- Jan 23, 2011
Assume you have to use premium high octane fuel? Really old post so if anyone else wants to chime in, please do.I currently am running this set-up (4.6 crank & rods with 4.0 pistons) and have done so for the last few years. I have a 96 GEMs disco running 4.6 crank 4.6 rods with 4.0 pistons installed on the 4.6 rods. You gain compression up to about 10.9 : 1. I am also running a 4.6 cam and using my old 4.0 heads, intake etc.
I noticed a nice gain in both torque and power. Enough that I really like this set-up. I've been told by others that if I were to put a chip in the GEMs computer I'd see even more gains but frankly I like what I have. It is much better than a 4.0 - a very nice upgrade.
I will share as to not over sell this, good friend has a stock 4.6 Bosh in a similarly outfitted disco II and I think the stock Bosh 4.6 still might have an edge on what I have (maybe the bosh injector system or computer?) BUT the change was such an improvement from the old 4.0 I feel good about telling folks it is worth doing - - I am not sure I would have needed the 4:10's if I had this motor first.
I DO think a chip would give more power to the truck but I do not have any knocking or pinging problems and it performs well much better than it did prior without a chip added. Looking into a chip it looked expensive so I have not gotten there yet. The engine has also held together nicely - - even though the first weekend it was in the limiter multiple times.
Others have it correct you cannot nun 4.0 rods on a 4.6 crank as you will hit the heads - the 4.0 & 4.6 pistons are the same height from the wrist pin to the top of the piston the difference is in the dish size of the pistons - the 4.6 has a larger dish thus why lesser of a dish of the 4.0 piston gives you more compression.