No one knows for sure...there is no contemporary development or dyno testing on the V12 that I'm aware of. Those racers that do know have spent many thousands figuring it out and the answers are probably so nuanced they would be difficult for a hobbyist to replicate.

What we do know is that Ford made the most tested and contemporary modification. They streached the V12 to 6.0L in 1994. This made a modest increase in power but the engine hooverd petrol like an exotic. That might not be a concern these days but it speaks to the effiency of the design and its ability to convert chemical energy to mechanical energy.

Have you seen this thread?
https://www.jaguarforums.com/forum/x...-pre-he-95447/
In summary, the OP poses a question, after 2 years and many posts there is no answer.

The v12 is a large engine. For a road car, there are and packaging considerations so intake design and exhaust design seriously limit the engines potential when expressed as a power-to-weight ratio. Unless your are using exotic materials, the V12 will always weigh 50% more than a V8 because you have 50% more pistons, crank area, block areas, head area, 50% more cost and so on. You dont get 50% more power though so the law of diminishing returns sets rather sharply.

V12's are exotic and that has intrinsic value to many including myself.

 

yeah thats what i am trying to figure out. i will most likely only change the camshafts and that might even be pushing it. as far as internals go, stock is good. i noticed the yellow hammond car has throttle bodies attached to a plenum. i dont want to go down that road. keep the stock injectors, fuel and ecu system etc, but just get more air in the engine easier. move the throttle body to the front so i can put a 90* bend down on it to a filter. as far as the header idea, once i get the engine out i'll look at the dimensions and over all geometry of the manifold and see if i can recreate with a 3-2-1 or 2-3-1 setup not going outside of the space they currently take. hopefully next week i'll be able to yank the engine and trans to see what im dealing with. thanks so much for the insight

 

Stuff:


One can do CI's with four or even two cylinders. But, the reciprocating weights are tremendous. And, a long stroke can limit rpm's because wild piston speeds.


Enter, more cylinders. 8, 12 or even 16!!! Smaller bores, shorter strokes, the buzz of a formula one engine.


OTH, in 64, Ford went old tech. Almost off the shelf, V8 power.
The lemans car originly used Ford's sbf and did well. But, stressed.
The far less stressed bbf, had the power, at the expense of weight.


Tis all a compromise....


Others get it far better than I.


Carl

 

The restriction on the HE version of the V12 is the combustion chamber design. This design has a very effective lean burn combustion chamber that gives good part throttle economy (for its era). It is not easy to increase power output, because the lean burn chamber is in effect a vertical pocket with the exhaust valve at the top end. So the difficulty is flowing extra gas past the exhaust valve, as it is in effect at the end of a "tunnel" the sides of which you cannot widen to aid gas flow out past the exhaust valve.

Almost all serious tuners of the engine have, and still do, use the first version of the engine with the "flat head" pre-HE design. This included TWR, and the pre-HE engine was used in the TWR racing XJSs. The TWR engine was a full race affair and used all sorts of better pieces, such as improved oiling, improved cooling, forged pistons, special rods and special cams. This engine did make high 400s BHP, even over 500 I think, but was not a street engine. It could have made much more; but the intakes had to remain standard OEM sized, as did the valves and exhaust manifolds under the ETCC regulations.

So the options are: using a factory 6 litre engine, which will give more power (say another 30 BHP) than the 5.3, but still not an absolutely massive increase; or using a UK/RoW spec 5.3 engine with the higher compression ratio and no cats, giving about 30/35 BHP more than the USA spec 5.3 engines.

The most economical and effective way to a great deal more BHP is to build up a longer-stroke version of a flat head pre HE engine. On the AJ6 website, Roger Bywater says that a 7 litre flathead V12 with bigger valves will give massive power relatively (ie relatively for an intrinsically expensive quest) cheaply. This is also supported by a passage in the book about the racing TWR XJSs written by Allan Scott the TWR engine guru. on page 314 of his book he explains how they developed an experimental road going engine (as a possible TWR offering to XJS customers) of 6.4 litres, with an 84mm stroke and standard bore, inlets of 44.5mm and exhausts of 36mm with a group A inlet manifold and a tubular exhaust running a flat head at 10.5:1 CR. This engine produced 410BHP at 5750 rpm and 420 ft/lbs of torque over a decently wide road-driveable rev range.

On the standard HE engine (whether 5.3 or 6 litre) a cam change will do just about nothing and might make things worse; ditto the intakes which are not restrictive until you are doing over 5000 rpm. A manual box will release quite a bit of extra BHP to the rear wheels (ie more power on the road) because the autobox will not be soaking up the 40 or whatever BHP in parasitic losses it uses, and there is a significant weight saving. FWIW, my opinion is that the AJ6 ECU and intake mods are the most cost effective way to perk up the standard engine, particularly so in the UK spec 5.3 engine with its 12.5:1 CR. Combined with a manual box that will give you around 60 to 70 more BHP at the wheels (maybe a 30% increase on standard). As far as everyone who seems to know about these things says, nothing else you can bolt on will make much more power, you have to get stuck into the engine in a big way to get (say) to 380/400 BHP. This would make fuel cost substantially higher, and possibly give driveability problems that can take a great deal of fixing.

If it were me, I would go nitrous as by far the best option for more power with streetability! Reading this over, it seems a bit pessimistic in tone, which I do not mean it to be; it would be great fun project to do, but it is best to be aware of what you are up against.
Greg

 

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plenty of automatic 400 to manual shift kits out there(i use one in my 700R4/4L60E trans), look up shift kits in Summit, Jegs, and performance automatic transmissions!

OK to get serious with a GM automatic, look for a GM 4L80E, there is a 6speed shift kit for them. lot of fun with close ratio gears,( just maybe some fool may swap out his Jaguar auto 4L80E for a 5-6 speed manual) that would be a nice combo!

i seen a nice trick shifting setup, that shifted the trans gears electronicly,
with panel near the steer wheel , shifting was done with just a set of 4 toggle switches, one up/one down was 1st, next set, was one down.one up was 2nd gear, next was two up was 3rd, then two down was 4th!

ALL shifting was done at full throttle(no lift shift), try that with a manual, over and over for 75 laps, it will seperate the boys from the men quickly.

none for the GM T400,(that i know of), they are hydraulic/ mechanical shift only,, needs to be a GM 4L60E/4L65E/4L70E for power under 375hp.

but for up to 600hp a kitted GM 4L80E/4L85E/4L90E.

the higher numbers are higher torque rated.

also(way out of price range) GM is coming out with factory 6-7-8 speed auto matics, but they fit the newer LS series engines, and the multi speed autos have adaptive drive computers, after some laps , they know exactly what gear you want, but some kool computer nerds just might know how to wire one up to some switches,( that would be for future moneys).

Gotta love modern car companies!! and the hot rod guys.

 

HEY Crafty, any chance on buying the chrome headlight surrounds, the plastic ones???

PM me ,let me know, my left side is cracked, but id buy both!

 

A Jaguar V-12 is going to weigh 50% more then a V8? How many times do we have to go over this nonsense? This isn't politics where you just "say it" which means it must be true. Good grief!

http://www.gomog.com/allmorgan/engineweights.html

 

ok... it says... almost 800LBS for the Jag v12 and 575 LBS for an SBC. If you consider the weight of the v12 & transmission and all additional fluids & radiator, as a package it's much more than 220 LBS of difference. Any one who has completed a v12 to lump has observed the attitude or height of the front suspension indicating a substantial weight difference.

Below was copied from your link...
Jaguar V12 792 (236) 1986 model
Chevy small block V8 575 (generic for '60s-'70s motors)

All in I estimate 400 to 500 pounds from v12 to lump but you can believe what you like. The tension between those who read and those who actually do will always exist.

 

theres not alot then of what can be done with the engine unless you dive into and start machining parts? just something as reliable as possible, fun to drive. once in a while track it but mostly day to day. instead of trying to get the power up, im going to get the weight way down. does anyone know how much the stock exhaust manifolds weigh? ball park?

 

once the car loses weight, say with a swap, and the front end raises up because of the weight difference, are there any after market lower kits or you just chop the springs? i cant find any type of lowering kit/springs, not that i'm ready, just looking

 

Typically lumpers use XJ6 springs but spacers on the lower spring pockets are still necessary to further lower the car to an original ride height. There is no specific spring that fits the bill. Lumps tend to vary in weight because they can be configured differently for example an iron headed lump with cast iron manifolds weighs about 90 LBS more than an alu headed lump with headers.

Personally speaking, I consider weight when building a lump. Presently I'm working on a lump using a XJS front cradle from a 1995 6 Cyl XJS (AJ16). With my latest light weight lump, the suspension is still fully extended and nose up with the engine installed and on the tires. I was very surprised by this but I still need to add the fenders, hood and cooling. If I sit stop the Motor, adding 195LBS it settles down about 1/2 of an inch, still not enough.

 

here are some rust issues i have found on the frame. the rest of the car is really good, rust wise just the trunk has the 2 pockets on either side that cover the mufflers rusted out but i'll get to that later. my concern is the rust here on the front suspension. from what i can see and feel the tops of the spring towers i think is pretty bad. once i get the front suspension off i'm sure it'll be worse. the rest of the suspensions looks and feels pretty good just surface rust with no holes. is this repairable if i sand blast it all and grind all the rust off of it and weld new pieces to fill?

 

i dont think it is that much difference , but a Big block chevy engine weighs just about the same as Jag V12, lot more cubes, and way to much power!
just a thought!

 

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if you have that much rust on a Jaguar, you most likely have alot more than you expect, has happened many times with jags!

thats why i was given 3 jags, mechanicly reasonable condition, not a lot of money to fix, 2 V12s and a 6, 70s and 80s models!

but the body rust and paint work was expensive( i dont like doing things 1/2 assed).

they are a unibody car, lot of nooks and crannies that you cannot see(and some you never will) unless you open up the main body rails/pockets and look inside them! you cant do that unless car is stripped bare.

for my 78 XJS ,was stripped to the bare bones shell nothing left on the shell/platform and put on a rollover rig for 360* rotation, media blasted, the only way to do a proper rust removl and replace all steel sheet metal pieces), welding upside down is hit and miss at best(my opinion).

then a complete spray with GOOD rust proofing Epoxy ,2 coats!


and for race purposes you should do a lot of reinforcing of the body, Jags,especially old flexy-flyers, that have been cobbled together!

anyway after reading thru your posts, i wouldnt at this stage worry much about engine/drivetrain, get a solid platform and suspension under it, that should give you some time to think about what will be best to power it!

 

crafty, if you get the Jag 4L80E it will bolt up to the V12s(78 up), if you get a GM USA 4l80E it will need an adaptor plate(thats what i use on my V12,BOP Summit racing).

if you are very lucky, most 6.0L V12 comes from factory with 4L80E trans, some had ZF or something like that

and i'm sure that some kind of Paddle switches can be done,VERY KOOL IDEA!

for a torque converter, i do use a light weight small diameter unit,(custom made with 400 internals,for strength), NO lockup,dont need stuff like that for autoX, it aint gonna be MPG queen anyway!

 

4L80E did not come along until the factory 6 litre. Engine blocks are different and It will not mate to earlier blocks without adaptor. No ZF's on the 6 litre.
The EZY-TCU from TCI can be setup to run paddles in manual mode.

 

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i think i said something to that effect!

4L80E came on 6.0L jags, for a 5.3L you will require a plate(thats what i use since 1994).

TCI has some nice pieces for trans mods.

also there is a trans company here in the states, that has a kit for the 80E that converts the 4 speed into a 6 speed by using overdrive between gears, nice close ratios and working to make a lower 1st ratio and working for a higher OD ratio!

but GM now has some 6-7-8 speed autos, that will bolt to some of the LS series blocks, maybe can be adapted, never know till we get our hands on one? the computer should make things interesting tho!

never say never can be done, like said gotta love those hot-rodders.

 

Yes you did say something like that but the (78 up) bit was misleading. Won't bolt straight on till 94.
I did look at that 6 speed valve block mod for 4L80E but reviews are not very positive. All the extra splitting is done by the overdrive which is ok as an overdrive but not up to the torque splitting lower gears. Very harsh on the shifts too aparently.

 

Hey Crafty, I get it. I am having Bennett Coachworks of Milwaukee install a Ford 3.5L ecoboost , also known as twin turbo, into my '93 with 6 speed auto. It's taken 18 months but it should be ready to fire up next month. The fabrication has been amazing. Don't try this at home. They have done several concours cars and don't cut corners. They are hoping to have a feature on their facebook page next week I'll post when verified . The lump should be close to 100 lbs. less than the 4.0.

 

i like it ,Ford 3.5L Ecoboost, has a lot of performance potential, i heard about 500hp numbers.

yup gotta love those American hot-rodders!

that car will deffinitly be outta the BOX.

nobody said it would be cheap!