Is that picture from your car? I will definitely say they both look dished in that pic, but obviously it is an HE head. But factory specs definitely say the inlet valve is flat while the exhaust remains dished

 

Hi Warren
Again fantastic information, the first two options don't really do it for me but the third is brilliant. Simply bore to 92mm and use Holden 202 pistons that are 1/10th of the cost of the jag ones. I looked up this morning and nearly fell over at the cost of the Jag pistons and liners, you need a kings ransom to pay for them. I definitely have to look into that further, it will freshen the block and give it a little more.
I was mainly thinking of getting the extra power through head work and inlet manifold with extractors, most likely I will have build the extractors and alter the inlet myself, but with a T5 this will make a nice Sunday toy for the odd gathering now and then.

 

allen scotts book in final conclusion, mentions a stroke of at least 80mm, or best of 84mm, was the best mod you could do to a Jag V12!

and a holden 202 piston would not have the best crown shape for V12. of course they would run but not how you would expect.

and trying to save money on a serious hi-performance engine usually turns out disapointing.

 

Holden 202 pistons come in flat top and have been used successfully here in Aus. At least one V12 XJS Targa race car I know of uses these pistons.

I do agree that doing things on the cheap usually does not reap the rewards. I went the route of purchasing a complete 6.0L V12 and will use the crank, pistons, liners and heads to rebuild my engine.

Katoh

Talk to Brett Thomas, Thomas Jag he has done this mod, he also has full machine shop capability. He can cut multi-angle valves and has a crank grinder. Off set grinding the crank costs about $500 last time I inquired.

 

Gentlemen
Please don't get me wrong, I realise there is a mountain of difference between cheap and doing things on the cheap. I am personally not building a race car here but would love to spend the money on stroking and boring ect, but I must put things in perspective and funds where they should go.
Still love the idea of the 202 pistons as my new motor still will need bearings and pistons/rings just for a freshen up, to save nearly $1200 on parts that was going to buy anyhow is a huge saving.
When it comes to heads, I will be sourcing them out, let the pros do it. Other things like opening up the inlet manifold and building a set of growlers, I can manage, same as extractors, but more than likely I will just build them out of black steel. The other thing I am seriously looking into is megasquirt for fuel and spark, I think there is more hp to be had just in that, also it may eliminate a lot of the gremlins we have.

 

I don't think using 202 race pistons is doing things on the cheap, there are Toranas in the historic class making 300hp with these pistons in a OHV cast iron I6.

Talk to Nass at Thorleigh Cylinder heads, they know the Jag V12 and were referred to me by someone in the Jag club. I spoke to the guy there and he knew exactly what to do to get the V12 HE breathing better. They quoted me $350 per head for the multi angle valve job.

 

Warren I was not implying that the Torana pistons are cheap(rubbish) far from it, what I am trying to say is I can buy 12 202 flat top racing pistons for $800 with molly rings where a set of Jag pistons to 92mm will cost me over $150 each that's over 2k with shipping, no that is why the 202 pistons are cheap or should I say a Bargain.

 

I was replying to Ron he is probably not aware that the 202 race pistons are excellent quality and plentiful here in Aus.

I looked at the 202 pistons before I bought the 6.0L V12. As I said Brett Thomas has experience with these. Be prepared for some machine work on the pistons, the pin holes will need to be modified.

 

Warrjon
Are these Holden pistons a direct swap for standard V12 5.3 HE pistons? It seems that replacement pistons are now NLA in the UK from Jaguar or specialists. If not, has anyone any ideas what to use in a standard rebuild ?

Thanks
Greg

 

Hi Greg,

No they are 92mm with a press fit pin, the pin needs machining as the compression height is different, but even with these mods they are good value if you plan to bore the liners.

I don't know of any direct swap pistons for the V12.

 

in the states we can have custom forged race pistons made for around $150.each.

a st of TotalSeal gapless rings.

thats what i would do, all specs reviewed before actual manufactured, call and talk to the guys, they always have some good ideas. after all they are in the custom piston business.
its the piston crown shape of most interest to me, all othe specs would be advised by them.

 

i read on the net, that MAHLE has a direct fit piston available for JAG v12!

mahle is a world leader in piston technology, very advanced manufacturing ideas.

 

Got a link, RB ? If Mahle are good enough for the Great James Hunt, they are good enough for me. Right here on my desk I have a mahle piston from the very engine he used in Japan to win the F1 World Drivers' Championship

Greg

 

I used ross custom pistons.and.they cost 2000$ for the set witj expedited ordering so they arrived in a week.

 

I didn't see (though I may have missed it) any reference to the specific combustion chamber size difference between 5.3 and 6.0. And what that means in terms of compression ratios/performance. Does anyone know? The heads on my '89 XJ-S are badly corroded and supposedly "beyond repair" but I have access to a nice set of 6.0L heads. Would that be a straight forward swap? One of my Jaguar professional acquaintances says it isn't a good swap but I am curious if there are other opinions or considerations. I am not racing or anything, just driving around, although I do enjoy a little power every now-and-then. Thank you.

 

I was once told by an engine guy (when i too was looking at a pair of new 6 litre heads) that the 6 litre head on a 5.3 block will reduce the CR to about 9:1. The chamber is larger on the 6 litre to accommodate the longer stroke of that engine and not therefore get a sky-high ratio. The engine will run but lose the efficiency of the design.
Warrjon knows all about chamber sizes, so he will chime in perhaps.

 

I didnt CC the stock 6.0 head as the valves were leaking and it would not hold fluid, so I'm not sure what the stock CC is. IIRC the 5.3 is about 27cc and guessing the 6.0L is about 33cc if yours is a 11.5:1 then this would drop CR to approx 10:1.

You could plane the head, but you need to be careful as the water jacket is close to the surface around the intake valve. I don't remember what the thickness is there but you should be ok with 0.005" - 0.010"