cam timing change

[twigworker]

I am in the middle of doing a normal valve adjustment on an 85 XJ6 and started wondering about the possibility of advancing the intake cam a few degrees. The thought occurred to me that the factory may have dropped the cams back a little from earlier specs in order to help with the emissions, something like the MG factory did to their single carb cars.

The car runs well enough as it is being set with OEM cam and ignition timing but I just thought that a little tweek might be a pleasant surprise for the owner.

My question is, has anyone had any real world experience with advancing the cams on these emission cars, and if so how far did you go and did you deal both cams or only the intake?

Jack

Edit: I am thinking 4 cam degrees or so, and probably both cams. Does this sound abvout right?

 

[Deleted member 8987]

I am going way back in the memory department, but advancing the intake gave you more low end, less top.
Advancing the exhaust cam gave you more top and less bottom end.
Or something like that.

The cam timing from the factory was set to give you the best of both.

One check would be to find what the factory lift point was on the cams for earlier XK engines and then check yours with a dial indicator.

 

[LarryK]

All cams were set with the same cam timing tool. Timing was advanced or retarded by distributor timing. Race cams were involved with dial indicators and were not used on the fuel injected cars. Too many resistor resets for the computer would have to be made. Arden and AJ Engineering makes a tuned computer and air boxes for the XJ6s and would be the best way to go.

 

[DrEntropy]

Arden and AJ Engineering makes a tuned computer and air boxes for the XJ6s and would be the best way to go.

That's th' truth, Jack. Larry hit it. "Fuel management" will end up being in charge, with a net gain of more twiddling than it's worth.

Better to stuff an older 4.2 with triple SU's in it and give th' bumpstix a bit of overlap.

:laugh:

 

[LarryK]

A lot of the early XJ6s with fuel injection were improved by replacing manifolds with the AJ40 manifolds and injections systems. Still able to use same ECU or even change ECUs with the 40s.