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[Ecotec] L67 Rebuild

DeathSammich

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I recently for an L67 that has been fully rebuilt but if course I'm going to strip it myself to make sure it's been done properly. He said it had JE forged pistons that has 20 thou over. Won't this make too higher compression? How can I add compression back to run more boost? Thanks
 

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The .020" overbore itself will make stuff all difference to the CR ratio but piston design can. I'd suggest though it will be a specific L67 designed piston with a nice big dish to get the CR right to suit a boosted application. IF the engine has just been built than it should have receipts with it so check out exactly what JE pistons have been fitted.
 

DeathSammich

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Thanks, I believe they were the ones from mace.
The .020" overbore itself will make stuff all difference to the CR ratio but piston design can. I'd suggest though it will be a specific L67 designed piston with a nice big dish to get the CR right to suit a boosted application. IF the engine has just been built than it should have receipts with it so check out exactly what JE pistons have been fitted.
 

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Won't this make too higher compression? How can I add compression back to run more boost?
No. Generally making the cylinder bigger reduces compression.

And very short answer to your question, lower compression means you can run more boost, higher compression will generally make it harder to run boost due to detonation and heat (tune plays a big part). Just look at the static compression of an Ecotec vs. an L67. A simple overbore won't do anything realistically, and compression isn't just something you can add in or take away without changing pistons or heads or head gaskets.

How and what exactly do you plan to check to "make sure it was done right"?
 
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DeathSammich

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No. Generally making the cylinder bigger reduces compression.

And short answer to your question, lower compression means you can run more boost, higher compression will generally make it harder to run any boost due to detonation and heat (tune plays a big part). Just look at the static compression of an Ecotec vs. an L67. A simple overbore won't do anything realistically, and compression isn't just something you can add in or take away without changing pistons or heads or head gaskets.
Oh okay so 20 thou over from the pistons won't make much difference at all then?
 

vr304

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Nope but the dish size of the piston will, it may be that the pistons are very similar to the stock ones just oversized?? Also deck height will influence your compression ratio, meaning the difference between the top of the piston and the block at top dead centre as the block may have been decked during the rebuild, same goes for your heads too if they have been decked during the rebuild your compression could be potentially a bit higher the only way to know for sure would be pull it down and measure everything then calculate your compression ratio from there
 
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