Hey guys i cant seem to get a straight answer out of anyone. I have a set of CNC'd 243 heads going on my carbed 5.3. Everyone i ask says they used ls1 gaskets on their 5.3 with these heads but i dont understand the reasoning behind it. As long as the firing ring doesn't over hang the combustion chamber, i see no reason for not using the 5.3 gaskets. These heads came on later year 5.3's anyway.

Can someone shed a little light on this subject, i feel that it may be helpfull to others as well.

Thanks in advance.

 

It's the same gasket. You want the one for the 5.3HO/5.7

 

the 5.7 and 5.3's use the same bore gasket depsite the drastic difference in cylinder bore size?

 

the standard 5.3 uses a different head gasket I believe.

Here's the part # you need: 12589226

 

#12575329 -4.8L/5.3L GM MLS Head Gasket SOLD AS A SINGLE
#12589226 -LS1 5.3L HO/5.7L GM MLS Head gasket LS1 02-04/ 05-07 5.3L HO SOLD AS A SINGLE
#12498544 -LS1 5.3L HO/5.7L GM MLS Head gasket LS1 02-04/ 05-07 5.3L HO KIT W/ 2 HEAD GASKETS

It's cheaper to by the 5.7 HO Kit but there is the number if you happen to need a single head gasket. I would assume that since the 243's have a larger combustion chamber, it would be a better fit to use the larger bore head gasket for sealing purpouses. It may also have something to do with the quench area too. Hard for me to say though with out actually having all the parts in my hands...