cr calculation confusion

**vinnY** · 19-01-2007 06:56 PM

was looking to doing a b16/b18 hybrid on an ek4
pieced together some parts and doing a little more research on the parts themselves to see if they'd work together.
parts in question;
b16a2 head
ctr cams
r dual valve springs
r valves
adjustible cam gears(haven't decided whether i really need them yet)

bottom end will consist of;
b18c2 bottom
ctr pistons
itr conrods
oem headgasket
b18 oil pump

doing some cr calculations and i seems to have gotten 2 very different results, i dunno where i'm going wrong here and i'm wondering if anyone can help clear it up for me

Code:

-- http://www.c-speedracing.com/howto/compcalc/compcalc.php --

block; b18c1/c5
		bore; 81.00mm
		stroke; 87.20mm
head; b16a/b - b18c5
		combustion chamber volume; 42.70cc
piston; pct (jdm b1b6b)
		piston dome displacement; 8.63cc
headgasket thickness; oem b-series 3-layer
		thickness; 0.0290in
		bore difference; 0.00mm
piston-to-deck height; oem b18a/b/c1/c5 - b20b/z
		height; 0.030in
*compression ratio; 11.7517:1
*displacement; 1797.56cc

Code:

-- http://www.zealautowerks.com/ --

block/crank; b18c - b16b/b18c
		bore; 81mm
		stroke; 87.20mm
		deck height; 212.3mm
head; b16a/b - b17a - b18c5
		combustion chamber volume; 42.70cc
piston; pct (jdm b16b)
		dome; 8.63cc
		comp height; 30.73mm
connecting rod; b18c1/c5
		rod length; 137.90mm
headgasket thickness; oem 3-layer
		thickness; 0.026in
		bore diff; 0.00
head milling and block decking; 0.000in
maximum operation rpm; 8000rpm
elevation; 0000feet
boost; 0psi
*static comp ratio; 12.74:1
*effective comp ratio; 12.74
*displacement; 1797.55cc
*rod/stroke ratio; 1.58
*piston-to-deck height; 0.006
*mean piston speed; 1930fps
*max piston acceleration; 132137fps^2

now idealy i'd like the cr of the first one, the second one sounds fairly high to me. and upon doing some research its quite high and hard to tune for reliability
anyone able to shed some light on this topic for me?

suggestions on parts and extra parts i might need are also welcomed

edit;
found another cr calculator, yet another different result!

Code:

-- http://technet.ff-squad.com/cr-calculator.htm --
pistons; pct
head; b16a
block; b18c
gasket; 3-layer
bore; 81mm
cr; 12

**BlitZ** · 20-01-2007 08:41 AM

yeah... its because of the pct (CTR) piston.. everyone uses different measurements for dome top

I wanted the above setup for 1 time in my life... the cr should be 12.8-13.1 or somewhere in that range.

WTF this doing in a noob section.. eheheh

**Hipowerracing** · 20-01-2007 09:20 AM

okay compression ratio can be calculated in different ways. what i have found out thru out the years is that different people use different methods.

example 1.
some mesaure compression ration assuming that a head is flat.. but in actual fact a head is not flat it has a concave surface, that extra volume in the concave does make a difference in the cals, depending on how accurate you wanna be.

example 2.
compression ratio pretty well means in a stroke, how many pistons (height) you can fit in the stroke..(dont really know how to explain with proper words.)
in this calculations above i do not know if they actually include the crown of the pistons.

example 3.
decking of the head and block? did hey do any surface machining of the block and head? that changes cr

many more instances that cr can be changed..

i hope the info has help.
Warmest regards
Ivan

**dsp26** · 20-01-2007 10:53 AM

heres another calculator to check against (Honda Specific)
http://www.ozhonda.com/forum/showthr...=cr+calculator

**vinnY** · 20-01-2007 06:12 PM

Originally Posted by dsp26

heres another calculator to check against (Honda Specific)
http://www.ozhonda.com/forum/showthr...=cr+calculator

thanks for the info guys
the above links calculated about 12:1cr which i'd be VERY happy with, but that just means its 4 different results

i'd very much like to use the above setup as it is all oem parts and should be great honda quality

also another question, if the cr is 11.75-12:1 would the stock ctr cams be up to the job?