Both. I know Norman has built 6.0L (95mm bore 70mm stroke) in pre-HE that made 500hp @ 7500rpm in street trim. The piston CR height is the same for HE and pre-HE with the Jaguar 6.0L (78.5mm stroke) being different. A 6.7L HE still makes enough torque to twist drive shafts somewhere around 500-600ftlb.

What limits power in the HE - The intake valve size is limited by the step where the exhaust valve pocket is. A 500hp NA V12 requires an intake valve that would be too close to the step and it would crack the head.

A pre-HE 6.7L would make 600hp with big valves, fast road cams and a good intake.

All the other 6.7L Norm has built have made about 400hp. But this is a bit academic because my heads have had the chambers modified and intake/exhaust ports matched but have kept stock camshaft and valve size, which will limit peak power but should make more power low in the RPM band (TORQUE).

 

Just in case you'd like to have a complete running engine. I still have a HE V12. It's still in my 89 XJS Parts car. Probably easier, and cheaper then finding pistons for yours. I'd sell the engine, and trans for $800.00. I'm in the Central US Arkansas to be exact. Let me know if interested.

Jack

 

Are you sure you need new pistons? I’ve taken apart more than 50 V12’s over the decades and unless there is obvious damage very few pistons need replacement. Some engines with over 100,000 miles on them still measure within factory specs. The reason wear is so minor on the V12’s is several things.
First
with its tiny short stroke and very long ( relatively ) connecting rod side thrust on the piston is absolutely minimal.
Second
these engines tend not to be abused by their older owners. Who because of the expense and complexity of the car tend to warm up gently, change oil on schedule, and seldom if ever race them.
Third
Because of the short stroke piston speed remains very slow compared to ordinary engines.
I used to carefully clean them and stored them for decades. Never once found a rebuildable engine to use them in. Eventually sold them all for scrap.
I realize this is one of those things everybody replaces, •••••while they are in there. But I’ve never had one that caused me to regret it

 

They do when the bore is 5mm bigger than the piston

 

Well that’s very unusual. I’ve pulled apart around 50 V12’s and except for obvious damage seldom found much measurable wear. The only time wear in that order was discovered the owner had driven it over 30 miles with oil pumping on the ground due to a loose oil filter.
The problem was the cam journals were shot, the bearings were shot, there was so much wear it would have been smarter to spend $300-500 and get another engine.

 

I think Warren was jokingly referring to having the bore increased by 5mm.

 

yeah we get it,, MG has a tendency to exagerate sometimes!! about yesterdays stuff!