6.0 cylinder heads on 5.3 HE engine

I have 2 NOS sets of 6.0 cylinder head assemblies and am also rebuilding my 5.3HE engine. A question. Can the 6.0 head assemblies be used successfully on the 5.3HE?
I am not after any performance advantage for racing, but the car has a 5 Speed Gearbox and a 3.54 diff, so would be driven differently to the normal auto.
Does anyone know if the 5.3HE pistons provide the same clearance from the top of the piston, to the top of the liner as the 6.0, when the pistons are at top dead centre?
If so I believe the CR should be as per the 6.0 engine spec? Oh and the engine will run an after market ECU and is individual coil to plug ignition using GM LS1 coil packs.

Yes the 5.3HE and 6.0 compression height (top of piston to top of liner at TDC) is about the same but you will lower the compression ratio about 2 points so if your 5.3L is 11:1 new CR with 6.0L heads will be 9:1

I would pull the 5.3L heads and look at refurbishing those. Or if you take the 5.3L to 6.0L then the 6.0L heads would be fine.

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Hi Warren, I understand your thoughts.
My position is that I have these NOS 6.0 cylinder head assemblies, ie complete from the cylinder head gasket face to cam covers and my hopes were to use these to create a hybrid. I am assuming the CR would be close to the 6.0 Litre, but I would need to chase down the math calcs to do this.
Using modern Engine management and ignition, I am hoping to recover some performance, but I guess using a ‘fast road’ cam set would only gain toward the top end of the power band (I have a set of H and S tubular headers also) and not aid much for normal UK road driving.

No the CR will not be close to the 6.0L it will be less.

CR is the ratio of total cylinder volume with piston at BDC to volume with piston at TDC.

A simplified explanation.

5300cc / 12 = 442cc per cylinder
If the total volume with piston at TDC is 40 cc then 442 / 40 = 11 so CR = 11:1

6000cc / 12 = 50cc

The 6.0L head is about 10cc bigger at so 442 / 50 = 8.8 so CR will be 8.8:1

This is very simplified and does not take into account the different piston dish volumes and head gasket thicknesses but it gives you an idea of how CR is calculated.

To get CR on a 5.3L back up to 10:1 with 6.0L heads you would need to deck the block and shorten the liners about 1mm or 0.040".

Hi Warren. After posting I went onto the JE Pistons site as it has a good explanation of the CR calcs and I realised I was being dub as I was ignoring the difference in stroke, I you rightly explained to me in your reply. Decking the block and reducing the height of the liners is possible but I realise much more thought and time needs to be applied before committing. I have found looking on the net 2 local (within 30 miles) established engine builders ( one quotes V12 experience) so I will attempt to ask the decking question to them first before thinking further, as it may be Difficult to achieve?

The other thing you could do is to use custom pistons and have the pin height set at about 1.690 and flat top will bring the CR back to about 11:1. You will need to measure as I only estimated 1.69 from the pin height of the 6.0L at 1.48 and chamber volume of 29cc that I measured.

You could also try planing the head take about 1-2mm of the head face this will reduce chamber volume (you will need to measure before deciding on pistons) and deshroud the intake valve. Basically plane the head until the intake valve is slightly proud of the head face.

The intake valve on the HE (5.3 and 6.0) is badly shrouded to about 1/2 lift really effecting low lift flow. I tested a 6.0L head on my flow bench and once my intake valve was deshrouded and a good multi angle valve seat with intake valve back cut low lift flow increased 40%

This is a 6.0L head going on a 6.7L V12 so I had to increase the chamber volume to lower CR to 10.5:1

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So a brand new 5.3 head is $320… sell the 6.0s and skip all this stuff


Warren, I do appreciate your input, they make very interesting solutions. I like all of the ideas especially the machining of the heads and de-shrouding the intake valves. I need to have a think and also detail measurements. If it is OK with you, once I feel I have a direction, would it be OK to pass my ideas passed yourself?

Yeah no problem, I am very intimate with the heads as I have spent 100’s hours on mine.

Here are a few pics of what I have done to my 6.0L heads.

Lightened stock rods, Exhaust port before and after in the last pic you can see the plug inserted in the air pump hole, and head marked up ready for chamber reshaping.

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Wow, I’ve always wondered what the V12 rods would look like without the big chunk on the side of the small end and the flat pad removed from the big end. How much weight have you taken off of them?

Thanks for sharing.

Very skilled workmanship. Is all of the re-profiling carried out using a die grinder and burrs, or did you remove the initial material using a CNC Mill and bull-nosed end mill, and then final dressing using the die grinder?
Did you manage to tap the air injection holes prior to plugging, or did the geometry not allow this? Also was the plug welded at all?

I removed about 90g from each rod so total weight reduction is over 1kg and that’s rotating\reciprocating weight,

I also balanced the rods end to end to ±0.5g and total weight to ±0.1g. That was the best I could get with the setup I had

I must add that I did all of this work with the guidance of Norman Lutz, he loaned me a rod from one his race engines,

No CNC, all the chambers and ports I did by hand with a die grinder. Those pics were before I polished the chambers and exhaust ports. All ports are sized within ±0.2mm diameter and all chambers ±0.1cc.

The air holes were plugged with aluminium rods I machined to be an interference fit. I was going to TIG them but the TIG torch would not fit in the bowl.

Just to add to the confusion, or deliver some clarity …

Swept volume of a 5.3 is 442cc. Swept volume of the 6L is 500cc.

I believe the 6.0 also had 11.2:1 CR? Therefore the chamber volume must have been 500/11.2 = 44.6 cc which suggests the difference is 5cc over the 5.3L, not 10cc as stated.

Putting this back into your example equation, we have a 6L head on a 5.3 block producing 442/44.6 = 9.9 CR??? Still a reduction, but not quite as bad as the 8.8 stated.

That assumes the chamber was all in the head. Given the 6.0L pistons are different from the 5.3L, there might be some compression volume differences taken up in the pistons. If so, the compression ratio might be higher still.

Further research may be necessary. Nick Truman measured his 5.3 heads at 41.4cc including 1.04mm head gasket (93mm bore) which is a 10.7 CR. And the 5.3L came out in 12.5 and 11.5 versions, did it not? If so the chamber volume was likely 35cc and this might lead to the idea that the chamber increased 10cc?

It would be great to have the definitive data recorded somewhere.

That’s incorrect math. CR is the total volume (swept plus chamber) divided by chamber. I think that means chamber volume must have been 500/10.2 = 49 cc.

That’s presuming the CR was actually 11.2. I heard it was 11.0.

My example was for illustration purpose only to show the OP that there would a reduction in CR.

6.0L CR was 10:1 not 11:1 I have measured my 6.0L heads with a 0.1cc burette not syringe so CC’s are accurate to ±0.2cc, I know this as I CCed the same chamber 10 times to ensure repeatability. After modification my chambers are 33cc. Original chambers were 29cc and pistons were 4cc this makes my 6.0L 10.1:1,

Assuming a 0.043" head gasket ( I chucked mine years ago and did not measure it) this gives a total stock chamber volume of 54.8cc on a 6.0L so (5993/12+54.8)/54.8 = 10.1:1

5.3L 442+54.8/54.8 = 9:1

Interesting that Jaguar lied to us about the CR. Any chance that the head gasket is really thinner, thin enough to make their claim of 11.0:1 accurate?

You can’t measure the chamber volumes without valves, can you?

It’s possible the gasket was thinner, I’ve just looked at my 6.0L engine manual and it does list the 6.0L as 11:1 so that would make 5cc difference. When I measured the piston compression height I did not stick it on the surface plate I did it with digital caliper so there may be a bit of error there too.

Thinking about it my other source of error may have been head surface. The original CCing was done before the head was machined and the final CCing was done after the head was machined, Even though I dressed the head face there may still be an error of a few CC’s if the perspex sat proud slightly, ie the head was not flat.

I was next time I visit Norm I’ll ask to borrow a 5.3HE head and piston. I’ll CC the chamber and piston and put the piston on the surface plate and measure the pin height.

The chambers were CCed with valves and spark plug installed, With valves lapped in I did not need springs for them to seal.

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It’s just that the picture of your rig shows it set up to measure volume without valves.