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DraXxus
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DraXxus Nov 12, 1:56am - #59781 
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compression ratio

would the changing of the compression ratio increase the engines performance by any chance, couse i trie it on my R/C car andi think i took off a bit too much when milling...and it just didnt start *shrugs* so yeah...the higher the compression ratio the beter? or is it the smaller the compression ratio the beter? and what would be some effects other then increased engine wear?
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fastceli2001
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fastceli2001 Nov 12, 2:10am - #59782 

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CT
wouldnt milling the piston cause you to get lower compression

a kid told me that celicas handle like crap... i laughed
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ssgsky
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ssgsky Nov 12, 2:18am - #59783 

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fort hood texas
Originally Posted by fastceli2001
wouldnt milling the piston cause you to get lower compression


ya dont mill the pistons, you balance pistons as they are reciprocating mass, you surface the head and the block, reducing the combustion chamber size, therin increasing compression slightly, some engines even have this head gaskets so you dont have to spend the money to surface the head/block, i have done it once, it is a pain in the ass to line up. micrometers everywhere.

10.7157 @ 131.31 on my bike
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ssgsky
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ssgsky Nov 12, 2:19am - #59784 

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fort hood texas
for a turbo application, a lower compression is optimal, but for N/A you want as high as you can afford, with more compression, you must run higher octane fuel, which burns faster, or the dreaded detonation occurs

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DraXxus
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DraXxus Nov 12, 2:28am - #59785 
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hmmm...thanks...
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Michael Aristide
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Michael Aristide Nov 12, 2:29am - #59786 
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I don't understand your logic. Reducing combustion chamber size reduces the compression ratio for a given stroke length. And to the original poster, a higher compression ratio is always better. But too high and you will have to start worrying about detonation. If you decide to do this, proper engine management is a must to pull the ignition timing back and maybe run a little rich to keep the cylinder temps down...
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Rave669
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Rave669 Nov 12, 10:27am - #59787 

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Lisle, IL
High compression is already there on the GTS, we're already at an 11.5:1 compression ratio (The nastiest Race-built V8 usually has about 10:1 compression) In fact the 2ZZ has the higest compression of any factory engine, period.

It's like this: When the piston goes down in the bore, air and fuel are sucked in, when the piston moves toward the head, all that air and fuel is compressed, at the peak of the "compression" stroke, the spark plug ignites the mess and sends the piston flying back down the bore with incredible force... "So what?" you ask.

An engine's compression ratio is a numeric representation of how much the air/fuel mixture is compressed, the more pressure the mixture is under, the more force will be produced when ignited. In the 2zz engine, the full volume of air and fuel in the cylinder takes up 11.5 times more space than when it's compressed at the top of it's stroke, in other words, it's under pressure cooker-type strains.

BTW, Higer octane fuels burn slower, not faster than lower octane fuels. if the fuel has too low an octane rating, the fuel will detonate from the pressure before the spark will ignite it. this is known as detonation. Therefore, you need a more stable, slower burning fuel in a high compression motor.

forced induction requires lower compression ratios for the same reason above, adding a thicker, copper head gasket, or putting in dished, 1zz pistons will lower the compression ratio anywhere from 11 to 10:1 compression.




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ev3
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ev3 Nov 12, 4:59pm - #59788 

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Rave..you dont usually post much, but when you do...WOW. So much good info im trying to comprehend! rice rice rice
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Michael Aristide
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Michael Aristide Nov 12, 5:13pm - #59789 
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Forced induction does not "require" lower compression. It just makes tuning a whole lot easier. If you have proper engine management that is rich enough to keep cylinder temps down and has a less agressive timing map and something like a J&S SafeGuard to pull ignition timing when it senses detonation and 2 step colder spark plugs, you can build a boosted engine with fairly high compression with minimal detonation. But of course no one wants to run on the brink of detonation. And the spark is not applied at the top of the stroke. This would be ideal if the engine was moving a 50 RPM or something, but that is impossible. At real engine speeds, the air/fuel mixture has to be ignited while the piston is still on the way up so by the time the piston has reached the top, the gases have already started to expand to make for a more efficient and powerful burn. With boosted applications or nitrous, the timing should be pulled back to prevent preignition and/or piston damage given a high compression ratio.
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psugts
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psugts Nov 13, 10:03pm - #59790 
2000 Spec Blue Mica Toyota Celica
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Originally Posted by Rave669
High compression is already there on the GTS, we're already at an 11.5:1 compression ratio (The nastiest Race-built V8 usually has about 10:1 compression) In fact the 2ZZ has the higest compression of any factory engine, period.



That's what I thought too, bro, but if you go check out the specs on the new prius, you'll see that toyota is running a 13.0:1 compression ratio eek. I wonder what toyota did to be able to run that kind of compression, without detonation. It almost makes you wonder if you could get away with running TRD's 13.0:1 compression celica pistons on 93-94 octane gas without detonating.


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Rave669
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Rave669 Nov 14, 12:22am - #59791 

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Lisle, IL
Yea, but I think the Prius has a two-stroke engine, they generally have higer compression ratios.

It's true that a FI setup doesn't require a lower compression, the Blitz SC kit for the GTS uses stock internals, but it's running low boost, like a 5 PSI pulley or something. any major application of boost will reqire a lower compression, however.

In my earlier post I was giving a primer for those that had no clue what compression was all about, of course, the spark can be advanced/retarded to pre or post-ignite fuel, dependant upon the engine configuration, and yes, there are ways to compensate on a high-compresion motor for running boost, but for a stable, reliable engine running ample amounts of boost, a lower compression will contribute to the longevity of the internals, if your car were to lean out under pressure, the damage could be catastrophic to a high-compression motor.

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