I am having a full rebuild and modification to my 3.8 mk 2 byPaul adams at Classic and modern engine services Bracknell.
He has suggesteda later 4.2 head with it's big valves and straight port head,and 276 cams.He said he can modify it so it looks the same (with appropriate blanking)as the existing head.
several questions please :
inlet manifold :
It presumably has to change or modified.what can I use?my 1.75 su's are good for the job,but what about HS8's ,and why does everyone roll their eyes when these are mentioned (as opposed to the expensive HD8's?)
What kit from which model would bolt on and do the job for me.
I have a 2 inch stainless inlet manifold.Is that ok for the later head?
Secondly
whilst the engine is out,any other useful upgrades I can go for?I have power steering,electronic ignition,havey bailey,adjustable gaz shock absorbers ,sorted heater etc .Is there a bigger capacity radiator without going to the expense of an alloy radiator,does anyone fit catch tanks,swirl pots etc?Where would I go ?
Lastly I have an alll synchro with overdrive gearbox with the overdrive button on the top of the stick.Is this appropriate for the mk2and can I move the overdrive function back onto the column?
thank you for your help,apologies it is longwinded.
sandy
head upgrade 3.8
Moderators:Aceman, ecosselynx
Hi Sandy,
Since I found out from an accurate rolling road that my 3.8 MkII only made 110bhp at the axle (approx 160bhp at the flywheel), down 10bhp due to gas carbs, I also started looking for ways to increase power. I found out that the power is about right and a 4.2 E type only makes 185 ish!!!!
Standard 3.8 'B' type heads use either the old 2 HD6 carb manifold or the 3 individual manifolds (E type) to used 3 HD8's. Later 'straight port' heads use later type manifolds (340, 420 2 carb or 4.2 E type 3 carb). But an old article by Ken Jenkins says the old 3.8 manifold can be opened out to fit the HD8's but only fits the 'B' head. 3 carb manifold will mean removing the clutch and brake master cylinders
Carb's:- the HD carbs are supposed to be better quality than HS carbs and have stuffing boxes on the throttle spindle to stop grit chewing up the bearing and spindle resulting in air leaks and rough running. The HD has the jet sealed by a diaphragm. HS carbs are shorter than HD's. I believe there are also minor differences but you would be better talking to 'Burlen Fuels' 01722 412500 as they are the experts. Fit HD8's and there is very little space for an air filter (engine will wear out very quickly with a filter). I've still got 4 HD8's from an XJ6 ser II, threw the manifold away years ago as it wouldn't fit the MkII.
A 2" SS manifold, where did that come from? it must be very heavy.
The modern tuning senario seems to be +9 : 1 CR, Late XJ6 big valve straight port head and high lift not high duration cams with fuel injection. As the XK head is hemispherical and now seen as inefficient, power is possible if worked correctly but loss of mpg is guaranteed. Torque is more important than BHP.
I fitted a reworked D45 distributor in place of the rubbish DMBZ6 one and although smoother and better mpg the well known company threw it together and it failed later. I'll be using an ECU and coil pack next for individual ignition maps.
What power output and mpg have you been promised, or only suggested?
In an attempt to get my wife to drive the car (complaints that she didn't know where the switches were) I managed to cram a sierra 3 stalk system below the steering wheel to control everything and replaced the plastic with SS stalks plus a big red light on the lower dash for overdrive, all operating relays. She still won't drive it.
I'm no expert but above is from old articles that I've stored and my own measurements.
I would be very interested to hear how you get on.
Brian
Brian
Since I found out from an accurate rolling road that my 3.8 MkII only made 110bhp at the axle (approx 160bhp at the flywheel), down 10bhp due to gas carbs, I also started looking for ways to increase power. I found out that the power is about right and a 4.2 E type only makes 185 ish!!!!
Standard 3.8 'B' type heads use either the old 2 HD6 carb manifold or the 3 individual manifolds (E type) to used 3 HD8's. Later 'straight port' heads use later type manifolds (340, 420 2 carb or 4.2 E type 3 carb). But an old article by Ken Jenkins says the old 3.8 manifold can be opened out to fit the HD8's but only fits the 'B' head. 3 carb manifold will mean removing the clutch and brake master cylinders
Carb's:- the HD carbs are supposed to be better quality than HS carbs and have stuffing boxes on the throttle spindle to stop grit chewing up the bearing and spindle resulting in air leaks and rough running. The HD has the jet sealed by a diaphragm. HS carbs are shorter than HD's. I believe there are also minor differences but you would be better talking to 'Burlen Fuels' 01722 412500 as they are the experts. Fit HD8's and there is very little space for an air filter (engine will wear out very quickly with a filter). I've still got 4 HD8's from an XJ6 ser II, threw the manifold away years ago as it wouldn't fit the MkII.
A 2" SS manifold, where did that come from? it must be very heavy.
The modern tuning senario seems to be +9 : 1 CR, Late XJ6 big valve straight port head and high lift not high duration cams with fuel injection. As the XK head is hemispherical and now seen as inefficient, power is possible if worked correctly but loss of mpg is guaranteed. Torque is more important than BHP.
I fitted a reworked D45 distributor in place of the rubbish DMBZ6 one and although smoother and better mpg the well known company threw it together and it failed later. I'll be using an ECU and coil pack next for individual ignition maps.
What power output and mpg have you been promised, or only suggested?
In an attempt to get my wife to drive the car (complaints that she didn't know where the switches were) I managed to cram a sierra 3 stalk system below the steering wheel to control everything and replaced the plastic with SS stalks plus a big red light on the lower dash for overdrive, all operating relays. She still won't drive it.
I'm no expert but above is from old articles that I've stored and my own measurements.
I would be very interested to hear how you get on.
Brian
Brian
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