383 vortec high compression

When I do quench, I look for any number between 0.040 and 0.060.

That range has proven to be just fine for an every day engine.
Since you are putting this into a heavy K20, you may want to rethink the overall package.
Torque is what you are after, not top end power.
A super flat torque curve will make you way happier.

Put the largest part of your budget to the heads that will best suit your need.
If that means you have to run a stock crank instead of the stroker, so be it.
With bitchin heads you will be able to make up for it in drivability.

A high compression engine like what I am seeing will not like being lugged around off road.
It will want to rev and breathe.

Build for torque and enjoy an engine that pushes you back into the seat when you punch it.

Last thing you want to do is lower compression by adding thicker gasket. That can easily make matters worse!

I didn't read all the advice above, but want to add that what you need is pistons with a D-dish, like these:

https://uempistons.com/series-2501-kb-automotive-hyper-chevrolet-383-6-3-kb102.html

The pistons are available with dishes of various volumes.

Catbox said:

When I do quench, I look for any number between 0.040 and 0.060.

That range has proven to be just fine for an every day engine.
Since you are putting this into a heavy K20, you may want to rethink the overall package.
Torque is what you are after, not top end power.
A super flat torque curve will make you way happier.

Put the largest part of your budget to the heads that will best suit your need.
If that means you have to run a stock crank instead of the stroker, so be it.
With bitchin heads you will be able to make up for it in drivability.

A high compression engine like what I am seeing will not like being lugged around off road.
It will want to rev and breathe.

Build for torque and enjoy an engine that pushes you back into the seat when you punch it.

Click to expand...

High compression is fine for low rpm and torque. That's all in the cam.
But to be fair, my personal experience with this was running propane. A torque cam with heads that flow enough to support 700 hp (BB 781 or 449, larger valves and open bowls), twin Impco 425 'pane carbs and what a wonderful combo.
Anyway, carry on.

MikeB said:

Last thing you want to do is lower compression by adding thicker gasket. That can easily make matters worse!

I didn't read all the advice above, but want to add that what you need is pistons with a D-dish, like these:

https://uempistons.com/series-2501-kb-automotive-hyper-chevrolet-383-6-3-kb102.html

The pistons are available with dishes of various volumes.

You must be registered for see images attach

Click to expand...

Why not add a thicker gasket?

Preston Tucker said:

Why not add a thicker gasket?

Click to expand...

Because you will destroy your quench. Lets say you are 9.5 to 1 compression at .060 quench with a cam that has a early intake valve closing point, so you are building fairly high cylinder pressure. A .060 quench may not like pump gas, (detonation), but that same engine with the same cam at .040 quench would be ok on pump gas.

So instead of running a flat top piston with a 64 cc head and a thick head gasket to get say 9.5 to 1 compression you would be better off to run a d-dish piston and a thin head gasket, (to tighten the quench), to get the same 9.5 to 1 compression.

I will throw this in for you, I just put this engine in my 1977 blazer.

It's a nice little 350 with vortec heads 9.5 to one compression with a 215/223 @ .050 , .473/.473 lift, 108 lsa , hydraulic roller cam. It's 357 hp , 410 tq and it pulls my blazer, (on 38 inch rubber), around really well. Also 9.5 to 1 compression is fine for lugging around off road , I do it all the time.

My current recipe I was going to try for was a 15cc d dished piston with a .038 head gasket which gets me around 9.5:1 and thats borderline 87 octane if i am right.

You have to measure the stack like I said earlier, if you run that .038 head gasket and your piston is .025 down in the block thats a quench of .063, (no good). If your piston is down .015 in the block then you are at .053 quench, (still no good). Do the math of your stack.

If your piston is .025 down you could run a fel pro #10094 head gaskets that are .015 thick and that would give you a quench of .040, (perfect), but your 15cc dish piston would be to high of compression. You would need to run a piston with like a 20cc dish but you have to do the math to pick the perfect cc piston for your combustion chamber size and quench distance.

Or you deck the block so your pistons are at 0 deck, (or close to it) then you can run a .039 to .041 head gasket and be at or close to .040 quench. Either way a 15cc d-dish piston puts you in the 10 to 1 plus range at .040 quench so you may want to re think your pistons if you want to be in the 9's.

The better the quench the higher compression you can get away with on pump gas and the cam comes into play with that as well, (intake valve close point) witch dictates cylinder pressure.

Hope this helps, do the math, get your set up right and you will have a daily driver that will be 400 plus hp with tons of torque.

Depending on your cam choice you may be in the 91 octane range.

hirschdalechevy said:

I will throw this in for you, I just put this engine in my 1977 blazer.

It's a nice little 350 with vortec heads 9.5 to one compression with a 215/223 @ .050 , .473/.473 lift, 108 lsa , hydraulic roller cam. It's 357 hp , 410 tq and it pulls my blazer, (on 38 inch rubber), around really well. Also 9.5 to 1 compression is fine for lugging around off road , I do it all the time.

Click to expand...

hirschdalechevy said:

@hirschdalechevy Do you recall what pistons and head gasket you used with this setup?

Click to expand...

When you start getting above 9 or 9.5:1 on a street engine it becomes more and more important to look at quench area and dynamic compression ratio with a specific cam. There have been many good suggestions here. I did flat top pistons with about 6cc of dish from valve reliefs and had .020" milled off the deck to bring the deck clearance to about .018". Then I ran .027" compressed thickness chevrolet performance head gaskets to get the quench and compression I wanted. So I ended up with around 9:1 static compression, .045" quench, and around 8.1:1 dynamic compression with a mild torque cam.

The power, response, and drivability are good and I have zero problems with detonation on 87 octane. I'm all-in on the motor for about $1500. That's about $550 in machine work and the rest in parts. Stock 75cc heads that have been cleaned up with minor bowl blending and chamber polish. If you wanted a real ripper you could easily do the same thing but only have .010" taken off the deck, run 64cc AFR heads and .018" shim gaskets. That would have you all-in at ~$3500 with high quality aluminum heads that would put you in the ~350-400hp range