Raising Compression - Head vs piston

[Lil'John]

Ideally, where is the best place to raise compression; at the head or at the piston?

I'd like to keep this generic but since I know some want super specific examples:rolleyes: I'll throw this out as specific: 6.0L LQ4 with 317 heads is the base. It is relatively easy to swap flat top rod/pistons from an LQ9 to get to ~10.1:1 compression with "known" results(~20hp/ft-lbs) since the mod is basically making an LQ9. Another option thrown about often is bolting on 706 heads from a 5.3L to get around ~10.5:1 compression; results seem to be known/unknown along with process being unknown.

In the above specific example, assuming no machine work needed, the cost of either mod is almost exactly the same.

 

[bdkw1]

Ideally, where is the best place to raise compression; at the head or at the piston?

Usually the head. Combustion chamber shape is way more important to taking advantage of the extra compression. Sometimes shortening up the deck will be more beneficial than the same bump using a smaller chamber.

 

[Bebop]

Another option thrown about often is bolting on 706 heads from a 5.3L to get around ~10.5:1 compression; results seem to be known/unknown along with process being unknown.

You need to search google for about 15 sec before saying stuff like that. Results are well documented. You can find dyno tests, flow bench results of the 2 heads etc.
As far as the process it is the same as swapping any head.

To answer your question, compression is compression, and, at these power levels it will not make any difference.

At higher power levels, plenty of other factors have to deal with proper chamber geometry etc will enter into effect, but I'm noit knowledgeable enough to tell you anything about that.



As far as the 6.0, do both, 706 heads and flat top pistons and profit.

Also, the cost of a used set of 706 heads at the JY is like $50. It's cheaper and easier to install than flat tops, which is why I usually choose that route when doing anything to a 6.0.

 

[Lil'John]

Bebop My experience with searches for 706 provided very inconsistent results. I'm glad you get the same data for everything. In my case, half the results had ZERO info about ending compression ratio and those that had the compression ratio, it wasn't agreed upon. Same thing with hp/tq results. It was all over the place. So when I say "known/unknown", I mean just that: you get compression and more power... just unknown what.

Same result with "installing 706s"...not a single result spelling out what was involved. Some implied "just bolt them on". Some had thicker gaskets.

And good on you for having a cheap junkyard. None of mine are. My ebay search showed heads and piston/rod set to be roughly the same($200-$300) My local junkyard was ~$160... for $40 more on ebay, fuck junkyarding. The easier install is true but only relative.

 

[Bebop]

Installing a 706 head on a 6.0 it involves removing the 317 head, and bolting down the 706 in place. You don't need anything particular, just swap them out.

Stock head comparison on a 6.0:

https://www.youtube.com/watch?v=N-E7aGP_rrg

 

[Will Scarlet]

Installing a 706 head on a 6.0 it involves removing the 317 head, and bolting down the 706 in place. You don't need anything particular, just swap them out.

Stock head comparison on a 6.0:

https://www.youtube.com/watch?v=N-E7aGP_rrg

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