My 4.6 V8 Rebuild Thread

[101RRS]

Assume your engine builder has advised what the compression will be using the 4.0 pistons? My understanding is the bowl volume is smaller on the 4.0's. I couldn't use the 14cc version (err5553) in my 4.6 rebuild as the CR would have been to high.

You probably know this. The 4.0 pistons I had were HC. LC pistons may be the ones you have and may have the correct bowl volume.

I ended up bowling out some 4.6 HC pistons to allow the deck height to be reduced to zero tdc. Producing a CR of 10.2.

Not sure if this is relevent or helpful to you so I'll butt out.

No you make some good points. The 4.0 pistons are out of a low compression engine so should give a compression ratio of about 9.1:1 in a 4.6 - were there any 4.0 high comps sold in Aussie vehicles? Now I have not actually ccd the pistons to make sure so I might just do that.

Thanks

Garry

[davidsonsm]

I sourced the err5553's out of the States. They were supposed to be out of a 4.6 high comp but I was sent the wrong ones. They are now left over.

The 4.6 HC pistons have a bowl volume of 22cc. The low comp 32cc from memory. My engine builder milled the 22 out to 25 allowing the deck height to be reduced. The reduced deck height us highly recommended according to those in the know.

[davidsonsm]

You might be onto a winner with the 4.0 LC pistons but 9.38 was the UK spec CR for a 4.6 so I'd be aiming higher. Reducing the deck height will achieve/help but obviously the calcs need checking. It may allow the deck height to be reduced <0.005"?

[Pedro_The_Swift]

When I had mine built by Turners they quoted 9.7, which is more than LC pistons but less than your quoted HC's. hmmm

[101RRS]

You might be onto a winner with the 4.0 LC pistons but 9.38 was the UK spec CR for a 4.6 so I'd be aiming higher. Reducing the deck height will achieve/help but obviously the calcs need checking. It may allow the deck height to be reduced <0.005"?

Thanks but other than levelling the deck it is not being reduced further. Likewise not looking to get super high compression just a bit more than normal low compression. I was lead to believe that putting the low compression 4.0 pistons in the 4.6 would give a compression ratio about mid way. The LC engines are 8.3:1 and the hi comp engines are 9.35:1.

I just water volume tested the bowls in the two types of pistons I have.

The 4.0 pistons have a volume of approx 29ml and the 4.6 pistons have a volume of approx 36mm. I understand the high comp pistons are 13.23ml for the 4.0 litre and 22.29ml for the 4.6 litre pistons (can anyone confirm these last numbers.

So I have the low comp versions. So on these numbers if a bowl size of 22.29ml gives 9.35:1 and a bowl size of 36mm gives 8.3:1 then a bowl size of 29ml should give a comp ratio of approx 8.8:1. I was told 9.0:1 but my numbers might be just a little off.

Garry

[davidsonsm]

You also need to consider any machining of the heads by measuring that volume and the gasket thickness. As this all affects the tdc volume.

I was told 4.6LC pistons are 32cc. The HC versions are 22cc. The 4.0 HC pistons are 12cc. Can't comment on 4.0LC's. These were the volumes measured by my engine builder - though I could never replicate this at home issuing a 0.5ML syringe. Probably because I didn't have a flat piece of glass over the bowl with a hole in it. So the surface tension curve always seems to produce higher volumes. That's my theory.

[davidsonsm]

I'd certainly recommend doing your research on the deck height/quench volume as there are those in the know that state 0.030" as the standard height, is way too much. It allows poor combustion. Maybe you have already satisfied yourself. Just passing on my learnings from a recent rebuild. The little I know.

[101RRS]

I was told 4.6LC pistons are 32cc. The HC versions are 22cc. The 4.0 HC pistons are 12cc. Can't comment on 4.0LC's. These were the volumes measured by my engine builder - though I could never replicate this at home issuing a 0.5ML syringe. Probably because I didn't have a flat piece of glass over the bowl with a hole in it. So the surface tension curve always seems to produce higher volumes. That's my theory.

Yes using water the meniscus was definitely visible so the actual volume may be a tad less that I indicated above but I had the same height of meniscus in both tests so should ok - but not really important to the test of enduring I actually had long comp pistons and working out an approx comp ratio.

I'd certainly recommend doing your research on the deck height/quench volume as there are those in the know that state 0.030" as the standard height, is way too much.

As the block was decked on this rebuilt and certainly when it was previously top hatted I am not sure how the pistons are going to sit at TDC. When I do the plastigauge bearing clearance test will be the first real time I can measure this so I will wait until then. Because of the double deckings a little may be needed to be taken off the pistons but I do not know yet.

This is a budget rebuild and the engine is certainly no going through a fine/bluprinted type of build - just as it runs. I am mainly looking at getting extra torque through going ftom a 3.5 to a 4.6 rather than ringing every possible horsepower and torque from the new engine. Afterall it is going in a 101 rather than some fast, sleek high revving machine.

I appreciate you comments as in some aspects it is reinforcing what I have been thinking and in others making me review what I intend to ensure I get what I want out of it.

Cheers

Garry

[davidsonsm]

Completely understand. Sounds like you're on top of it. Like you say, it needs assembling up to see where you stand. Then decisions can be made. Totally agree with the aim being mild enhancement rather than hot rodding.

[davidsonsm]

Meniscus. That was the word I was looking for! A great word in its own right. Much under used.