4.6 pistons

neal1980 · Post by **neal1980** » Fri Jun 29, 2007 10:06 pm

Hi,

I have a 3.9 small journal engine, can i fit the later style 4.6 pistons to my rods? or with any modification??? Ive been told they are a much better piston to use...

Thanks

Neal

ihatesissycars · Post by **ihatesissycars** » Sat Jun 30, 2007 9:07 am

They have a different size gudgeon pin so no.

neal1980 · Post by **neal1980** » Sat Jun 30, 2007 12:34 pm

is it not possible to modify the rod at all ? or the pin?

The Original Tom · Post by **The Original Tom** » Sat Jun 30, 2007 1:29 pm

Rods tend to have quite limited material on the small-ends, so I'd not risk drilling them out to acept bigger pins. But if the 4.6 pins are smaller then the only way would be to use the bigger pins and drill out the holes in the pistons.
I'd not trust either way as the speeds and forces they're subjected to are horrendous, so eroding the safety-margins is just asking for a nice big hole in the side of your block IMO, unless snyone else has already tried it with (or without!) success.

ihatesissycars · Post by **ihatesissycars** » Sat Jun 30, 2007 4:56 pm

There is another option, get a 4.0 rotating assembly and have the mains turned down so that the crank fits in your block and use the 4.0 crank, rods and pistonswhich are the same strength as the 4.6 stuff other than dimensions.

You got a better rod ratio too as the 4.0 rods are alot longer than 3.9 rods (the gudgeon pin is higher up in the piston) so a mroe reliable, stronger setup, or so I've been told.

I just so happen to have some mint looking 4.0 rods, pistons and crank. . . .

Post by **katanaman** » Sat Jun 30, 2007 5:45 pm

that's another reason you cant use 4.6 pistons, the rods are a diff length so the pistons have a diff crown hight.