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Heads
Having read A Graham Bell and other various engine tuning books, I was gagging to have a go modifying the cylinder heads for better performance.
Excellent condition cams were kindly supplied by Chris Coleman were sent to Kent Cams to be re profiled as Race spec with 308 degrees duration, 49/79-79/49 @ 0.50", 105 degrees LBA, inlet 10.66mm lift, exhaust 10.61mm, overlapping of 98 degrees. Original figures are trademark Jaguar for its engines, with minor variations, 256 cams, 17/59-59/17.
Unfortunately, I did not notice some microscopic marks on the edge of the lobes, caused by a sharp object (grinding apparatus?) in the journal number 3, 4 and 5 as I trusted Kent Cams to do a sterling job, causing the cam to seize on start up and ruining number 4 cap.
Fortunately I had spare caps and cam carrier and was able to rebuild the head. I did contact Kent Cams, enclosing photos of the offending cam (RH) explaining the problem and to make them aware of this problem. I was not looking for a refund or compensation as I should have checked the cams with a loupe if necessary when it arrived, not a couple of year later. Still, they never dignified me with a reply.
I embarked on the long journey to gas flow the heads, using an air grinder with hardened steel die to remove the bulk of material, relying then of special flap wheels (conical and cylindrical) proper for this job, acquired from Demon Tweeks, finished off with abrasive sponge wheels to give a smooth, satin finish as polished surface causes a drop in suspension of the gas flowing, not promoting good charge velocity and turbulence. The inlet valve guided boss was completely removed as it is not detrimental to heat dissipation and gas velocity performance, on the exhaust side it was removed as much as possible without creating a too thin of a barrier with the water jacket and still providing decent support for the exhaust valve guide, promoting good heat dissipation in this critical area.
Excellent condition cams were kindly supplied by Chris Coleman were sent to Kent Cams to be re profiled as Race spec with 308 degrees duration, 49/79-79/49 @ 0.50", 105 degrees LBA, inlet 10.66mm lift, exhaust 10.61mm, overlapping of 98 degrees. Original figures are trademark Jaguar for its engines, with minor variations, 256 cams, 17/59-59/17.
Unfortunately, I did not notice some microscopic marks on the edge of the lobes, caused by a sharp object (grinding apparatus?) in the journal number 3, 4 and 5 as I trusted Kent Cams to do a sterling job, causing the cam to seize on start up and ruining number 4 cap.
Fortunately I had spare caps and cam carrier and was able to rebuild the head. I did contact Kent Cams, enclosing photos of the offending cam (RH) explaining the problem and to make them aware of this problem. I was not looking for a refund or compensation as I should have checked the cams with a loupe if necessary when it arrived, not a couple of year later. Still, they never dignified me with a reply.
I embarked on the long journey to gas flow the heads, using an air grinder with hardened steel die to remove the bulk of material, relying then of special flap wheels (conical and cylindrical) proper for this job, acquired from Demon Tweeks, finished off with abrasive sponge wheels to give a smooth, satin finish as polished surface causes a drop in suspension of the gas flowing, not promoting good charge velocity and turbulence. The inlet valve guided boss was completely removed as it is not detrimental to heat dissipation and gas velocity performance, on the exhaust side it was removed as much as possible without creating a too thin of a barrier with the water jacket and still providing decent support for the exhaust valve guide, promoting good heat dissipation in this critical area.
It was calculated that if I require 95% Volumetric Efficiency (VE) @ 7000rpm, it would require 633 cubic feet per minute (CFM) at atmospheric pressure (14.7 psi). Original ports had to be modified as original configuration was 1.25" (31.75mm) for the inlet port, 1.3575" (34.48mm) for the exhaust port. Inlet valves head diameter were 1.623" (41.22mm) /1.627" (41.32mm), exhaust valves 1.358" (34.5mm)/1.362" (34.6mm), giving a formula of 77/100% for inlet/exhaust relation between ports and valve heads diameter. It uses a fairly long inlet manifold design to enhance low range torque figures, typical of a sedate luxury saloon.
New oversize 21/4 Stainless Steel valves, sized 43.5mm inlet and 36mm exhaust plus matching set of Colsibro valve guides (used in race engines, superior to bronze) were purchased from Rob Beere, along it his excellent cam timing tool which takes the hassle away of setting up a timing wheel, magnetic base, micrometer etc. Jaguar itself produces a similar tool (originally produced by Churchill's) albeit in STD form. Rob Beere allows you to advance the cam in increments. I did set up with its recommended setting, which is 4 degrees, trying to counter act the 105 LBA of inlet reverse impulse and over scavenging, therefore still keeping the 308 duration albeit with inlet and exhaust lobes opening and closing earlier, giving now 53 BTDC / 75 ABDC - 75 BBDC / 53 ATDC.
In hindsight, I should not have chosen such radical cam, even if I was going to use brand new four SU HIF44 carburettors, as weak vacuum signal would always be a problem at idle, coupled with poor manifold design and cold temperatures, it would enhance poor fuel vaporization, crippling fuel economy.
After talking with Mitsu, a Honda R&D engineer in Japan, who also was tuning his XJ-S for track days (apparently to swipe local competition from Supras, Skylines etc), he kindly informed me of his mods and that included a softer 282 cam, albeit with large size valves in Titanium, sourced from NASCAR racers (their life span, measured in life cycles, is very reduced to normal Nimonic 80 or Stainless valves, but OK in a race car).
I try to counteract this by increasing valve clearances, not much as I can't stand valves tapping noise, so instead of Kent Cams figures of 0.15mm for inlet, 0.20mm for exhaust, I went to great pain to adjust and shim all valves within 0.01mm, to give a more balanced cam figure (it's called blue printing, balancing all similar components to same weight, dimensions etc), achieving 0.18mm for inlet and 0.23 for exhaust, thus incrementing clearance by 0.03mm, reducing this way duration, admittedly by not much. Many thanks to Mitsu from Honda who kindly provided the oversize shims for the engine, produced in SK11 steel, apparently used in Honda racing motorcycles.
Ports were increased to 33.5mm on the inlet tract, keeping Jaguar original figure of 77% and exhaust was increased to 36.5, just over 100% relation valve/port. Valve seats were re cut for the oversized valves, altering for a triple cut of 45 (instead of original 44.5 degrees), 32/60, for better gas flow properties. New cores plugs were fitted and head were cleaned, removing sludge and other debris. Original double valve springs and retainers were kept as original specification is very high and use was quite low. Valve guide seals were fitted, not only on the inlet but also on the exhaust stems, trying to stem oil consumption, usually created by excessive oil film on the valve stems. Not a particular problem with Colsibro guides due to its high resistance to wear and heat, but notwithstanding, it was fairly economical to be done, so it was done.
Most likely this set up would work well with Weber downdraught carburettors but at £3000, I cannot justify the expense against the much superior independent throttle bodies EFI arrangement, so 12 x 39mm throttle bodies out of several BMW K1200RS' will be drafted along with a MegaSquirt ECU. Watch this space!
New oversize 21/4 Stainless Steel valves, sized 43.5mm inlet and 36mm exhaust plus matching set of Colsibro valve guides (used in race engines, superior to bronze) were purchased from Rob Beere, along it his excellent cam timing tool which takes the hassle away of setting up a timing wheel, magnetic base, micrometer etc. Jaguar itself produces a similar tool (originally produced by Churchill's) albeit in STD form. Rob Beere allows you to advance the cam in increments. I did set up with its recommended setting, which is 4 degrees, trying to counter act the 105 LBA of inlet reverse impulse and over scavenging, therefore still keeping the 308 duration albeit with inlet and exhaust lobes opening and closing earlier, giving now 53 BTDC / 75 ABDC - 75 BBDC / 53 ATDC.
In hindsight, I should not have chosen such radical cam, even if I was going to use brand new four SU HIF44 carburettors, as weak vacuum signal would always be a problem at idle, coupled with poor manifold design and cold temperatures, it would enhance poor fuel vaporization, crippling fuel economy.
After talking with Mitsu, a Honda R&D engineer in Japan, who also was tuning his XJ-S for track days (apparently to swipe local competition from Supras, Skylines etc), he kindly informed me of his mods and that included a softer 282 cam, albeit with large size valves in Titanium, sourced from NASCAR racers (their life span, measured in life cycles, is very reduced to normal Nimonic 80 or Stainless valves, but OK in a race car).
I try to counteract this by increasing valve clearances, not much as I can't stand valves tapping noise, so instead of Kent Cams figures of 0.15mm for inlet, 0.20mm for exhaust, I went to great pain to adjust and shim all valves within 0.01mm, to give a more balanced cam figure (it's called blue printing, balancing all similar components to same weight, dimensions etc), achieving 0.18mm for inlet and 0.23 for exhaust, thus incrementing clearance by 0.03mm, reducing this way duration, admittedly by not much. Many thanks to Mitsu from Honda who kindly provided the oversize shims for the engine, produced in SK11 steel, apparently used in Honda racing motorcycles.
Ports were increased to 33.5mm on the inlet tract, keeping Jaguar original figure of 77% and exhaust was increased to 36.5, just over 100% relation valve/port. Valve seats were re cut for the oversized valves, altering for a triple cut of 45 (instead of original 44.5 degrees), 32/60, for better gas flow properties. New cores plugs were fitted and head were cleaned, removing sludge and other debris. Original double valve springs and retainers were kept as original specification is very high and use was quite low. Valve guide seals were fitted, not only on the inlet but also on the exhaust stems, trying to stem oil consumption, usually created by excessive oil film on the valve stems. Not a particular problem with Colsibro guides due to its high resistance to wear and heat, but notwithstanding, it was fairly economical to be done, so it was done.
Most likely this set up would work well with Weber downdraught carburettors but at £3000, I cannot justify the expense against the much superior independent throttle bodies EFI arrangement, so 12 x 39mm throttle bodies out of several BMW K1200RS' will be drafted along with a MegaSquirt ECU. Watch this space!
