Hey guy, I'm sure this topic has been covered before but I did a forum search and didn't find anything. Anyway, I have a 91 Ranger with a 4.0L OHV engine that I'm in the process of tearing down to do a reseal, and whilst I was in there, I thought about swapping out the pistons for the ones for a 99 SOHC engine. The original pistons are dished, as I'm sure you all know. The pistons I'm looking at are slightly recessed but flat for the most part. My question is, will this work and not cause further problems? I'm looking to get a bit more power out of the engine, I mean come on. It's a large displacement V6 that produces way less power than it should. Will I have to run premium gas? Will it cause head damage? Any information is welcomed and definitely from those who have done this or similar. Thanks in advance!!

I've attached pictures of the 91 piston and the 99 piston.

91 Piston

99 Piston

 

I would say no right off the bat for a few reasons
But first, bore and stroke were the same so piston diameter and rings wouldn't be an issue and I think they used the same crank so connecting rods and piston height from wrist pin to top "should be" the same, if connecting rods are the same, thats an IF

The 4.0l SOHC runs 9.7:1 compression so can NOT run regular gasoline, Ford HAD TO add a Knock sensor so it can run regular gas
You couldn't, so you would have to use 91 and maybe 93 octane fuel all the time

It would also then be an interference engine, not that it matters

I know some people did use 1995-1997 heads with the 1990-1994 pistons, to get from 9:1 to 9.2:1 compression, so extra power but could still run regular gas