4K Compression Ratio Calculator?

[Evan G]

i need abit of info on how to calculate my static compression ratio for my head, ill be going a large cam.

 

stock 4k head is around 22CC? in the combustion camber

 

head gasket would be 1mm thick?

 

bore 75mm + .60' oversize pistons (flat top pistons

 

73mm stroke.

 

stock compression ratio "FAQ says is 9.1" but my gegory book says "8.5:1 auto, 9:1 manual?" this engine was orginally auto.

 

Piston To Deck Height is also needed? why is this calculator showing 34.1:1 with these inputs? fml

 

http://www.gtsparkplugs.com/CompRatioCalc.html

[Mitch-12]

your using some metric and some imperial measurements and you confused it

i used this:

bore. 3 inch

stroke. 2.87 inch

chamber. 22cc

HG. .040 thou

HG bore. 3.05 inch

piston to deck. 0 i guessed this would be close though

piston type. flat top

and 0 dish

came out with 13.41:1

 

stock 4k head is more like 37cc if i remember right from doing mine D dish 5k is 18cc

[Evan G]

thanks for that champ. tried another calculator.

 

Cylinder Diameter (mm) - 76.5 (.60' oversize = 1.5mm?)

 

stroke - 73mm

 

chamber in cc - 37

 

gasket thickness - 1mm

 

I'm getting comp ratio of 9.07:1. how would i calculate roughy how much i need to skim the head to get 10:1 compression

[Mitch-12]

honestly i don't know maybe get the machine shop to skim it untill the correct amount of cc's are reached to be 10:1

[Evan G]

sounds like a plan! gonna drop the head off tomorrow :D here i want 10:1 compression :fuzz:

[altezzaclub]

your using some metric and some imperial measurements and you confused it

i used this:

bore. 3 inch

stroke. 2.87 inch

chamber. 22cc

 

Mitch!!! inches & cc !!

 

Evan, look at my build thread. You put a piece of graph paper over the chamber & draw the outline, then count the squares to get the area in square cm.

 

You can then find out how much you reduce the head volume by removing half a mm etc and thence the new CR.

[ae824ate]

Never mind my rambling. But always work off a dynamic CR. Especially with a different cam. My tighe 150A has an intake valve closing/sealing @ 71 deg abdc, and a loss of static volume. Work off and calculate from the dynamic CR, not the assumed static CR. I'm sure most of you guys know all of this. Thanks to philbey for this link, please read it.

 

http://www.empirenet.com/pkelley2/DynamicCR.html

Edited September 19, 2011 by ae824ate

[Evan G]

went down my engine builder, he told me to measure my deck height & cc of the heads

 

i measured the cc of the heads. 33cc and the deck height of 0.13mm

 

mr altezzaclub - your method worked a treat! i used diesel and a syringe instead :y:

 

my engine builder also said i might need to shorten push rods or space the rocker arms up because plaining the head might play havock with my push rod geometery? has anyone had a problem with this at 10:1 compression?

 

also does anyone know the thickness of a 4k HG?

Edited September 20, 2011 by Evan G

[tojo2]

went down my engine builder, he told me to measure my deck height & cc of the heads

 

i measured the cc of the heads. 33cc and the deck height of 0.13mm

 

mr altezzaclub - your method worked a treat! i used diesel and a syringe instead :y:

 

my engine builder also said i might need to shorten push rods or space the rocker arms up because plaining the head might play havock with my push rod geometery? has anyone had a problem with this at 10:1 compression?

 

also does anyone know the thickness of a 4k HG?

 

A compressed 4k headgasket is about 1.3mm

[Evan G]

Thanks champ

[altezzaclub]

..and I haven't had a problem with rocker ratio using 10 to 1 compression.

 

As you can imagine, the more the head moves down the more the pushrods stick up and so the steeper the angle the pushrods point down when they open the valves. Eventually the end of the pushrods wipes off the edge of the valve top.

 

How hard would it be to cut some brass shim metal to the footprint of each rocker shaft tower and space them back up 20thou??