from the very limited sources i have (omniman, c-speeds compression calc, and various HT users) there seems to be a rather large difference of opinion on the effective compression ratio's of CTR pistons in blocks other than the b16b

personally the range of difference is the problem. to me .2 or .3 difference wouldnt bother me, but recently people have been talking of 1+ point differences in the compresion calcs available online today!

i really trust omnimans opinion, i have spoken to him once about a particular head he ported, and the #'s he achieves speak for themselves.

i woul like some help in getting to the bottom of this. i have a set of of overbore ctr pistons available to measure if anyone can point t me what needs to be measured.

 

What you are looking for is the actual compression height of the CTR pistons, the compression calculator is correct but the info on the CTR piston is not. They did not factor in the higher compression height of the CTR piston. Once you have the compression height you will be able to calculate the correct compression ratio for CTR pistons in any head/block combo.

 

Yeah, most people forget about piston to deck height wich with pct's is about 0.0(at least on b18b block), since the pct's are taller by about .03''...
Another misunderstanding is dome cc's.Some people say its 6.15 and another say its 8.63 .
using 8.63 as dome cc's compression would be:
on b18c=13.22 (with gsr head)
on b18b=13.47 (with gsr head)
Using 6.15 as dome cc's with gsr head
b18b=12.68
b18c=12.44




Modified by mmuller at 2:10 AM 5/31/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Altered &raquo;</TD></TR><TR><TD CLASS="quote">What you are looking for is the actual compression height of the CTR pistons, the compression calculator is correct but the info on the CTR piston is not. They did not factor in the higher compression height of the CTR piston. Once you have the compression height you will be able to calculate the correct compression ratio for CTR pistons in any head/block combo.</TD></TR></TABLE>

gimme a way to find the #'s i need to know. lets end this **** right her and now

 

you need to measure the compression height of the CTR piston. Once you have the actual compression height you will be able to calculate the correct compression ratios for each aplication.

 

where is the compression height measured? I think that is what he is asking.

 

You would have to puddy the top of a ctr piston. Fill the puddy with water and messure the cc's. Than (unless it is figured out already?) fill a chamber in the head messure the cc's. Subtract the piston cc's from the head cc's and calculate off of that, adding in the headgasket and figuring Piston to deck height.

 

All you really need to do is subtract the compression height difference from the deck clearance on the compression calculator to get the correct compression.

So the only needed factors would be the compression height of both the standard OEMB series pistons and the CTR pistons, calculate the difference and subtract it from the deck clearance which on the compression calculator shows either .020 or .030 depending on the block being used.

Easy stuff, you just need the correct factors.

 

Omniman, do you have the compression height info for the B16A/B18C and CTR pistons? If so can you post it up?

Just the actual compression heigts are all the info Ill need, Ill post all the compression ratios once I have that.

 

omniman, i appreciate you coming in to clear things up i swear this shoud be a sticky since so many people are asking about the ctr in this motor ctr in that motor

 

Edit:

<U>PR3 head/B16 Block</U>

STD = 11.643438609136867
.25 OS = 11.703231023151065

<U>PR3 head/B17 Block</U>

STD = 12.193487116069006
.25 OS = 12.256369577319077

<U>PR3 head/B18C Block</U>

STD = 12.58636786521145
.25 OS = 12.649248792586258

<U>P72 head/B18C Block</U>

STD = 12.924594026551906
.25 OS = 12.989047869209281

<U>PR3 head/B18A/B Block</U>

STD = 12.825536009218106
.25 OS = 12.88971493738735

<U>P72 head/B18A/B Block</U>

STD = 13.170743903246784
.25 OS = 13.236528215133324

All calculated using OEM 3 layer gasket @ .026 and the compression height provided by Omniman


Modified by Altered at 6:37 AM 1/3/2004

 

my lord there is a big difference between 12.7:1 and 11.7:1

 

What kind of compression would I be looking at in my LsV with by PR3 head and P73-A0 pistons. I thought 10.8:1, but you're saying it will be higher than that?

 

Holy Crap I might sell my CTR pistons now... Jesus

 

My b16 with CTR pistons and B16 rods has a - deck hieght they are actualy out of the cylinder-.011 with no decking. This makes the compression 11.87

 

It's easier if you just measure the piston-to-deck height clearance directly. The tools to do it are not out of anybody's reach who's interested in knowing the numbers.

And, about cc'ing the piston domes...
The way I learned to do it is by calculating a theoretical volume at a given piston depth, setting the piston (crown) into the bore to the given depth, cc'ing it the sme way you would cc a head combustion chamber, and then subtracting the measured volume (minus the volume of the valve reliefs - more later) from the calculated volume.

You use the modeling clay to fill the valve reliefs level with the piston crown (do not include the dome) then pull them out and measure them in a graduated cylinder to see how much volume you lose in the reliefs.

Also, when you measure piston-to-deck height, the exhaust side tends to the higher. Dont' use that measurement. Iinstead, use the intake side, which I have seen to be .002" less than the exhaust side (reference: https://honda-tech.com/zerothread?id=579672). cc'ing the piston will account for the rest (but it won't give you the true dome displacement).

I'm really glad that omniman is able to confirm Tom's .026" compressed head gasket thickness. Maybe that's where he got it from....hmmm.

 

so im looking at a 12.9:1 with the PCT in my b18c1? man thats why higher then i expected when i bought the pistons. anyone wana trade for some jdm ITR?

 

the calcs I did were all with what Ive known the CTR dome to be which is 8.62cc's... I just recently heard its actually only 6.7cc's.

Anyone know what it actually is?

If its 6.7 Ill edit that post and correct it all

 

I'll try to get'er done if I can find some time on the two motors we have in the garage, both with PCT .25OS slugs.

I kinda suck at cc'ing tho b/c I've got an unsteady hand and I'm using a 10mL +/-1cc pipette instead of a 100cc +/-.1cc buret on a stand. I have to reload several times and with water wetter in the solution, and it tends to have a bit of leaky bowel syndrome when moving back and forth, so the readings are almost always higher than they're supposed to be.

I need to get a buret and stand from the lab to make it easier on myself.

 

What would the CR be on a lsvtec with a b16 head, stock headgasket and pistons with a -8.4 dish?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Altered &raquo;</TD></TR><TR><TD CLASS="quote">Edit:

<U>PR3 head/B16 Block</U>

STD = 11.643438609136867
.25 OS = 11.703231023151065

<U>PR3 head/B17 Block</U>

STD = 12.193487116069006
.25 OS = 12.256369577319077

<U>PR3 head/B18C Block</U>

STD = 12.58636786521145
.25 OS = 12.649248792586258

<U>P72 head/B18C Block</U>

STD = 12.924594026551906
.25 OS = 12.989047869209281

<U>PR3 head/B18A/B Block</U>

STD = 12.825536009218106
.25 OS = 12.88971493738735

<U>P72 head/B18A/B Block</U>

STD = 13.170743903246784
.25 OS = 13.236528215133324

All calculated using OEM 3 layer gasket @ .026 and the compression height provided by Omniman


Modified by Altered at 6:37 AM 1/3/2004</TD></TR></TABLE>

so are these the correct CR? my build up depends on the CR that the CTR's will give me in my b17.

 

Does anyone actually put the CTR pistons in their B18C? By reading this post, it seems that everyone is pulling stuff from other sources.

 

Hello 13.236528215133324 !! Here I come!

 

Maybe this thread will finally set people straight.
Im so tired of hearing 11.X for CTR piston in b18

 

this post should be stickied