hello
Im a NYC resident and my dalily car is a xjs coupe 1985, which I love. Since this car, due to her age is free to do the yearly emission test in my state, I was wondering what it would be necessary to bring the engine from the actual us specs to the less restrictive and happier British specs. Out of the states the v12 5.3-litre HE was working a higher compression. what elements on the US version should be modified?

 

You've already mentioned the higher compression ratio....but that's not something easily changed.

I'm guessing ignition advance is the next most significant difference and you can probably replicate the UK/Euro scheme fairly easily.....although simply using a direct ported vacuum hook-up is likely as good as it gets. The distributor itself and the vacuum advance capsule were the same for all markets.

After that, catalytic converters.....although those may have been included in UK spec by 1985. I dunno.

Cheers
DD

 

Doug has answered it pretty well.

We got the 12.5:1 engine also, and almost NO emissions on the '85, and NO cats until '88.

The comp ratio will require piston change and I reckon the 11.5 engines did have a different cam lobe profile, but that is from memory, so if I am incorrect, so be it.

I found some PreHE carby camshafts for mine, and that really transformed the thing, but I ramble too much.

Open the exhaust up to 2" thru the rear cradle, and that will assist a little also.

Redialing the camshaft timing will also bring the beast back "on song", and compensate for the stretch of the chain.

That port take off for the vac advance is what I do to any I get at.