Need help figuring out my best course of action with this engine. L77 Gen 4 6.0 with stock 823 heads, block was honed and went with k1 crank, summit pro ls rods and pistons. Pistons are 12cc dished. is 9.16:1 gonna be too low? Is there anything I should do or change? This is my first motor I am doing and my first performance build and now that is nearly done I am reading a ton of conflicting things. TIA



2011 Chevy Caprice LSA 93 Octane and Potentially E85 down the road, BTR Red Hot Cam

 

So I think it's fine. Sure the compression is a little low compared to the popular sentiment to run 10-10.5:1 compression.

But It's a PD blower and a 6.0 the car will not be a turd from a dig at all even though your car is kinda heavy.

 

Okay thanks. My only issue is if I use 68cc for the heads I get 9.1. If I use 70 which I’m reading they can measure up to that I get 8.98. Should I use a thinner head gasket just to be sure? If I use a .040 head gasket it brings it back to 9:1

 

You could go tighter on the head gasket and get a bump pretty easily there. I calculate a .040 (4.030) gasket would take you to 9.55

 

Could you explain how you got to that? Even with a .040 at 68cc I’m only getting 9.3. Thanks

 

well, looking at it again, off the bat a 4.030 gasket is a no go with ls3 heads.
but I’m thinking I may have entered the piston as .005 out vs your in the hole

 

Suggest you go up in compression.

 

It’s too late for that. Already have the short block balanced and assembled. Lsa 6.2s are 9.1 and that was the advice of summit so that’s what I went with and then started digging

 

IIrC, rule of thumb is 1 point of compression is worth about 4% power, NA.

Don’t over think it… Just run it at whatever CR it works out to and pulley down if you want more power. The tuning window will be wider with the lower compression.


Best of success with your build.

 

Don't forget that without camshaft into this is only calculating your static compression ratio. Which serves and informational purpose but much more is and should be taken from your dynamic compression ratio. Find a calculator that does that for you, it will require cam shaft info.

 

This gasket would get you to 9.25:1.


https://www.summitracing.com/parts/c...make/chevrolet

 

Given this I would keep your compression down in the low-mid 9s, 93 octane is your limiting factor.

 

I have a hi compression built 370” lq9 with 64cc ls3 heads on it with a 2.45 pully’d LSA and it is a riot, the compression is a **** hair over 11.0:1 and i live in comifornia….so all i have access to is really expensive 91….theres not even no e85 near my home…with that said my engine is not happy with just straight 91 in it and sounds horrible when its under load during acceleration….i quickly remidied that by adding a bottle of boostane (professional) at EVERY fill up, yeah it gets expensive but i just buy it by the case from summit and keep a bottle in the car and basically run it dry every time before i fill up, i built the motor to be 11.0:1 because at the time i was not even thinking about boost and 91 worked just fine with it, but not even a year later i stumbled upon boost district’s website and they have COMPLETE packages at killer prices so i couldnt resist, but ive learned my lesson and now im building a 408 for that car but i had to be rational and my compression on this build it gonna be at the sweet spot of 9.75:1,…..im hoping the 91 octane will be enough, then when its said and done im gonna put back on the standard 68cc 823 heads on the 370 and swap it with the 4.8 in my c/10 which has a vortech centrifugal supercharger on it……at that time i will take the stock stroke L96 crankshaft that came out of the 408 and convert the 4.8 into a high compression 5.3…..i did a 5.3 with 4.8 slugs a few years back for another c/10 (‘68 lwb) with an ASA cam and 3000 stalled th350 and that thing had the powerband of a 250cc 2stroke dirtbike, it was a ripper…..id like to keep the hi compression 5.3 motor as a back up motor just in case, or if i get the urge to LS swap my sons ‘67 c code mustang cause we all know the best mustangs have chevy motors in them!!! Long story short is i think the OP is gonna be just fine with the compression ratio in the 9’s since he is gonna have that LSA blower putting in some work…..and at the end of the day my cts-v is a low 9.1:1 ratio and it does just fine on 91

 

Don't worry about the power level, haha. That combination you have will still blow the tires off and scare the heck out of you haha. If it's your first performance build, you'll be more than happy with the results. If you do have any down the road, just get a larger lower pulley or smaller upper and enjoy the newfound power.

 

IMO stick with the mid 9’s if you’re going to be running pump gas at all. Especially in a heavier car. I have a lq4 with ls9 gaskets with 823 heads. It can cruise with out pinging. I tuned an lq9 Silverado SS with the same heads that were supposedly only milled .004” and we had to put 93 octane with octane booster to get it to not audibly ping on the highway while cruising. He put thicker head gaskets on and it completely went away even with 91 octane. You can easily get to the edge of detonation depending on pulley size and compression.

 

I have a 2013 Caprice that I added an LSA blower to a stock L77, with a summit 8715 cam(222/233 .600/.575 115+3) and 1-7/8 long tube headers. The stock compression ratio is supposed to be 10.4:1.

I make a peak of 4.8psi of boost and don't have any issues on Costco pump 93.

 

Why only 4.8 psi??

 

Stock pulleys, larger cam and a better flowing exhaust.

Less restriction makes for less boost is my guess.

 

I believe Summit was spot on with their recommendations. Heavy car on pump gas, 9-9.5:1 is what I would target for static compression with a PD supercharger.

Side note, My Dad recently went with a LSA supercharger along with a BTR red hot cam and Precision triple disk converter on his 2010 Camaro SS A6. It baselined 360whp with catted headers/cai only, then made 550whp 570wtq @ 6psi on 93 octane with 17 degrees of timing. Boost was kept low due to cats. Will probably pull a degree out of it, add a flex sensor, then run it around 20 degrees on E85...maybe a little more since the boost is low.