For those of you who care, and I know there’s a few on here about compression ratio’s and not just how altezza’s look. Someone over at honda-tech made a nice compression ratio calculator, pretty complete and VERY informative, check it out…
Re: Compression Ratio Calculator
Originally posted by Josh
[B]For those of you who care, and I know there’s a few on here about compression ratio’s and not just how altezza’s look. Someone over at honda-tech made a nice compression ratio calculator, pretty complete and VERY informative, check it out…
http://www.bojangz.com/calculator/ [/B]
Awesome find Josh. Very cool indeed.
Jordan
this was actually mentioned already over in the hybrid forum here.
unfortunately this CR calculator doesn’t seem to be 100% accurate. I tested out some stock engines and it seemed to get their CR’s right. But when i started messing around with different pistons in different blocks the numbers started to look a bit strange.
I LOVE the idea, and i really hope whoever made it will go back and fix the errors, but until then I’m not gonna trust it.
Originally posted by 91IntegGS
[B]this was actually mentioned already over in the hybrid forum here.
unfortunately this CR calculator doesn’t seem to be 100% accurate. I tested out some stock engines and it seemed to get their CR’s right. But when i started messing around with different pistons in different blocks the numbers started to look a bit strange.
I LOVE the idea, and i really hope whoever made it will go back and fix the errors, but until then I’m not gonna trust it. [/B]
Colin, how far off is it, in terms of hybrid engines? Would you say that it is a good approximation?
Jordan
well, i myself am not all that familiar with what pistons should give what CR’s. I’m still pretty new to all the internal mixing and matching (that is what i’ve been trying to learn here online for about the past 6 months).
I didn’t test out much on it. Basically i just tested what i was sort of familiar with. I plan on building a b17a, and i have been trying to figure out what compression to run. I figured (with help from ff squad, my own calculations, and dan) that if i ran p30 pistons i should get about 10.5 or 10.6. I checked this in the CR calculator and came up with something like 10.0 or 10.1.
go over to the hybrid forum and read the post over there, i posted some numbers that the ff squad had, and some info that people had given me —and it was pretty conflicting with what the CR calculator gave.
I think maybe he just has the wrong specs on some of the pistons. Because i got close to the right answer when doing a stock b16a and stock b17a. But when i tired to put p30, usdm p73 and jdm p73 the answers started getting odd.
I agree with Colin. The calculator seems to indicate around .4 to .6 points lower than what should be expected on altered engines.
Maybe the FF squad isn’t right, this was created my more of the smarter people over at honda-tech…
I’m not saying that this is the end all of compression ratio info, but I’ve also heard that the FF squad site isn’t always accurate…
josh: yeah, i didn’t say that the ff squad was right, if you read my other post i just said i wasn’t sure who was right.
its just that when i find conflicting info its hard to figure out what is correct.
also, i’d like to point out that i think the CR calculator has been changed since last night. I’m not getting some numbers slightly different from the same setups i put in last night. So, maybe there are/were some errors and he’s working on correcting them.
i really hope that he gets it all worked out, because this thing would make calculating CR MUCH easier.
Cool calculator and it may come in handy for a lot of people in the future so ARCHIVETHIS
Well, no…if you work the comression numbers through the proper formulas (with BASIC MATH), the numbers end up slightly different than what that “calculator” gives. Use the formula yourself and see. I would like to see the formula they used if any at all. Just because they are over at Honda-Tech does not mean they are all that smart. I’ve seen some real dumb-a$$es over there. I’m not saying the guy that created it was dumb, it’s just that even to insinuate that Honda-Tech people are smarter in general just irritates me. If you are serious about building a motor and want to know the compression ratio you’ll end up with, you’ll work your own numbers instead of just using someone elses “calculator”. Are you willing to pay for their mistakes?
I also agree with Colin though, seems like they fixed an error. It is coming a lot closer than it was.
I noticed that a LS block w/ PR4 pistons, 81.25mm bore, 3 layer gasket, and B18C1 head had higher compression than B18C5 head. Does that seem right? Wouldn’t you think the Type R head would be higher? Dunno
EDIT: DOH
b18c1 and b18c5 heads are different castings. the b18c1 is a p72 (i might be wrong on the #), and the b18c5 head is a pr3 head (same as b16a’s and b17a’s, but the b18c5 head comes w/ a slight port/polish on it).
the cylinder head volumes are as follows:
b18c1: 41.6cc
b18c5: 42.7cc
so, since the b18c1 has a smaller cyl head volume, it will decrease the volume of the combustion chamber in relation to using a b18c5 head. Thus, raising compression.
The ITR does have higher compression than the gsr engine, but they use pistons to get a 10.6:1 or 11:1 CR instead of using a head w/ smaller volume.
DAN: Did you happen to read through my email? I was just wondering if i did all that right.
oh, and one thing i was wondering about. When we do the calculations maually we use the stock CR numbers like 10.2:1 or 9.7:1 or whatever that engine is rated at. I would assume that these numbers are just rounded from the actual values, right? Just like the displacement numbers for b series engines, how they are just rounded to the nearest 1.6 or 1.8 or whatever. Could the rounding of CR’s have anything to do with slight discrepencies between our calculations and his??
thanks dan!