The 243's I have came from an LS2. They also came stock on LS6's. Never heard of them being available on 5.3L's, but I've led a very sheltered life.

 

Using your 3.779 bore and a OEM MLS .051 gasket and assuming the deck height to be about -.008 and 2.0 cc's for the piston head volume gives a compression of 10.397. A set of 243's will drop you down to 9.98 and 317's lower you to 9.25. I think the 243's will require a lot of Meth and reduced timing to run 15lbs. If your not going to run Meth, I think you would be better off running the 317's. With a 220 cam, I wouldn;t be surprised if a good tuner could make ,ore power with the 317's. That said, the 243's will be more responsive off boost.

This is a link to the Compression calculator I used if you wnat to play with it -
http://www.kb-silvolite.com/calc.php?action=comp

Rick

 

I think GM changed the casting number to 799 on the "243" castings they use on the LS2's and the new 5.3's.

Rick

 

At only 15psi if you run good fuel or meth you can get away with your current compression. A set of 243's or 799's would flow better though.

 

I stuffed together a forged 5.3 with flattop pistons, 241 heads, GM MLS gaskets, arp studs and a LPE gt2-3 cam. @16 lbs boost this thing really sings. It gets regularly beaten like a drum and asks for more. Pump gas and no meth.

 

I got on commetics site all they make is ls1 gaskets with bigger bores dont know if thats gona seal properly.... yah im sure wiseco could but it would cost some more money

The cam is not huge at all its a meduim size cam it is already installed before the engine blew

I can get a set of 317s for cheap or next to nothing cheapest ive seen for 243s is 500 bucks... just talked to my tuner today they recomended 317s as well.... Ide like to keep it streetable and dont wana run race gas all the time or meth....

241 heads??? what are those

 

Nvm i found it 241s= LS1 heads 66.7cc chamber gives me 9.79:1.....

Found a pair on ebay for 100bucks, sounds like my awnser thanks.....

 

I also have 6L 4" 5 layer MLS gaskets on my 347... A little bigger gasket than the bore shouldn't hurt anything.

 

241s would work well but I'd still go with either 317s or 243s

 

2nd that. The 243's are so expensive because they flow so much better than the LS1 and LM7 heads. The 317's have the same ports and flow as the 243's but the big chamber turns most people off unless they are going boosted (as in your application). They are so cheap because there are a million sets around.

Cylinder Valve Lift in Inches
Head .200 .300 .350 .400 .450 .500 .550 .600
LS1 137 187 207 223 228 237 242 243
LS6 156 204 225 243 257 267 275 278

Go with the 317's.

Rick