High compression pistons?

Tech discussions on the L77 6.0L V8.
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Seabass
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High compression pistons?

Post by Seabass » Thu Jan 23, 2020 7:17 pm

I've searched a bunch but have failed to find any info besides milling the heads to bump compression up. Anyone on here have a high compression (pump gas) build? I'd like to find a domed piston in factory bore size if possible.
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kevink
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Re: High compression pistons?

Post by kevink » Thu Jan 23, 2020 7:26 pm

Most guys who build LS engines are cheap and never even touch their bottom ends, so milling heads the is how they bump compression. There should be tons of pistons available, though. You can likely get all the compression you can handle with pump gas by milling the heads and maybe fly cutting. What kind of compression are you looking for?
2011 9C3: 11.48 @118.

Seabass
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Re: High compression pistons?

Post by Seabass » Thu Jan 23, 2020 8:13 pm

Milling the factory heads to service spec gets you 10.8. There's a lot left for premium fuel, especially if your running a cam with lots of overlap. If I'm spending aaaaaall the money for bolt ons and a tune I don't think the extra 800-1000 bucks (pistons and gaskets) would be to bad to put some new slugs in with just a hone.
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kevink
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Re: High compression pistons?

Post by kevink » Thu Jan 23, 2020 8:37 pm

You can easily get over 10.8 with milling and thinner head gaskets. What kind of compression are you looking for?
2011 9C3: 11.48 @118.

Seabass
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Re: High compression pistons?

Post by Seabass » Thu Jan 23, 2020 8:50 pm

Not 100 set on anything just weighing my options as of right now. 12ish:1 can work well with 91 octane and would really shine on e85.

Depending on cam/converter/gear maybe even higher but I don't want a race engine just a healthy sleeper that can be daily's that still has torque down low
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s/c'd cav
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Re: High compression pistons?

Post by s/c'd cav » Thu Jan 23, 2020 9:23 pm

most would be either boring the motor out , or a stroker

not worth the labor to go in slap in some pistons and reassemble the whole thing , just to raise the compression a point or so

Seabass
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Re: High compression pistons?

Post by Seabass » Thu Jan 23, 2020 9:47 pm

I just penciled out what the theoretical gains may be and agree there is definitely cheaper power to be made than 1000 bucks for 30-40 horse

Kevink what kind of numbers have you gotten doing what kind of machine work? Are you going past service limit? I don't know what factory gasket thickness or cylinder to deck clearance is. I want to avoid flycutting reliefs. One because that's a ton of work, two I'd be losing compression again, three I'm reading the pistons are the weakest component on the bottom end.
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kevink
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Re: High compression pistons?

Post by kevink » Fri Jan 24, 2020 10:35 pm

I'm at about 11.2:1 after milling 0.020" with 0.040" head gaskets. Lots of guys mill 0.030" with no problems. Don't worry about valve reliefs reducing compression. The reduction in chamber volume is huge compared to the valve reliefs, meaning that if you mill x and cut valve reliefs x deep, you're still gaining compression since the valve relief volume is negligible.

Pistons may be the weakest point of the bottom end, but they're not a problem NA.
2011 9C3: 11.48 @118.

Seabass
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Re: High compression pistons?

Post by Seabass » Fri Jan 24, 2020 11:46 pm

Really? That's great to hear! I haven't been able to find what piston to deck is so all of my number crunching has been educated guessing. I'd be very happy with getting that much from milling the heads.

You clearly done your homework on this, know if you lop off .03 from the heads how much lift you can get and have ptv clearance? I still have a lot to learn as far as calcing out cams and clearances. Any input is appreciated

This is the cam I'm aiming for
Lift: 0.585"/0.585"
Duration @ 0.050": 228°/230°
Advertised Duration: 283°/286°
Lobe Separation: 112°
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leadfoot
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Re: High compression pistons?

Post by leadfoot » Sun Jul 26, 2020 4:24 pm

kevink wrote:
Fri Jan 24, 2020 10:35 pm
I'm at about 11.2:1 after milling 0.020" with 0.040" head gaskets. Lots of guys mill 0.030" with no problems. Don't worry about valve reliefs reducing compression. The reduction in chamber volume is huge compared to the valve reliefs, meaning that if you mill x and cut valve reliefs x deep, you're still gaining compression since the valve relief volume is negligible.

Pistons may be the weakest point of the bottom end, but they're not a problem NA.
What was your cam lift?
Did you add valve reliefs to the pistons?

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