Hey everyone, I’m considering buying a 1998-2003 Jaguar XJ8 or XJR, and I’m planning an engine swap to improve reliability and power. My goal is to keep the original transmission and drivetrain intact, but I’m looking for a more reliable V8 engine that can either bolt onto the existing transmission or be adapted to fit.

I’m hoping to hear from anyone who has done similar swaps or has experience with these options. What engine would you recommend for this project, and what challenges should I be aware of?

Thanks in advance for your input

If you base a build on the transmission, it's not the XJ8. That gearbox has very well documented issues. The XJR trans is built for the added torque of the supercharged engine.
Dare I say these engines are as reliable as their servicing internals, I know of 300K mile units that have produced 370bhp front day one and never had one issue. It's a fallacy they're unreliable.

If I was doing this today, I would put a battery and a couple of tesla motors in one.

Search the forum for LS conversions, there's a few threads on it. You'll be changing the box too though.

As said by others though, these cars aren't unreliable in standard form.

Yea I would not plan to keep the xj8 zf with another v8.

The only idea kicking around in my head is to put in lt4 supercharged v8 with the 8l90e 8 speed. They make a $20k package that has most of what you need plus the jagspecialties stuff.

Its true that the" sealed for life" tranny may have issues
if not serviced well. (after what Jaguar considered it's
anticipated "life") It is also true that they can last considerably
longer if they are serviced well.















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As @Hooli mentioned, there are several of us that have done LS swaps, I am one of them. You can do something silly like I did (LS3 with 500hp/6L80E into XJR) or practical like @pcolapacker did (6.2 L99/6L80E in XJ8) that will still burn the tires off if you wanted to. Both options are well documented and with the aforementioned Jaguar Specialties kit, you get a car with fully functioning dash, gauges, HVAC etc. There are at least two other builds active right now that I know of, but neither has threads here. I daily drove a 2001 XJR while building the LS-powered one and it's plenty quick in stock form.