Technical question on compression?

[1991h9]

On rebuilding a motor for a turbo (ka-t) i`m confused on what compression i`m wanting to run. i know the little difference like:10:5:1 is more for all motor builds9:5:1 is sometimes run for low boost cars9:1:1 i dont know the difference besides the 5 to 1.8:8:1 higher booted cars8:5:1 so on an so forth.

The big question i`m asking is what does it mean exactly,example;what`s the first number represent, second, then third.And or difference with the change of the second number like instead of going 8:5:1, going 8:8:1?i looked on the search button but i couldn`t find anything that explans exactly what i`m looking for. Thank you.

[RCA]

On rebuilding a motor for a turbo (ka-t) i`m confused on what compression i`m wanting to run. i know the little difference like:10:5:1 is more for all motor builds9:5:1 is sometimes run for low boost cars9:1:1 i dont know the difference besides the 5 to 1.8:8:1 higher booted cars8:5:1 so on an so forth.

I am suprised you haven't been flammed yet

Well I know why you had problems with your search.It is not "10:5:1 compression".There are only two numbers when mentioning compression ratios.

Some thing like this:10.5:110:19.5:19:18.5:18:1 ect

Also compression ratios like 9.5:1 are usually run when people want to boost factory high compression engines.EX) Honda S2000 F22c:Factory Compression Ratio = 10.5 or 11:1 (not exactly sure)After Market Turbo Compression Ratio = 9.5:1

Toyota Supra 2JZGTEFCR = 8.5:1AMTCR = 8.5:1

The big question i`m asking is what does it mean exactly,example;what`s the first number represent, second, then third.And or difference with the change of the second number like instead of going 8:5:1, going 8:8:1?i looked on the search button but i couldn`t find anything that explans exactly what i`m looking for. Thank you.

I can't really answer this question but hopefully I made it possible for you to find results when searching.

[1991h9]

well i know the higher you go in compression the higher you hp and reponse, and lower you go you dont get as much so usually you go higher boost on those, its what exactly is the difference between the 3 numbers,Example, whats the difference between 8.5:1 and 8.8:1. what does that middle number do for you?but thanks for help with the why you`re supposed to write it.(form :to.)

[RCA]

its what exactly is the difference between the 3 numbers,Example, whats the difference between 8.5:1 and 8.8:1. what does that middle number do for you?but thanks for help with the why you`re supposed to write it.(form :to.)

What you call "form" is how you are suppose to write ratios. The question you are asking is some thing you learn when in grade school.

The number "8.3" is One number and Two digits

8.5 is one number and two digits also. The period is just a decimal, it does not make the numbers after it "another number".

Your question is like asking what is the difference between a 1.6 liter engine and a 1.8 liter engine. Or what is the difference between having 4.5 fingers and having 5 fingers. (Please feel free to replace fingers with brain cells)

The second number in a compression ratio is 1EX 10.7253:1

The numbers after the period are just decimals places. The number after the colon " : " is the second number.

Example, whats the difference between 8.5:1 and 8.8:1

The diffrence is .3 compression. The diffrence between then is that the combustion chamber ingredients are being crushed 8.5 times and the other is crushed 8.8 times.

* Not sure if this is exactly how it works but this is an example.:: EDIT = That is exactly how it works ::
Modified by rcabrita at 8:22 AM 6/26/2008

[r3v_v3ng3]

can't really remember but i think 11.1:1 means something like 11.1 air to 1 fuel

not sure if its cubic or maybe some other measurement

[RCA]

OMG r3v_v3ng3 you posted on the last 6 threads! Thats allot of typing.

can't really remember but i think 11.1:1 means something like 11.1 air to 1 fuel

not sure if its cubic or maybe some other measurement

That would be Air:Fuel ratio and not Compression ratio.If turbo cars (EX Supra) ran a 8.5 air:fuel ratio pistons and rods would be a knockin.

Since I am at home using my PC (not at work using my phone), I decided to come up with the definitive answer to this Q:

http://en.wikipedia.org/wiki/Compression_ratio

"In a piston engine it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke.

Picture a cylinder with the piston at the bottom of its stroke containing 1000 cc of air. When the piston has moved up to the top of its stroke inside the cylinder, and the remaining volume inside the head or combustion chamber has been reduced to 100 cc, then the compression ratio would be proportionally described as 1000:100, or with fractional reduction, a 10:1 compression ratio."

So yea I was right from the get go. YAY!

[vanquish2]

Nissan set the comp on an SR at 8.5....they got it right! Most will raise it slightly to 9 but for a KA I would still run anything under 9.5.....8.5 being the lowest.

[r3v_v3ng3]

oooops. it sounded right when i was typing it early in the morning but thanks for catching it

[Se7in]

The best way to answer a question like this is with... google (yay google) I was kinda disappointed that I didn't know the answer so i did a search. I came up with this http://www.kennedysdynotune.co...h.htm. Explains it very well.

[RCA]

^After reading that...I have to say it is alittle to complicated for my liking. I think most "new members" wouldn't go throught the trouble of reading all of that.

But most guys with 47 posts (Your post count) wouldn't do that much research. So Kudos to you bro!

[Leachguy]

Great info on that link to Kennedy's.