GM 706 heads are a great choice for your Chevy LS engine build since they are cheap and easy to find. – Hot Rod

GM’s 706 heads are the cheapest and most effective heads you can use for your 5.3L, or 4.8L, or even some 6.0L LS engine build. Bold statement? Well, not really. You see, these heads have been around a long time, and dozens of dyno tests have shown that the often overlooked 706 head can give you great performance.

These cathedral offerings come stock with great flow and, unlike many truck heads, smaller factory combustion chambers (61.15cc) that won’t drop your compression into the basement. These heads came on hundreds of thousands of 1999 and up GM 5.3L and 4.8L engines, so they are super plentiful in scrapyards. And according to our Econ 101 class, a large supply generally equates to a lower price.

Are 317 Heads Better than 234 or 799 Heads?

Most people tend to grab up 317 heads because they have the same improved ports as the more expensive 243 and 799 heads. But the 317 heads have much larger combustion chambers (71.06cc), which will cost you performance, especially on a naturally aspirated engine. This loss in compression ends up being a net horsepower loss even with the 317 heads’ superior ports. Dyno testing on an LM7 5.3L has shown that the 706 heads were worth 20 hp and 15 lb-ft over a pair of 317 heads, even with the 317’s slightly larger valves. Yeah, you could mill down the 317 heads, but that costs cash, so in stock form the 706 heads are still king of the budget-friendly hill in terms of cost versus performance.

The 706 heads are even slightly superior to the commonly found 862 heads. The reason is that the 706 heads are SPM (semi-permanent mold) made, while the 862 heads are sand cast. The SPM method is considered to be a more consistent process, but once you port the 862 head, any difference to the 706 head goes away. Again, porting (unless you do it yourself) costs cash, so in stock form the 706 head still beats the 862 casting. Shopping around online, we’ve found remanufactured 706 heads as low as $350 for a pair! Used prices are often much less, which helps make the 706 heads some of the best-performing, affordable, cathedral-port factory heads out there.

Common cathedral-port production casting numbers:

9331997 aluminum perimeter bolt 5.7
806199798 aluminum perimeter bolt 5.7
853199900 (LS1) aluminum center bolt 5.7: 66.67cc
241200103 (updated LS1) aluminum center bolt 5.7: 66.67cc
2432004 and up (LS6/LS2) aluminum center bolt 5.7; also in some 2005 and up trucks: 64.45cc
706/852/8621999 and up 4.8-5.3 truck heads: 61.15cc

035 /317/873 1999 and up LQ9 and LQ4 6.0L truck heads: 71.06cc
7992005 and up 4.85.3 truck heads; these are basically 243 heads

Casting Numbers 706, 852, and 862
1999+ LM7 5.3L/LM4 4.8L
Material: Aluminum
Part Number: 12559862/12561706
Combustion Chamber Volume: 61.15cc
Intake Port Volume: 200cc
Exhaust Port Volume: 70cc
Intake Valve Diameter: 1.89 inches
Exhaust Valve Diameter: 1.55 inches

Casting Numbers 317, 873, and 035
2001+ LQ4 and LQ9 6.0L truck/SUV
Material: Aluminum
Part Number: 12562317 (LQ4)/12572317 (LQ9)/12572035 (LQ9)
Combustion Chamber Volume: 71.06cc
Intake Port Volume: 210cc
Exhaust Port Volume: 75cc
Intake Valve Diameter: 2.00 inches
Exhaust Valve Diameter: 1.55 inches

Why 706 heads make a great choice:

  • 706 heads are very affordable
  • 706 heads are plentiful and easy to find
  • 706 heads have smaller chambers, so you don’t lose compression
  • 706 heads are slightly superior to 862 heads due to how they are manufactured
  • 706 heads flow great and, overall, are superior to 317 heads for many builds

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