Need Options/Opinions
 

Alright so here it goes.
I've been wanting to do this build for a long time now. I finally got my hands on a motor for a reasonable price. Guy sold me what he said was a 5.3 out of an 02 truck with 160k. okay cool went picked it up I'm a happy camper yada yada ya. So i get it mounted to the stand. Been slowly picking it apart over time since I work a lot. I finally get to pull the heads off. Discovered that it wasn't a 5.3 because it had flat top pistons. It's a 4.8. so here's where I get stumped. I had a decent plan for a 5.3 build in mind (not completely made up but generally what I wanted to do with it.)
I had planned on taking a 5.3 and boosting it since it seems to be cool and bank account friendly for the most part and also sounded like fun to me. I had done all kinds of research on top of things I already knew and decided I was gonna give it a shot. Planned on keeping the stock bottom end with some good hardware upgrades. Wanted to do flat tops since the 5.3 didn't come with them til the high output l33 that I know of. I was pondering on upgrading to gen IV rotating assembly to try and prevent having the crank re balanced for gen IV rods and pistons because they seem a little better built to take more abuse and have floating pins. Planned on trying a btr stage 2 turbo cam and doing away with the 706 heads and searching for 243/799 heads to put on with the trunion kit and good springs and all that good stuff. Throw a decent intake and fuel system on it with a turbo in the 70-80mm range and see how it rolls. Was shooting for somewhere in the 500-700hp range to have some fun with and put it in an s10 for a street/strip deal.
So now my questions are. After discovering that I have a 4.8 instead of the 5.3 like I wanted, what can I do with it? Would I be able to apply most of what I wanted to do to the 4.8 and it be okay? Would I have to find certain parts specifically for a 4.8 to make it work like for the cam an stuff? Would I maybe be better off trying to find a Gen IV 5.3 rotating assembly with flat top pistons to make it what I want so I don't have to do any balancing with the crank or changing plans? I already have the engine so I don't want it to go to waste and start from scratch again to wait for an actual 5.3 at a good price and trying to avoid a machine shop at all costs except to clean the block. I can do the cylinder hone myself.
What do you guys think? I need more options and opinions. I've considered leaving it at the 4.8 to save the hassle of trying to find parts to make it a 5.3 but I wanted a 5.3 since that's the one I originally had plans for.
Thank you thank you and thank you again in advance!! (Sorry for the long story)

Just use the 4.8 as-is. Don't swap heads. Leave it. I probably wouldn't even remove the heads.

Anything that isn't rotating assembly related is completely interchangeable. You can swap a 5.3 rotating assembly into the 4.8 block if you want to. I'd personally just run it.

What kind of power would I make though? I want it to be fun but I also want it to be fast too. I was gonna disassemble the whole thing because it looks terrible and needs a good thorough cleaning inside and out. Probably do new crank and rod bearings as well as piston rings too while I have it apart. I wanted the other heads for the better flow so I wouldn't have to worry about doing anything to them instead of doing anything with the 706 heads. I've pretty much been lost with it since I found that it's a 4.8. I know the only real difference between them is the pistons and the stroke with the crank and rods but like I said. I already had a half decent plan for a 5.3 so discovering that I didn't have one really threw my plans off lol. I'm still a rookie here. I need some advice on it for sure.

The loss of compression with lower your power more than the flow difference will gain it. You're downgrading.
The smaller engines don't have much CFM demand even when boosted, so they're not straining with the 706/862 heads and don't gain much upgrading to 243/799.
I'd personally avoid ever putting them on a 4.8, except for a few specific circumstances.

If your power goal is 500-700, then I'd say you'll make 500-700.

So I should keep the 706 heads then? Is there any recommendations on what I should do with them to maybe squeeze a little extra power out of them then or just leave them as they are and upgrade the valves, rockers and maybe push rods??

Leave them stock. Don't overthink it. Stock valves and rockers. Roller rockers are really only necessary above ~.620 lift where the stock rocker tip starts to become unstable on the valve stem.
Pushrod choice will depend on cam/springs. Mild cam and springs will allow you to run stock pushrods.

You WILL need to upgrade valve spring with boost, even without a cam. My 240k mile stock 4.8 had major valve float issues at 5500 RPM with boost.
The springs lose seat pressure after a lot of miles and can't keep the valves closed like they should.

I figured I'd have to do springs for sure. Was just considering the rockers and such for logevity. I was looking into a stage 2 turbo cam from BTR. Actually since I made this thread I went back and looked and they do have a stage 2 listed for a 4.8 as well so I may go with that one since I've been talked into keeping the engine as is. How does the push rod selection work? Like how do I know which ones to get or what size?

You'll have to get a length checker to be sure.
If you use stock thickness gaskets, don't mill the heads, and run a cam with a stock base circle, then you will run stock length pushrods.
As far as which ones, pretty much any hardened pushrod will be fine.

What do you mean by stock base circle

The diameter of the lobe that the lifter rides on. If its smaller than stock, the lifter sits down farther in the engine and the pushrod will need to be longer. If its larger than stock, it'll hold the lifter up higher and you'll need a shorter pushrod.

Personally not a fan of BTR cams. If I wanted a Comp cam I would just buy one from Comp. But if you want to go that route, the stage 2 4.8 turbo cam is a very good choice.
I don't see any reason for it to have a different base circle. That is usually reserved for larger cams. The stage 2 4.8 cam should be fine with single beehive springs and stock pushrods as well.

Would I have to buy the cam first and measure before I do pushrods or what's the math behind it? I'm full of questions now that I got to thinking about all this. Lol

Everything will have to be installed minus pushrods.
There shouldn't be any reason for you to need anything other than stock with the stage2 4.8 cam.
I've never ran anything other than stock pushrods on countless combos, but I'm careful to keep my tolerances in check.

Right. That makes sense. I'm just getting these questions out of the way now so I don't have to make more threads as I go with the build. Is there a set of stock size pushrods on the market that are better than what's in the engine or?

There are probably dozens of 7.400" pushrod options out there.
Don't run super stiff springs or an unnecessarily aggressive cam and the stock ones are fine. I've had them up to 30+ pounds of boost and 7600 RPM with no issues.

https://www.briantooleyracing.com/single-bolt-4-8-turbo-charged-stage-ii-camshaft.html
Thats the link for the cam I'd like to get. There's actually 2 stage 2 cams listed for the 4.8. the one in the link says sigle bolt and the other one doesn't say anything about single bolt. Not sure what the whole single bolt thing is or if I need it or not. But I'll let you guys see the specs on it and tell me if the stock push rods will work with it or not...

You just clicked on the single bolt version instead of the 3 bolt version. You'll need the 3 bolt version.

https://www.briantooleyracing.com/4-8-turbo-stage-ii.html
so it's this one then.

That's the one.

Will the stock push rods work on this one?

As long as your valve springs aren't too aggressive, yes. The intake lobe on that cam isn't super friendly.

I'd probably get a cam with duration in the mid .500s, PAC1218 springs and be done with it.
Stock pushrods and rockers, stock heads, stock shortblock.
In order of power production from lowest to highest:
https://www.summitracing.com/parts/c...make/chevrolet
https://www.summitracing.com/parts/t...make/chevrolet
https://www.summitracing.com/parts/h...make/chevrolet

First one is very tame, last one will have a little bit of a cam lope at idle. I've used the last 2, and as for the first... Cam Motion does awesome work.

If you can get ahold of an Isky Triple 12, its basically a CNC unicorn horn for 4.8/5.3 turbo setups.