Hi All:

Does anyone have ALL the values of a stock L03 from 1990 to enter into the online formulas to calculate compression? The stock L03 had a 9.3:1 compression ratio. My 1990 manual (you know the BIG one) doesn't have the piston values, or deck height. Want to play with the values.

Thanks all!

 

The reason why I am asking is that I am putting vortec 906 milled heads on my 305 TBI L03 with the fel-pro 1094s. The cam will be an LT1 out of a 97. The machine shop said if I take the 906s down to 58cc, it would be bad (crack) so he says they are around 61cc? If stock is 9:3.1, what would the new compression be if all is the same except the heads, head gasket and new 1.6 rollers. If lower than 9:3.1, would the performance be bad, or better given vortecs flow way better than the stock heads.

Thanks again all!!

 

In general the stock piston to deck is .025 - .030 in, on these engines.
The stock written 9.3 CR could be a little optimistic.

LO3 pistons look like 12cc dish https://www.thirdgen.org/forums/post...77-post32.html should be around 10 cc dish to get around 9.3 CR with 58 cc heads and 0.015 gasket.

Here is a recent post obout 350 heads on a LO3 https://www.thirdgen.org/forums/tbi/...bi-intake.html

Your plans sound good, I doubt 8.6 or 9 CR would make a huge difference. Make sure to set up the heads for the increased lift.

 

Make sure to set up the heads for the increased lift.

I changed the springs and are using 1.6 rockers.
How can I get the compression up to around 9.3:1 without milling anything else off the heads and using the fel-pro 1094?

 

LT1 cam with 1.6 rockers gives around .480 - .490 in lift, sprigs alone will not do it, need some specific retainers or backcut valve guides.

To increase compression, change pistons or use heads with smaller combustion chamber.

 

need some specific retainers or backcut valve guides.

Can you be more specific? The heads have new pushrods and the opening is now larger for the rods.

 

More specific? Mesure the distance between the spring retainer and the valve seal. This is the absolute max lift the head can support.