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ok i was going thru the honda site looking at different specs, when i came across the civic gx

ok yes that is natural gas, but then i looked at the compression ratio

12.5:1 compression ratio.. now if u ask me thats really high, so if i were to get those pistons, i would have to switch to premium gas... any thoughts on this? i dont think i would change the redline because i dont know if these pistons are forged or stamped out... can anyone clarify this for me?

btw the piston's bore and stroke are 75 X 94.4 the same as ours

 
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humm, the reason that it is so high is beacause that is the best compresion ratio for nautural gas, some desil engines are like 18:1 turbo charged. they could probly fit but can the engines stand the temp?

 
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yes i realize its designed for natural gas, but hypothetically speaking, if i were to use these in my ex, i would have to run with high octane gas

 
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probly 100 octane, but i don't think they will fit because of tall pistons and you probly need to change the fuel management to accomadate the new set up

 
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the pistons are the same bore and stroke as the normal civics

 
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imagine the power. you could probably make 150 hp with them instead of our puny 127 we have in the ex

 
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I say try it... True seeing as how we are running around 9.5 or so:1, 12.5 would require at least 93 octane, maybe with a good octane booster per tank, but with 12.5:1 you should pour out a good 150 if not more. Make sure to look into any kind a reliability issues, maybe go with some personally forged pistons made from a certian material for long life and durability as well as performance. And decking you combustion chamber will give you a small bit of raised compression ( but do not mix both decking and high-comp pstons.. bad idea!)

 
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yeah... maybe 93 octane will work with minimal knocking, but if you want no knocking, use like the 100 octane gas, made by an octane booster and you will have maybe, i mean maybe about 25-30 more hp. anyway, our compression is 9.9 so 9.9/127=12.5/x where x = 160... if it works this way...

 
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well we will see if honda carries these parts, and its like $40/piston i wouldnt want to run turbo on those tho... so ill try it... and dyno it... cause personally i think 200 for pistons without doing any serious mods or raising the rev limit could be the next big thing

 
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Well if you wanna rev higher you'd need to change you valve springs, retainers, and valves. Aside form then raising the rev limiter set upon the ecu.

Well that is possible. If you can spend the money to install the pistons after the fact then it might be worth trying.. pm me that link and ill check on it a little bit. That might be a good way to go, although running premium or 100 octane on a daily driver would suck, it would be nice..

Then you can change the cam timing to be copesetic with the new pistons. Also that would go far with n/a, then being able to change the camshaft... oowiee..

Sounds like I could make a good autox set-up with the 7gc..

 
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yeah, i'd love to see the dyno of this 12.5:1 compression civic... im getting impatient... maybe i'll go try that in alternative to a turbo.

 
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I like autox so i might try that, but maybe a turbo for highway fun.. i dunno.. turbo = bad for autox usually..

Lol, it's hard to see a dyno for anything.. it's so expensive..

There is of course a fork in the road.. certian mods will render a turbo unuseable, but assuming 12.5 pistons, new camshaft, cam gear, intake manifold, bored tb.. maybe a port/polish and i/h/e and you could probably be close to a 5-7 psi turbo, but all motor.

A more aggressive cam... Damn, sorry... thinking aloud, need to open a word document... lol.

Only thing would be maybe with the i/h/e camshaft cam, piston. That could hit around 190 maybe.. most i bet though. Assuming an all out all motor.. Aggressive Camshaft, cam gear, im, bored out tb, p&p, i/h/e, hf-cat maybe. Then for ***** to the wall, 2025 valves, retainers, springs, change the rev limiter.. oh god.. gotta stop thinking aloud..

*Due to most of this post having little or nothing to do with the topic I would like to apologize for making you read this entire section of my ramblings... Please forgive me, thank you.

 
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go for it, but id rater have 11:1 instead, dont want to be running racing gas

so 9.9/127=11.0/x
thats 141.1

 
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If you find out anything about this let me know. I am about to get a stage 2 Crower regrind and AEM Gear and with my VAFC working and all I will be up near 150 hp already. so this will just be the Greatest. PM ME when you all do and test this!!! So exciting

 
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I'd think you could run 12.5:1 with Premium , I know that the 911 GT3 is 11.7:1 and It only requires premium. Though I may be wrong on this, If you decide to go ahead and do this, i'd probably consult with the Honda techs first to see if you'd need some anti-knock stuff.

 
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Good thinking renamazazo.
THis is what I mean by check stuff out. I can go ahead and call Tim or Dave at my Honda about this, see if they can help.

I hate you guys.. I was up nearly 2 hours debating on turbo for highway and daily driving/drag, versus all motor for autox and track..

To hell with you all..

 
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You guys better figure out the height dimension of these things, and make sure they're not dome top or something. It would suck if you put these in and slammed them up into the head the first time you start it. Guys may also want to realize that the rings in there now have worn into the cylinder walls... might have to get the walls re-surfaced and definately get a new set of rings. I'd also recommend not doing this with the stock ECU. Get something that will let you control the fuel, cuz you're gonna need more of it to run compression like that. New plugs wouldn't be a bad idea either.
You can also alter the compression with the head gasket thickness. I think thicker raises it, thinner lowers it, but don't hold me to that, I'm not sure

 
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Yep.. Im gonna start an all motor vs. turbo thread..

 
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well the bore and stroke are identical to that of the regular civics, there really isnt any reason why these would not fit

 
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Bore is a diameter dimension, and stroke is related to the length of the connecting rod and the crank offset.
Compression ratio is (TDC Volume+Cylinder Volume)/TDC Volume (TDC is top dead center)
So the 12.5:1 pistons are going to be different in some dimension that gives them the higher compression, if everything else is equal.

Since TDC Volume is: T.D.C. Vol.= Head vol. + gasket vol. + deck vol. + dish/dome vol.
If the Cylinder Volume is the same, then the something in the head has to change so TDC volume becomes smaller. I'm guessing the head is totally different than the head in the gasoline engine. Do some research on what the volume of the D17A1 or A2 head is, find out what the GX head volume is and compare them. All said and done, if the gas engine head flows more, you could end up with around 11:1, OR I don't know if you guys checked into this, the pistons could be exactly the same as ours, and all the extra compression comes from the design of the head and gasket.

 
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the total displacement for the d17(dx, lx, and ex) is 1668 cc's
so does the gx so the total displacement for the gx is the same

 
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Listed displacement is just the Cylinder volume... (pi* bore^2 *stroke)*# or cylinders.
3.14*75^2*94.4*4=1668

It DOES NOT account for the head, but compression ratio does... you need to find out what the volume for the deck, gasket and head is. Otherwise you're going to be shooting blind. Go to google and type in "compression ratio" and look at some of the calculators that are listed.

 
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A Thinner gasket makes a higher compression, and a thicker gasket makes a lower compression, you had it backwards. You're totally right though about the shape of the pistons, Usually high compression pistons have a raised center. This link was posted here a while ago, you can compare the different pistons on the page, it even has our pistons and the gx pistons. http://www.heeltoeauto.com/dseries/dseries1.html
If i had a lot of money, I'd buy a few extra d17 blocks and heads and just play doctor and throw random pistons in and see what comes out...

 
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and for the lazy...

DX/LX



HX, EX



GX



Notice how the higher the compression the more material on the top of the piston, The difference between the ex, and dx is very slight, but still there.

-Mark

EDIT: forgot to link one... DOH!

 
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Renamazazo, thanks for all that info. it said that the compression height is 27.00mm on all of them, but the total height for the gx is 1mm more then the others. so it looks like they may work.

 
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so if the gx is is 1mm higher, it would mean the compression on like an ex is gonna me lower than 12.5 sweet

 
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so... who's gonna be the guinea pig to try these pistons out??? huh??? cause whoever it is needs to get on with it... cause i want these ponies...

 
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i think i will... but first i will have to special order the pistons. i got this cash flow from my work and i have my former college spending money back... yay

 
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sounds good to me... or find a wrecked GX chrissy... it'll be massively cheaper

 
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.. kewl, thanks crissy.. geniu pigs are kewl..
but i doubt it will be near any possibility to find a wrecked gx.. im never seen and until know never heard of it..