dizwiz24

Im getting some used AFR heads cc'd and need to know what the stock lt1's head combustion chamber, head space, and piston dish size is.

I tried to calculate using : 58cc (combusion chamber); .060 inches (deck to piston clearance + compressed head gasket); -4.5cc dish size and I ended up with 10.57:1 which is too high.

Heres everything converted to units of cm^3 (cc):
Chamber: 58
head space: 12.355308
Cylinder size: 716.6079474
piston dish: 4.5

CR: 10.57324:1

So im wrong somewhere. Anyone know where?

Hopefully I wont have to pay them to mill them, but its possible i might.

lt1-xjs

Stock chamber is 54 cc.

dizwiz24

OK using a chamber size of 54 cc really throws it off.

(all units in cm^3)
Chamber: 54
head space: 12.355308
cylinder: 716.6079474
piston dish 4.5

Compression ratio 11.11368051

compression ratio = (chamber volume + head space (at TDC) + cylinder swept volume + piston dish volume) / (chamber volume + head space (at TDC) + swept volume + piston dish volume)


I went out (heads are off the car) and measured the 'head space' and its correct. I am using .060" which is equal to .015" at TDC + .045" compressed gasket thickness. Again these are from measurement so I am sure they are correct.

Are we sure of the piston dish size? Could it be more than 4.5 cc?

RamAir95TA

You're overcomplicating this. All you need to compute CR is:

Bore size in inches
Stroke length in inches
Deck height (eg. .015" in the hole)
Gasket thickness
Head volume (in your case, 54cc using stock heads)
Piston dish size (in cc's)

That's it. Post it up.

97 6SPEED Z

Yep, you're on the right track here! Most people forget that the stock LT1 piston is a four (4) valve relief piston. The piston "dish" volume on the stock piston is more like 6.5 to 7.0 cc's.

For a TOTALLY factory stock 5.7L LT1 engine use these numbers:

Combustion chamber volume = 54 cc's
Bore size = 4.000"
Stock deck height is 9.025" = i.e. piston is .025" "in the hole"
Compressed head gasket thickness = .042"
Crank stroke = 3.48"
Piston "dish" volume = 7 cc's

That's what you were asking for, correct?