Some interesting information regarding the HE Head. From Bonner Engineering in the UK.

Engine Development | Bonner Engineering


Example 2. Bonner-Jaguar-Turbeau V12 Turbo Marine Project.

Bonner-Jaguar 830hp engine

This was a hugely challenging project brought to us by Turbeau Ltd. The specification was for 800 bhp from the Jaguar 5.3 litre V12 engine in turbocharged and marinised form. On the road the engine gave about 250 bhp, for short bursts. This needed to be more than tripled for continuous running at full throttle for up to 3 hours. We had many problems: Rear main seal turning crankshaft blue, Rear bearing failing due to a) rear seal : hot crankshaft, b) fillet radius fouling bearing, c) asymmetric bearing cap, Turbo disintegration, Exhaust manifolds cracking through water jacket, Lucas mechanical fuel injection failures.
But the biggest single problem by far was Detonation at 20+ lbs/sq” boost.
Initially the current production model had a completely flat faced cylinder head, which is a recipe for bad combustion. Symptoms were: a) an unduly long ignition advance; b) high exhaust gas temperature, around 1000 deg C; c) failure through burnt out pistons which is itself a symptom of detonation. All of the above are a symptom of bad combustion, which is itself a symptom of a bad combustion chamber.
( Jaguar Cars were sponsoring Turbeau who were running a powerboat team, and as a result we had a generous supply of new engines, spares and free access to their engineering hierarchy, with whom we had a cordial relationship.)
Jaguars came to the rescue with a new cylinder head, to counter the atrocious fuel consumption of the XJS*: the May head.
* Further symptom of bad combustion.
They sent down two pairs of pre-production heads to try out. The initial results were as follows: we had lost 200bhp, down from 800 to 600, and instead of burning out pistons, we now burnt out the heads. Jaguar came to the rescue again and offered Bonner Engineering a sizeable budget to solve the problem.
More information on this story in the Combustion Chamber Design section.
We then revisited the May head and redesigned the combustion chamber so that it had a reason why it should work, subject to testing it. Furthermore, our proposals could be machined out of what was now about to be a production head. We were also able to include excellent port and airflow characteristics. We called it the May-B head.
We produced a pair of cylinder heads accordingly, built them into an engine, and ran a test on the dynamometer.
The power was back at 8oo bhp, ignition advance back to 36 deg, fuel consumption .58 pts/hp.hr, the engine was smooth as silk and detonation a thing of the past. No more burnt pistons, no more burnt heads, no more burnt exhaust valves, no more burnt turbochargers. What a relief!

 

Como
This must have been done quite a long time ago, mid-1980s at a guess. Do you or anyone else, happen to know what they did to the May head combustion chambers? Considering they say that the mods were a matter of machining a standard may head, it might be doable at a reasonable cost. Warrjon, for example is modifying his May heads, I wonder if he is interested in this? There is also question of whether in normally aspirated form the engine would still produce similar efficiency gains, albeit at lower power outputs levels.
Thanks for posting the item,
Greg

 

Thanks Como! nice link... I guess if some one wanted and could pay they could have bonner one off a May-B head pair for them ?
(with appropriate agreements signed I am sure...) (not reverse eng and reproducing them )

 

hey guys you gotta remember any boat engine rarely has overheat problems,, it has an OCEAN of water to kool it, always has cool water available!

if you have overheat probs. you have something wrong anyway!

and that engine,altho great, is getting very expensive!

any pix of manifolding and comb. chambers?

 

and like i said before,"you cant beat cubic money"

 

I am restoring a 72 XJ12 and would like to improve the performance of the V12. Seems to me the engineers at Jaguar and Michael May weren't fools and better compression ratios meant less emissions and better economy at the expense of overall high rpm performance which is pretty acceptable compromise for a road car.

I have contacted Mr Bonner to see what the story is with these heads. From the web site he worked for Harry Weslake of the BMC B Series, Jaguar XK and single cylinder speedway bikes fame. Those speedway bikes make 80hp from 500c running alcohol. Harry Weslake also designed an F1 V12 and the all conquering Cologne Ford V6 Touring car engine.

I imagine, and this is complete conjecture here, that the combustion area in the head would have been cleaned up to resemble a ported B Series head as designed by Weslake which is a very well understood head and similar in overall design other than it uses pushrods and rockers to drive the valve train.

I am hoping to get some useful engineering information - before and after maths. The emphasis from the web site seems to favour test dyno results. I have been able to find flow figures for the flat head V12 cylinder head but nothing concrete for the May head as to its flow characteristics.

 

This is why I am going 6.7L. Increased torque = increased HP through the rpm range, all things being equal.

Here is a really good article on chamber shape and making power. So laying back the wall (as in the pic) where the plug is is probably not the way to go. I will be machining this part of the chamber more vertical. It will be difficult with HE heads, to get the chamber shaped correctly I believe would require welding the exhaust port and then recessing the intake valve to keep CR up. Then there is the cost of 24 new custom valves.

 

that Pic looks(ed) like my 1275 sprite head... ( the metal strip in between 2 and 3 was a lot narrower on mine )
and from my calculations that 5.3 with out boost would have put out around 331hp normally aspirated. "the bonner may-b"
but it would have done it forever and EVER! and EVER!!!

 

At the risk of upsetting people this is starting to go around in circles.
Multi Nationals have spent a fortune designing the best combustion chamber shape for a 2 valve head with vertical valves be if push rod or SOHC. As a result we have either flat heads with shaped pistons or chamber heads with a combustion chamber like the B or May or whatever you like to call it + flat top pistons. The similarity is very noticeable between all the chambered head designs, be it the custom V12 heads on the previous page, the LS1 style or the modified MGB. The HE head is however a little different as it has valves recessed by different amounts for mainly economy reasons; you cannot argue it doesn't work compared to the Pre HE flat heads. BUT to get these heads to something like a B or LS design with valves at an equal depth will require work and money. Valve seat removal (both, you want to retain the inlets with all the work being done next door and the known dropped seat problems?)
TIGing of the exhaust to allow the raising of the valve following recutting and installation of the seats. SO you are in for some expensive ali welding, seat removal and recutting, New seats and new valves (custom exhausts)
Then of course you need to tidy up the chambers / modify them. All this to just get the exhaust valve down a bit. You had better fly cut the heads too.
Are you still sure you want to do this?
You will of course still have the standard restrictive ports with the exhaust and its oh so tight bend, try straightening that out and you will break through junking the heads!
Guess thats what motivated a chap in the UK to make his own heads.
Maybe the alternative way, the Flat Head way is a more sensible option after all! ?
It was of course the choice of Group 44 and TWR who both cast there own heads, I tend not to argue with guys who had unlimited (ish) budgets design and testing facilities added to some of the best brains in the world. I also tend not to try and re design and try to improve what they have achieved. Independent of each other they came up with almost exactly the same design and answer. But as you dont want or need 40mm inlet ports you can achieve what you want with the STD Pre He heads.
Your call chaps....

 

By the way, The F1 powerboats that actually won ran V12 Jaguar engines.
Not from Bonner (I am sure they make wonderful engines and their v6 is epic) but from Group 44 with the Flat Heads.
Engine # 016 and 018. I now own both and have their Log Books with remarks/ notes from Lanky.
After the F1 boats they went into a modified yellow XJS that used to race, afterwich I aquired both engines.

 

my 1978 V12 flatheads, have Grp 44 3MM oversize single piece SS valves,inlet and exhaust.

i aquired them from Lanky, along with a set of springs,he recomended for street use!

back 1994! i cut the exhaust valve diameter, 1mm smaller, for a little more space between valves, and fit the seat diameter properly.

Note; all the valve stems were 13MM to long, so i had to shorten all of them,(very carefully), it is possible that they were for a custom tall head,after all?? donno?

 

I am thinking the extra length of the valves was for use with the custom cam carriers that are taller than standard. Actually sufficiently taller that the chain needs and extra link over standard.

 

after reading so much of this 500hp thread, and actually making NEW cast heads, been thinking and reading much about the DI (direct chamber injection) heads!

the more i think about it, in this modern day and technology that is becoming available!

there is so much potential in a DIRECT CHAMBER FUEL INJECTION engine!

a jag V12 with a 4 valve pent roof chamber, and DI , has so much more to offer, and many parts are showing up to do it!

never said it would be easy. quest; any takers?

 

I'll bite

if you are doing 4 valve New head... pent roof and all new pistons

4 valves and NO CAMS and no direct injection
and NO throttle body....
they found that direct injection was not necessary...

 

jonathan, better not tell 75% of the new car engine designers, that is what most everyone is using!

that electro valve stuff is somewhat old already, some guys here in the states were trying it around 20years ago, on a 4cylinder ford engine!

and i would think that if it showed potential it would be around already, i'm not saying it wont work i'm saying nobody is using it!

most of the DI engines already have done away with the throttle body/plate, to reduce pumping losses, and they get great MPG and power, simply put DI does work.

 

I know and I found it odd when koenigsegg stated it did not give his design any benefit over port injection...
I though it would but right in his video he stated that...
F1 don't ask don't tell

 

pix test,, this is the type of stuff i study, by the way this is around 10years ago!!!

 

Bringing this thread back to reality; I have just finished loads and loads of grinding an boring opening out a pair of heads to 38mm inlet port x 40mm slightly oval as the port is at an angle. The inlets going on it were fitted and I bored/opened out the lot together. Real happy with the result; huge huge increase in flow.
I read on another thread about inlets being down to 1" at the valve guide? Sorry dont we heat the heads put in the stepped drift and whack the guides out then port all the way through? Easy enough. The exhaust guides can go back as is but I taper the ends of the inlets before they go back. I'll post up some pics shortly. Give me a day or 2 first for the buzzing in my fingers to go away. Worn out over £100 worth of flap wheels on these heads never mind the boring and die grinders.

 

HEY,xjr5006,, go for it, sounds like great stuff.

 

Hey there!

So some of you may have seen my post here about manual swaps (and if any of you could provide some input that would be wonderful) but if you did glance in there you'll have noticed I don't actually own an XJS yet. I'm trying to plan my purchase as perfectly as possible to minimize the necessary modifications. That brings me to my current question: What would be the easiest way to get more power and redline out of the V12? and what components fail at what RPM? For example, I've heard the stock cast crank is no bueno after 7500 RPM. But what about camshafts, rods, bearings, etc?

I plan on solving the airflow issues with one of these and porting the head.

I'm not looking to make more low-end power. People call low-end power streetable, but to me that's not true nor the essence of what a Jag is. Smooth running at the low end with the ability to scream and move at the top end is what I'm looking for, and I'm fine with losing torque at the low end. I'm swapping in a manual so I'll be able to stay in my powerband whenever I want to.