4.0 to 4.6 conversion

[debaron]

Hi all.

Happy new year to everyone first of all!

Secondly, I have been thinking about doing some work on my standard 4.0 engine over the winter months ahead - stripping it all down and doing a rebuild etc

I was struck by the idea of possibly doing a 4.6 litre conversion. In my limited knowledge I think it would be possible seeing as the block is the same size - it's only the stroke that is different.

Anyone have any advice or comments?

It is

a) reasonably possible

b) worth doing


So far I reckon I'd need

upgrade heads to 4.6
4.6 cam
4.6 crank
4.6 fueling chip

The rest pretty much stays the same right?



Many thanks and have a great 2011!

Ryan

[assynt road]

Hi, I believe the 4.6 engines had the stronger, cross bolted engine block, wouldn't dropping in a 4.6 out of a scrap range rover be easier? I've heard they drop straight in. Hopefully somebody who actually knows what there talking about will be along in a mo though!

[spend]

Heads are the same, conrods are different, you can reuse the 4.0 pistons.

If you have a 3.9 based TVR (ie small journal generally not crossbolted) forget it cranks / rods / pistons are all quite different.

[phillpot]

debaron said:

it's only the stroke that is different.

If stroke is longer then rods must be shorter or pistons will be popping out the top of the block !


(unless piston crown to gudgeon pin distance is reduced ??)

[debaron]

Being a 4.0 then I *should* have a cross bolted block. Therefore I can reuse the heads, pistons etc.

Definitely will need new rods Philpot - you're quite right about that.

Fueling wise - does everything else stay the same (apart from ECU chip)
No need for bigger injectors or uprated AFM etc etc.

Does anyone know what the standard trumpets were on the 4.6? Are they overly different to the 4.0

[spend]

TVR called all their equivalent of the LR 3.9's 4.0's so you can easily get confused between the terms Essentially you have the LR equivalent of a 4.0 only if your block has the crossbolting - check that first before pipe dreaming.

[debaron]

3.9?

Rats....


ok thanks Dave will check crossbolting and go from there!

[neal1980]

Just get the Crank mains turned down to the correct size.....

I was going to do this on mine then a top hat linered late block come my way so didnt need too.

Regards

Neal

Edited by neal1980 on Sunday 2nd January 13:48

[saml666]

neal1980 said:

Just get the Crank mains turned down to the correct size.....

I was going to do this on mine then a top hat linered late block come my way so didnt need too.

Surely better to use a proper cross-bolted block with larger journals etc? The non cross-bolted blocks get pretty jelly-like at higher revs. Be wary of 2nd hand though, porosity etc being the enemy. As Neal says, top-hats are one solution.

I'm restoring my 4.0 right now, and will be fitting my tuned 4.6. It was a brand new block though and only did 5k in my last car so I have no experience of top hats etc.

To get it running right I'll be having a Mark Adams chip and the necessary rolling road time. This is really necessary though as the heads are flowed big-valve jobs, pretty lairy cam etc so standard map unlikely to be much use.

Cheers,
Sam

p.s. Build it right and you'll have a quick motor. My 4.6 originally ran on a 4-barrel carb and was rolling roaded at 280bhp. It was fitted to an old Reliant Scimitar I had, and was a touch quicker than a standard Chim 500. Good

Will post results when it has been on the rollers.