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Hey guys. I have a c10 with a 5.3 in it. It’s got a tsp 224/224 600/600 110lsa cam. I have my hands on a set of nice 243 heads. My 5.3 has dish pistons in it and I was just wonder how much I can mill them down without hitting the valve and still running pump gas. I want the most compression on pump gas I can get. This is a NA build but might put a small shot on it one day.
Last edited by John David Long; Aug 7, 2019 at 03:23 PM.
862 heads? Smaller combustion chamber=higher compression. Or thinner head gaskets.. A .040" or .041" head gasket will also start you in the right direction. Or, pair the thin head gaskets with the 862 heads... Definitely a good bump in compression.
Run the 5.3 with the 243 heads as they are. You should make good power with those heads and that cam. Sometimes it's better to get your project up and running and then circle back to get other parts installed.
You would need 60cc chambers and a .030" thick head gasket to get 10:1 compression with those dished pistons. That's a lot of work for a small bump in compression. I'm not sure you can mill 243s that far down anyway.
Your best bet is to pull the pistons and put some flat tops in there. Either that or just put the stock 706/862 heads back on there and boost it. Either way, I don't recommend running stock 243s with those dished pistons. That would be about a 9.1:1 compression ratio with stock head gaskets.
The difference in heads that flow well like 243 heads with a .600 lift cam over the lowly 862 heads is so big that a drop in compression is acceptable. If you've ever bolted on a set of good heads you'd know to never go back.
Send the 862's to Texas speed and get their CNC job with 2.02 intake valves and 1.57 exhaust ( same as 243-799) they will give more compression and flow as good as the 243's (or better) . I did mine along with a .030 mill job and they came out great!!
I think milling beyon .030 will run you into intake manifold angle issues at the gasket mating surface.
My advice: Bite the bullet and get flat tops in there and then put those heads on. (Look at the factory L33 5.3 they ran 799(243) heads but ran flat top pistons).
The intake bolts are vertical, not perpendicular to the head like old school engines.
True, but the heads are angled. At some point you will have mating issues. I have no idea what that point is, but it is something to keep in mind. I took my heads down .030", and have no issues. FWIW....
The difference in heads that flow well like 243 heads with a .600 lift cam over the lowly 862 heads is so big that a drop in compression is acceptable. If you've ever bolted on a set of good heads you'd know to never go back.
There is more to heads than cfm. Alot more.
Port shape can make a dramatic difference even if cfm is the same. Air quality can be worth more than quantity.
Velocity around the valve . Goes on and on.
Here some molds I made . Sometimes a pic is worth more than words.
Besides the port shape and valve size
being alot different between the 2 heads. The squish pad and squish velocity is also different between the 2 heads. clay under the valve is a mold of that heads combustion chamber. Both heads have correct valve size in pics.
I've seen that article. One thing I've learned is that magazine numbers are usually skewed to reach a predeterminded conclusion. Youtube can give a better real-world idea of the performance of the different castings and 243s and 799s are the castings that the LS community uses on their rides. I wouldn't use anything less than at least the stock 241s on my '01 Camaro.
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5.3 with 243 heads 
