Cylinder head swap...
Dec 9, 2018 | 02:10 PM
#1
Cylinder head swap...
I have been reading these 706 cylinder head articles lately...
I am under the impression that 862s are similar.
Basically, I have a set of 862s off of a 2003 4.8L sitting on the shelf. Wondering if it would be worthwhile to redo them and swap in place of my factory 317s. Seems like a step backwards due to the smaller valves. My combination is in my signature line. The cam is 214/220 @ .050 .598"/.604" 111 LSA. Was more of a max efort cam for a bolt on 4.8/5.3, it's very tame in my 6.0L The truck is a daily that tows car trailers several times per year. It peaks at 5400 RPM now and I am fine with that. I have given up on trying to go fast with this truck. I want to focus on power under the curve and more torque without losing any HP.
I am under the impression that 862s are similar.
Basically, I have a set of 862s off of a 2003 4.8L sitting on the shelf. Wondering if it would be worthwhile to redo them and swap in place of my factory 317s. Seems like a step backwards due to the smaller valves. My combination is in my signature line. The cam is 214/220 @ .050 .598"/.604" 111 LSA. Was more of a max efort cam for a bolt on 4.8/5.3, it's very tame in my 6.0L The truck is a daily that tows car trailers several times per year. It peaks at 5400 RPM now and I am fine with that. I have given up on trying to go fast with this truck. I want to focus on power under the curve and more torque without losing any HP.
Last edited by Bluecollar Hotrods; Dec 10, 2018 at 05:23 PM.
Dec 9, 2018 | 08:19 PM
#2
862/706 are the same. Some engines reportedly left the factory with one on one side the other on the other
there is a member here who felt a major increase in the bottom end when he took his ported 317s off and put on 706/862s
i dont have data for you, but I've read the articles and talked with some engine builders. There are differing opinions out there. On my 408, my builder talked me into larger intake valves to help down low torque.
however several tests have shown that the small valve heads on larger motors make more power, and most ppl say it's the CR making the power even tho peak flow is much lower.
I cant tell you what to do, because I have no data or experience first hand on this. Maybe the guy who swapped will chime in. I know cutting the head on my Saturn .055 made a ton more power than a stock height head ported to infinity. It was ~.5sec slower in the 1/4, ported than the bumped CR, but cam timing also advances on a DOHC when you cut the head, so I am hesitant to point to that experience and claim it works in all conditions. Plus, valve size never changed for me in that scenario. So, not enough data.
there is a member here who felt a major increase in the bottom end when he took his ported 317s off and put on 706/862s
i dont have data for you, but I've read the articles and talked with some engine builders. There are differing opinions out there. On my 408, my builder talked me into larger intake valves to help down low torque.
however several tests have shown that the small valve heads on larger motors make more power, and most ppl say it's the CR making the power even tho peak flow is much lower.
I cant tell you what to do, because I have no data or experience first hand on this. Maybe the guy who swapped will chime in. I know cutting the head on my Saturn .055 made a ton more power than a stock height head ported to infinity. It was ~.5sec slower in the 1/4, ported than the bumped CR, but cam timing also advances on a DOHC when you cut the head, so I am hesitant to point to that experience and claim it works in all conditions. Plus, valve size never changed for me in that scenario. So, not enough data.
Dec 10, 2018 | 07:10 AM
#3
On The Tree
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Dec 10, 2018 | 08:04 AM
#4
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I pulled off my TMS CNC 317s in favor of a set of 706s. Damn world of difference. It's much more snappier and I get better fuel mileage. This was about 4-5 weeks ago.
I used LS3 gaskets when I put them on.
I used LS3 gaskets when I put them on.
Dec 10, 2018 | 04:56 PM
#5
I have been reading these 706 cylinder head articles lately...
I am under the impression that 862s are similar.
Basically, I have a set of 862s off of a 2003 4.8L sitting on the shelf. Wondering if it would be worthwhile to redo them and swap in place of my factory 317s. Seems like a step backwards due to the smaller valves. My combination is in my signature line. The truck is a daily that tows car trailers several times per year. It peaks at 5400 RPM now and I am fine with that. I have given up on trying to go fast with this truck. I want to focus on power under the curve and more torque without losing any HP.
I am under the impression that 862s are similar.
Basically, I have a set of 862s off of a 2003 4.8L sitting on the shelf. Wondering if it would be worthwhile to redo them and swap in place of my factory 317s. Seems like a step backwards due to the smaller valves. My combination is in my signature line. The truck is a daily that tows car trailers several times per year. It peaks at 5400 RPM now and I am fine with that. I have given up on trying to go fast with this truck. I want to focus on power under the curve and more torque without losing any HP.
More compression will be the answer to where you're trying to go. If you want good flow and a compression bump put a set of 243/799's on it. The 706/862 should still flow decently and provide even more compression. If it were mine I'd do 243/799's and shave them down a hair to 60-61 cc
Ws6store has head gaskets that measure .045 compressed rather than the factory .052 and that will give you a little bump in compression and tighten up quench a hair which will help prevent detonation, something you'll want towing.
With 61 cc heads and the .045 gaskets it'll be at 10.8:1 and you'll definitely feel that over the 9.4:1. With stock .052 gaskets you'll be at 10.6
If you go with stock 243/799 64.45 cc chambers and the .045 you'll be at 10.3-10.4:1 with the .052 you'll be at 10.1-10.2
The .045 gaskets from ws6store are really nice and they're cheap too. Close to same price as OEM gaskets. The cometic thin gaskets are more expensive.\
These are the ones you would use, I believe the work on notched heads and non notched.
RPM Speed HD MLS Head Gaskets 6.0L & 862 Heads (Pair | Gaskets/Kits/Accessories | Engine | 98-02 Camaro/Firebird | WS6store.com
You'll need to run premium fuel too if you don't already.
Dec 10, 2018 | 05:12 PM
#6
Running 87 now, going to switch to 89. Really do not want to go to 93 with the amount of driving I do.
I have two sets of 799s sitting around, but those didn't seem to fare well in any of the dyno tests.
I have two sets of 799s sitting around, but those didn't seem to fare well in any of the dyno tests.
Last edited by Bluecollar Hotrods; Dec 10, 2018 at 05:21 PM.
Dec 10, 2018 | 05:13 PM
#7
Safe to say that the 706s were ported too? What size valves in both sets of heads?
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Dec 10, 2018 | 05:19 PM
#8
This is a moment when I wish I could get my hands on a set of AFR 205s with 66-68cc chambers.
Dec 10, 2018 | 05:27 PM
#9
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From: Somewhere north of 285, south of 985.
I love the way it runs now. Pulls like a damn freight train off idle. With the 317s, they were a 23x intake port.
Velocity was to low. If I were boosted I would’ve kept them.
Dec 10, 2018 | 05:52 PM
#10
You said you wanted power under the curve and torque. Compression will get you there. It will also not cost you hp and it will gain MPG.
The added MPG will more than pay for the difference if fuel cost.
I read that article, and the one where they ran it boosted. WCCH offers a "truck" speciffic porting package for 862/706 heads. Kind of curious to see how those would do on my LQ4, but really do not want high compression and premium fuel for a daily driver.
This is a moment when I wish I could get my hands on a set of AFR 205s with 66-68cc chambers.
This is a moment when I wish I could get my hands on a set of AFR 205s with 66-68cc chambers.