243 heads on 5.3
 

I'm gathering all the parts to swap a set of 243 heads onto my 05 5.3. And as I was doing some reading i came up with a few questions that I found weren't being answered.
1. I don't plan on milling the heads to get closer to the stock 5.3 heads compression, is there any problem with that or will they preform better if I have them milled?

2. What size of gasket are recommended? 5.3 head gaskets or 6.0 head gaskets?

3. Should I swap out the lifters, 63k on the motor, been looking at swapping lifters, some say it's needed, some say it's not.

4. I have 7.400 pushrods from Texas Speed, do I need different pushrods? Or will these work?

Also plan on running about a 150 shot on the truck in the future, don't know if that will make a difference or not.

Thanks in advance.

243 was a stock head on L33 5.3L's as early as 2005. L33's have flat top Pistons though, so you may need some thin gaskets.

You'll go from 9.5:1 to about 9.1:1 by swapping on those stock 243 heads. N/A low-RPM torque will suffer a bit. Milling them to regain the compression would be a good idea.

Nitrous would show gains due to the larger intake valve of the 243, but only marginally because you're not changing the cam, intake or exhaust system.

You would need to use a head gasket that is slightly larger than the chamber diameter. I believe you would need 3.91" bore (LS1 bore). Verify by laying an old 5.3 LM7 gasket over the chamber. IF the edge of the gasket protrudes into the chamber, you need the 3.91" gasket.

With no other changes, I really don't see the sense in swapping heads on a stock LM7. You're not modifying it enough or revving it high enough to take advantage of the better head flow. Put a cam and a tune in it first.

Swap to 4.8 pistons and you will keep your compression and gain the flow from the 243s.

Or mill the heads 0.030" to get compression back and don't mess with the bottom end. Seems easier to me and that's what I will be running.

The stock lifters are fine and will be good through 200K+ with the stock cam. Yes it would be nice to swap them out while the heads are off, but its over killl so save your money.

Yes mill the 243s and you will need a push-rod length checker, but it will probably be around a 7.375" pushrod

Honestly I would not put the 243s on the motor unless you have a cam to go with it. GM put the 862s with smaller 200cc 70cc runners and smaller 1.89" valves to keep up velocity for low end tq for the tiny 4.8 and 5.3L. The 243s will decrease velocity and if not milled will lower compression. This will probably turn your truck into a dog bellow 2500 rpms.

Air flow volume = top end hp
Air flow velocity = lower end tq

I would sell those 243s and use the money towards a set of long tubes to gain power throughout the rpm range, and nitrous will love those headers more than stock 243s

Forgot to add the truck already has full exhaust, longtubes, y-pipe and full 3in exhaust out the back and is already tuned. Also, I already have my cam and will be doing the head cam swap at the same time along with 3600 stall, cam is 221/221 .575/.575 on 108 lsa.

Wow, that thing is going to be choppy as duck.

Oh well in that case....have the heads milled get a thinner 0.04 thick gasket (I would double check that these gaskets wont cause and issue with nitrous) and a pushrod length checker. With how aggressive this build is, might want to consider having the 243s ported.

The Ls1 gasket will work and will be slightly larger than the bore, which is what you want like mentioned before.

Haha, that's what I'm going for.