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I recently built a Gen-4 5.3L similar to what you are wanting. It started as an LMG (flat top pistons). It didn't have heads (799/243) when I bought it, so I put some 706 heads on it. I used a BTR stage-2 truck cam, and did the DoD delete. With stock intake and exhaust manifolds, it made 425hp / 408tq on an engine dyno. I wish I had headers to run on it. Headers probably would have added 10-15hp and torque.
I wouldn't buy "rebuilt" heads online or from any shop. It's too easy to "rebuild" heads yourself. You can replace the springs and seals yourself. I ported mine a little, but it's not necessary. Just find some junk yard heads, and clean them up. I have bought two sets of 706 heads off of Facebook Marketplace. Your local junk yard could also be a good source. You should be able to get a set of 706/862 heads for about $100-$150.
There was talk about octane and compression in an older post on this thread. The engine I built has about 10.7:1 static compression with the flat-top pistons and lightly milled 706 heads (61cc). The engine dyno guy said he used Mid-grade fuel from the local gas station (out in the hills). At best, the gas might be 89 octane. I wouldn't recommend trying to run Regular (87 octane) gas with this much compression, but anything else seems to be fine.
I'm not sure which cam you were looking at, but here's what the BTR stage-2 truck cam does on a 5.3L. More or less cam duration will move the curve one way or the other.
All very good info, I have found plenty of 706 heads on eBay for around $250 a pair used. I will see about getting on Facebook marketplace, is it possible without a Facebook account? I’m on FB messenger but deactivated my regular Facebook account 2.5 years ago.
I don't think you can access Marketplace without an active account. Why not just reactivate your account? You can keep your posts private, and unfriend everyone if you don't want to be disturbed. I mostly use Facebook just for Marketplace. You can find some good deals there.
I prefer 862 heads to 706s. The 862s and 706s are practically identical, just the 862s are not Castech or much less prone to be. Look for the battery symbol on top of the casting as a Castech identifier. I cannot remember having ever seen a Castech 862, but I know someone will probably point out that I am wrong.
Interesting, I’m curious now. What’s your like about the 862 over 706? Reason I ask is that my engine will live in the 1500-4500 realm. Only time it will see over 4500 is when there is an emergency or shenanigans involved and I’m getting too old for shenanigans (highway cruiser/daily driver). I do want good lower end torque and it may see a fun run or two at Beech Bend.
There is nothing more to like about 862's over 706's other than SOME 706's are Castech, SOME of which exhibited cracking after a while. Since the last 706 head was made about 16 years ago, I would bet the cracked ones have been discovered by now.
So, for all intents and purposes, in the 300-400HP / TQ range, the 862 and 706 heads are very similar and the chance of getting a Castech head is significantly reduced by getting 862 heads, correct?
To clarify here, your saying that Castech only did the 706 castings out of all LS heads?
As far as I've ever heard. Have others had the "battery" casting mark? I haven't heard about any, though they might exist.
Plus those are the only ones that had consistent cracking issues of all LS heads.
Castech was likely contracted to do the most common LS heads (706) as GM production likely exceeded existing production capacity for 706 heads.
The need for 706 heads FAR exceeded any other LS head then in production
As far as I've ever heard. Have others had the "battery" casting mark? I haven't heard about any, though they might exist.
Plus those are the only ones that had consistent cracking issues of all LS heads.
Castech was likely contracted to do the most common LS heads (706) as GM production likely exceeded existing production capacity for 706 heads.
The need for 706 heads FAR exceeded any other LS head then in production
I have a set of 8452 heads (LS7) with the Castech stamping on them in the shop. I’ve also seen the Castech stamping on 317’s, and 5364’s, which are L92 heads. The only set of heads that I haven’t seen the Castech battery symbol on are 862 castings. I can’t remember if the 243’s ive had come through here had the symbol, but I’m fairly certain that they did. There could be other castings that Castech wasn’t involved with out there, but from what I’ve seen, the company had their hands in most of what GM did for the retired LS program.
OK, thank you Scott. Here on the forums and other places the only mention of Castech has been with the 706, and the associated problems with cracking. Apparently those issues have not surfaced on other heads of their manufacture. Also, the mark was cast in on the 706 heads. Stamped on others?
OK, thank you Scott. Here on the forums and other places the only mention of Castech has been with the 706, and the associated problems with cracking. Apparently those issues have not surfaced on other heads of their manufacture. Also, the mark was cast in on the 706 heads. Stamped on others?
I mis worded that G. It’s definitely cast in on them all.
Interesting, I’m curious now. What’s your like about the 862 over 706? Reason I ask is that my engine will live in the 1500-4500 realm. Only time it will see over 4500 is when there is an emergency or shenanigans involved and I’m getting too old for shenanigans (highway cruiser/daily driver). I do want good lower end torque and it may see a fun run or two at Beech Bend.
In that RPM range, you won't be anywhere near 400hp. My 5.3L started making 400 ft. lbs around 4000 RPMs, so that goal is possible. Take a closer look at my dyno chart if you want to have a better idea of HP/Tq numbers that you would be working with in your listed RPM range.
If I can manage 320-340 on the torque side, I will be happy. Again, as far as spicy goes, this engine will be the medium Taco Bell sauce. It will be pushing this around when done.
My machinist sent a message that the rotating assembly is ready, balanced to within a gram. Flattops, Scat floated rods, stock crank with 20/20 on the journals. 58 tooth ring. It’s getting close to final decision time on cam.
Sounds like its just gonna be babied around and anything more than a stock cam would suit your needs.
Of your transmission choices the 4l60e would be the way to go for cruising and fuel mileage, For your needs I would run a trail blazer torque converter (should stall around 2500) and a Truck Norris cam, Ls6 valve springs and something in the 3.50 rear gear range.
I have a TH350 in there now that I will probably leave, but I will put the Truck Norris cam on the list along with the springs. Im running a stock 3.36 rear.
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