Newbie: Compression Ratio?

[l/l/rX]

alright welpz im just learning about the engine slowly as we mod our car. SO DONT FLAME ME hehe for any stupid comments i make im just curious to what is compression ratio. er, actually no, what do the Numbers stand for. such as this:12,4:1 that is the compression ratio for a 2003 yamaha r6. now what tha hell do the numbers stand for?

and also i know higher octane gas gives you some more hp, but i dont get how higher octane gas gives you that lil extra boost. because the way i understand it, higher octane only works when you increase the compression ratio of your car.

uuh yea my questions are silly, but i hope you guys understand its comming from a newbie that wants to LEARN, and not read some b/s remarks. hehe thanx in advance! and yes i have checked out several sites on compression ratio but none have given me answers to what i want to know.

[Autodream]

its the ratio of the amount of space you have in the cylinder when the piston is all the way at bottom (BDC) to the amount of space you have with the piston all the way up (TDC) the higher the compression ratio the more power the motor will make, but you will need to use higher grade fuel..to reduce chances of detonation. keep in mind when fuel mixtures are compressed to a certain point, they will self ignite, and blow everything up

Sorry if I am wrong guys

[^SkylinE^]

Octane is just how stable a gas is under heat and pressure. The higher the octane the higher presure and heat it can take before it detonates!

[rice_eater]

yes...it was in a post earlier...higher level octane takes longer to burn...in the summer when it's really warm, the engine runs hotter and the charge pre-ignites so the computer retards the timinig...with the slower burning higher octane the computer wont have to retard timing...

[2M6]

Also note that if you put 110 octane in your stock Civic, you will prob loose power because the piston start heading back down before the mixture has been fully ignited. This will be a slight loss

[StrokeD z]

Originally posted by sr20det95
its the ratio of the amount of space you have in the cylinder when the piston is all the way at bottom (BDC) to the amount of space you have with the piston all the way up (TDC) the higher the compression ratio the more power the motor will make, but you will need to use higher grade fuel..to reduce chances of detonation. keep in mind when fuel mixtures are compressed to a certain point, they will self ignite, and blow everything up

Sorry if I am wrong guys

ok you are wrong.......compresion ratio is how much the piston commpresses the gas before it explodes

what your talking about is total volume clearance

btw (TDC)=top dead center (BDC)=bottom dead center

[rice_eater]

why do they call it dead centre? then again....why is this room spinning...

[90_Shelby]

Originally posted by StrokeD z
[B]


ok you are wrong.......compresion ratio is how much the piston commpresses the gas before it explodes

what your talking about is total volume clearance

Actually you are wrong and SR20DET95 explained compression ratio correctly.

[StrokeD z]

Originally posted by 90_Shelby




Actually you are wrong and SR20DET95 explained compression ratio correctly.

i dont know man i would read his post over again and it sound clear to me he is explaning total volume clerance

i did i big project in school about it

[l/l/rX]

soo would this be true.

this is the compression ratio of a honda del sol vtec. 10.2:1

sooo if those numbers were to go up, then we would assume that this car would be pushing bigger hp/tq numbers right? and also using higher octane gas if neccessary.

[StrokeD z]

ya you will get more hp

[mwdguy]

Originally posted by 2M6
Also note that if you put 110 octane in your stock Civic, you will prob loose power because the piston start heading back down before the mixture has been fully ignited. This will be a slight loss

LMAO:tongue: :tongue:

[rice_eater]

Originally posted by mwdguy




LMAO:tongue: :tongue:

what's so funny? it's true! And StrokedZ is right also...compression ratio is how much the air is compressed by the cylinder at TDC...

[2M6]

LMAO

what's so funny? it's true!

WTF are you laughing about anyway? Take a stock NA car and do some dyno runs back to back with 91/110 and see what happens. I bet you won't be laughing when you see the results




mwdguy

[StrokeD z]

ya and 90_shelby is braging about how he rebuilds engines all day..............

ya i am 16years old and i know ten times as much as yo

mmmuuuuuhhhhhhhhaaaaaaa genius i tell ya

my instructor in mech doesnt ever argue with me

[l/l/rX]

sooo how do you increase compression ratio? bigger turbo or put in a turbo if you dont already have one? hmm, rebuild the engine uuh pistons etc? and also is it practical to increase compression ratio, or just stick with your bolt on mods?

[StrokeD z]

Originally posted by l/l/rX
sooo how do you increase compression ratio? bigger turbo or put in a turbo if you dont already have one? hmm, rebuild the engine uuh pistons etc? and also is it practical to increase compression ratio, or just stick with your bolt on mods?

you willl have to ask someone else about that not too sure

[JustinL]

Originally posted by StrokeD z


i dont know man i would read his post over again and it sound clear to me he is explaning total volume clerance

i did i big project in school about it

How did you do on that project?

Sr20DET95's explanation of compression ratio is bang on. He left out a couple of nitty gritty details, but this is a thread for a newbie. Check out this site for more info: http://www.mix-net.net/~red/uccr.html or just do a google search for "compression ratio formula".

The "uncorrected" compression ratio is mechanically fixed for an engine, so to increase the compression you have to either increase the swept volume of the piston in the cylinder, or reduce the volume of the combustion chamber. Both of these are very expensive to do properly.

Justin

[rice_eater]

Originally posted by StrokeD z


you willl have to ask someone else about that not too sure

fuckin mister i know so much about cars that i teach my teacher, can't even answer the guy's retarded question...actually you cant even pick up that his question is retarded. So first i'd like to say that you are a morron and that 90_shelby worked on my block and his work was amazing!

Now...You don't increase compression by putting in a turbo that's just retarded! If you had bothered to read and think about what i said earlier you would have never asked something like that...AGAIN!!! Compression ratio is how much the piston compresses the air! A turbo on the other hand will provide more air in the combustion chamber but it wont compress it...it'll dump it there and that's it! Along comes the piston and packs all the air in tightly! So you up or lower compression by changing the pistons. You can also up the compression by shaving the head...

[Alpine Autowerks]

Originally posted by StrokeD z


ok you are wrong.......compresion ratio is how much the piston commpresses the gas before it explodes

what your talking about is total volume clearance

btw (TDC)=top dead center (BDC)=bottom dead center

You are wrong, the ignition point has nothing to do with static compression.

A turbo adds to dynamic compression but has no effect on static (mechanical) compression. Compression ratio is:
combustion chamber volume / swept displacement + combustion chamber volume