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Discussion Starter #1
Swapping in a 4.6 for my tired 3.9 into my 94 RRC I have an idea of what I need but just looking to see if anyone could steer me in the right direction, I think there may be a typo in the Rave. Its says on page 12 of the 4.0/4.6 overhaul manual the the big end journals on the crank should measure 2.20-2.22in but other sources claim 2.185in to be the diameter of the big end journal. My crank spec is 2.499 for the main journals and 2.185 for the big end journals. My measurements seem to be the spec according to this other source http://books.google.com/books?id=gmSavy1RPxEC&pg=PA12&lpg=PA12&dq=rover+4.6+crankshaft+big+end+2.185&source=bl&ots=nh0x9w8nrY&sig=tn8gKrWzfkqqcsw4b0t7DvHzZ4E&hl=en&sa=X&ei=8lpkVL2aPImcygT5pIH4DA&ved=0CB4Q6AEwAA#v=onepage&q=rover 4.6 crankshaft big end 2.185&f=false (page 12)

Am I just looking at the rave incorrectly?

Additionally I have a 3.9, a 4.0, and a 4.6. so is it worth running the 4.0 pistons with 4.6 crank and rods? Are the heads from the 3.9 interchangeable with the 4.0 heads?
 

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Discussion Starter #2
There is a typo in the rave 2.185 converts to 55.499 mm
 

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1995-2002 Range Rover P38A
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3.9 and 4.0 litre heads are the same (as are 4.6) except later 4.0 litre heads don't have the 4 lower holes for the bolts you don't want to fit anyway. 4.0 litre and 4.6 litre pistons are not the same, despite having the same diameter, the gudgeon pin position is different. 4.0 litre and 4.6 litre con rods are a different length too.
 

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Discussion Starter #4
I understand the pistons are different between the 4.0 and 4.6 from what I've seen and read this difference relates to the dishing on the crown of the piston. The 4.0 pistons are dished smaller so when used with the 4.6 crank raises the compression ratio to somewhere around 10.9:1. I already use super have both sets of pistons and can simply turn the dizzy to correct the timing. But will raising the CR give me anything more than theoretical internet horsepowers?
 

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1995-2002 Range Rover P38A
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The difference isn't only the crown, it's the gudgeon pin height too, there's about 2mm difference. Raising the CR will only benefit if you can get fuel to suit, what do you regard as Super? Over here, Super is 98 or 99 Octane but normal is 95 RON and I understand it is lower in the US. If you can't get the fuel you'd need to retard the ignition timing to prevent pre-ignition so would gain nothing. If you were in the UK I'd say set the car up to run solely on LPG, which has an Octane rating of 113 RON, so you could run higher compression and more advance.
 

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Discussion Starter #6
I see what you are saying about the gudgeon pin hight. From examining the design of the pistons it would make sense that with the shallower dish in the crown of a 4.0 piston, that the whole piston can be moved up 2mm. This seems more logical than a 4.0 piston just being a 4.6 piston with more material within the dished crown.

You bring up an interesting point with regard to fuel. After some research it seems our fuels in the US are rated differently across the pond you guys use RON while in the US we use the average between RON and MON. So its (RON+MON)/2

US regular is 87octane, 91RON
US midgrade is 89octane, 93RON
US Super is 91octane, 95RON
US SUNOCO Super+ 93octane 98RON

Its all a bit confusing
 
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