5.3 Heads on a 6.0

[JJAB]

Guys, will I be okay with this modification?
I have a customer that wants to bolt some 5.3 #862 heads on a LQ4 6.0 shortblock and i was wondering if that combination would have piston to valve clearance issues? Thanks in advance!!

[jorgensensc]

I'm sorry I have no idea, but I wanted to ask why they wanted to do this? I thought the point was to get better flowing heads, not more restrictive? I know we used to use 305 heads on 350s to build compression. Do 5.3 heads on a 6.0 do the same thing? Not trying to be a smart ass, just curious. For what it's worth I thought I read somewhere recently that you could go up in heads on blocks, but not backwards. Example: 6.2 heads on 5.3, but not 5.3 heads on 6.2.
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[softballnrd27]

It would be a better idea to mill the stock 317s or find some 799/234s. The 317s are the same as the 799/234 casting just with a bigger combustion chamber.

[Robznob11]

well yes they are for compression but give up flow. a lot of people try this mod because tsp has a big push for how much you can gain with the 5.3 heads. but that's only if you port and polish them like they do. your going backwards with stockers. I don't know all the part #s but I know that hot rod mag said that 317 are identical to the ls6 heads with bigger chambers. im pretty sure ls6 heads are cast #243 if im not mistaken the only diff from the 243 and 799 was that the 243s had sodium filled valves as opposed to regular ones and I think different springs (in stock form) casting I believe is the same

[68GMCCustom]

Originally Posted by jorgensensc

For what it's worth I thought I read somewhere recently that you could go up in heads on blocks, but not backwards. Example: 6.2 heads on 5.3, but not 5.3 heads on 6.2.
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Have to be aware that the 6.2L heads are genIV (L92/LS3 style) with rectanglar intake ports...and with the big valves they have are made for 4" and larger bore's and to my knowledge won't fit on something smaller then the 6.0.

[jorgensensc]

Originally Posted by 68GMCCustom

Have to be aware that the 6.2L heads are genIV (L92/LS3 style) with rectanglar intake ports...and with the big valves they have are made for 4" and larger bore's and to my knowledge won't fit on something smaller then the 6.0.

Great Info!! That is exactly why I'm not an expert on these ls engines. Thanks for clarifying for us!

Shawn

[BR3W CITY]

If you are running a 4"+ bore, the l92 setup is pretty sweet. I would be running it but I don't want to give up my dbw setup, and from what i can find it doesn't fit the l92 manifold.

[68GMCCustom]

mines dbw? You have the old 3 bolt TB right?

newer style (LS2 and beyond) TB is a 4 bolt.

[Robznob11]

Originally Posted by 68GMCCustom

Have to be aware that the 6.2L heads are genIV (L92/LS3 style) with rectanglar intake ports...and with the big valves they have are made for 4" and larger bore's and to my knowledge won't fit on something smaller then the 6.0.

This is correct! Also be aware that square ports require an intake change as well. Because of this i always recommend that a person looking to do a conversion should go with a 6.0 or larger so they can grow. Unless you just want a stocker/d driver. But lets face it how many of us are satisifed with what we have. Dont we always want more. Dont find your self kicking you own rear!lol
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[BR3W CITY]

Originally Posted by 68GMCCustom

mines dbw? You have the old 3 bolt TB right?

newer style (LS2 and beyond) TB is a 4 bolt.

yep i believe mine is the 3 bolt, and going with that expensive tac adapter on top of the l92 stuff is pretty cost prohibitive.

[68GMCCustom]

oh OK.....was just gonna say remind you I had replaced my intake thinking it was causing my low vacuum...meaning I have a "spare" genIV truck (L92/LY6) intake laying around.

[softballnrd27]

Originally Posted by Robznob11

well yes they are for compression but give up flow. a lot of people try this mod because tsp has a big push for how much you can gain with the 5.3 heads. but that's only if you port and polish them like they do. your going backwards with stockers. I don't know all the part #s but I know that hot rod mag said that 317 are identical to the ls6 heads with bigger chambers. im pretty sure ls6 heads are cast #243 if im not mistaken the only diff from the 243 and 799 was that the 243s had sodium filled valves as opposed to regular ones and I think different springs (in stock form) casting I believe is the same

243/799 are the same and not all 243s had the sodium filled intake valves, just the ones on the ls6 vette motor. My 2010 has 243s. I wouldn't put the 862 heads on a 6.0 unless they were ported. 243/799s are the best cathedral port stock heads when it comes to flow and since engines are just big air pumps.....
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[Robznob11]

Originally Posted by softballnrd27

243/799 are the same and not all 243s had the sodium filled intake valves, just the ones on the ls6 vette motor. My 2010 has 243s. I wouldn't put the 862 heads on a 6.0 unless they were ported. 243/799s are the best cathedral port stock heads when it comes to flow and since engines are just big air pumps.....
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well that's cool to know! I knew the heads were the same but I thought that the 799 came on truck motors and the 243's were only on ls6 meaning they all had the sodium valves. but guess you learn something new every day. I just wonder what the difference is , I mean the reason for the diff cast #. I know in bbc heads many people claim the 783 are the same as 049 but the 049 heads are a lot more $$$ and in actuality have a few ccs of exhaust runner volume. I just wonder if that's the case with these new heads?

[softballnrd27]

I wish I knew that one too.
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[6.0 1955]

The 5.3 heads, 862's and 706's, have a smaller combustion chamber and smaller intake valves than the 243's, 799's, and 317's. Now as stated above the 317's have the largest cc of the bunch. With a 6.0l one could take the intake valves out of the 317's and place them into the 5.3 heads. This will improve flow especially with a good valve job. The l92's and ls3 heads are a different breed.
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[Kainedogg]

If the lq4 is an iron headed verson then the 862's would not be a bad idea...if they were free. Otherwise grab a set of 243' or 799's. I believe 799's are similar but not the same as 243's. A popular member on Ls1tech "Denmah" put a 799 and 243 on a 5.3 and the side with the 5.3 had lwoer compression. Not by a large margin though. I personally don't think l92s are worth the effort on a stock lq4. They can't touch the 243's for throttle response and power under the curve. Now you punch out that 6.0 to a 6.1 or better and the L92's come into their own and become an epic bang for the buck feature.

My 2 cents.

[BR3W CITY]

Wouldn't the valve still be shrouded by the smaller bore?
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[Jon01]

Originally Posted by Kainedogg

If the lq4 is an iron headed verson then the 862's would not be a bad idea...if they were free. Otherwise grab a set of 243' or 799's. I believe 799's are similar but not the same as 243's. A popular member on Ls1tech "Denmah" put a 799 and 243 on a 5.3 and the side with the 5.3 had lwoer compression. Not by a large margin though. I personally don't think l92s are worth the effort on a stock lq4. They can't touch the 243's for throttle response and power under the curve. Now you punch out that 6.0 to a 6.1 or better and the L92's come into their own and become an epic bang for the buck feature.

My 2 cents.

Wrong. 799's and 243's are identical castings. Hardware (valves, springs) may differ but castings are the same. LS2 powered C6's and TBSS's came with 1 243 and 1 799 head.

I'll agree with your thoughts on L92/LS3 heads on a stock displacement LQ4.
Now, if you're planning on a stroker motor down the road I would definitely do it once and be done.

[68GMCCustom]

Why would GM put a different head casting on one side? I have a LS2 powered TBSS....and it must be rare as it has a "pair" of 243's.

And as for the L92/LS3 heads.....I seem to hear more negative things about them from folks that don't actually own an engine with a set of these heads. I do own a truck with a stock displacement VVT delete LY6...a 6.0 with L92 heads. Just has a high lift cam (+ springs and c-moly p-rods) and headers. Guess I need to make a few videos and get it dyno'd.....plenty of power down low, in the mid-range, and up high.

[jorgensensc]

I have to chime in on the TBSS. We had an '06 and Our heads matched also. I remember looking at them one day just for grins.