compression ratio calculations

[tom91ita]

i'm doing the motor work and want to add essentially 0.45 compression points.

i have a decent understanding of how to know/calculate everything except the compressed gasket thickness.

can i do a ratio of a new gasket (e.g., assume 50% of original thickness) when compressed?

or do you pull the head of a car and measure that? do i sacrifice a gasket and assemble the motor and then disassemble for a measurement and then begin the head shaving process?

btw, this is for a honda engine.

tom

[Dyno]

The best way that I know of
Drill a small hole (1/8") in a non-critical area of new gasket. Place the gasket on the block. Place a piece of lead shot in the hole. Bolt down head. Remove head, measure thickness of lead shot. The advantage of this method is that unlike the gasket, the lead shot will not decompress upon removal.

The way most people do it
Measure the thickness of an old gasket. Good enough, methinks.

Another good way
The gasket supplier may have compressed thickness values

A bad way
Use the uncompressed thickness

[Eric Parham]

That's a very thought-provoking response to a question for which I *thought* I already knew the answer (measure used gasket of same type/brand). Your lead shot idea sounds like it would be more accurate as long as the head material is much harder (e.g, good for iron, not so sure about aluminum). How would gasket volume be measured during a teardown? Whatever the answer turns out to be, we should probably use the same method when building to get as close to the same results as possible.

[tom91ita]

i like the idea of the lead shot but might try squeezing it with some aluminum to see the difference also.

but basically, if we do not get the measurements when disassembling, we are looking at sacrificing a gasket to find out right?

or could we take the lead shot method and compress a gasket with no gasket seating material, get the measurement and then machine the head and reuse the gasket?

i know that most head gaskets i have had the pleasure to deal with are not in any shape to measure when taking apart. there is always quite a bit stuck to the block and head.

do we need to have a fresh gasket with us to sacrifice in impound?

[MMiskoe]

I asked a friend who's done a lot of engine work, his comment was to sacrifice a gasket. He also said that any gasket maker worth their salt should be able to tell you the compressed size.