supercharged111

I apologize if I suck at searching, all I found was that the truck pistons were dished and car pistons weren't. If anyone knows the cc's of both that'd be great, I'm debating on whether or not to shave my Vortec heads to achieve 9.5:1 comp on the L05 bottom end or leave them stock for later applications utilizing better pistons (which may not ever happen).

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ericjon262

is your short block apart? is it in the car? there are two methods I know of to cc the pistons, one uses oil, so it wouldn't work if the motor is in the car(because the oil will flow out of the cylinder). the other uses modeling clay, and a strait edge,

btw the piston down bore and the piston dish added up to be an additional 25 cc of combustion space. but thats on a truck short block.

supercharged111

My L05 is in my daily driven C1500 truck so I'm not going to pop a head off to cc it. The L31 is in the trunk of my car at the moment in long block form so I could pop the heads off that to cc those myself, but I was hoping someone knew offhand or knew where to find said info.

92droptopws6

the CR is pretty low like 9-9.5:1 w/64cc heads

ericjon262

in a C1500, I would expect between 8.5:1 and 9:1. the truck shortblock I have is 8.5:1 with 64 cc heads.

supercharged111

I thought truck engines were 8.2:1 with 76cc heads. The more I search on that the more conflicting answers I get.

ericjon262

well, the figure I came up with was from Me cc'ing the piston dish and downbore(25cc total), and then punching that into desktop dyno using a 64cc chamber, and a 0.028" compressed thickness headgasket. all 4 inch bore with a 3.48 inch stroke.

I used 64 cc because thats the size of the chambers on my World Sportsman II's

-Eric

zipfast

All the 350's I have checked were 30 to 33 down in the hole.
The pistons in my 93 LO5 have 6cc's worth of eye brows.
You should use a .018 steel shim not the .028.

supercharged111

Well another valuable source just said 64cc for the TBI truck heads and the only difference was in the pistons: 12cc for light duty and 18cc for heavy duty, which apparently gave 9.3 for LD and 8.75 for HD. Now if I could just find out what cc's the Vortecs used I'd have all the pieces of the puzzle. Worst case scenario I have to cc them myselves.

92droptopws6

We have not had 76cc heads on any gm 305 or 350 since the late 70s called smog heads. all 5.7L from 86-97 were 64cc heads guaranteed....you can check www.fullsizechevy.com

supercharged111

Yeah, I'm waiting on an answer there too. I figured I'd pick you guys' brains since I've been asking a million questions over there lately.

Fast355

I have checked several engines of the engines I have personally pulled apart. Here is a quick run-down.

1997 L31 Vortec Stock G1500 Van engine (Hydraulic Locked on #2)

Piston Dish is = 12cc total (same exact piston as a Light Duty TBI 350)
Head = 64 cc.
Piston was .026" in the hole
Head gasket was a .028" compressed composite gasket.
Calculated = 9.2:1
Advertised = 9.4:1

Stock GM Goodwrench HD TBI replacement engine

Piston Dish = 18cc total (Same piston as Scyclone/Typhoon FWIW)
Head = 65.3cc
Piston was .025" in the hole
Head gasket was a .028" compressed composite gasket.
Calculated = 8.6:1
Advertised = 8.75:1

Stock 1992 LD TBI 350

Piston dish = 12cc total (Same piston as L31)
Head = 65cc
Piston = .027" in the hole
Head gasket was .028" compressed composite.
Calculated = 9.1:1
Advertised = 9.3:1

Stock 1983 LE9 305 4bbl (The highest compression conventional smallblock GM truck engine I have pulled apart, I almost wonder if the pistons were a factory mistake as others I have seen had deep trough dishes like the early LG4s but this engine was 100% original in every way, unless it had the engine replaced prior to 100 miles).

Piston = Flat-top with 6cc worth of eybrow reliefs
Head = 53cc
Piston - .025" in the hole
Head gasket was a .016" compressed steel shim
Calculated = 10.4:1
Advertised = 9.2:1

Just what I have found through measurements I have carefully taken.