slowcrx954

i was wondering how high of compression people have went.i am thinking of going 10 to 1 on a b18b with a gt30. all input is welcome thanks

rmcdaniels

Go low. I've done from 8.4-12.2 . Lower is easier to tune, gives you more room for error, lasts longer, etc.

b18sihatch

higher compression=lower boost levels with lower hp numbers

medium compression = moderate boost levels with good numbers'

Low compression= high boost levels with high horsepower output (given great turbo application)

all in all if you arent fulley built dont try the 10:1 compression and turbo its a waste and will limit your ability to run higher psi levels and make good power numbers

juda7

HMMMMMMM?

I have 10:1 Maybe I'm the exception?

b18sihatch

i have 8:1 plan on runnnig 15-25psi & full race turbo kit

that just gives you an idea of the jump from compression ratios to psi levels you can run with lower compression rather than high compression

you can make decent power with higher compression however there are drawbacks because you cant run as high of psi levels making the block tap out at a certain psi level, (tuned right)

slowcrx954

well i want to make 400 to the wheels so 9 to 1?

adseguy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b18sihatch &raquo;</TD></TR><TR><TD CLASS="quote">i have 8:1 plan on runnnig 15-25psi & full race turbo kit

that just gives you an idea of the jump from compression ratios to psi levels you can run with lower compression rather than high compression

you can make decent power with higher compression however there are drawbacks because you cant run as high of psi levels making the block tap out at a certain psi level, (tuned right)</TD></TR></TABLE>

Sorry, that's just completly wrong. I can't even begin.

high compression makes more power and raises cylinder pressurses. You may need better gas at a certain torque, but don't leave out 10:1 compression due to PSI or whatever you are thinking of.

b18sihatch

HIGHER compression addss more natural absoloute cylinder pressure off the bat, then you are adding more cylinder pressure with turbo psi adding even more pressure to the cylinders that why low psi is needed for high compression turbo motors.

low compression makes less absoloute cylinder pressure right off the bat giving the cylinders less stress and making it able to handle more psi pressures

bigbadboy

as long as your tuned right, got it sleeved, and are running the right kind of gas there is no reason why you can use 10:1 or higher with power levels over 500+

nowtype

run the highest compression you can run while remaining safe on the gasoline available.

drtysohc

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nowtype &raquo;</TD></TR><TR><TD CLASS="quote">run the highest compression you can run while remaining safe on the gasoline available.</TD></TR></TABLE>^^^^^agreed

i ran 10.5:1 compression and 10psi on the street with 91 octane for almost a year

B18Flip

http://www.evans-tuning.com/comp2.html

rmcdaniels

And I ran 8.4:1 with 23 PSI of boost for two years, it proves nothing. If you're building a turbo motor, then go with lower compression. You can make just as much power, if not more, run more boost on pump gas, and have less chance of blowing your **** up if something goes wrong.

adseguy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b18sihatch &raquo;</TD></TR><TR><TD CLASS="quote">HIGHER compression addss more natural absoloute cylinder pressure off the bat, then you are adding more cylinder pressure with turbo psi adding even more pressure to the cylinders that why low psi is needed for high compression turbo motors.

low compression makes less absoloute cylinder pressure right off the bat giving the cylinders less stress and making it able to handle more psi pressures. I'm picking on you because I've noticed in posts that you are far from being correct sometimes, and I just want to clear things up.

</TD></TR></TABLE>

Cylinder pressure do have to do with higher compression pistons, but NOTHING to do with PSI, so leave that out of the equation. "50psi of air isn't going to effect 2,500psi of explosive force" I use this quote to prove my point again and again.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rmcdaniels &raquo;</TD></TR><TR><TD CLASS="quote">And I ran 8.4:1 with 23 PSI of boost for two years, it proves nothing. If you're building a turbo motor, then go with lower compression. You can make just as much power, if not more, run more boost on pump gas, and have less chance of blowing your **** up if something goes wrong.</TD></TR></TABLE>

Agreed

For the OP: choose whatever compression you want as long as you know the advantages and disadvantages of each. I personally prefer lower compression for a street car.

HiProfile

If I was to guess, 25psi will shove more air into the cylinder than 7psi. I don't think we need any facts/formulas to back that up. But if we really needed to, I'd surmise a few datalogs from groups running MAF systems (VW, Nissans, etc) would back this up 100%.

Higher compression makes the burn more effecient. Higher boost stuffs much more air into the cylinder. Both increase cyl pressure, one by adding air, one by decreasing combustion space. The goal for FI is <U>finding the ideal midpoint between compression, boost, and turbo effeciency</U> (IAT's).

I'd rather have a healthy C/R, healthy amount of boost, with a healthy eff % number from the turbo than run a big turbo out of its optimum range (low boost), running high comression and near-NA IAT's.

turboteener

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HiProfile &raquo;</TD></TR><TR><TD CLASS="quote">If I was to guess, 25psi will shove more air into the cylinder than 7psi. I don't think we need any facts/formulas to back that up. But if we really needed to, I'd surmise a few datalogs from groups running MAF systems (VW, Nissans, etc) would back this up 100%.
</TD></TR></TABLE>

Not true. It will put the same volume of air no matter what boost you are running. The only way you will get more volume in the cylinder is to have a bigger cylinder. Last time I checked we do not have a variable displacement engine.

It will increase the density of the charge but it will not increase the volume.


According to the numbers i am running a compression ratio of somewhere between 11.1-11.8 with 13psi on a D16Z6. I will blow 230psi on a compression tester with with a stock Z6 camshaft. AS soon as I get the boost by gear stuff on my Hondata, I will run more boost. I am stuck with a 13psi spring in my wastegate right now. Anyone want to trade for a smaller spring?

Anyway, I think the super high compression ratio explains my high gas mileage. Ain't been to the dyno yet but I am pretty sure my baby T3 is maxed out. I can spin the tires in the top of 2nd gear from a roll. I need traction before I need a bigger turbo. Plus the engine is super responsive.

rmcdaniels

He said "more air", not "the same volume of air".

speedlabx2005

what is stock gsr compression because my engine builder buit me a motor with stock compression 84 mm bore sleeves. i'm getting a little worried now. should i go get a thicker head gasket. my turbo size is t3t67 and he said with my compression and bore size that it should spool up nicely. but now i'm worried that i can't run pump gas 91 octane past 10lbs.

adseguy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HiProfile &raquo;</TD></TR><TR><TD CLASS="quote">If I was to guess, 25psi will shove more air into the cylinder than 7psi. I don't think we need any facts/formulas to back that up. But if we really needed to, I'd surmise a few datalogs from groups running MAF systems (VW, Nissans, etc) would back this up 100%.

Higher compression makes the burn more effecient. Higher boost stuffs much more air into the cylinder. Both increase cyl pressure, one by adding air, one by decreasing combustion space. The goal for FI is <U>finding the ideal midpoint between compression, boost, and turbo effeciency</U> (IAT's).

I'd rather have a healthy C/R, healthy amount of boost, with a healthy eff % number from the turbo than run a big turbo out of its optimum range (low boost), running high comression and near-NA IAT's.</TD></TR></TABLE>

Most of that is right, but you are forgetting one key thing. Volumetric efficiency, aside from heat at higher PSI a smaller turbo stops power production because of gas reversion back into the cylinders. Gas reversion does not make power

b18sihatch

why would you have someone build you a motor with stock compression, if it was supposed to be a turbo motor? higher compression really going to limit you on how much psi you are going to be able to run safely.

is it oem sleeves,pistons,rods ect or all aftermarket

speedlabx2005

all after market arias pistons eagle rods, etc etc i guess i'll just go buy a thicker headgasket to lower the compression

turboteener

who cares how much boost you are running. Everyone is obssesed with more boost. Boost is a measure of restriction in the intake tract. If you lower the restriction levels boost will drop but airflow will go up.

MidShipCivic

Laff, I'm building 11:1 turbo motor! Methanol bitches.

JDogg

this is easy

lower compression = more boost
higher compression = less boost

JDogg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by turboteener &raquo;</TD></TR><TR><TD CLASS="quote">who cares how much boost you are running. Everyone is obssesed with more boost. Boost is a measure of restriction in the intake tract. If you lower the restriction levels boost will drop but airflow will go up.</TD></TR></TABLE>

yeah, but turbos have wastegates so.... that really dosnt apply