What are your HP goals again?

 

I would like to be between 600 - 700 rwhp on pump gas with a little water meth added in. I dont want to go over 6k rpm on it so no crazy *** cams. I know I loose over 100 through the drivetrain with the 80E and 9.5 14 bolt.

 

408, with 9.5:1 with 170ish kpa 16* of timing with a 220/220 116 cam.... 600 or 700 hp..

 

There are your typical hypereutectic pistons, then there are T6 alloy hypereutectic pistons. Two different processes. T6 hypereutectic alloy pistons have similar strength properties to forged pistons, but T6 pistons have the advantage in ring land area where great strength is most important. The T6 pistons also have a high percentage of silicon, making them great for minimizing thermal expansion and heat transfer. Though forged pistons will do the trick, T6 pistons at least merit some investigation before purchasing a set. I believe our heads are made from T6 alloys, but correct me if I'm wrong.

As for what compression...you need to figure out at least 4 important things, but I could name off dozens of variables to consider. In order of no particular importance: highest octane available in your area, amount of boost over atmo, cam selection and thermal management. A turbo engine should never be reduced to a low-compression slug just to have the boost turned up. One should shoot for the highest compression ratio allowed without pre-detonation or pinging, at the desired boost level. Yes, the goal here is to turn up the boost and that is what we're really after, but remember you wont be at WOT 100% of the time so make a friendly engine so you can actually enjoy driving the thing off-boost.

As for what kind of cam...well maybe I missed this earlier but what is in the 6.0L now? For a 408 there can be many many cam choices, but a few more variables are needed first. Try to answer a couple questions regarding what compression ratio to run and we can go from there.

 

More info on T6? I haven't hear of anyone making such for lsx engines. Custom only? I've done a bit of research about pistons , it is the lack of silicon that make the 2618 pistons so strong, they deform rather than break in pieces..... Are you sure the T6 stuff you are mentioning isn't 4032?

 

We went with 9.1 which runs great without any boost. The 408 starts with plenty of torque so I wouldn't be concerned with drivability unless you really dropped the compression. With todays tuning, there is really no need to drop the compression below 9. You can still boost the crap out of it if need be but with the 408 I think you'll meet your hp goal without huge boost if you give it enough cam to run a little.

 

We have 93 at the pump here and we arent too high above sea level. I definetly wont go below 9:1. Im thinking in the 9.5 - 10:1 range so that it does have good driveability out of boost.

Right now it has a GT2-3 in it for the cam.

 

Through your research, you must have read about the differences of any alloy when it's forged. Forged alloys are more ductile, meaning they can take more bending and abuse before failing. Stating the lack of silicon is what makes the 2618 forging so strong might be somewhat of an overstatement, or at the very least I feel you might be hanging on the wrong assumptions as to why forged metals are strong. The likely answer is that the 2618 forging is...well...forged, same with the 4032 alloy. Adding silicon to any aluminum alloy dissipates heat extremely well, which is why more automakers are choosing hypereutectic alloys for stock high compression motors so that the combustion heat is kept off the piston and in the actual combustion process, leading to a more efficient burn and lower emissions (which we all know are getting tighter these days).

Other advantages to a higher silicon content in the alloy are improved scuff resistance which remains smooth and quiet, especially when cold, but most importantly for the OP's application, a high silicon content means a relatively low expansion rate! This means as boost temperatures rise, the piston will be able to withstand the heat and ask for seconds. You asked about T6 pistons...T6 is a level of hardness I'm sure you read about during your research. Bringing an aluminum alloy up to a T6 grade means starting with a T0 aluminum, then heat treating it to AQ condition, then annealed (which is the process which allows hypereutectic T6 pistons to have similar strength to forged), then heat treated to T6 concluding with a cool down. Since after this heat treating process the hypereutectic piston has similar ductile strengths as forged, the hypereutectic gains the advantage in ring land area where boosted motors need it most.

To me, and this is solely my opinion unless someone else shares it with me, forged pistons in a boosted motor can only mean one or two things: 1) the engine builder intends the motor to remain at high revs longer than what a hypereutectic piston is capable of handling (which is unlikely due to the valvetrain limitations of our V8 motors) and/or 2) the engine builder is expecting the engine to detonate or see extremely high cylinder pressures for sustained intervals, which to me shows a lack of care and/or understanding of the inner workings of a motor, or the engine builder simply just means to be overcautious - which is probably the case 99% of the time...I hope.

With that said, the OP needs new pistons. Since I am assuming nothing is purchased yet, it is my hope that the OP at least looks into alternative piston options before buying parts and learns to control detonation (which shouldn't be a problem anymore now that a 408ci will need ~10% less boost to reach his power goals...right? )...because no one here wants a motor detonating regardless of what pistons are going in.

 

9.5-10.1:1 is great, good choice! If it were my motor, I'd stick with the GT2-3 cam you have. Talk about a monster idle-6000 cam in the 408!

 

Synergyv8 you sold me, now where can I find these T6 hypereutectic pistons for a LS engine?

Thunderwagen, I think your going to be fine running 9.5+ CR as long as you keep your quench in check...