quick noob head question
heads well yes and no the 5.3 have smaller combustion chambers raising your compression ratio BUT they for what ive seen have smaller intake valves - one helps one hurts. now a Aftermarket ported set like TSP 5.3's have bigger valves, more compression and being CNC ported - great bargain set of heads! I have a set of '03 706 casting 5.3 heads f/s if you are looking to buy a set that is stock - hope this helps ya out 
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No, that is "fly cutting". Lapping the valves is like a mini valve job, where (correct me if im wrong) but you only refresh the angle on the valve face instead of cutting your classic three angle on the seat and then the specified angle on the valve face.
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soo....what he's saying is that the 243 heads would make more power than a set of ported 5.3 heads?
I kind of thought it was the other way around.
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Lapping the valves in is as simple as going to Advance or Auto Zone getting some lapping compound and just making sure the valves seal. That's really the whole deal with lapping in the valves, just making sure they are sealling properly. Even some of the new ported heads sold on this site have valve sealing problems and should be checked before installed.
I didn't say the stock 243's would make more than ported 5.3's but they will come close to some of the ported 5.3's. Your question was will stock 5.3's make power on a LS1. And IMO they're not worth the time or money to swap them on your engine. A stock set of 243's will give you better gains and will give you a head that can put you in the 500rwhp range if you decide to have them ported later.
I didn't say the stock 243's would make more than ported 5.3's but they will come close to some of the ported 5.3's. Your question was will stock 5.3's make power on a LS1. And IMO they're not worth the time or money to swap them on your engine. A stock set of 243's will give you better gains and will give you a head that can put you in the 500rwhp range if you decide to have them ported later.
To say a stock LS6 head outperforms any decent ported 5.3L head is ridiculous. And lapping in valves doesn't make an LS6 head flow any better than an out of the box LS6 head. It just ensures, in most cases, that the valves will seal as good or better.
We've seen an average of 30rwhp, depending on camshaft and other mods, by swapping from stock LS6 to the PRC Stage 2.5 5.3L heads. You get the benefit of the bump in compression because of the smaller chamber, and better flow across the entire lift range, with one of the smallest CNC'd intake ports available for the 5.3L heads today!
Call, e-mail, or PM us if we can help. We invest countless hours and thousands of dollars on engine and chassis dyno testing each year (not to mention track time) to ensure that when we say one of our products will gain you XXrwhp that you do!
We've seen an average of 30rwhp, depending on camshaft and other mods, by swapping from stock LS6 to the PRC Stage 2.5 5.3L heads. You get the benefit of the bump in compression because of the smaller chamber, and better flow across the entire lift range, with one of the smallest CNC'd intake ports available for the 5.3L heads today!
Call, e-mail, or PM us if we can help. We invest countless hours and thousands of dollars on engine and chassis dyno testing each year (not to mention track time) to ensure that when we say one of our products will gain you XXrwhp that you do!
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Largest Stocking Distributor of LS-x Engines / CHECK OUT OUR NEW WEBSITE!
COMP - FAST - PACESETTER - DIAMOND RACING - EAGLE SPECIALTY PRODUCTS - CALLIES - COMETIC GASKETS
RAM CLUTCHES - MOSER ENGINEERING - KOOK'S HEADERS - ARP - GM BOLTS AND GASKETS - MSD - NGK
POWERBOND - ASP - AND MORE!