4.2 vs 3.8 Cylinder Head Question

[TheMadBadger]

Good evening,
My ‘68 E-type has a 4.2 bottom end from a ‘67 Mk10, with a 3.8 E-type cylinder head and 4.2 type triple SU carbs and manifold. I have a rebuilt 4.2 E-type head I am in the process of swapping onto the engine. When pulling the intake manifold I discovered the plugged round water passages in the head, but these correspond to open water passages in the intake manifold.
Should these plugs in the 3.8 head be removed? I have plans for this 3.8 head for future use on a ‘67 3.8S bottom end that might one day be used in a C-type replica, if I live long enough.

Thanks for the advice
Mark

[mgcjag]

Hi Mark....if fitting a 3.8 manifold to a 4.2 head then you need to fit those plugs in the 4.2 head....so i would think its a reasonable assumption that you need to remove the plugs in the 3.8 head when fitting a 4.2 manifold.....on a 4.2 head to 4.2 manifold these are open.......Steve

[TheMadBadger]

Thanks Steve. That seems to be the common sense answer. Match the cooling passages to whatever intake I would be using. Speaking of intakes, I like this twin carb intake. I think it would look good on a C-type replica. Does anyone recognize it?

Mark

[mgcjag]

Hi Mark ...yes its a Realm C type replica.....xj6 S1/2 manifold with twin HS8,s...very similar to the one im building...im useing HD8,s but with these nice top fakery sandcast look slip on covers ...Steve

[abowie]

As Steve says, looks to be XJ6. There will be a number of holes in the bottom that need tapping and plugging.

I'm using one of these on my Mk2 which has a 4.2 motor.

[TheMadBadger]

Ok thanks for the replies. The big question now becomes do SU carbs bolt onto the US XJ6 Stromberg manifold? I’ve always wondered about that when looking at my ‘71 E-type with Strombergs.

I’ve had my eye out looking for a 3.8 intake and carb setup for quite a while and they just don’t show up here, so it might have to be the XJ6 intake.

Mark

[mgcjag]

Hi Mark.....not a straight fit but see here viewtopic.php?t=4137

......get yourself on the US Jag lovers forum they also have a classified section as we do here.......iv seen 3.8 setups..xj6 manifolds etc....just post what your after someone will have it on there.....Steve

[Geoff Allam]

Mark. Yes hd8's bolt onto xj series 2 manifolds. No experience with series 1 or 3. I did it on my series 2 xj6 years ago. The su's are slightly longer than the strombergs so e type under bonnet clearance would need to be checked and air cleaner fitment might require some modification. I did it to get rid of the god awful water chokes on the xj6 and it did make tuning easier. At the time needle change was not needed but the piston spring did need to be changed to richen the mixture a bit at cruising speed.

[christopher storey]

M At the time needle change was not needed but the piston spring did need to be changed to richen the mixture a bit at cruising speed.

I tell you this with some diffidence, Geoff, but the function of the springs is only to ensure that the pistons reach full lift only at full throttle and full power rpm . If you use a stronger spring to richen part throttle mixture your calibration at most speeds will be woefully inaccurate ( and usually over-rich) . If you can, go back to the original springs, and select a needle which is richer at the lower to mid shank level to richen the cruise mixture. The charts of needle specs are easily downloadable

[Geoff Allam]

That is not entirely correct. Remember this was a series 2xj6. If you check the specs for hd8's on a xj6 you will find that the springs specified are different than the springs specified for e types or even mk 10/420g. The car has been parked for over 20 years so I am not changing needles now! Btw, with the hd8's power and fuel economy were both improved over the strombergs. I am not suggesting that either needles or springs should be changed on a 2 carb e type. Just reporting what worked on my xj6.

[TheMadBadger]

Hi Mark.....not a straight fit but see here viewtopic.php?t=4137

......get yourself on the US Jag lovers forum they also have a classified section as we do here.......iv seen 3.8 setups..xj6 manifolds etc....just post what your after someone will have it on there.....Steve

Thanks Steve, and everyone else for replies.

Mark