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Old 04-07-2009, 08:58 PM   #1
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Default 243 Heads on 5.3

I know this mod has been beaten to death, but I need some clarification.

I have a GMC 99 Stepside with a 5.3l engine, Radix 112 Magnacharger w/3.0 pulley, Dynatech longtube headers, stock heads (LS6 cam and yellow behive springs).

I have a set of LS6 243 heads, which I would like to install, but I'm not sure how much to mill off the decks. Since I have a supercharger, do I want to mill less than the .030" than what's been suggested in the forum?

Is this mod a good idea or a waste of time and money, not enough bang for the buck??

Any expert advice would be appreciated. Thanks.
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Old 04-11-2009, 12:00 AM   #2
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lower compresson, you can run more boost, 243's flow better than stock by far, and you would have a ls6 top end. I would run them as is.
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Old 08-06-2009, 03:53 AM   #3
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i would like to know also
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Old 08-06-2009, 10:34 AM   #4
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Agree with fastrt. However, depending on their age/condition you may want to mill .010" just to true them up.
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Old 08-06-2009, 12:27 PM   #5
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What CC are the stock heads...the LS6 heads are 64cc making 10.5:1 on a 5.7L. I am sure you know if the 5.3 heads have bigger chambers or by milling them you make the LS6 heads smaller then you are bumping up compression. I do agree if they have many miles on a slight mill to true them up is a good thing.
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Old 08-07-2009, 09:30 AM   #6
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All heads will vary slightly but I think that stock 5.3's are about 61 and the LS6 (243) heads are 64 or 65. I think that head volume will decrease 1 cc for every .005" of milling. Even with a slight mill, the LS6 heads would still be 63 cc or so which would decrease his compression ratio slightly. He can play around with head gasket size if he wants to fine tune it.

*disclaimer, number noted above are off the top of my head (and therefore approximate). If you wany exact numbers, do you own search.
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Old 08-22-2009, 02:11 AM   #7
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so are 234s left alone the best for a 5.3 with a radix.
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Old 08-22-2009, 02:17 AM   #8
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It is only my opinion, but I have seen the radix perform very well on cars and trucks running at or just under 10:1 compression. Putting the 243's on a stock LM7 will drop CR, sure you can run more boost and maybe better peak HP but at the cost of your power out of boost. I'd set them up to at least keep the stock CR. Just my observations/opinion.
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Old 08-22-2009, 03:51 AM   #9
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ya im wanting to stay close to the same compression. i have a 5.3 with stock 706 heads, gt2-3 cam with a radix. Just wanting some opinion on installing stock 243 (ls6) heads will help out any or just go with aftermarket ls6 heads?
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Old 08-23-2009, 08:58 AM   #10
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If your going to use #243 heads dont mill them, OEM or aftermarket if your going boosted.
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Old 08-23-2009, 08:58 AM
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01, 07, 243, 53, 53l, 706, headers, heads, lm7, ls6, magnacharger, mill, milling, silverado, supercharger


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