I have been researching an up and coming head/cam/intake swap for my ls1. I found a porter but I can't decide on which heads to use, I'm stuck between ported 5.3 or ported 243 castings. The 243 castings flow good and low/mid lift numbers are great however on the 5.3L heads would bump up compression but because of the smaller chamber would loose 3-10cfm throughout the range. My question is is the added compression of the 5.3L head worth sacrificing the CFM or is the added CFM worth it. I plan on running 1 7/8 headers and a FAST 90/90.

PS I am already set on my porter.

Thanks for the help,
Mike

 

You can have your cake and eat it too. Mill the LS6 heads.

 

I'm having LE Portworks do my heads, and came across the same issue you are. He says the same flow numbers are possible on 243, 241, 853, 706 hand ported. He had ported the heads on my ls1 swap chevelle and it ran very strong, so I feel comfortable with his statement. He swapped me some 5.3's, we'll see pretty soon how they flow.

 

OP: Are you talking about 10.5:1 LS6 vs 10.75:1 5.3's?? If so I would definately go with the LS6's.

But I have heard if you mill heads then the flow numbers are no longer the same. So find out if you mill the LS6's to get that extra bit (for example make it a 10.75:1 CR), will they flow the same or less than your 5.3's that you are also thinking about. So I would start by talking to people that port on a daily basis. And please keep us informed. I have been wanting to know this answer for a while too. LOL

 

NinetynineSS I'm also going with LE portworks.

fastvet I think the compression of the 243 heads is around 10.5:1 but with the 5.3L heads it would bump to 11.1:1 depending on head gasket size.

 

Sweet. He does good work. He told me for figuring cr, take the stock chamber volume and subract 1 cc for each 0.010" milled. I found that the 5.3 is 61 stock.