Pistons are the obvious and well documented difference between normally aspirated and supercharged engines. The external components and ancillary setup is different. I am wondering if both engines use the same crankshaft, rods, cylinder heads, valves and so on. Other than pistons, are there any other differences in engine internals?

 

Valves are different. Dimensions are the same, speculation here is that the SC engine has a higher grade material. The heads do have a different part number, valve seats are the possible difference, as they do physically interchange.

You can browse the parts catalogue here: https://parts.jaguarlandroverclassic.com/

 

Cam timing is different, but profiles are the same. It is therefore possible to re-time NA cams as SC cams or vice versa, if you now how to set MOP timing , rather than using the slots on the cams.

 

Could you elaborate on what MOP timing is? That's not a term I've heard.

I have a XJR engine that I am swapping into a different car and when it was in the XJR it didn't feel particularly fast compared to my XJ6. It certainly didn't feel 75hp quicker. I know the head has been off previously and the valves done, I'm wondering if the cams were not set correctly? I'd like to check while I have the engine on a stand.

 

MOP stands for Maximum Opening Point. TDC is found by reacting a Dial Test Indicator on an adaptor screwed into the spark plug bore of cylinder No.1 and resting on the piston crown. A timing disc is mounted on the TV damper. The engine is turned to the MOP settings for the inlet and exhaust cams one at a time. The cam timing is adjusted using the slotted / vernier sprockets to achieve max lift at the MOP timing. In the case of the XJR engine this is 121deg aTDC for the inlet cam and 121deg bTDC for the exhaust cam.

If you just want to set the standard cams with standard timing, then you can use the Jaguar cam timing tool, which should engage in the slots in the cam at TDC No.1

 

Thanks! Is the standard setting optimum, or like your timing bracket can it be tweaked for additional performance? I'm putting the engine into a DS420, so I'm looking for maximum low end torque over high rpm horsepower.

 

Std cam timing on XJR is set for maximum power. Advancing the inlet cam and retarding the exhaust cam would reduce peak power but increase low speed torque. However, it will also make idle quality worse because it will increase valve overlap.If you would prefer such a compromise , then you could try re-timing each cam by 5-10 crank degrees. I wouldn't recommend changing the cam timing by more than this amount, as you might risk valve to piston clash

 

Andy,

I can't remember - is the compression in the S/C engines lower than in the N/A ones? If so, could that be one of the reasons for different heads?

Cheers,

Don

 

Yes, 8.5 SC, 10:1 N/A

 

I found this thread a bit late while building my 1995 AJ16 S/C engine. Trying to set the cam timing to MOP and get a different reading every time I move the dial indicator to a different cam or back to the other cam. I am using the the #6 cam lobe because it points up, (easy access) With button on moving end. When I time the lobe to be the maximum height, I then adjust the cam slightly to advance or retard to the specification of 121 BTDC exhaust or 121 ATDC intake. I get it close or on the number suggested. I then move the dial indicator to the other cam, set to spec. Go back to other cam, to recheck, and can't get same number I had before because the dial indicator was moved from previous cam. I've come to realize that I need a better way of measuring the MOP while the head is on the block. Any idea's or should I use two dial indicator's on each cam?

Thank you

Larry Louton





Using # 6 intake cam lobe for MOP on # 1 cylinder

 

Never mind, I mounted two dial indicators to each of both rear camshaft stands to monitor both camshafts at their timing points. Reset both camshafts to proper spec and now I am moving on.

Thank you.

Larry Louton