The V8 Owners Forum -

I would like to have the crank of the 4.6 RV8 engine I'm building offset ground to increase capacity. The journals will be taken down from 2.2" to 2" same as 3.5 3.9 and 4.2 crank journals.

Anyone got experience of this mod? Does anyone know which rods I need to use? If I can use modified yank rods that's fine as I'm off to the states next week and can collect when I'm over and bring home for machining.

Any info would be appreciated, thanks.

Paul.

The big ends on a 4.6 are 2.2" dia not 2.5" as you have stated.


Probably was a typo

Denis

Yea sorry 2.2! amended.

Hi
The 2" rods are small block chevy small journal, handy in that you can add chevy pistons without bushing the small ends, you could go further and co for NASCAR 1.8" rods, that size takes a honda accura big end bearing (from memory) they are also very light and good for 850+ bhp n/a they are usually pretty cheep on ebay, especially this time of year.
Both would need slimming down to fit (though you may find 1.8" rods with narrow journals) good luck.
Best regards
Mike

Blimey Mr. Muscle, it did not take you long from finding out about this mod to posting something up!

I will also have to do this mod now because there is no way that you can have more BHP than me!

Guys, I believe that there are rods which can be used that allow you to keep the Rover pistons, it would be great to know which ones they are. (I've googled this a bit last night and it might be the Honda rods or was that just the bearing?)

What do you lot think with regards to the con-rod ratio, I guess it will have to get worse if I stick with RV8 pistons as the rod will have to be shorter.

Anyone know what the stoke ends up being, I guess I could work it out but if someone knows that would be great!

4,6 big ends are 2,185".

As for rods, you need to consider also the comp height of the pistons. Longer the stroke, closer the deck the piston will be at TDC. With poorly mismatched parts the piston will be above the deck.

With 2,0" big end common SBC rod lengths are 5,7", 5,85" and 6". Big end size is 0,927" (Rover 4,6 has 0,940"). Most Rover pistons have quite big comp height so best option would be to find a piston with Chevy pin size.

With longer strokes you actually need to buy longer rods: at BDC the piston skirt needs to clear the crank counterweights. I have a 91 mm stroke crank with pin width machined for TVR500 rods. These rods (normal Rover rod length) with TVR500 piston will not allow the crank to rotate, the skirts hit the crank.

Hi
Sorry I thought the advantage of chevy pistons was so obvious not to need stating, however, they come in many many compression heights, they are much cheeper than rover (for any given equivilent) and they are available as cast, hyperutetic and forged all without breaking the bank! if you want to use rover rebush them or ream out the rover pistons.
Best regards
Mike

Thanks for the info guys. Sounds like I need to go for Chevy rods and pistons. How do I work out which length of rod and which Chevy piston I need.

This article should have all the tech explanation you require:
http://www.hotrod.com/techarticles/engi ... ewall.html

'Nascar' rods really require custom pistons made, better to go all Chevy (302/5 pistons & small journal rods) and select a stroke to suit the deck height rather than try to eek out every last cc of stroke IMHO.

Or you could ask V8D about their 5litre, or if they can do a 94mm based version?

Hi
now that is a question. . . there are several places to start, the easiest way is first decide on which rods you want to use. . Say 2" diamiter 5.7" long small journal rods, are you starting with a blank un machined crank (boosted LS1 used to have a supply of them) or an already machined 4.6?
if it is the already machined 4.6 then your new stroke is the 4.6 stroke plus half the differance in journal diamiter less about .02" so you can machine down to a clean surface all around.
Now find out the rover deck height (crank centre to top face of block) and get take away .02" so you can machine it to give you a flat deck square to the crank. Take away half the new stroke take away the rod length and see what you are left with, now hunt through Ebay, piston catalogs etc and see if there is a chevy 305 piston with a compression hight close to that number. You want to be within about 10 thou and you want it to be 10 down the bore so you can either get 10 thou more left on the stroke (from that 20 thou you put in as a fiddle factor in the first place) of chop another 10 thou of the deck of the block. If this doesn't work then try a different length rod and have another go or tweek the deck machining or stroke a bit more. From recent memory the 5.7 rod, .02" off the deck and a 4.6 crank machined down with 10 or 20 thou off the max works out with one of the common chevy 305 piston deck heights. One last thin you need to bore the engine to a 36 thou overbore it should give you about 4.8 to 4.85 litres.
For an unmachined crank then it is much the same process but you probably start with the compression height of the shallowest piston you can find and the rod length and work toward the stroke as that is the easy thing to change.
Best regards
Mike

Thanks Mike, sounds a bit beyond my basic skill level.

The crank I have is a used 4.6 which I was hoping to get reground with 2 inch journals. The idea came from a conversation I had with Roy Burrell -who has a long association with John Eales. Roy will be doing the work on the heads for me.

I am going to call Roy again tonight to see if he has any more info as I'm sure he said there was a conversion using the earlier Rover rods and rover pistons which gave a capacity of around 4.8 or 4.9, perhaps I got it wrong maybe they are bespoke JE items.

All you need to know for 4.6 crank stroked to 3.4" (see bottom of the page ): http://www.aluminumv8.com/tech/tech.htm

minorv8 wrote:4,6 big ends are 2,185".

As for rods, you need to consider also the comp height of the pistons. Longer the stroke, closer the deck the piston will be at TDC. With poorly mismatched parts the piston will be above the deck.

With 2,0" big end common SBC rod lengths are 5,7", 5,85" and 6". Big end size is 0,927" (Rover 4,6 has 0,940"). Most Rover pistons have quite big comp height so best option would be to find a piston with Chevy pin size.

With longer strokes you actually need to buy longer rods: at BDC the piston skirt needs to clear the crank counterweights. I have a 91 mm stroke crank with pin width machined for TVR500 rods. These rods (normal Rover rod length) with TVR500 piston will not allow the crank to rotate, the skirts hit the crank.

Jukka,

have you seen last offer of Paul : http://www.v8tuner.co.uk/product.php?id=874

Muscle-Manta wrote:Thanks Mike, sounds a bit beyond my basic skill level.

The crank I have is a used 4.6 which I was hoping to get reground with 2 inch journals. The idea came from a conversation I had with Roy Burrell -who has a long association with John Eales. Roy will be doing the work on the heads for me.

I am going to call Roy again tonight to see if he has any more info as I'm sure he said there was a conversion using the earlier Rover rods and rover pistons which gave a capacity of around 4.8 or 4.9, perhaps I got it wrong maybe they are bespoke JE items.

Paul,

3.4" stroke with rover 5.66 rods, some pistons for you : http://www.v8tuner.co.uk/product.php?id=425

Dimitri, interesing indeed !

Now I know what I want for Xmas... ! Pity I have to finance it myself.

I doubt the Missus will pay for that lot...