velox65

iTrader: (9)

Got porter 706s on my car have a shot at some 243s what would I gain. And what are the worth need a answer pdq please.

frazierboy98

Do you mean you have ported 806s?If so vs. stock 243s or ported 243s?

velox65

iTrader: (9)

No 5.3 706 heads ported vs stock 243

frazierboy98

Oh ok thought you might have been talking about the 806 perimeter bolts.In that case its according how much your heads were ported.A stock 243 is 66cc and yours are I believe 59cc which means you will lose compression unless you have them milled before you put them on.A 243 has 210 intake runner 75 exhaust.Id say if you have them milled then you may pick up 10 or maybe 15 if you are very lucky but like I said its according what kind of port work you have on yours already you may not gain any at all.Some people prefer the 5.3over the 243s.

wytry

iTrader: (6)

Personally myself, if you have a good port job on the 5.3's, I would keep them. I will be going with those shortly because they flow well and give a bump in compression (btw I DO have the stock 806's, and ANYTHING flows better than those lol)

velox65

iTrader: (9)

Ok so what if I have em milled and have them Cnc ported? They came off a ls6 vette

wytry

iTrader: (6)

You could certainly have the 243's milled to up the compression. Just remember PTV clearance, but I would imagine it would be similar to the 5.3's, so guessing you should be alright there (but deff check). As far as porting, depends on who is doing them and how reputable they are. Same guy that did your 5.3's? I've seen P&P 243's that cost twice as much or more than P&P 5.3's. Yes, they flow better throughout the entire range, but not usually more than 10-12cfm or so (just judging from the flow numbers I've commonly seen). You be the judge whether or not paying for port work and milling would be worth that little flow difference. I believe intake runners on both are generally in the 215/220 range for both, so very similar. So my opinion, unless he is especially skilled at working over 243's, keep your heads or sell both sets and buy Trick Flows, AFRs, or other well known, tested, high-flowing heads. Research, personal experiences, and budget is what it boils down to. Good luck on your quest!

hammertime

iTrader: (1)

There are too many variables here for anyone to give you a solid answer. Your ported 5.3 heads could be junk, or they could have given you a four MPH gain in the 1/4. Stock for stock, 243 heads are definitely better than a 5.3 head, but once the castings are ported, it's anyone's guess. If you have them ported by the same person who ported your 5.3 heads, one should expect an incremental improvement over them simply because of the advantages of the LS6 casting.

Another thought, spending all that money to switch from one ported stock head to another ported stock head might have you end up where you are now, or might give you results +/- 20hp. For the money you'll have in both sets, you could have started with an aftermarket head of your choosing.

The only way to know is to get some independant flow numbers on your existing heads. From there, you can decide if it is worth anywhere from $800.00 up to $1500.0 to get 10 - 20 HP improvement. Much over that will likely cost you a great deal more.

velox65

iTrader: (9)

My father ported the 706's(doing it for 40+years so he's experienced) and will likely do these, another ? if I left the 243's unmilled what compression ratio would I run on a lq4, with my 706's im right around 10:5:1. If not a huge improvement it wont be worth my time to pull my heads and new gaskets for 10 hp, so they may go up for sale soon.

frazierboy98

If your heads were not milled and you have a 10:5 then bolting on the 243s without milling them will drop you to 10:0.

hammertime

iTrader: (1)

Are you still running the stock 1.89" valves, or did he upgrade to 2.00" or larger valves? If the valves are still stock, you are missing out on some potential power there.

Do you have any/before & after data from just the head porting? That would be your best indication of what you could gain by having him port the LS6 heads. Figure that LS6 heads are usually a 15rwhp gain over LS1 heads, and that 5.3 heads have basically the same ports with smaller valves and combustion chamber, giving a slight advantage to LS1 heads in stock form.

If you mill the LS6 heads .018" - .020", that should equalize compression between the two. The rest is up to the quality of the porting on the 5.3's vs how much he is able to improve the LS6's. I've seen a lot of people say that some experienced porters trying their hand as LS style cathedral port heads may not necessarily get the expected results. Of course, the ones saying that are usually porters themselves, so their motive is certainly to sell heads.

Personally, I plan to practice porting on some junk 5.3's that a friend scored, then tackle a set of 241's that I picked up dirt cheap in the for sale section. I'm willing to bet the cost of gaskets, milling and a valve job - plus my time - that there is substantial room for improvement over mass production quality work.

Good luck!

velox65

iTrader: (9)

Stock valves and no data, no where around here does flow benching. I trust him though as he's been doing this for twice as long as I've been alive with good results.