Has anyone ever attempted to Turbo or Twin Turbo the 4L in the XK8... Or possibly doing an engine swap with the XJS V12? (not that I'm convinced the V12 would fit)

 

The conventional answer is that you are better off getting an XKR. The long answer is that the N/A 4.0 and 4.2 compression are somewhat high compression; 10.5:1. To avoid engine damage, you would have to swap to the XKR lower compression pistons or custom pistons, or run very very low boost pressures. At that point, is it cost-effective to turbo an XK8 when an XKR can be had for a nominal amount more and is already supercharged, and thus has more power potential?

What I haven't seen is anyone twin-charging an XKR. We have seen swapping the roots supercharger for a twin-screw. Upwards of 600 wHP can be had that way. However, what if you keep the stock supercharger and add a turbo? Perhaps that's too complicated and maybe there isn't enough space in the engine bay for the turbo and another intercooler.

The V12 might fit. The XK8 is based off of a heavily updated XJS chassis, the same applies to the DB7 to a lesser degree.The dimensions of the engine bay are possibly close to the XJS's and could allow the V-12 to fit. However, that mess of vacuum lines and other stuff gives me nightmares. The DB7's V12 might be an alternative. Either V12 is bound to be a tight fit, and I think you will need to make custom motor mount brackets. If you do a swap, you will also need to swap electronics and possibly a transmission (get a manual), unless you want the gauge cluster to throw a hissy fit and display the wrong part message.

 

Adding to what's already mentioned, a centrifugal supercharger might be a option. A lot easier fit compared to a twin turbo installation. But the problem with compression ratio should be the same here, not much boost to apply before risking the engine

 

Or you could swap in an LS motor and trans like I did recently... great performance (with unlimited options for increased horsepower) coupled with solid reliability. The biggest issue with the 4.0L n/a cars is the crappy ZF 5-speed transmission... it's a ticking time bomb that made me decide to swap it all out when my motor threw a rod with 38,500 miles on the odometer. My car is like a brand new car now... couldn't be happier!!

 

TurboCharging a SuperCharged engine might net some HP because it takes about 60 crankshaft HP to run an Eaton M112 at 12,000 RPM at boost.

Finding room in the engine bay might prove difficult. (maybe in place of the cataverters?)

 

Cpoling1983,

The problem with Turbos is they need mid-range revs to generate max boost and you don’t have revving freedom when coupled to an auto transmission. I suppose it could be specially mapped to eliminate the apparent lag but why do it when the compressor system has already been engineered on the XKR ?

 

Unfortunately my cat has been down for a while and cant bring myself to sell it and Ive got a couple turbos sitting around collecting dust. As for compression, I knew of an XJ that was twin turbo-ed featured on Top Gear... Anyway that's where I had the Idea while making plans for my xk8 while trying to recuperate from this cancer BS keeping me from working on my cars... But I'd Love an XKR or LS Swapped XK with a T-56, but then again I'm getting away from the British experience. Who am I kidding, I grew up working on american muscle, I Love experimentation, Pushing limits and Custom everything. With my engineering background I really hope once my Jag is up to par, I get to do some of the 007 stuff Ive designed... looks good on blueprints (promise it'll only be used for shows), Not many non-Jag lovers know the Xk was once a James Bond car... And if I get to do what I want, which my wife probably will not allow it, it would be a true 007 Ride! Thank you for your guys' input! I absolutely love this forum!