# safe compressin ratio???



## himbo (Sep 20, 2003)

hey guys, as you know, i've decided to try and go all motor on my GA16. so i was talking to a mechanic who does polish/porting and other shit about my car. i told him that i'm looking to get 11.0:1 compression ratio pistons on my car, and he said that its way too high, and that no pump gas will support those pistons. he said i need 105 octane gas, minimum. 

what do you guys think? i figured that 11.1 pistons seem reasonable, but he said not to go higher than 10.5.

thanx in advance and rock on!!!! :thumbup:


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## chimmike (Oct 17, 2002)

I say get the headwork and everything else done before moving on to the pistons. full n/a headwork (a good job) will cost a LOT. then you should extrude hone the intake manifold....get a good header and have it port matched to the headwork you have done...good intake, etc.

dollar for horsepower, you're wasting your money. Much better off in the long run going boost.....cheaper too in the end. But, if n/a is what you want, go for it.


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## lshadoff (Nov 26, 2002)

himbo said:


> hey guys, as you know, i've decided to try and go all motor on my GA16. so i was talking to a mechanic who does polish/porting and other shit about my car. i told him that i'm looking to get 11.0:1 compression ratio pistons on my car, and he said that its way too high, and that no pump gas will support those pistons. he said i need 105 octane gas, minimum.
> 
> what do you guys think? i figured that 11.1 pistons seem reasonable, but he said not to go higher than 10.5.
> 
> thanx in advance and rock on!!!! :thumbup:


If you have big cams with lots of overlap you can run high CR. You may have to back off on the timing advance with 11:1 CR to avoid detonation, though. If you install the 11:1 pistons I would start with moderate timing and work your way up until it pings at low rpm in high gear.

Lew


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## himbo (Sep 20, 2003)

well, i'm getting estimates on headwork right now, but i have a couple of friends who can actually do polish and porting, and they might be able to do it for free or cheap. its weird, our compression ratios are at 10.6:1, i didnt figure at all that 11.1:1 would make such a difference in terms of work involved, i thought they would drop right in (with all other mods of course), i didn't think that there would be this much fine tuning


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## lshadoff (Nov 26, 2002)

himbo said:


> well, i'm getting estimates on headwork right now, but i have a couple of friends who can actually do polish and porting, and they might be able to do it for free or cheap. its weird, our compression ratios are at 10.6:1, i didnt figure at all that 11.1:1 would make such a difference in terms of work involved, i thought they would drop right in (with all other mods of course), i didn't think that there would be this much fine tuning


You want to run as much timing advance as possible for maximum power. The SOTP method of timing I mentioned above is an easy way to find the optimum timing for your setup. Just find the point where it pings and back off 1*.

Lew


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## himbo (Sep 20, 2003)

so why the hell would that :dumbass: mechanic tell me that its not streetable to go 11 cr or higher on pump gas???

i wasn't really sure of believing him on that point, and he offered to polish and port my cylinder head, guess not anymore!!!


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## lshadoff (Nov 26, 2002)

himbo said:


> so why the hell would that :dumbass: mechanic tell me that its not streetable to go 11 cr or higher on pump gas???


Who knows. It's not a simple thing. It depends on the particulars of your engine. If you are running a typical emissions cam, then 11:1 is too high for pump gas because the cylinder pressures are too high at typical driving rpms. If you have a race engine with big cams, free-flowing intake and exhaust, where you run high rpms all the time, 11:1 is reasonable. If you can run race gas, go to 12:1. 



himbo said:


> i wasn't really sure of believing him on that point, and he offered to polish and port my cylinder head, guess not anymore!!!


He's being conservative, perhaps. It doesn't mean he can't do a good job porting an engine. However, I would talk to some of his knowledgable customers to find out what kind of work he does. 

Lew


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## himbo (Sep 20, 2003)

sorry, just venting. its just that everybody tells me different things, ranging from "dont do it man, 160hp will never happen" to "oh yeah bro, thats easy man, sure, you can do it"

i dunno, looks like i'll just have to try it :thumbup: 

thats awesome though, imagine a 160hp out of a n/a 1.6? (crank power, not wheel)

now i gotta find pistons and good gasket, i almost wish i had a honda, b/c they have so many parts. almost :thumbup:


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## himbo (Sep 20, 2003)

what do you think, is 160hp doable?


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## Marty01 (Dec 20, 2004)

himbo said:


> sorry, just venting. its just that everybody tells me different things, ranging from "dont do it man, 160hp will never happen" to "oh yeah bro, thats easy man, sure, you can do it"
> 
> i dunno, looks like i'll just have to try it :thumbup:
> 
> ...


160HP out of a 1.6 should be doable.. now keeping it streetable? that i think would depend on HOW you do it... im 100% sure you can get to about 140-150HP steetable on pump gas and all that good stuff.. that last 10 HP might be tougher to get though.. but the secret will be in the head work and compression and tuning.. if all these are optimized for one another.. id say you can hit your goal.. in the end.. itl only make as much HP as the weakest link in the whole kit-n-kaboodle will allow.. just like anything else.. you will also lose some torque out of this...

someone mentionned going boosted instead.. i think that would be MUCH more streetable and keep you on pump gas.. maybe even give you a couple more ponies too boot


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## Marty01 (Dec 20, 2004)

Marty01 said:


> 160HP out of a 1.6 should be doable.. now keeping it streetable? that i think would depend on HOW you do it... im 100% sure you can get to about 140-150HP steetable on pump gas and all that good stuff.. that last 10 HP might be tougher to get though.. but the secret will be in the head work and compression and tuning.. if all these are optimized for one another.. id say you can hit your goal.. in the end.. itl only make as much HP as the weakest link in the whole kit-n-kaboodle will allow.. just like anything else.. you will also lose some torque out of this...
> 
> someone mentionned going boosted instead.. i think that would be MUCH more streetable and keep you on pump gas.. maybe even give you a couple more ponies too boot


after i post of course i have a brain storm hehe

ever consider stroking/boring the engine out?? it wouldnt be a 1.6 anymore.. but who can tell by looking at it in your engine bay


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## Marc Z31 (Jul 25, 2004)

I've seen hondas run 12.5:1 CR on 93 octane.

Inferior designs on domestic engines can't really see any more than about 10.5:1, but with the DOHC design, it is a hemi type head. This design reduced the point when flash occors, thus allowing you to run a higher compression. 11.1:1 should be fine.


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## Zen31ZR (Mar 24, 2004)

Marc Z31 said:


> I've seen hondas run 12.5:1 CR on 93 octane.
> 
> Inferior designs on domestic engines can't really see any more than about 10.5:1.


And that's where you're wrong. Obviously you've forgotten the 97 vintage LT1 was running higher than 10.5:1. A lot of that had to do with the reverse flow cooling system, the heads were kept cool enough not to cause detonation at that CR.


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## Zen31ZR (Mar 24, 2004)

Sorry, in the post above it was actually the '92 LT1 Corvette engine which featured a 10.5:1 compression ratio. The LT5 ZR1 engine featured 11.1:1 compression. The late LS1 dropped back to about 10.1:1, but the new LS6 features 10.9:1 compression. Inferior domestic engines, indeed.


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