This is what my porter said about going with some 241's on my truck...



Hey Ben,

I dont think using these heads is the right thing to do.Your factory heads have a 61cc chamber and the 241's have a 66cc chamber.Milling .030 off the 241's and a thinner head gasket give you only around 9.8 compression.Milling .020 off your heads and the thinner head gaskets give you around 10.4 compression.The second reason is the combustion chamber in the heads are 3.900 diameter,with your smaller bore there will be a lip and the top edge of the cylinder reducing flow.the third is the bigger valves will come real close to the cylinder wall above .450 lift shrouding the valve real bad reducing flow.All the research ive done says the the only difference in flow is the smaller valve.The runners are the same.I believe with the small bore the smaller valve would be better-less shrouding.If it were me i would mill your stock heads,thinner head gaskets and some porting.I think it would run tons better.

 

I think I would have to agree. Have the work done to a set of 5.3 heads instead.

 

sound reasonable enough, you could throw some under cut valves in there to help out a little with flow if you want or are worried about it.

 

Your head porter is 100% correct. The port cores are identical except in the bowl area of the intake. I use a 1.940" dia. intake valve on our Stage 1 heads and with some hand prep work our heads are worth over 40cfm peak flow and nearly 20 bolt on hp. The smaller chambers keep the compression where it needs to be. With the larger valves one thing is certain, you will lose torque at 1600-1800 rpm. The torque will even up above 2500 and at 3000rpms you'll see your torque gains improve.
Mill the heads to gain the compression. It carries torque from bottom to top. Just don't get too crazy or you'll end up with a pump gas nightmare. About 10-10.25 should do the trick.

Good luck,

Richard

 

i'm not going to say a word.

 

kinda what I figured... the castings were given to me so I was just mainly seeing what they could be turned into... I'm looking for about 10.5:1 comp...

once this fifepointree goes, its getting bored to 3.898 and maybe then I can do something with these heads... Thanks Richard. Always helpful

 

Yeah, the 5.7l conversion is a great upgrade. An increase of nearly an 1/8" in bore can't hurt. Then you can up size the valves and do a more thorough port job on the 5.3l heads.

Good luck,

Richard

 

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