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This is my latest dyno. This involves both the new cam and my modified intake. My exhaust is done up too. I bumped my timing up to around 18-20 degrees at idle. It has a nice broad power curve. My A/F ratio is bad. Super rich at the bottom and too lean up top. The dotted line was my old, original dyno for comparison. The only modification on my original car was my exhaust. I then cut off the air filter snorkels. It gave me 10 HP and 10 torque more than the above numbers on the sheet. Then I increased my A/F mixture to around 13:1, it moved the power up to 207 FT Lbs of Torque and 183 HP. And now my final dyno numbers.
Yes, everyone has higher numbers. This dyno is super difficult. It mimics the car on the road. It adds resistance to the back tires to take the weight of the car into consideration (4000 pounds), then it adds wind resistance. But, I have a before and after on the same dyno, so I know what has helped the engine out the most. It is pretty much taped out for this displacement (5.3L), compression (9:1), cylinder head valve size (flat heads).
As discussed previously Bonner Engineering in the UK made a revision to the May HE head called the B head with a revised combustion chamber and valve setup. I'm not going for 500Hp from my 5.3 more along the lines of improved performance with vastly improved efficiency using throttle bodies and a Motec system.
Mr Bonner is making up a set of heads for me and I thought people might enjoy a picture of the combustion area which is unique but similar to a Weslake type design and along the lines of where Chevrolet were heading with their 2 valve designs.
We are doing some before and after dyno comparisons.
This may be covered elsewhere but was there ever a fully counter weighted crank for the v12 and if so did it still need the crank damper?
Are these stock heads that have been modified? or are they new castings?
Are these stock heads that have been modified? or are they new castings?
The heads in my case were NOS HE heads unmodified. They were CNC'ed to the May B spec which is looks like something closer to a Chevrolet LS type head. Bill Bonner of Bonner Engineering worked for Weslake who developed the A and B Series heads for MG and other BMC cars. The final spec is for 10:1 as opposed to 12:1 with the original HE head. This is an attempt at improved combustion efficiency and more power without an increase in capacity. Doing lots of simulation on Engine Analyzer Pro.The heads aren't on the engine as yet but I will be doing a before and after dyno of the engine. As the before is a pretty much as unmolested 4 carb, 5.3 from 1973 it shouldn't be too hard to improve on. It's an XJ12 and my daily driver so its fun to bring it in to the 21st century.
The heads in my case were NOS HE heads unmodified. They were CNC'ed to the May B spec which is looks like something closer to a Chevrolet LS type head.
Nothing like an LS combusion chamber. LS has a 15 degree valve angle and heart shaped swirl inducing chamber with a centrally loctated and unobstructed plug. I cannot see that double pocketed obstructed plug HE head flowing well, especially at mid lift when piston speed is highest. At low and mid lift 1/2 the valve will be shrouded by the pocket. Mid lift is super critical becasue this is where the valve spends most of it time. Sorry but this 'aint gonna work.
It's well known the exhaust port on the HE is a compromise and flows poorly because it sits in a pocket. Pocketing both valves is just silly. And to reduce compression and have less quench area... double silly. You are going to loose 30 HP to the reduction on compression alone. And now the combustion chamber has been enlarged and the plug is now offset to one side and is partially blocked by an obstruction. This will increases flame travel time and destroy propagation, very bad on a short stroke engine. You are going to have to run lots of advance and have the same detonation problem the Pre-HE head had. The enlarged combustion chamber is very bad as much of the thermal energy will be absorbed in to the head becasue of all that surface area milled in to the pocket. This head is going to detonate, increase the tendancy towards over heating and flow poorly.
The may head with it's quench area and detonation tolerance is a good design considering what they had to work with. Chevy didnt get a high compression detonation resistant mass production head until the 90's.
Below is a 317 LS head found on the most pedestrian chevy product like trucks. It's a design study in flow and ease of production. No similarities to whats shown above other than that it has 2 valves.
Last edited by icsamerica; Feb 26, 2019 at 07:50 PM.
i,m not gonna touch this thread with opinions , i have my own theories !
altho my Buick has a 6.0L LS2 and it has the 317 heads , reviews say they are one of the best early LS for turbocharging because of detonation control!.
, lets wait and see what COMO ends up with! be interesting and educational for any body with HE 5.3L Jaguar V12 !
looks like the inlet seats are not installed yet, may just bring it up higher to the deck surface !
The main problems with HE head are :-
1 - Heavily shrouded intake valve, when I did my heads I found the intake valve shrouded to nearly 50% lift
2 - The exhaust valve pocket limits intake valve size.
3 - Spark plug is offset in the chamber, the pre-HE plug is much more central in the chamber.
I spent time de-shrouding the intake valve, I only increased the exhaust valve pocket to lower CR to 11:1 for a 6.7L, According to my modelling this 6.7L should make 400-450hp. I could model the 5.3L pretty accurately and used the same parameters for the 6.7L and only changed bore and stroke. So with the additional efficiency of a multi-angle valve job, port matched heads (intake and exhaust) removing all sharp edges in the combustion chamber this push hp to low 400's
Como
Please keep us informed, it looks very interesting on what you are doing and it will be very interesting on what you can get out of it.
Just a stupid thought is why is everyone is trying to copy the LS shape, I was looking at what you did and what came to my mine was "Chrysler" and Hemispherical head design.
This still is really good stuff, if anyone comes up with a cracker design, I hope they are willing to share their DXF drawing on it!
I’m awaiting eagerly for results.
Thougt you might wanted to see.
I am makeing some manifolds in Boadspeed style.
And also injector upgrade kit for std system.
I will let you know when finished and possible to order in my webshop. www.mobeck.com
Ole Mobeck
modern EV6 injector solution, clamps and hose fitting for std manifold and fuelrail, bolton
If I do the math for an answer to the OPs initial question, with a volumetric efficiency value of 1 the 5.3 liter v12 appears limited to 475hp. Go over 1 or increase displacement to get to 500. 6L could do it at VE=1. Larger displacements at could at lower, realistic VEs.
Significant gains are possible with way-out thinking and new tech options.
3D printed camless heads could be created to be used for casting. Pick up a set of 24 of those fancy Koenigsegg freevalve marvels. A camless head offers highly flexible inlet, outlet, valve placement and chamber design. Choose on the fly if you want torque, horsepower, or efficiency.
but in this modern day of engine performance ,, nothing can beat a set of TWIN TURBOs on a Pre-HE V12 Jag. engine! at much less costs than all the fancy modifications!
when the air is forced in instead of being sucked in a lot of flow restrictions are reduced or eliminated!
ron
This is a pre-HE head with hand shaped chambers and Chev LS1 valves.
Originally Posted by ronbros
but in this modern day of engine performance ,, nothing can beat a set of TWIN TURBOs on a Pre-HE V12 Jag. engine! at much less costs than all the fancy modifications!
when the air is forced in instead of being sucked in a lot of flow restrictions are reduced or eliminated!
ron
The only issue with this is in Australia adding a turbo to the V12 requires engineering certification. My brother went through this process with his Shelby GT500 Mustang and it cost him over $20,000 to get the car engineered, they made him de-tune it and provide dyno sheets from an approved facility or it would not be registered. 700hp was too much.
There are a couple of twin turbo XJS V12 road cars in Australia but these were built in the 1980's before fun police put all the rules and regulations in place.
