zblee

background;
I am getting my transmission built this week and the next step on the list is to upgrade the heads on my silverado RCSB. When the transmission goes in, it is getting mated with a 3600 stall. The truck is most likely going to be a daily driven street machine. I am leaning towards more aggressive and willing to sacrifice a bit of steet-ability for the bump in track performance, but since its a daily driver I do not want to go full out track star. After the heads go in I will be doing a cam swap . Cam will be spec'ed based on the heads that I end up going with (along with rest of the setup).

Choices;
I am specifically looking at two heads. texas speed PRC 243 stage 2.5 and texas speed PRC 5.3l stage 2.5. the price difference only seems to be about $200-$300.

243 option = $400 (for used cast) + $1250 = $1650
706 option = $000(new cast incl) + $1470 = $1470


$220 difference plus shipping variances ( receive the cast and send the cast out) so probably closer to 300$. This price difference has no effect on my choice of head, so for this comparison - price is not a deciding factor. I like the idea of new cast as less risk of unknown issues with a used head. This is the max I am willing to spend on a head. I have $2k budgeted but need the extra money for gaskets, bolts and other parts that i need that I have not thought of yet...

Texas speed told me that the 243 will have higher gains in high end and 5.3l will have better numbers down low. I am assuming that either option will be an improvement over stock heads. texas mentioned they can mill either head up to .03". now my dilemma is should i go for better flowing and less compression, or more compression and less flow?

I was thinking my choices would be (assuming a .04 gasket,243 are 64.45cc, 706 are 61.15cc, .007" to remove 1cc, will be using 91 octane)

243 milled .03 - apprx 60.16cc with 9.86:1 CR
OR
706 milled .02 - apprx 58.3cc with 10.08:1 CR



so assuming these milling options on the respected heads are 'safe' even with a reasonably larger cam, still unsure about the 706 heads safe milling amount, what are you opinions ? I am also open to other suggestions. I would rather not mill past the 'safe'/popular milling of .03 as to not limit my choice of cam on the next step. If i mill too much I will have valve clearance issues that I do NOT want.


Here is a snapshot of data used to get the stock CR of 9.5:1 for the lm7, from here I adjusted the chamber volume and gasket thickness to get the ratios above.
Engine Compression Ratio (CR) Calculator



thanks!
_zblee

zblee

bump still not sure which way to go, but I do like the idea of minimal milling on the 5.3l/706 version to allow for a compression bump

Tuskyz28

Go over to ls1tech and make this exact thread. It's more members over there I believe to help you achieve your goal.

1FastBrick

iTrader: (17)

If it's more of a street toy, I would stay toward the 706 heads.

The 243 will give you the most gain in the Mid to upper RPM range.

I don't think anyone has ever done a back to back testing on this specific type of combo to give you real world difference of what you're in for as far as possible trade off.