getting ready to order some pistons. any benefits to using a 8.5:1 piston rather than the 9:1 piston? it's a b18b block and head.

 

It's easier to tune with more boost. I ran 8.4:1 and later 8.5:1 on a B16, both with over 20PSI of boost, they ran great.

 

9:1 would give you more "out of boost" power.

 

thanks, I actually just found some info on this on the evans-tuning forum.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flood &raquo;</TD></TR><TR><TD CLASS="quote">9:1 would give you more "out of boost" power. </TD></TR></TABLE>

I've heard this said soooo many times... but my lower comp D feels just like my normal comp D did out of boost I think people put way to much emphasis on the compression ratio and gains.

Now for an NA setup...raising the compression up...matching it with cams and tuning it... will feel gains all over... but beyond that... meh.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by splitime &raquo;</TD></TR><TR><TD CLASS="quote">

I've heard this said soooo many times... but my lower comp D feels just like my normal comp D did out of boost I think people put way to much emphasis on the compression ratio and gains.

Now for an NA setup...raising the compression up...matching it with cams and tuning it... will feel gains all over... but beyond that... meh.</TD></TR></TABLE>
And for using the word meh

 

the time "off boost" will be minimal to even feel the difference..
But yeah i agree with Splitime on the matter..I ran my 8.5:1 Y7 N/A at the track before boosting it and it even ran better times than with the stock/higher CR.. and it actually felt better even when off boost.

 

See and I totally disagree. Stock D16Y8 has much more out of boost power at 9:6:1 than it did with forged internals at 8:5:1.

To each their own.

SanJuan PR!!! NICE MAN!

 

my y8 feels the same and i dropped to like 8.6 or somethin

 

i love high compression turbo motors....on race gas of course

the difference between 8.5 and 9:1 to *most* people will be pretty minimal

to whoever posted that their low compression motor felt better....thats probably just a matter of having aftermarket parts in there, not the compression......built motors are soooo much more responsive than factory.

 

Lower CR generally neccesitates more ignition timing for optimum power vs. higer CR to put it simply.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Turbo-charged &raquo;</TD></TR><TR><TD CLASS="quote">i love high compression turbo motors....on race gas of course

the difference between 8.5 and 9:1 to *most* people will be pretty minimal

to whoever posted that their low compression motor felt better....thats probably just a matter of having aftermarket parts in there, not the compression......built motors are soooo much more responsive than factory.</TD></TR></TABLE>

hey joe, i am gettin gready to build an 83mm gsr (finally loosing the b16) would you go with 9.8:1 with the b16 head? or go 10:1? it isnt a track only car but it isnt a daily either. i will drivve it every now and then on the street. turbo is the t3t67ho 28psi till i change the ems to handle a 5 bar map.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTC_CiViC &raquo;</TD></TR><TR><TD CLASS="quote">Lower CR generally neccesitates more ignition timing for optimum power vs. higer CR to put it simply.

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

correct which can be tricky and cause major headaches when our instincts start to kick in.

the only reason we use to go with lower compression was to fight detonation, now that we have such great tuning software and compatible parts, why not go with a slightly higher compression...........yeah it may net you only 10-15 ft/lbs of torque, but we all could use 15 ft/lbs of torque right!?!?!

i have an 8.5:1 B16 and i have had it 3 years, i just ordered 9.7:1 pistons for the new build, i really want my 15 ft/lbs of torque

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mrbsponge &raquo;</TD></TR><TR><TD CLASS="quote">

correct which can be tricky and cause major headaches when our instincts start to kick in.

the only reason we use to go with lower compression was to fight detonation, now that we have such great tuning software and compatible parts, why not go with a slightly higher compression...........yeah it may net you only 10-15 ft/lbs of torque, but we all could use 15 ft/lbs of torque right!?!?!

i have an 8.5:1 B16 and i have had it 3 years, i just ordered 9.7:1 pistons for the new build, i really want my 15 ft/lbs of torque </TD></TR></TABLE>

Bingo

 

Lower Compression = More Power on Pump Gas
Higher Compression = More Power on Race Gas

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Suprdave &raquo;</TD></TR><TR><TD CLASS="quote">Lower Compression = More Power on Pump Gas
Higher Compression = More Power on Race Gas</TD></TR></TABLE>

not necessarily, a good tuner can make a high comp setup work fine. I ran 8.5:1 and out of boost it sucked but in boost it was alright.

I am running 9.8:1 on my next boosted setup....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by turbotime &raquo;</TD></TR><TR><TD CLASS="quote">not necessarily, a good tuner can make a high comp setup work fine. I ran 8.5:1 and out of boost it sucked but in boost it was alright.

I am running 9.8:1 on my next boosted setup....</TD></TR></TABLE>

What are you talking about? I didn't say you couldnt run higher compression with pump gas...but you will see it shine with race gas...Its a fact that you can run more boost on a given octane with 8.5:1 compared to 10:1. I don't care who your tuner is, that is fact.
If you run a good racegas, you can get the best of both worlds...tons of boost and all the benefits of compression.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Suprdave &raquo;</TD></TR><TR><TD CLASS="quote">Its a fact that you can run more boost on a given octane with 8.5:1 compared to 10:1. </TD></TR></TABLE>


I see a trade off.

You have a neccesary increase in ignition advance and subsequent increase in mechanical drag inside the combustion chamber with a very low CR, and an ability to get away with more boost on lower octane fuel.

But then you kinda have to think about how much you need to make power. Higher CR/greater static pressure will generally need less advance, reducing the drag against the pistons on the compression stroke and will typically yeild greater power with less boost than a lower CR would. So which do you prefer.. low CR and more boost, or higher CR and less boost? Two means to the same end.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTC_CiViC &raquo;</TD></TR><TR><TD CLASS="quote">


I see a trade off.

You have a neccesary increase in ignition advance and subsequent increase in mechanical drag inside the combustion chamber with a very low CR, and an ability to get away with more boost on lower octane fuel.

But then you kinda have to think about how much you need to make power. Higher CR/greater static pressure will generally need less advance, reducing the drag against the pistons on the compression stroke and will typically yeild greater power with less boost than a lower CR would. So which do you prefer.. low CR and more boost, or higher CR and less boost? Two means to the same end.</TD></TR></TABLE>

well put, additionally building a turbo car for out of boost performance? seriously... if your car spools that slow more thought should go into turbo sizing

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Suprdave &raquo;</TD></TR><TR><TD CLASS="quote">Lower Compression = More Power on Pump Gas
Higher Compression = More Power on Race Gas</TD></TR></TABLE>


thats a very good way to look at it in my opinion.....when doing a primarily pump gas car i usually do something in the 9:1 range. in a primarily race gas based car, i go higher.

im not a fan of pushing the limits on pump gas. everybody always says crap like " you can make 1,100 horsepower on pump gas if you have a good tuner" there is too many variables when running pump gas, why push the limits? race gas sure is a whole hell of a lot cheaper than an engine failure over something even your tuner couldnt controll!

 

i agree that a lower CR will yeild better pump gas results but i think 9.0-9.8 is a good low cr whereas 8.5:1 is a little to low [imho].

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by splitime &raquo;</TD></TR><TR><TD CLASS="quote">

I've heard this said soooo many times... but my lower comp D feels just like my normal comp D did out of boost I think people put way to much emphasis on the compression ratio and gains.

Now for an NA setup...raising the compression up...matching it with cams and tuning it... will feel gains all over... but beyond that... meh.</TD></TR></TABLE> whats the cr on your d? im at 8:1 on my built dohc zc and during my break-in im na (and it sucks) i hope things change when the zc is boosted again

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hatchinprogress &raquo;</TD></TR><TR><TD CLASS="quote"> whats the cr on your d? im at 8:1 on my built dohc zc and during my break-in im na (and it sucks) i hope things change when the zc is boosted again </TD></TR></TABLE>

Somewhere from 8.5-8.7:1

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by splitime &raquo;</TD></TR><TR><TD CLASS="quote">

Somewhere from 8.5-8.7:1</TD></TR></TABLE> oh so your cr is still higher than mine, i screwed up when i was using the compression calc. (i thought i would be 8.8:1) i ended up with 8:1