Increased Compression Ratio - LS2
 

I am interested in increasing the compression ratio on my LS2 from stock (10.9 to 1) by some amount t.b.d., maybe in the 11.4 to 11.5 range for Tier 1 93-octane gasoline.

I have done the computations for head gasket thickness effects. Our 364 cubic inch engines are 45.5 cubic inches or 745.6 cubic centimeters (cc) per cylinder. Using the 10.9 to 1 number, the total combustion chamber volume should be about 75.31 cc. This would include the head, the gasket and any above-piston volume below the block deck surface.

The 4.000” bore on our LS2 engines has an area of 12.566 square inches, or 81.1 square cm. If I want to raise the compression ratio 1/10 of a point to 11.0 to 1, the volume of the total combustion chamber must decrease to 74.56 cc, a decrease of 0.75 cc. To do this with the gasket, the gasket should thus be thinner by 0.75/81.1 cm, or 0.00925 cm, or 0.0925 mm, or 0.0037 inches (for the metrically challenged).

Thus I extrapolate that to increase the compression ratio by half a point to 11.4 to one, the head gasket should be thinner by 18.5 thousandths of an inch, or 0.46 mm. Does this seem about right to you experts, or did I slip a decimal place somewhere?


Now for milling the heads: I do NOT know what the area of the combustion chamber in the head is at the cylinder head deck, but it is less than 81.1 square cm. (Duh!) Thus the typical milling of the heads by 0.030 inches should not raise the compression by the 0.8 point that 0.030 inch thinner gaskets would accomplish. So – you panel of experts reading this far in this post – how much of an increase in compression does a milling cut of 0.030” on stock 243-based LS2 heads produce on a stock LS2 short block assembly?

And yes, I know that if there is a valve job, that changes the cc volume of the combustion chamber. I also know that any good tuner will take all the above into account in putting together a proposal for my engine upgrade, but I want to play around with the parameters myself ;) in anticipation of contracting with one for my work.

Thanx in advance !

If you don't get some good answers pm Gtodoug. He knows all this stuff and is a great guy and a local buddy of mine.

how much compression can be run on 93? 93+ torco? race gas 110?

I'm interested in this thread simply b/c I live at elevation and "lose compression" from that alone. Subscribing.

Thanx Joe, I will hold that in reserve. Maybe Spin or Craigster can comment on my question.

I sent Dougie a note.

one compression point is worth about a 4% hp increase. I would not go more than 12:1 on 93 octane unless you plan on running a partial mix of race gas.

You can run a lot of compression, as long as you can "keep it cool."

If you increase the compression by lowering the head, you'll have to take special care if you add a cam down the line. Also, the shape of the chamber can make a huge difference in detonation thresholds.

I put a simpler version of the question in Post # 1 in a new thread, try this one on for size:

SIMPLE VERSION

haha. Lee, I love the simple version. The math works out, however im not an expert on these things but, it seems logical to me.