Generation IV Internal Engine - Milling L92s.....how much can I remove?

Hi guys here is my new motor specs coming along.

4.010 bore, manley 2618 pistons-4cc reliefs, manley 6.125 rods, full balance, 3.622" stock crank, slp pump, double row chain.

Cam is a 240/242/111 dialed in at 107.5 deg ICL. Heads are obviously ported L92s. I have heard some people going 80 thou off the L92 heads. The manifold still fits then. This is through a respected workshop.

Comp is at 10.6:1 atm with 20 thou removed. I want to increase cranking compression somewhat enough to overcome the late IVC and big overlap of the camshaft.

I should still be able to run a lot of timing and have excellent average power with more comp. I am hoping to get it to 11.4:1 region.

The G6x3 brigade in LS3s I would presume would be running more comp too. What do you guys think? I have found these heads love comp and timing. They do take a lot of timing before knock but still make best torque up to 5 degrees before in in most cases. So I have thought through the tuning process.

.080" off the heads? I don't see that happening.
This is zero deck, .035 head gaskets and 4cc valve reliefs.
Heads milled to get a 62cc combustion chamber

Bore 4.01
ST = Stroke 3.622
RL = Rod Length 6.125
Number of cylinders 8
Deck Height (how much pistons come out of the hole) 0
Piston Dome or Dish (- for a dome + for a dish) 4
Compressed Head gasket thickness 0.035
Cylinder Head Chamber Volume 62

Static Compression Ratio 11.23 :1
Dynamic Compresion Ratio 8.29 :1
Rod to Stroke Ratio 1.69 :1
Bore to Stroke Ratio 1.11 :1

I milled my CNC ported L92/LS3 heads .030" and with a 223 @ .050 cam only had .045" piston to valve clearance. I had to back down to a 219@ .050 intake lobe. This is with an untouched block and stock head gasket.

I would think you will run into ptv clearance issues milling the heads .080. What is your head gasket thickness?

Guys the pistons have 4cc valve reliefs, they are aftermarket forged items, with stock 51 thou gaskets the pistons protrude 9 thou from the block. I have lots of clearance.
cheers

.080" off the heads? I don't see that happening.
This is zero deck, .035 head gaskets and 4cc valve reliefs.
Heads milled to get a 62cc combustion chamber

Bore 4.01
ST = Stroke 3.622
RL = Rod Length 6.125
Number of cylinders 8
Deck Height (how much pistons come out of the hole) 0
Piston Dome or Dish (- for a dome + for a dish) 4
Compressed Head gasket thickness 0.035
Cylinder Head Chamber Volume 62

Static Compression Ratio 11.23 :1
Dynamic Compresion Ratio 8.29 :1
Rod to Stroke Ratio 1.69 :1
Bore to Stroke Ratio 1.11 :1

Sams Performance has milled them 80 thou and he has built a lot. I am just asking in general.

You are at 62cc with only 30thou off the heads? Did you cc them?

With a 51 thou gasket and piston coming up through the block 9 thou. I have a 12cc volume (this is including -4cc from the reliefs). Between the top of the piston and the head I have 42thou, My quench is 7 thou more then yours LT1.

Anyway I get 750 from the cylinder add 66 for the chamber plus 12 for the remainder divide by 78 I get 10.6:1.

A fast calculation with yours LT1, 750+73 = 823/73 = 11.27:1.

80 thou appears excessive just letting ppl know it has been done on NA 6L with no issues by one of the best LS builders in the world.

While majority build tough strokers it is harder to get the comp up with L92 heads on a 366ci so I was asking in general what people did to get it up there. I am aiming to get a cranking compression of 200-220 psi to get this with my cam I need to get into the 11s. I am sticking with the stock gaskets as my piston is already past the deck. I will start with 40 thou and see how it pans out I can always go more then. This will start me with 11.1:1 compression. A few sponsors believe 11.8:1 is a good figure for my combo.

Yes, I did CC mine. I was at 10.8 with the .045 head gaskets, went back to stock, .052 and I am now at 10.6.

Well to keep your quench at .035 you will need .045 head gaskets. Mill the heads .030 will get the combustion chambers to 62cc. That gets you to 11.25:1. Take .054 off and get 11.5.

Bore 4.01
ST = Stroke 3.622
RL = Rod Length 6.125
Number of cylinders 8
Deck Height (how much pistons come out of the hole) -0.009
Piston Dome or Dish (- for a dome + for a dish) 4
Compressed Head gasket thickness 0.045
Cylinder Head Chamber Volume 60

Static Compression Ratio 11.49 :1
Dynamic Compresion Ratio 8.48 :1
Rod to Stroke Ratio 1.69 :1
Bore to Stroke Ratio 1.11 :1

Thanks very much LT1

cheers

mine are shaved .040 and i have no ptv issues

mine are shaved .040 and i have no ptv issues

Yeah but what are your cam specs???

.080 and then the intake manifold geometry is going to need looking into. I've heard of shops routinely going .020 - .030 but not more (on average).

230-242 600/600 110

I milled my CNC ported L92/LS3 heads .030" and with a 223 @ .050 cam only had .045" piston to valve clearance. I had to back down to a 219@ .050 intake lobe. This is with an untouched block and stock head gasket.
But you are also the only one on several forums who has this issue. So either the measurement was taken incorrectly or you have some odd setup than no one else has ever duplicated.

Heck, the LG G6x3 works in a stock LS3 Camaro and that has a ton of duration.

But you are also the only one on several forums who has this issue. So either the measurement was taken incorrectly or you have some odd setup than no one else has ever duplicated.

Heck, the LG G6x3 works in a stock LS3 Camaro and that has a ton of duration.Couldb be, but it doesnt make me wrong. My story says no matter what you MUST check for yourself!! If I were to assume what everyone else says on the forum, I would have a dead engine and no one who said a bigger cam would fit would be sending checks to help rebuild.

My measurements were done with a solid roller lifter, adjustable pushrod, checking spring, and dial indicator. It doesnt get more exact.

Yes no matter what ptv needs to be checked. Its not a matter of the duration of the cam that causes ptv issues its the timing events. Its obvious that the g6x3's timing events allow it to be used with no ptv issues and the cam Sweets10v8 has different timing events which had caused ptv issues and that causes you to flycut or like he did and change the cam.

checking spring is the easiest. LS7 lifters are not so easy to bleed down

The cam I am using fits straight up no problems, Advance it a little and take 40thou off the heads and it will have 60 interference with the piston on the intake lobe. Lucky I have 6mm reliefs lol.

My friend runs 40thou off the heads with a 224/228/114+0 no worries with ptv.

Anyway the context of this thread was not ptv clearance. That alters engine to engine and with aftermarket valves you have even less. My question was how much material can be removed without issues with manifold misalignment or running to thin on the deck of the head etc. But its ok I have already found that answer. I have milled them 40thou and comp is a tad over 11:1. Thankyou all for the replies.