They are forged Cosworth items and exhausted in supply for their original purpose.

 

That is rather discouraging news xjr5006. Is there a suitable substitute available, that you know of?

 

Zilla , spend the money for a proper made forged piston, know what you want , order it, 12 pieces, and be done with the subject.

we have many custom piston manufactures here in USA, even MAHLE has a plant here now!

you will have more things to think about before all is said and done! like the final piston crown shape, things like swirl, turbulence, squish, homogenized mixture control,ETC.

i have bought custom forged pistons for for around $100.-135. each, depending on how many are made, and how much lightening is recomended,of course TOTAL SEAL rings.

 

looking at the pix, 1st on left, is a 5.3 HE piston ,flat top.

center is a preHE piston, bowl in piston top.

3rd must be a custom forged HE style piston(Cosworth), looks like slight valve reliefs and pressure relief grooves above top ring.

and i think 7-7.5 compression ratio is to low(would not make much torque until boost has come up), my preference would be around 8.5-9.0 to 1, boost limits around 12psi .

also a known weak link in the Jag V12 ,is the open deck block, sealing can be an important project, gas filled liner rings(Coopers and other makes) seems to be the best way,(at this time at least).

Grp44 and TWR lost more than a race because of coolant loss, just say you have a perfect running engine, and no overheat probs. then you may start to blow out cooling(just a little per lap,2-3 oz) but you got 20-50 laps to go, I seen 44 go 20-22 hours at speed in Daytona 24, then lose out because of overheat.

i'm not a great believer in a comp plate, unless done properly, like shorten the block and welding on the plate(or leave stock hite), and use a long stroke shaft, liners pressed in and O-ring sealed top and bottom!

Heck ,may as well cast some custom Mag blocks, made to order,closed deck, its only money!!

 

Ron,
Actually, 7-7.5 is just about right for what I want to do, and the way in which I want to go about it. Twincharging (Quadcharging?) is the name of the game. Torque won't be a problem, because there will be two small, positive displacement superchargers (Eaton M90, Toyota SC14) stuffing air into the motor from idle up to about 3200rpm, where the turbos should seamlessly pick up the action and carry things up to redline.

Let me say right here that I am NOT throwing my hat in the ring for building a forced induction V12 at this time. I have too many other expensive projects lined up for the coming year, including earning a private pilot certification (about $7k). I'm just thinking out loud about the best & most cost-effective way to put a consistent 600-700 hp on the ground with a V12, and I'm echoing the thoughts of better minds than mine, which have already theorized about such things on this forum in the past (and, If I'm honest with myself, I'm probably talking myself into doing it. lol).

I already have a spare H.E. with ported heads, which needs pistons anyways, and I have an Electromotive unit to handle fuel & timing. I can get rebuilt M90s or SC14s for $400 or less all day long, and new GT45 turbos for under $250 each. I would just need a set of forged pistons with a lower CR, larger injectors, matched to the fueling requirements, and to figure out the plumbing.

But, as I said, at this point, it's all about just floating some ideas out there, getting opinions form guys much more knowledgeable about such things than me...and maybe inspiring someone else out to take that plunge in the process.

 

I am a big fan of twincharging, however I think with the limited space in the XJS engine bay it may be almost impossible to fit everything in. I have seen a TT XJS and had a good look over it and there was no room left for SC's.

With electronic ignition the V12 has much better low torque than the earlier V12's, lowering the CR to 8.5:1 by modifying the chamber in the head and then a couple of large turbo's.

Believe me this will provide enough torque to light up a set of 280/680 17 slicks, I have seen it with my own eyes at Eastern creek

 

Warren,

You were exactly the person I wanted to hear from on this, since it was you who put the thought in my head when I recently read the conversation that took place between you, and M90power in 2011, on the Twin Turbo V12 Project thread.

I'm pretty sure there will be room enough for everything, because, if I were to go that route, I would have absolutely no intention of completely concealing all of it under the bonnet.

While I'm sure you're right that two properly sized turbos and 8.5:1 CR would be more than adequate, the smooth linear power delivery of the V12 would be interrupted by turbo lag. I really like the whine of a supercharger. I can only imagine how two of them would sound. But, we also know that, left unaccompanied, those blowers will run out of steam long before the V12 hits its peak. A pair of turbos are just the thing to carry it further.

Is it wretched excess? Yes, but, I've never been one for subtlety, and, I can think of no better way to help JagZilla live up to its name. Perhaps, I'll do it....someday.

 

Zilla, thats a marvelous dream, but what i can see is who is going to tune it up and make it run smoothly?

it has to start up and idle.
it has to respond smoothly.
it has to run out thru the entire rpm range, part throttle, full throttle,smoothly.
it has to not over heat, in most conditions.
it has to stay together for some extended power runs.

the most interesting would be transistions from supercharging to turbocharging in a reasonable fashion, i dont think 12 injectors would be enough, 24 injectors maybe!

YUP! a tuning nightmare, it would require a much better Electromotive than ECU 1,
computer would go nuts trying to keep an A/F ratio and ignition timing ,so as to not blowup the engine, and control manifold pressures going from negative to positive, opening flaps and valves ETC. in the piping of inlets sides and hot side exhausts!

but HEY , go for it, we see what happened to the guy who started this long thread 3yrs ago?

and lets not forget the money involved, i think i''ll dream of my XJS Diesel!!, 700hp 850lbs.ft. super reliable/dependable, much better MPG, and quiet!!

Dreams are one thing ,,reality is another!

 

That's the beauty of these forums. I can write out some crazy idea I have, and my rationalization for why I think it might work, and, have people with more experience, reveal all the details that I either didn't think of, or, didn't know about.

It's a great way to save both money and heartache.

 

Why not go Whipple SC's these twin screw units will keep boosting way past when the V12 runs out of puff and their temp output at boost will be much lower than twin charging. In fact if you run 10psi they do not need intercooling.

Just a thought

 

As someone who is not an engine builder, mechanic, or tuner - something strikes me; why does everything need to fit under the bonnet? The XJS has vestigial rear seats at best. Why not remove them and use that recovered floor space to house rear mounted turbos? All you guys chasing big HP are surely not trying to haul your kids around, right? You have a Panamera, Cayenne, S-Class, 7 Series or Audi for that.

 

I think that's an interesting assumption, Flint, since my luxurious family car is a 15 year old Dodge Grand Caravan, on which I just spent this chilly afternoon replacing the radiator, just to keep it on the road, & hoping that nothing else breaks down on it before the weather warms up in the Spring.

 

How to properly balance the weight of the pistons? Together with the rod or separately?

 

I have medical scales

 

What...?

 

not a bad idea, but remember ,exhaust driven turbochargers, run very very HOT, riding around in Texas on hot day, aint no A/C that can make it cool.

if going rear mounts just put them in the area of the mufflers space, been done hundreds of times , google rear mount turbos! STS, couple companies that make parts.

 

its a simple project but i doubt that anyone has ever lost a race because he did not balance his pistons!

 

there are available many nice digital read out medical scales today.
very accurate also.

prices are also quite reasonable.

 

There's a pretty good chance that if you blow your engine during a race that your going to lose.
If the engine is apart then not balancing the engine would be a huge mistake.

 

you say if you dont balance your pistons you will blow your engine?