Lets take a step back here; the Jaguar V12 was designed and 1st made 50 years ago, around the time of the Hi Po 289 and SOHC 427. Yes heavy and down on power by modern standards but things thankfully have moved on in the last 50 years.
20 years after the after the 1st E types ran a production version (never mind the earlier prototypes) the V12 was winning at Daytona and at Le Mans, so it must have had something going for it.
Poor flow? thought the tests showed that it flowed somewhere between 2 valve and 4 valve engines, after all with race inlets you can tune by watching flame colour so straight are the ports.
You can get 450 from a stock 6 litre just with a decent exhaust system and a mildly reprofiled cam (aka XJR15) so 500bhp would not take too much work ie a bit of flowing or larger stroke/ bore even without other work.
Mild cams? yes on the std engine but I run .54 in my Le Mans engines and dont dare to fit the .6 cams as I have problems with valves and springs with the former. So did the works teams, viz Group 44 with a .45 lift in 85 and TWR Inc at various times (.54 /.60) but most notably when a Bud Light car was leading by a mile at Daytona.
Cam timing; I run 102, thats centre of lift inlet at 102 degrees, the real problem is getting the compression high with such deep valve cut outs necessary because of the wild cams. Valve control is via 1.5 springs in 1.6 buckets or even larger in 1.625.
No it cannot compete with the later turbo cars once spooled up but it can take half a straight for a turbo car to recover the jump you get on them coming out of the corners.

 

Since Thermal Efficiency was brought up I'm gonna jump on the v12 bashing bandwagon and prove using geometry that the Jag V12 is a dead end for a modern road car Unless you increase the stroke significantly. The short stroke 70mm is best suited for engines that see 6000 to 9000 RPM. Even the 78.5mm of the 6.0 is not sufficient for a road car. Bottom line is the bore stoke ratio severely limits thermal efficiency and power potential during the running conditions a road car will see.

Lets compare what we know with the Jaguar V12...

Nascar motors have a 4.185" Bore and 3.25" stroke for a ratio of 1.29. These motors routinely sustain 9000 RPM. The Jaguar V12 has a similar bore to stroke ratio at 1.285. Would anyone put a Nascar motor in a road car...NO!

The well respected Ferrari beating Ford GT40 had 4.232 bore and 3.784 stroke for a ratio of 1.18. With peak power coming on at 6200 RPM and peak torque coming on at 4000. With clear success on a Lemans road course maybe this type of engine is more suited for a road car. Perhaps they knew something back then.

The Chevrolet LS7 engine which enjoys success in everything from Escalades to Drift cars has a bore of 4.125 X 4.0 for a ratio of 1.031.

Another unsuccessful engine I'm personally familiar is the Porsche 928 V8. Its underpowered, peaky, ineffecient and with a bore of 100MM and a stroke of 78.9mm and an unfavorable ratio of 1.26

Conclusion...If you want to make the Jaguar V12 have the same ratio as the Gt40 you need to increase the stroke to at least 78MM with the stock bore. The stock 6.0L Jag v12 has stoke of 78.5 now we're getting there... If you want to get it to the ratio of the LS7 then you would need a stroke of 87MM. 87MM is what I would shoot for because there are so many other factors related to thermal efficiency that need to be overcome with the Jag V12.

On to the valves...The 500 HP LS7 has a total intake valve area of 121 Sq/in and HE head has 98 sq/in (supports 404HP) . The LS7 has a exhaust valve area of 65 sq/in and the V12 HE head has 69 SQ/in. This suggest the HE can support 500hp with an intake valve upgrade to and some work on the exhaust to improve flow on the side of the exhaust valve that is pocketed.

The cam. The LS7 needs just just 211 degrees of intake valve timing to make 500HP and the V12 with less stringent emissions requirements could run a bit more cam timing to crutch the lift deficit. I don't know what the stock v12 cam shaft duration is I suspect its more than 211.


My low cost v12 500HP formula would be...a 6.0L block with a stock bore offset ground and stroked to 82.6MM using small journal chevy rods. Custom pistons. HE heads with slightly larger 1.75 inlet valves and re-profiled exhaust port to un-shroud the valve to increase flow and lower compression. The compression would increase because of the stroke increase. This engine would almost have the valve area of the LS7 and favorable bore Stroke ratio of 1.08. Would it make 500HP? Maybe...hard to know for sure but the displacement, valve area and geometry is there so the intake and ignition would have to be up to the job.

My mega buck V12 would have a stock bore, flat heads with 2.0 inch inlet valves, D dished pistons for squish. Billet or Welded and reground crank to 88MM for a road car excellent 6.7L engine with a 1.02 bore stroke ratio. It would end up with more valve area then the LS7 on the intake and exhaust and could be a 600HP torque monster with a smooth idle.

Empirically...I happen to have had a 6.0L XJ12 and an Escalade 6.2L with a mild 405 HP LS7 at the same time. I can tell you the LS7 is smooth and motovates the 7500 pound Escalade with great swiftness up to its 5500 red line. The LS7 in the Escalade has smaller 2.165 valve and a stingy 198 degrees of intake timing. The total valve area is closer to that of the V12 Jag. Even so the Jag engine was sluggish off the line even considering the 2500 pound advantage. It was also peaky like the 928 engine I had and just didn't respond the way I would expect a 6.0L engine to do so. Performance enthusiasts often over focus on bore and aggressive cam shaft duration. For a road car you need stroke.

 

hey guys give the nitwiy from a place called baltic states(where ever that is) a break, its full moon and the lunas are out!

isc, not fair to compare the LS engines to the antique Jag V12, anyone with some engine experience knows LS is the ultimate push rod v8 in the world for a usable road car!

and good,bad or indifferent its still a 12 cylinder engine, and to casual onlookers its SUPER KOOL! its all about the TALK not about the WALK.

nobody will ever again use a V12 of any brand for SERIOUS racing,not drag racing,F1 racing, road racing, hill climbs ETC.

 

well as the original poster on this thread, I will say that I wanted to build a v12 cus it's effin cool to have a v12. When the motor blew I could have threw in a bbc an lsx block or an rb25 block with a turbo, and although they are all cool and all can make a ton of power, I really wanted the same appeal when u had the v12 and had everyone asking questions.

But in the v12 defense, the stock motor is incredibly powerful in its setup not in it's raw power but in the size of it's powerrange. I had the stock.motor and a 5 speed and giving much more powerful cars a run for their money.

 

XJR5006, what is a decent exhaust? Do you have one in mind that is available that fits the car?

 

I haven't posted here for a while, and have just been reading when time permits.
In comparing the engine to engine the thing that really needs to be taken into consideration is the operating systems of both.
Had the V12 been built with the same operating tech as a new LS version of the GM V8 there would be a similar result in efficiency.
I am building a 5.3 HE engine now for customer as you might probably know, with a bit of different approach.
I am using the stock bore and stroke as the engine was low miles and in near perfect shape.
I'm using a mild set of cams Ron Iskenderian is grinding for me, and doing a lot of work on the heads which is where the power comes from, (on the basic engine itself).
I have been doing head work for a long time, and have a different view of what can be done without going to extremes, although I have gone beyond extreme at times to get a desired result.
I am using the stock valves which are actually fine considering the head design.
I am actually decreasing the size of the exhaust and also the intake, but a bit less.
The reason is that I'm increasing the bowl size, correcting the port shape, and narrowing the seats.
The exhaust is very shrouded in these heads, and a larger valve would be going in the wrong direction as it would just be in the way more.
The smaller valve is less in the way of the flow, and the area behind it is bigger.
Jag did a much better job of the seats and valves than they get credit for as the workmanship is there.
It just needs tweaking.
They even round off the exhaust valves which I've been doing for years to help flow, a very smart thing to do, (coming from the factory, back then?...!).
The bottom end I find no real fault with as it's strong enough to do the job.
With the new IR injection and ignition I'm creating for this engine and another I have in the shop, along with some good exhaust tailored for the cars they are going in I feel this will be a way to see just what these engines can do built with today's tech, and without the restrictions imposed on the cars they were put in.
If the factory were unencumbered with those limitations, (fuel economy/emissions etc.) they would have been able to refine them to what their potential really is.

PS: Cal, the intake design you drew is OK, but really only good if a supercharger was sitting on it.
There is no real advantage, just a different look.
If that's what you're going for that's fine.
An 8V-53 Detroit is a long, low profile blower that is suited for a V12.
I built one for a Lincoln V12 Flathead that looked very correct on it.
They are hard to find and need a lot of work to drive them but are really a nice piece if a person wants to take the time and energy for a project like that.
It was a lot of work to make a drive.
Fortunately some else did the drive, I just built the blower.

 

I would go got a Lister style set up. It fits, and it works, there are a number of places world wide that copy the design Bob Tilley I believe does them too.
Not the ultimate set up but space under a std hood is very tight and frankly anything is better than the standard headers.
When racing 'stock' v12s 25 years ago we used to spend a couple of weeks with burrs in die grinders opening out the required std cast iron manifolds, huge difference (and weight saving), TIGing up the holes when we broke through.
The secondary's where also altered, the 2 into 1 was too tight and as I recall most of the 2 into 1's we split where so poorly produced that internally one pipe might be half blocking the other. So we simply remade the 2 into 1 section. Going further back we always lost the back box for a straight through which no doubt assisted flow but also made the car sound cool too.
So yes I realize the fitting of real extruders in a stock car is not practical nor do you want to pay the price, but the Lister style works fine and is available which is most important. Stainless is good, only costs a little more and lasts, unlike mild steel.

 

I think some people are misunderstanding what I'm saying...So let me try again. The Jag V12 can compete with modern engines including the LS if you apply modern technology and principles. The vast majority of moden efficient and powerful engines are near square or under square. Square off the V12 and you've got a winner because the valve area is there even with the HE head. Question is if its possible at reasonable cost. Monday I'm calling Scat to find out. I'd love to build a square v12.


Another case in point is Jaguars modern V8 engine. The AJ V8 which replaced the v12 is square 3.6 inch bore and stroke for a great ratio of 1.0. The more recent Jaguar 4.2 v8 is under square at 3.6 bore and 3.8 inch stroke. For a ratio of... 0.95. The point is for a road car square or under square is more efficient and powerful so if you want to bring the V12 up to date you need more stroke with the same bore. I wont bring up the LS again, they seem to make some people myopic.

 

Well......some Jag lovers get a little touchy when you say something like.....




It's probably wrong (or even stupid) of me to jump in since I haven't been followng this thread too much but, misguided or not, some people really like their Jag V12 engines. Bashing, or preceived bashing, the object of their affection isn't the best prelude to making them less myopic even if, technically speaking, your analysis is spot-on. On a Jag-specific forum it's perfectly understandable that most of the members are have a sense of loyalty toward Jag engines.

I think everyone knows that if you want a 500hp XJS there are many modern engine choices that are better, easier, and less expensive than clinging to the V12. But for whatever reasons some people get sentimental about these things. Heck, I know some guys who think the sun never sets on the 425 Nailhead Buick engine and decades later are still try to get more power of 'em....even though they know full well there are better/easier alternatives out there

I'll shuddup now . No ill will intended, I assure you.

Cheers
DD

 

The bore stroke argument is a question of where the engine will rev with maximum piston speed. Rather than power range.

Someone did an article with a buick.455 vs an.olds 455 which is stroke vs bore. And they made equal torque curves but the olds 455 has much more trouble spinning to high rpm due to the physics of the motor.

Big bore motors deshroud the valves giving more room to breath and ultimately have less rotating mass. Because the additional weight on the crank weighs much more.than the pistons

(My forged 96mm pistons weigh less than the cast 90mm ones)

The lemans 7l motos is a 94mm bore.by 84mm crank.

 

The trick to building a motor is build.the botom end to rev in the range you design.the heads to flow in.

 

You're kind of making my point. The rev happy buick with its 4.3 inch bore and 3.90 stroke has a favorable 1.11 ratio.

 

old story here 1950, when someone would say" he is bored and STROKED",

you mean we havent progressed since then?

and its been known for around 75yrs that a square bore/stroke ratio has many benifits.

also on any overhead valve engine,for making decent power its always been in the heads(ala breathing air flow).

so explain what you think,in your ideas, is gonna be better than whats already been done?

what IS being done(today)is new technology of DIRECT INJECTION AND FORCED INDUCTION! and modern transmission/drive systems.

and without being a BSer, when i was teaching at a technical university, late 70- 80s, thats what i would stress to my students, future is DI/FI boost.

and just to open some thinking; top fuel engines are only 8L,V8, 2 valve,pushrod engines , and they make over 5000-7000HP!

 

We all know that the closer the bore and stroke match each other the more efficient it is . Like cslvin has said its about ssetting up the bottom end too match the heads power range. The v12 and the straight sic are fully balanced motors compared too v8's do not get me wrong i love my muscle cars but there are a few of us who like the abnormal roar of a v12 . I believe if bore and stroke are matched you would see quite the power range and a very reliable motor in high rpms.

 

Theory if fine but wont get a practical v12 built. especially to any kind of budget. If you want more power as opposed to torque then raising the rev range will assist as BHP is a function of revs. Might not make the engine any more usable and you dont know how to make the bottom end hold together at elevated revs (will cost you money too) so bore and stroke increases are an easier method. Seems that bores of 90 92 and 96 are practical as are crank strokes of 70 75 78 and 84; reasons are obvious if you think about them. bigger bores may be possible with offset boring of the block but where are you getting the gaskets? bigger strokes than 84 are possible but how are you going to recess the heads or are you going to add spacer plates and get custom liners machined? So that leaves you with 7.3L ish. If you cant get 500 horses from a 7.3 seriously consider another pastime. (or engine builder!)

 

88 please explain how you are gonna build a Jag V12 ,with a 96MM bore and a 96MM stroke??

and its gonna make a hi-rpm also? HMM thats interesting!

 

You wanted to see what a decent exhaust looked like

 

 

My new project, just 3 weeks out of the mold