For the supercharged AJ-V8, new dished pistons (instead of flat topped) were fitted for a revised 9:1 compression ratio. The pistons of high strength aluminium alloy were designed to resist high thermal and mechanical loads of the supercharged engine. Other changes included: new crankshaft damper; new inlet cam sprocket (shared with the 3.2-litre); new cylinder head gasket featuring stainless steel bore eyelets in place of mild steel; new intake system with a pair of intercoolers, one for each bank of the engine and an improved intake with a larger inlet and an extra resonator to match the supercharger’s needs. Running at 1,600 rpm the supercharged AJ-V8 was producing more torque than the naturally aspirated AJ-V8 at its optimum. The supercharged engine did not use variable cam timing as the normal benefits of improved volumetric efficiencywere not noticeable on the boosted engine.

The only thing for sure about the difference between the two short blocks are the lower compression pistons. The XKR does not have VVT, but I'd bet oil system ought to still power the the XK8 variable intake cam as it shares that oil feed with the upper cam chain tensioner. It seems the head gaskets are interchangeable, so that's a good sign.

I'd suggest starting with a $5 Bluetooth OBDII scanner (or pay a tad more for a wired scanner) and eliminate the simple variables before thinking about a laborious, time consuming task of removing, rebuilding a complicated engine and then reinstalling it. Too bad the mechanic didn't take the next logical step and perform a leakdown test to either find a mechanical deficiency to repair or eliminate hardware as the problem and shift the focus elsewhere.

 

Hi all;
I replaced the driverside O2 sensors. Engine is running better,and the gas mileage is creeping up. The convertor is apparently OK, no codes. Mechanic says engine running fine. But , between 1500 and 3000 rpm under load, car vibrates. Now that we,ve ruled out O2 or convertor , and apparently the engine in general, mechanic swears it,s coming from drivetrain. To catch up 98 convertible 102,000 miles. I just recently replaced the trans with a used unit from an xj with 58.000 miles. replacement box and convertor were serviced before install. Had bad vibration after install. Was driveshaft with big dent on side. Was mystery how that happened as shaft never left car. Trans shop replaced shaft with used unit. I,m guessing there were 2 seperate issues at play here. Dead O2 sensors, and whatever this is in driveline. My european car specialist stumped. Anybody have any idea what this could be? At least overall, car getting better, so I know it,ll get fixed eventually, but this is dragging on.
Thanx
Don

 

If the engine is generating the vibration, chances are good the ECU will create faults for "engine misfire." If no codes, the engine is likely running smooth enough not to create the issue, so engine, flexplate and torque converter can be removed from your checklist.

If you say it is an rpm related problem, run the car in that range in all the different gears to see if it happens exclusively within that engine speed.

It is more likely a vibration related to vehicle speed from drivetrain, shocks, brakes or wheels & tires. Make sure tire pressures are correct. Replacement driveshaft would be at the top of my list. I'd try attaching a dial indicator on the floorpan and rotate the driveshaft to see how far out it is. You don't even need an indicator, just a magnet with steel rod along side of the shaft can give good measurements with feeler strips but chances are, it will probably be quite obvious just eyeballing it whether it is true or way out..

 

Hi all, i know it,s been a while. car still had a vibration, altho less than before, which is why i thought it was something else, probably engine related. I took it to a european [read;german] car shop. They confirmed that the vibration between 30 and 50 , and worse uphill was certainly drivetrain related but they didn,t have the time to figure it out. At least they didn't charge me. Then I took it to a new shop. Turns out that one of the 6 flex disc mounting bolts was missing. So, to recap, somewhere between the shop that changed the trans, to the place that replaced the driveshaft, to the next place, someone forgot a bolt and the rest didn't see it. Next, while the current shop is waiting for a new bolt from the dealer,[it's been weeks], i've been looking for a used replacement. Finally i found the dimensions of said bolt and found same in the machine shop i work. I put bolt in today. No vibration, The car is now somewhat back to normal, it's smooth and gas mileage has crept up to over21. That circus did not afirm my faith in car repair shops. Thanx for reading my rant.
Don

 

Persistence pays!
I always enjoy a reading a mystery story over most TV programming these days. Too bad it was a mechanic oversight, but there are so many items to insure a proper job on modern equipment.
Your rant was entertaininly informative. Glad your feline steed is back to its intended, if aged condition.

 

Well done....

 

And this is why I prefer to work on my cat myself whenever possible.