Is there any difference between the two? And what are the cfm ratings of each?

 

I believe the only difference beteen the 5.3 and 6.0 is the stroke (lengthened in 6.0), bore and heads remain the same. Have no idea what the CFM rating is. You sure you're not looking for the CC capacity of the combustion chamber in the heads. You can determine CFM on a flow bench...

 

Cal. the heads are from two different PLANETS, both are engineered for two different reasons.

PRE-HE for performance ,,,,,,,,,,,, HE for fuel savings.

 

Im talking about the he on the 5.3 vs the he on the 6.0

 

OK , the 6.0 has a slightly larger chamber, so as to lower the comp.R a little. because of probs with detonation.

CFM? not much out there on HE , but there are some numbers for pre type. you could get a flow bench(mentioned here), and come up with your own numbers!

SERIOUS race guys dont. use HE heads for SERIOUS racing, simply because they just do not flow well at hi rpm, no matter what you do to them.

the HE exhaust valve area is prone to hot spots and dropped seats,along with possible detonation that can pound a bearing and then go into a spin.

the pre with big valves and a big bore with a top liner relief flows the highest CFM , of any Jag V12, you should be aware that just a hi CFM port flow does not mean you can get the air into the cylinder, or out of the cylinder.

as you are finding out,ther is a lot to building a hi-performance engine,and it aint cheap, even if you do the work yourself.

 

I plan on using pre he heads eventually. It's a streetcar that won't see much over 6.5k rpms. With approx 7l in the motor displacement. Run 12:1 comp goal 450+ HP

 

You will not get 12:1 from pre HE heads there is not enough squish.

Broadspeed used flat heads and then machined chambers in the heads, they didn't run flat heads in the XJ-c.

The 6.0L heads flow better than 5.3 because the chambers are larger in order to keep CR at 10:1 or so depending on market.

I have attached a pic of both chambers. You could machine the 5.3 chambers to de-shroud the exhaust valve and smooth the step on the inlet. I was talking to the guy I bouht my 6.0L from he used to build V12 race engines for power boats and also built engines for the XJS racers. He believes opening out the chambers in the HE will work, not quite as good as starting from a flat head and machining but worth the effort.

 

How much should i go about machining off?

 

How long is a piece of string...lol

It depends if you leave the capacity at 5.3l and machine the chambers you will drop the CR. If you increase the capacity and leave the piston TDC the same deck height and do not increase the chamber volume you will increase you CR.

CR is the ratio of swept volume to compressed volume, so (for ease) lets say 5300/12 so each cylinder has a swept volume of 441.67cc if the volume above the piston at TDC is 44.167 your CR is 10:1.

If you increase the engine capcity to 7.0L and do not change the compressed volume your CR will be 13:1.

You need to first decide what configuration your engine will be If you decide on 6.5L then DO NOT change your mind.

Next you need to set the piston deck height. I would keep it stock so you have good squish. I think stock is Zero ie the piston is flush with the deck at TDC*********YOU NEED TO MEASURE THIS*************

TO set the deck height with the selected stroke requires the piston pin to be a certain distance from the piston crown.

Once you have this locked in stone then you can calculate your chamber volume, remember to take in account head gasket bore diameter and thickness. I would not go any thinner than 0.043thou on the gasket crushed.....

 

HI All.. I was trying to locate a set of 5.3 head studs and wonder if any one knows if there is a difference between a set of the studs for a 6.0 .. Im sure having a time trying to find a set and thought if they were the same , it gives me a broader search area... Thank you so much for any response. Mack

 

The studs are identical. You can buy a full set from (eg) David Manners, SNGB, etc. Not cheap in total because there are so many of them!
Greg

 

Warren
From your photos its a bit hard to compare sizes, are the inlet's the same size on each?
Funny this has come up, as I am trying to find a design to alter the standard 5.3 HE heads to give a little more, I can see the difference in the exhaust but I need to get a little scale in the equation. With an NC mill you could easily alter the complete thing, any ideas there?

 

Thank you Greg for the information.. I will try to locate him on the internet..

 

just noticed between the 5.3 and 6.oL valves are, they lighter weight slightly tuliped for the 5.3= higher rpm, probably didnt help much
performance tho.

also you can use a custom piston in the pre-he for both squish and turbulence, and raise the comp. ratio to at least 13-1

 

Allan Scott's book has quite a bit about how TWR achieved this on pre-HE heads, special pistons were required to get it, but a decen-tish squish and atomisation was achieved. All within the standard bore, too, so quite relevant to CDK's situation.
Greg

 

The valves are the same between the 5.3 and 6.0 going larger valves in the same bore is just going to make shrouding worse. A better way is to re-profile the valve and seat to increase flow.

Talk to Eddie at Headstud Developments in Melbourne. He is probably one of the best head developers in the country. Worked on the Holden Bathurst development in the early days.

Here is what I would do
- Re-cut seats for multi angle (Thronleigh Cylinder heads can do this)
- CC chambers.
- Ceramic coat chambers and piston crowns.
- Match intake manifold. There is a very rough 45° angle cut in the head intake port where the manifold mates.
- Enlarge the exhaust manifold, Ceramic coat inside and out

If you leave the engine 5.3L then the chambers will need to be welded and re-shaped to keep CR around 10:1. Easiest way to make power in a Jag V12 is FI, a couple of Subaru TD04's low boost 6-9psi.


Ron the 5.3 valves are the same Part number as the 6.0L (valves did differ for market)

 

Thanks Warren, Fantastic information. Not really interested in the FI as I have to the leave the car as standard looking as possible due to the classic plates its on, but nobody knows any better to what's in the inside.

 

funny you mention the V12 mods,

my build of my V12 ion 1995, almost a repeat by you!

recut valves seats multicut angles to match oversize valves.

CERAMIC coat flat chambers and piston tops,plus coat exhaust ports(i consider important) in heads.

match inlet mani to head before internal abrasive machining/Extruded honing same.

enlarge exhaust manifolds then ceramic coat inside and out side to reduce under hood temps,and keep exh. flow velocity up, along with larger down pipes.

the pix you posted show a difference in head of valve, 5.3 are hollow tuliped, and the 6L show a flat top of valve, usually that indicates a better under head profile of the 5.3 valve, and reduced weight, of course best way is to hold the valves side by side!

as usual a may have been ahead of the curve back then, especially in the USA Jag world.

plus a number of other mods etc.

 

Hi Ron
No those 5.3 valves are not tuliped this is just discolouring of the valve

 

Yep I get this.

You could offset grind the crank to 74mm stroke and bore the liners to 92mm for about 6.0l

Or weld and grind the crank for 78mm stroke, about 6.2L

Or just bore to 92mm for 5.6L. I know 202 Holden pistons have been used in the V12 before.