862 cylinder heads interchangeable with 706s?

[Sintek]

'02 Tahoe, 5.3 flex

Replacing only one and want to confirm fitment before ordering. For some reason used 706s are a lot cheaper than 862s.

Or if there's another that would fit, I'd appreciate that info as well.

 

[Sam Harris]

My understanding is that the 862 heads have a higher compression ratio than the 706 heads. I wouldn’t mix them.

 

[mofokriss]

'02 Tahoe, 5.3 flex

Replacing only one and want to confirm fitment before ordering. For some reason used 706s are a lot cheaper than 862s.

Or if there's another that would fit, I'd appreciate that info as well.

They will fit directly no problem. Chamber size, valve sizing, stock spring rates are all the same. I was opting for replacement 706s on my 5.3 but inky had 862s available. Main difference is the casting in which the 706s were slightly better than 862.

 

[mofokriss]

I was thinking of only Replacing one head and not the pair as my cylinder 7 spark plug got cross threaded but I figured might as well get the pair to "keep the balance" of a more complete burn on both banks. I know it the difference in amount of fuel burn might be negligible but it's probably my OCD that wouldn't have let me sleep at night with only 1 head replacement. I paid $425 for rebuilt 862s and they sell 706s for the same price too

 

[iamdub]

'02 Tahoe, 5.3 flex

Replacing only one and want to confirm fitment before ordering. For some reason used 706s are a lot cheaper than 862s.

Or if there's another that would fit, I'd appreciate that info as well.

I don't recall if it was exclusive to the 706s or just mostly, but there are a lot of questionable castings for the 706 heads. Educate yourself on the "Castech head failure". Maybe they're cheaper since there's a higher risk?

 

[Mudsport96]

They are for the most part identical. There are a few differences, but at stock power level you would never notice them.

 

[Sam Harris]

They are for the most part identical. There are a few differences, but at stock power level you would never notice them.

But would you run different heads on the same engine..?

 

[iamdub]

But would you run different heads on the same engine..?

Lots of engines came from the factory with two different heads. I've seen plenty of 243/799 head combos on nearly-new (read: all original) GenIV 5.3s.

 

[mattbta]

Mine has an 862 and a 706. My factory 706's cracked. Got a refurb set of 706's and one cracked almost immediately (<~500 miles). They kept delaying sending me out another set and they said they had one but were waiting on the second. Knowing they were near identical except for casting method, I had them send just the one.

 

[Mudsport96]

But would you run different heads on the same engine..?

In the late 90s I ran a 350 with flat tops in the even holes and a 64 cc head and 5cc dished pistons in the odd holes with a 59 cc head. Built it out of spare parts in a bucket, used 260he cam and mismatched used lifters.
Daily driver for a year and a half. You do what ya gotta do, pulled the car around just fine. Sub 200hp you really dont know the difference as long as the compression is close lol. You wouldn't want 8:1 on one bank and 11:1 on the other.

So for 2 heads basically identical other than the casting number ... yeah i have Zero issue running them that way.

 

[tomloans]

You might want to check out this thread. I had one bad 706 . I replaced them both with the help of this crew here. Obtained the heads from... Chuck and Charlie ( his son )at Aluminum Head Rebuilders I used shaved 799's. Vehicle is running like new...

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