ok so im trying to figure out my compression ratio exactly and i want to be as sure as possible

ive tried some formula's and using some compression calculators online. Now the formula's i was doing seemed horribly inaccuarte.

i guess i should mention my engine set up 1st

d16a6 block
d16z6 head
pm7 pistons
other then that BONE stock

75mm bore
90mm stroke
-7.2cc dome pistons
34.60cc head combustion chamber


Anyways the formula's i was using was getting me readings like 8:1 or like 15:1 way to off an exagerated i tried them multiple ways and conversion and still no go the closest i got with on of them was 14.21:1 still seems really high.

The compression calculators were giving me high 12:1's and low-mid 13:1's. BUTTTT When i used this formula
CR= (Pi/4)x(borexbore)x(stroke)+(head cc)
. D i v i d e d .
(head cc)

(this formula http://en.wikipedia.org/wiki/Compression_ratio)


i got 11.48:1 which honestly seem way way more acurate then anything i got so far

can anyone tell me does this seem correct and am i doing the math correct based on that formula i posted? let alone does 11.48:1 sound accurate for my engine setup? as i think it does but i dont/cant be wrong on this so thus why im double chekin

 

the 34.6cc combustion chamber volume will be higher due to the height of the head gasket. To compensate, take combustion chamber volume minus offset from the pistons dome and add PI * cylinderbore^2 * the measured thickness of the headgasket.

overall, that will lower the compression ratio a small amount, but my guess would be you will get somewhere around 11.0:1.

The reality is that deck height also matters in the same fashion that the head gasket does, because it effectively elongates the combustion chamber. the various d-series have tiny variations in deck height. If the block has ever been machined in its life after leaving the factory, there may also be a slightly smaller deck height than what might otherwise be considered stock, which funtionally reduces the volume of the combustion chamber, causing higher compression.

 

depending on head gasket thickness, you will be between 11.6:1 and 12.1:1

http://www.zealautowerks.com/dseries.html

 

that zeal autoworks calculator is a peice of crap it is no where near accurate let a lone a good guesstimation


so sanimalp in taht formula i should add in the deck height as well( isisnt it only 0.002 inches? on the d16a6 block?) as well teh block has NEVER been machined


ugh man this is so dumb so i did what you said and now im getting 14:1 everytime

what the heck

frig what am i doing wrong this is what im adding up 3.14(pi) / (cylinders) 4 x (stroke)75 x (bore)90 x (bore)90 + 34.6 (CC) + 0.002 (deck height) + 0.048(gasket thickness) - 7.2(dome pistons)=476914 / 0.048+0.002+34.6-7.2=27.45
= 14:1+ what the gay

 

compression ratio is total volume at Bottom Dead Center divided by total volume at Top Dead Center

Total volume at BDC = cylinder volume + deck height volume + head gasket volume + combustion chamber volume - piston dome volume

Total volume at TDC = deck height volume + head gasket volume + combustion chamber volume - piston dome volume

For D16A6 block with D16Z6 head, PM7 pistons and D16Z6 head gasket:

Cylinder volume in cc's = Pi/4 x bore in mm x bore in mm x stroke in mm / 1000 or
Pi/4 x 75 x 75 x 90 /1000 = 397.60cc

Deck height with PM7 pistons is 1mm, so deck height volume:
Pi/4 x 75 x 75 x 1 / 1000 = 4.42cc

D16Z6 head gasket thickness = 0.037" = .9398mm, so head gasket volume:
Pi/4 x 75 x 75 x .9398 / 1000 = 4.15cc

D16Z6 head combustion chamber volume = 34.60cc

PM7 piston dome volume = 7.2cc

Compression Ratio:
397.60 + 4.42 + 4.15 + 34.6 - 7.2 / 4.42 + 4.15 + 34.6 - 7.2 = 12.05:1

 

wow thnx dude ! :D

ah i think i see what i was doing now in my math

curious though why did you add 1000 in the cyl. volume?? i dont understand that part

 

Wolfram|alpha confirms jli's calculation with this input:

((pi/4)*(75mm)^2*(90mm) + (34.6cc - 7.2cc+4.15cc+4.42cc))/(34.6cc - 7.2cc+4.15cc+4.42cc) = 12.05

 

awesome dude! that's going in my fav's

thnx a bunch for the help guys :D!!!

 

Hi, I'm new here.

I was reading on the FJDistributors homepage, this combination for my D16z6:

D16Z6 + .037" Head Gasket + P29 pistons: 12.06:1

As I read here, this thickness of the headgasket is from the d16z6 oem headgasket, am I right? So, what if I use on this combo, a D16Y8 headgasket, what is the thikcness of it? And what wolud be my compression ratio with this stuff?

Sorry for anything that I couldn't do, thanks for the atention.

Bye

 

If memory serves it is .028" thick.

 

Thanks!

My doubt about the service that I'll do, is that I will have to make a full service on my cilinder head, because of a headgasket burned, it obviously get a increase of compression ratio, because of the material removed from the cilinder head. I don't know what the name of this service in english, sorry, but I believe that you'll understand what I'm talking about... (is this "shaver"?)

Anyway, I wondering if I use a headgasket of the Z6 + P29, or the gasket of Y8 + OEM Pistons. In any case, there will be added some ratio from the "shaver" service.

What I have to use?

Thank you guys!

 

That would all be awesome in a perfect world.