Originally Posted by XJRengineer

The 4.0L AJ6/AJ16 engine is indeed a long stroke (90mm bore x 102mm stroke) engine so is better suited to producing high torque at lower speed than making high specific power (eg 100bhp/litre) at higher speeds. The 4.0L AJ16 engine produces 400Nm (ie 100Nm/litre) which is still to this day a respectable output for a naturally aspirated engine, especially one without variable valve timing or direct injection and without the benefit of any computer simulation techniques to help with optimisation. With its 102mm log stroke, it would be difficult to tune the engine to produce peak power at a high engine speed, by modern standards. However, it would be quite practical to tune this engine to produce peak power at over 6000rpm, as this would only equate to 20.2m/s mean piston speed. This is quite a modest piston speed to make peak power. The 3.8 litre 6 cylinder BMW M5 engine of the same period produced its peak power at 21.8m/s with its 94.6mm stroke engine running at 6,900rpm. The standard rev limiter on the AJ16 engine is set at 5,950rpm, but could be raised by reprogamming the ECU. I would disagree that the port design of the AJ16 is in some way inherently unsuitable for producing high power outputs. The valve/ piston area ratio is reasonable for a 4 valve pent roof combustion chamber design. The mean port velocities would be reasonable (108m/s) at a mean piston speed of 20m/s. The port to valve angle axis is about 40 degrees and the intersection of port to valve axis allows for a large inner corner radius. With careful modification it is quite possible to achieve a port flow coefficient of over 0.68 at high valve lifts. This is quite respectable. If the cam profiles, intake and exhaust geometries were optimised to produce peak power at 6000rpm, it should be possible to produce about 300bhp from a Jaguar AJ16 engine. However, nobody has ever commissioned me to produce such an engine for them.

Originally Posted by XJRengineer

Over-boring a 3.6L engine in order to create a less under-square engine of a larger capacity seems like a lot of work., but feel free to have a go.


These engines have never been developed to run beyond 5950rpm, so I don't know what would be required in order to get them to reliably run at much higher speeds. They did suffer from torsional vibration problems with the crankshaft due to its length and long stroke. Unless you want to make peak above at very high speeds, the 102mm stroke isn't really the limiting factor. 7000rpm equates to a mean piston speed of 24m/s. This is quite routine for high specific output naturally aspirated engines. However the mean port velocity will be quite high on a standard AJ6/AJ16 cylinder head by this point, so the valves and ports would need to be enlarged if there is enough wall thickness in the casting.

Originally Posted by juha_teuvonnen

Catching resonance harmonics and breaking the crank is something that scares me, when it comes to revving an i6 engine high. While enlarging the ports will allow the engine to breathe at high RPM, it will necessarily sacrifice some low end torque. You can't have both without VVT, sadly.

I looked at an XJR6 today. I kinda like it, but it has a bit of a lag when accelerating. Otherwise it looks nice and clean. I am wondering if I should start with a less ambitious project. Has anyone on this board used an m90/m112 hybrid supercharger, or an aftermarket positive displacement unit?

Originally Posted by countyjag

Juha,
If you found the acceleration in an XJR disappointing, I am wondering whether the luxury saloon sector will be the best way to meet your requirements, but given your concern with resonance in an in line six cylinder crankshaft, and desire for an m112 supercharger, might I suggest an X308 XJR? A much simpler and cheaper option, although for what it is worth, in my view the x300 is the better car.

Originally Posted by countyjag

Juha,
If you found the acceleration in an XJR disappointing, I am wondering whether the luxury saloon sector will be the best way to meet your requirements, but given your concern with resonance in an in line six cylinder crankshaft, and desire for an m112 supercharger, might I suggest an X308 XJR? A much simpler and cheaper option, although for what it is worth, in my view the x300 is the better car.

Originally Posted by AL NZ

I think, from memory, peak torque is at 3050rpm, and is about 500Nm
My XJR has the powerhouse drive pulley which is 10% bigger, and maxes out the airflow meter at about 4000-4500 rpm. It has great torque from 2500-4000 rpm.