So I got a Gen IV 5.3 on the cheap for another project (install it in a Jeep Cherokee). It has 243 heads and I've read the benefits of milling them and throwing them over my Gen III 5.3 so it got me thinking.

The question is, what will happen to the project engine (Gen IV) if I install the 862?

 

It will up the compression.

 

How much? Is it a good thing or not? For a street vehicle

 

It's a good thing, to raise the compression up a little bit. You get more torque, and better throttle response. The 863's don't flow as good as the 243's however. That is why they are a good upgrade over the 863's. The 243's have a larger combustion chamber, hence why they need to be milled to get them back down to the stock compression of the 863's. Also, the gen IV motor has flat top pistons to raise the compression with the large combustion chambers of the 243s, where the gen III has dished pistons. So its really in all what you want to do as far as swapping the heads. Just look around on here and find more info on each platform and think about what you are wanting to do with each, and then make a better educated decision as to what direction you want to go.

 

Thanks man, I've read several posts about guys installing 243's in Gen III engines with good results so I have an idea on what to expect there, and it should help once I get the TVS1900 installed.

What I can't find is info on installing 862 heads on Gen IV engines as no one goes that route. I just want to know if it will be a significant loss of power or drivability issues that I should be aware of.

 

I really don't think you are going to notice a loss of power on the Gen IV because of the increase of compression, especially if you leave the factory intake on the gen IV because it's a 90mm vs the Gen III 80mm.