What would happen if I increase compression to 12.5:1? - Honda Civic Forum



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Old 12-06-2017   #1
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What would happen if I increase compression to 12.5:1?

I know that I can put D17A7 (CNG) pistons in my D17A2 block to increase compression to 12.5:1, but I don’t think that anyone actually tried it on 93 octane pump gas. I Can use use 93 octane gas, but I’m not sure that 93 octane is enough for 12.5:1 compression. So my question is will it work? I really want to try it, but I don’t know what would happen, which unfortunately makes me want to try it more lol. I think it would either work great, or knock and not work. Also, IF it did work, would I gain a noticible amount of power? What do you think about this?
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Old 12-06-2017   #2
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Re: What would happen if I increase compression to 12.5:1?

I think if your gonna start messing with radical changes to the engine, your going to need a standalone ECU such has Ktuner (the experimental one im running) or Hondata to adjust fuel maps and timing.
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Old 12-06-2017   #3
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Re: What would happen if I increase compression to 12.5:1?

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I think if your gonna start messing with radical changes to the engine, your going to need a standalone ECU such has Ktuner (the experimental one im running) or Hondata to adjust fuel maps and timing.
What would happen if I donít?
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Old 12-06-2017   #4
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Re: What would happen if I increase compression to 12.5:1?

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What would happen if I donít?
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Old 12-06-2017   #5
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Re: What would happen if I increase compression to 12.5:1?

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img]https://cimg4.ibsrv.net/gimg/www.civicforums.com-vbulletin/800x600/80-8piston003_78af86c4fafba21134f6685ddfcd0e835932ca1 d.jpg[/img][img]https://cimg7.ibsrv.net/gimg/www.civicforums.com-vbulletin/1536x1024/80-detonationfailure01_03a270f851b517e404e2053cbfe20f 4612ec4d88.jpg[/img
Why wouldn’t the knock sensor protect the engine?

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Old 12-06-2017   #6
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Re: What would happen if I increase compression to 12.5:1?

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but I’m not sure that 93 octane is enough for 12.5:1 compression.
Jet fuel is in the 100+ octane range, isn't it?
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Why wouldn’t the knock sensor protect the engine?
Octane and timing aren't the only factors that lead to or prevent detonation
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Old 12-07-2017   #7
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Re: What would happen if I increase compression to 12.5:1?

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Jet fuel is in the 100+ octane range, isn't it?
Octane and timing aren't the only factors that lead to or prevent detonation
Isnít E85 105 octane or something? That would certainly be enough. If I could afford to convert to it, which I canít. Jet fuel and race fuel is not an option.
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Re: What would happen if I increase compression to 12.5:1?

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Isnít E85
Did you learn all about stoichiometry yet?

How much more fuel (injector) delivery do you have to have available in order to safely run E-85 without going too lean??
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Old 12-07-2017   #9
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Re: What would happen if I increase compression to 12.5:1?

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Did you learn all about stoichiometry yet?

How much more fuel (injector) delivery do you have to have available in order to safely run E-85 without going too lean??
I said “If I could afford to convert to it, which I can’t.”, meaning that I know that I can’t just fill it up with E85 and be good to go. And yes, I did learn about stoichiometry.
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Old 12-07-2017   #10
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Re: What would happen if I increase compression to 12.5:1?

I asked that, along with other comments about compression and timing because a lean condition can cause detonation too.
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Old 12-07-2017   #11
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Re: What would happen if I increase compression to 12.5:1?

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I asked that, along with other comments about compression and timing because a lean condition can cause detonation too.
I see. Thank you for explaining.
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Old 12-07-2017   #12
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Re: What would happen if I increase compression to 12.5:1?

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Isnít E85 105 octane or something? That would certainly be enough. If I could afford to convert to it, which I canít. Jet fuel and race fuel is not an option.
the problem with alcohol is the acidity, it will eat away seals, etc.
Also, low calorific content, need much more fuel per air.
I am from a country that at some point in time 95% of new cars were alcohol, so i should know that.
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Old 12-07-2017   #13
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Re: What would happen if I increase compression to 12.5:1?

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the problem with alcohol is the acidity, it will eat away seals, etc.
Also, low calorific content, need much more fuel per air.
I am from a country that at some point in time 95% of new cars were alcohol, so i should know that.
You're right about low energy content and acidity. I believe that E85 can be a viable fuel though.
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Old 12-07-2017   #14
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Re: What would happen if I increase compression to 12.5:1?

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Did you learn all about stoichiometry yet?
You have made about 50 different threads so I'll just stick these thoughts in this thread here
(I've been considering consolidating all your posts into a single thread too )



Stoichiometry isn't the only factor to consider, but I figured it to be a starting point if you want to educate yourself.
I should have asked if you figured out some ideal AF ratios for maximum power using various fuels too.

The gasoline 14.7:1 stoich is not ideal for power, nor economy....It's ideal for emissions. The best balance and control of HC/CO/NOx emissions occurs at this ratio....that's why they make engines run at that ratio or as close as they can to it during low demand conditions.




Best power with gasoline is achieved at what, 12.5:1 (?) and an engine can be run extremely lean, 20:1 and beyond....but only in certain conditions.. Honda marketed some cars with engines designed to run that lean and they could get great fuel economy in the right conditions.

Alky ~97% pure Ethyl Alcohol, 9:1 ratio for stoich, probably 7:1 for power..... (Methyl Alcohol has similar properties, 5:1-6.1 ratio, and is even more corrosive) needs twice as much fuel or more to make the same power because it has half the heat energy of gasoline, it burns half as fast as gas so you have to almost double the ignition timing. You can run very high compression on alky to take advantage of the higher octane.
Cooling system performance becomes a little less critical because it burns so cool

Alky engines do not run great cold nor run well in very cold climates.

Add in....Alcohols are hygroscopic, they absorb moisture....which changes their properties, stability, and shelf life

Plenty of people run E85 in turbo and S/C applications with few or no mods to the fuel system components (other than fatter injectors), because most of todays vehicles are designed to tolerate some amount alcohol in the fuels.
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Old 12-13-2017   #15
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Re: What would happen if I increase compression to 12.5:1?

You gave negative rep because I didn’t know something? I did search, and I didn’t find anything that answered my questions.
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Re: What would happen if I increase compression to 12.5:1?

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You gave negative rep
I hope you aren't talking to me....
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Old 12-13-2017   #17
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Re: What would happen if I increase compression to 12.5:1?

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I hope you aren't talking to me....
I'm talking to whoever gave me negative rep. I don't know who did it.
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Old 12-31-2017   #18
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Re: What would happen if I increase compression to 12.5:1?

still confused,, if i ran 93 octane , 12.5 natural gas piston, couldn i use bigger injectors and still be safe?

i see on craigslist a low millage natural gas d17a6.. is listed cheap for parts..
what are the diffrencess? it has diffrent intake manifold .. couldnt i converted to gasoline .. ?
does it have vtec?

it has automatic tranny. are transmissions the same? i lost reverse on mine


i was hoping cheap all motor power might be better insted of fixing few issues I have on mine // thats if possible


couldnt i create a good combo , use my intake, reruns wires, not sure if it has vtec, vfac2 if it does, and then see what happens...

or maybe i fix the issue on mine and run cheap nitrus per dollar to kinda supprize people..
i still like all motor better, then nitrus runs out eventually and it costs to refill

Last edited by dsm482; 12-31-2017 at 10:48 PM.
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Old 12-31-2017   #19
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Re: What would happen if I increase compression to 12.5:1?

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still confused,, if i ran 93 octane , 12.5 natural gas piston, couldn i use bigger injectors and still be safe?

i see on craigslist a low millage natural gas d17a6.. is listed cheap for parts..
what are the diffrencess? it has diffrent intake manifold .. couldnt i converted to gasoline .. ?
does it have vtec?

it has automatic tranny. are transmissions the same? i lost reverse on mine


i was hoping cheap all motor power might be better insted of fixing few issues I have on mine // thats if possible


couldnt i create a good combo , use my intake, reruns wires, not sure if it has vtec, vfac2 if it does, and then see what happens...

or maybe i fix the issue on mine and run cheap nitrus per dollar to kinda supprize people..
i still like all motor better, then nitrus runs out eventually and it costs to refill
A D17A6 is a VTEC-E gasoline engine. The D17A7 is the CNG engine. Just so you know.
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Old 12-31-2017   #20
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Re: What would happen if I increase compression to 12.5:1?

sorry CNG i meant d17
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Old 01-01-2018   #21
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Re: What would happen if I increase compression to 12.5:1?

Honda doesnít just slap together parts, everything is well engineered to work for its role.
CNG and Gasoline have different burn speeds as well as different burn temperatures. so the camshaft is different.
Pistons made from a slightly different alloy maybe. Torque band different so different gearing in transmissions would be expected.

Common issue people running Japanese transmission is pcm code because they have a different gear ration so the computer thinks something is wrong since itís not getting the expected results.

I am sure all that stuff can be sorted out with enough trial and errors.
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Old 01-01-2018   #22
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Re: What would happen if I increase compression to 12.5:1?

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Honda doesnít just slap together parts, everything is well engineered to work for its role.
CNG and Gasoline have different burn speeds as well as different burn temperatures. so the camshaft is different.
Pistons made from a slightly different alloy maybe. Torque band different so different gearing in transmissions would be expected.

Common issue people running Japanese transmission is pcm code because they have a different gear ration so the computer thinks something is wrong since itís not getting the expected results.

I am sure all that stuff can be sorted out with enough trial and errors.
I understand that Honda engineers things for the application. I was just curious what would happen. Also, since you seem to know about the JDM transmissions having different gear ratios, what is the gear ratio differences between a BMXA and SLXA transmission? Thanks.
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Old 01-01-2018   #23
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Re: What would happen if I increase compression to 12.5:1?

They're right you know, without some sort of means to correctly adjust the timing and fuel maps independently you're most likely going to continuously run into knock, which even if there's a knock sensor telling the ECU/PCM to retard timing to save the engine, it's still knocking for a moment, and may continue if it can't retard ignition timing enough, in my experience sometimes once an engine starts knocking under throttle it doesn't want to stop until you let off the throttle. If E85 is local to you then I'm sure you can run that compression in that engine, but you will need the ability to tune larger fuel injectors and adjust the maps, otherwise it's going to have a very short life. Also I don't know anything about CNG pistons and the differences between them and the stock unit, but i'd look them over carefully and weight them to see if they don't look to be designed to withstand the same load, as I don't think CNG combustion pressures are as high. Some proper pistons like Mahle units would be what I would go for, they use a different alloy than most every after market forged piston maker, it's a little less ductile / more brittle but weighs a lot less and is still a lot stronger than factory pistons, they make great street/strip use as you can set your piston to wall clearance tighter than with normal forged units which expand a lot more at operating temp. There could be other design differences between the CNG pistons and stock that could promote hot spots and knock, Are they dished, domed or ?
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Old 01-02-2018   #24
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Re: What would happen if I increase compression to 12.5:1?

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Also I don't know anything about CNG pistons and the differences between them and the stock unit,


There could be other design differences between the CNG pistons and stock that could promote hot spots and knock, Are they dished, domed or ?
This post kinda got me curious so......
CNG cars just don't exist in my corner of the planet so I dug into the parts catalogs a little bit.....comparing 2003 GX CNG D17A6 with the other versions D17A1 and A2

GX Pistons and rods have unique part numbers, I'd expect the pistons would be domed to raise compression, and rods might be a smidge different in length but I have no specs to go by on that...


Crank and wrist pins are the same for all 3 engines
Rings are the same too

GX Cam is the same part # as non-vtec D17A1,
that means the GX head can't be vtec


Quote:
as you can set your piston to wall clearance tighter than
Stock piston to cylinder wall clearance spec is already dang tight.... 0.0004"-0.0016"
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Old 01-02-2018   #25
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Re: What would happen if I increase compression to 12.5:1?

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This post kinda got me curious so......
CNG cars just don't exist in my corner of the planet so I dug into the parts catalogs a little bit.....comparing 2003 GX CNG D17A6 with the other versions D17A1 and A2

GX Pistons and rods have unique part numbers, I'd expect the pistons would be domed to raise compression, and rods might be a smidge different in length but I have no specs to go by on that...


Crank and wrist pins are the same for all 3 engines
Rings are the same too

GX Cam is the same part # as non-vtec D17A1,
that means the GX head can't be vtec


Stock piston to cylinder wall clearance spec is already dang tight.... 0.0004"-0.0016"
Very interesting, thanks for sharing. I have heard that the GX rods are stronger so they can handle higher compression, but I'm not certain about that.
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Old 01-02-2018   #26
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Re: What would happen if I increase compression to 12.5:1?

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This post kinda got me curious so......
CNG cars just don't exist in my corner of the planet so I dug into the parts catalogs a little bit.....comparing 2003 GX CNG D17A6 with the other versions D17A1 and A2

GX Pistons and rods have unique part numbers, I'd expect the pistons would be domed to raise compression, and rods might be a smidge different in length but I have no specs to go by on that...


Crank and wrist pins are the same for all 3 engines
Rings are the same too

GX Cam is the same part # as non-vtec D17A1,
that means the GX head can't be vtec


Stock piston to cylinder wall clearance spec is already dang tight.... 0.0004"-0.0016"
Are the part numbers for the head and intake manifold the same as a D17A1 too? Thanks.
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Old 01-02-2018   #27
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Re: What would happen if I increase compression to 12.5:1?

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Are the part numbers for the head and intake manifold the same as a D17A1 too? Thanks.
you can check for yourself

https://www.hondapartscheap.com/

https://www.bkhondaparts.com/

https://www.hondapartscheap.com/auto...-manual-engine
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Old 01-02-2018   #28
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Re: What would happen if I increase compression to 12.5:1?

there is complete car here , 100k miles for parts cng ..

the owner bought at an auction he is sick and tired of trying to find natural gas to fill it up.


maybe i should start a go fund me page ... all chip in I do the testing and build.

i use to work [email protected] in delphi in emissions testings and valvetrain back in the day.. no joke...

on serious note am curios now to, i think i can make it work 12.5 compression with 93 octane, if i get big enough injectors and uses the same manifold.. plus i would have two cars to combine...

now ezone both are automatics,, that means i got a trannny for my reverse loss on my current? it should fit somehow..

so i only have electronics and else to deal with/..

Does Hondata offer tunning capability of timingg and spark retard as sofware?

not sure if i want to pick up a huge project right now, but an easy one might make me consider it.
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Re: What would happen if I increase compression to 12.5:1?

IMO, 12.5:1 is a little, optimistic on pump gas. E85, okay, pump I think you're getting into "no man's land" where the ratio is too high for pump, but isn't enough of a performance increase you justify the expense of race gas.

can it be done? Probably, the question is to keep it from knocking will you have to use such a rich A/F mix and low ignition timing that there's very little gain in power? I can't recall any factory performance engine designed for pump gas, even those that say explicitly (premium only) with a ratio higher than 11.5:1.

All I'm saying is I would target that ratio or go big since race gas will be a requirement. You can target 11.5:1 using those pistons by either using a thicker head gasket which I think is a crappy way to do it, or calculating how much capacity you need to add to the combustion chamber by removing material from the cylinder heads chamber. Motor Trend has a decent write up on how to measure and calculate everything. Wouldn't need to add but a few cc's of capacity and be safer for pump. I would practice porting the chambers on a junk head first.
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Old 01-02-2018   #30
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Re: What would happen if I increase compression to 12.5:1?

The trans in the GX is CVT, not automatic. NO swap.

Head has different #
Intake is very different
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