs” for the use of oxygen sensors.
  • Equal Length Header – This header has the primary tubes looping around in an arc before routing between the frame rails and the engine block. This nuance does two things; first, it permits the exhaust gasses to exit the exhaust port before encountering any serious obstruction (such as a 90 degree turn right out of the cylinder head), and second, it allows the primary tubes to achieve an desired length of 36” before emptying into the collector. This length has been determined to optimize bottom end torque with our cylinder head. These headers have intermediate pipes that connect each collector to one of the silencer inlets. These pipes are fitted with “bungs” for the use of oxygen sensors.

HIGH PERFORMANCE EXHAUST:

RG has dyno engineered a 2‐1/4” stainless steel exhaust system that augments the performance of the RG XK6 Cylinder head – especially when tubular headers are used. If tubular headers are ordered, the system has adaptors that link them to the main silencer. If one is using the cast iron Jaguar exhaust manifolds, the system comes with downpipes that are properly sized to the application (i.e. 3.8 or 4.2 liter).

The RG HP exhaust system is unique, as it has a single chambered main silencer. RG’s dyno testing has found that this produces a better overall torque curve when used with the RG cylinder head. It also has four 1‐3/4” intermediate pipes leading to two twin pipe resonators with twin tips. This is similar to how a Ferrari exhaust system would be designed. The primary purpose of going from two inlets to four outlets has to do with getting sufficient clearance under the IRS while flowing sufficient exhaust gas. RG’s systems are complete with all brackets, hardware and fittings required to hang it on an E‐type.

 
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S P E C I F I C A T I O N S :

Cylinder Head:

• New chill-cast camshafts with high performance profiles:

– Intake Lift = 0.466” Duration 252 @ 0.050”
– Exhaust Lift = 0.426” Duration 248 @ 0.050”

• Large, 37mm Flat tappet Cam Followers, which run in the aluminum without the requirement for a bucket bore

• Ferrea® stainless steel valves sized to the 4.7 liter displacement:

– Intake 1.950”
– Exhaust 1.562”

• Nano material valve seat CNC radial cut & blended to runner bowls
                                                Read More

Twin Spark Ignition:

• RG Twin Spark distributor with hall effect sensor for crank position detection
• Preprogramed Spark Controller with MAP sensing
• Temperature sensor & Fan control relay
• Two Bosch coils with separate Bosch coil ignitors
• Wiring harness that conceals Spark Control unit inside left door hinge cavity

4.7 Stroker Kit:

RG truly believes that anyone rebuilding a 4.2 liter Jaguar XK6 engine should seriously consider stroking their engine – if they can afford to.  It makes a HUGE difference in driving experience!  When you stop to consider that pistons are expendable and that connecting rods and crankshafts must be reconditioned at a substantial cost to properly rebuild an XK’s bottom end, converting to a Stroker engine is not much more expense.

Each component in the kit is designed to work with the other components to yield the very finest stroker kit available. The RG Stroker crankshaft is unique from other 4.7 liter crankshafts on the market.  It uses Chevrolet “Clevite” Small Block rod bearings instead of the standard Jaguar rod bearings to reduce rotating mass.  Lower rotating mass means higher safe RPM operating range:

  • Forged piston & rod castings designed as high performance replacements for heavier original parts
  • Rods use Small Block Chevrolet “Clevite” bearings to reduce crankshaft rotating mass and connecting rod mass
  • Standard Jaguar connecting rods cannot be used with the RG stroker crankshaft
  • Pistons will yield a 10:1 compression ratio with RG cylinder head
  • RG Stroker crankshaft is made from S7 tool steel on state of the art CNC machine in the USA
  • Rod journals are hollowed to reduce rotating mass
  • Counterweights are balanced to lower mass connecting rods and pistons
  • Rear main journal has been machined to fit a modern rear seal to reduce oil leaking
  • Rear seal adaptor is included

S P E C I F I C A T I O N S :

Cylinder Head:

• New chill cast camshafts with high performance profiles:

– Intake Lift = 0.466” Duration 252 @ 0.050”
– Exhaust Lift = 0.426” Duration 248 @ 0.050”

• Large, 37mm Flat tappet Cam Followers, which run in the aluminum without the requirement for a bucket bore
• Ferrea® stainless steel valves sized to the 4.2 liter displacement:

– Intake 1.875”
– Exhaust 1.562”

• Nano material valve seat CNC radial cut & blended to runner bowls
                                                Read More

Twin Spark Ignition:

• RG Twin Spark distributor with hall effect sensor for crank position detection
• Preprogramed Spark Controller with MAP sensing
• Temperature sensor & Fan control relay
• Two Bosch coils with separate Bosch coil ignitors
• Wiring harness that conceals Spark Control unit inside left door hinge cavity

Optional CP‐Carrillo® Connecting Rod Set:

Going to high grade forged CP‐Carrillo® connecting rods makes higher safe RPM possible. Higher RPM allows the engine to extract more potential from the RG cylinder head. When upgrading these components, it is advisable to recondition the OEM crankshaft and to have it nitride finished.

• Forged rod castings designed as high performance replacements for heavier original parts
• Rods designed to connect to OEM crankshaft
• Pistons will yield a 10:1 compression ratio with RG cylinder head (as will original Jaguar “9:1” pistons)

S P E C I F I C A T I O N S :

Cylinder Head:

• New chill cast camshafts with high performance profiles:

– Intake Lift = 0.466” Duration 252 @ 0.050”
– Exhaust Lift = 0.426” Duration 248 @ 0.050”

• Large, 37mm Flat tappet Cam Followers, which run in the aluminum without the requirement for a bucket bore
• Ferrea® stainless steel valves sized to the 3.8 liter displacement:

– Intake 1.875”
– Exhaust 1.562”

• Nano material valve seat CNC radial cut & blended to runner bowls
                                                Read More

Piston Set:

• Universal forged CP‐Carrillo® piston for all bores – lighter than originals
• Piston accepts standard Jaguar connecting rod
• Piston profile produces 10:1 compression ratio when used with RG 3.8 liter cylinder head

Twin Spark Ignition:

• RG Twin Spark distributor with hall effect sensor for crank position detection
• Preprogramed Spark Controller with MAP sensing
• Temperature sensor & Fan control relay
• Two Bosch coils with separate Bosch coil ignitors
• Wiring harness that conceals Spark Control unit inside left door hinge cavity

Optional CP‐Carrillo® Connecting Rod Set:

Going to high grade forged CP‐Carrillo® connecting rods makes higher safe RPM possible. Higher RPM allows the engine to extract more potential from the RG cylinder head. When upgrading these components, it is advisable to recondition the OEM crankshaft and to have it nitride finished.

• Forged rod castings designed as high performance replacements for heavier original parts
• Lightweight forged connecting rods fit to OEM crankshaft