So, kind of working through the nuances of getting turbos on my 96 xj12, and everything is pretty much solvable. But! I thought the he head would be prime for boost due to its ability to resist detonation. On a separate thread, 1 of 19 said this, "The chamber design will not give you the proper swirl. Combustion will be uneven. The spark plug location is not ideal and is far too recessed. Useable boost will be so low not much benefit."
​​​​​​So, let's discuss, as far as chamber efficiency with boost, what's better, flathead or he head? Not flow, but chamber efficiency with boost.

 

Turbo's on a HE or 6.0L head (which is almost identical to HE except for larger exhaust pocket) would work depending on what you plan to achieve, maximum torque or maximum power (RPM needed) if max power then pre-HE would be needed as the intake valve size in the HE is limited to about 1.8" because of the exhaust pocket.

You are correct the plug position is offset in the HE chamber, whereas the pre-HE has the plug more central. A longer plug can be used in a HE, just be careful it does not hit the exhaust valve and the exposed threads are removed.

CR can be lowered with a decompression plate (copper gasket) and or custom pistons. The HE does make more low end torque than the pre-HE but as said is power limited by the intake valve. I have seen V12 race heads (pre_HE) with machined chambers and 2.02 intake valve making over 600hp @ 7500rpm NA from 6.0L. Not a good street engine but would run at full throttle in a boat.

 

No need to increase flow since I'm boosting, 15psi roughly doubles what it's already making. So what are the adverse side effects of boost and the he head? Pre detonation? And i wish I could look at the set ups for those people who have already done it, turbo tech has come a long ways since then and gotten much more efficient.

 

we all will be waiting for your results?
there have been many discussions on this subject, but so far no one has come up with an actual build, for V12 and forced induction sysytem, for a street engine!
and like warrjon said , a boat engine has the cooling water of the ocean to cool continuosly, many force fed marine engines can run more compression, leaner AFR, more ignition timing,= morepower!

also the latest results for a GREAT engine(not jaguar), dyno build contest, was a GM/ LS series V8, 7L, made 801hp at just 7100rpm Natural asperation!
Engine Masters Challenge 2020, you tube it!
i do love my Jag V12, but if i wanted serious power, i would look at other ideas!

this engine has MANY performance mods, BUT not what i expected.

 

Cooling plays a part, in sustained throttle, but not much in running more compression, and leaner afr, since peak power is at 12.5:1 af/r. With turbos pressure isn't everything, maybe those people who ran 20 lbs and only made 600hp like Bonner weren't running good turbos, on top of that no intercoolers which at that boost level causes a serious holdback. I just want to hear more about the he head and what the problems where, like if it was just lack of ability to make good numbers or if it was detonation.

 

a gigantic mls gasket and ***** of steel will probably hold the answer to your problem


surely someone can do better with modern turbo tech

 

No need to drop compression, just have to have knock sensors and the ability to tune. A tuner local to me owner of vlm spec said the only reason to drop compression for boost is if you want to eliminate the chances of destroying an engine with even a whisper of knock. He said lowering compression only allows for more error, so as long as I or him don't mess up walking in the set up we'll be fine, so yeah going to need knock sensors. So at the moment I will be moving forward with the project and attain eeprom writing hardware and software for my current ecu, changes will of course be bigger injectors, gm 3 bar map, and a standalone knock sensor set up.

 

the Denso ECU in the 95-96 XJ12 is very rare, little about it online. let us know how it goes

 

Yeah absolutely! So far I have found I will need to buy a eeprom programmer, but today I will open my ecu up and see what type I need. Yes I will post everything I find out.

 

In stock form across the board the HE engine makes more power than the pre HE. Apparently the pre-HE suffered from charge stagnation at part throttle and that resulted in poor mixing and poor combustion and high emissions. I don't see how boost would cure that as it's fundamental to the chamber design.

 

You also have to ask, how does boost change the behavior? The he chamber is the best ever made, but once it sees boost does it become immediately neutralized and inefficient?

 

Neither engine is ideal for boost for very both similar and different reasons. Any engine can be boosted... but to what degree is the question and at what point does it become worth it or not. I've never tested any of this and it's just an option based on experience.

Issues with HE Engine.
1. Exhaust valve is in a pocket when under boost you are pushing more air in but it has to come out too, Leads to over heating of the valve and high EGT
2. Exhaust port is too long, lots of surface area for heat to transfer into the head and not the turbo hits efficiency
3. High static compression knock limits boost pressure
4. High Exhaust gas temps from turbo charging exacerbates dropped valve seat problem.
5. Open Deck block not ideal for high boost.

Issue with Pre-HE
1. Flat head and Dished Piston. Dished piston has more surface area and will absorb much heat than the head which leads to ring issues.
2. Imprecise ignition system leads to having to run safe timing which exacerbates EGT issue
3. High Exhaust gas temps from turbo charging exacerbates dropped valve seat problem.
4. Open Deck block not ideal for high boost.

Many of these problems can be over come with newer technologies such as a stand alone fuel injections systems, machine work, and newer parts but at great expense in time and money. Many other issues cant be resolved at any price, like the long exhaust port and open deck.

 

Lots to think about, mostly tuning and datalogging. Since extremely few have turboed the he motor, I guess I'll just have to do it and find out the weaknesses in reality.

 

sounds like a good plan, time will tell, many have tried !
if you can make a Jaguar V12 handle 15 psi in the inlet manifold ,for any length of time, you will be considered amazing!
bring lots of money!
we all love to see a plan come together!!?

 

something of interest ,, the PreHE has the chamber in the piston!
the HE has the chamber in the head!
a big difference between the two!

 

The HE head will not flow what the early flat head does. Identical engines and the early Flathead will make more power than the HE does turbo charged or not.
Plus better plug location etc.
the swirl is induced by the angle the mixture entered the cylinder. And finally squish can be achieved by the piston not the shape of the head.

HE means help emissions. It was designed to meet California’s new emissions laws not make more power.

Put an 11&1/2 -1 compression ratio in the early engine and it will make more power than the HE does. You aren’t comparing apples to apples

One other design consideration. Every place you put a notch, cutout, depression etc you are shrouding flame propagation. Look at modern 4 valve heads. The pistons tend to be Smooth, free of notches.

Finally while heat increases detonation. Coolers also have their short comings. Each alteration in direction of flow decreases the effectiveness of boost. Usually offset by bigger blowers ( induced lag ) or spinning the blower faster ( more heat)

Stop thinking coolers are the only answer. You can cool the intake charge two other ways. One is fuels. Methanol has 116 octane rating. Ethanol has 114 octane. Methanol is nasty stuff. Drink it you go blind and then die. Ethanol is in beer wine and booze.
Methanol will attack a lot of things aluminum, rubber plastics etc. Ethanol won’t. *.
There are other fuels that reduce the tendency to preignition, we know about Lead but toluene also helps. Both are nasty things with toxic potential.

The wonderful thing is E85 is 85% alcohol and 15% gasoline. Use that and your need for cooling just went away. Plus right now 92 octane gas. Is about 80 cents a gallon more expensive than E85.

How often is cheaper better? Rare but here it is.

Finally what about if you really want to make big horsepower? More boost right? Yeh but•••••
OK
cool the charge even more! How ? Windshield washer fluid. The good stuff has 20% alcohol ( methanol so don’t go drinking it) but, it’s the water that does the magic.


Know how on a rainy day your car runs really nice. ( assuming you’re wiring is up to snuff? ).
the reason is the intake charge is really cool and dense. A modest amount of water will dramatically cool the intake charge and you can add timing advance And still not get detonation.
In the early 60’s GM sold turbo charged cars with boost fluid. ( windshield fluid with coloring)

 

You lost credibility when you said H.E. means "help emmisions". It means high efficiency man.

 

it’s a joke. kind of like the mpg of the flathead engine

 

The two things the HE design does is it warms up the air fuel mixture by swirling it over the hot exhaust valve, and concentrates it around the spark plug.
Buick in the early days had that design and it was adapted by Chevrolet in their straight six of the 40’s and 50’s.
It was called the fireball head.
Guess what May’s called the head design he sold Jaguar?

Next look up horsepower ratings of the Flathead 1971-1980 and then look up the power ratings for the HE
Finally. With regard fuel mileage what was the final drive of a XJS in 1975-1980? And what did it have in the HE? Hint one had either a 3:30 or 3:07 and one had a 2:88.
oh and the early V 12’s suffered from a Borg Warner transmission designed in the early 1950’s while the HE all had the GM turbo 400 designed more than a decade later. that’s most of the reason fuel mileage is better on the HE. But one thing the HE does is it fires a leaner fuel mixture than the Flathead.
And the reason that was needed? Look at California’s emission laws.
Without that new head 50% of JaguarV12 global sales would have been lost.
You need to look beyond marketing to find the real truth.

 

So how does the th400 allow for better fuel economy over the bw? That makes no sense, you'll have to elaborate. They both have a 1:1 and are 3 speeds.