Will altitude affect compression #'s?...
 

I have always wondered this and never got around to posting it...

So, does it really effect anything?

I don't think it would, but then again I think about a lot of stuff.

Re: Will altitude affect compression #'s?... (Bryson)
 

I think it would depend on what altitude we are talking....high up in the mountains where the air is very thin you might see a small difference, but I dont think you would see any major change.....

Re: Will altitude affect compression #'s?... (genop)
 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by genop &raquo;</TD></TR><TR><TD CLASS="quote">I think it would depend on what altitude we are talking....high up in the mountains where the air is very thin you might see a small difference, but I dont think you would see any major change.....</TD></TR></TABLE>

Its a small different..but the numbers arnt very much. The power output however is huge.

At 5500feet you loose about 30% power in a N/A application.

liam

Re: Will altitude affect compression #'s?... (liam821)
 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by liam821 &raquo;</TD></TR><TR><TD CLASS="quote">

Its a small different..but the numbers arnt very much. The power output however is huge.

At 5500feet you loose about 30% power in a N/A application.

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

Thats about right for Littleton Co. It's around 5800 up here... https://honda-tech.com/forums/images/smilies/emsad.gif

God I love boost... https://honda-tech.com/forums/images...es/emsmile.gif Your just that much faster then everyone else up here. https://honda-tech.com/forums/images...s/emsmilep.gif

Re: Will altitude affect compression #'s?... (Bryson)
 

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

Thats about right for Littleton Co. It's around 5800 up here... https://honda-tech.com/forums/images/smilies/emsad.gif

God I love boost... https://honda-tech.com/forums/images...es/emsmile.gif Your just that much faster then everyone else up here. https://honda-tech.com/forums/images...s/emsmilep.gif </TD></TR></TABLE>

I used to live in arvada, CO. My car went (N/A) from a 15.7 (in san diego) to a 17.9 (at bandimere). After that i turbod my honda...running a best time of 13.4 @ 106 at bandimere.

Now i live in san diego and dont have to worry!

liam

Re: Will altitude affect compression #'s?... (Bryson)
 

compression ratios cannot be changed.....9:1 pistons dont change to 10:1 at 100 below sea level. your volumetric effeciency increases due to a higher atmospheric pressure. so far i have only seen saab or volvo have a variable compression engine.

http://popularmechanics.com/au...gine/

Are you talking about compression ratio, or the compression as you would read it with a gauge in the spark plug wells?

If you're talking about ratio, it ccannot change. It is the ratio between the volumes at BDC and TDC, and unless you have variable length rods, this is constant.

I think theoreticially, compression by gauge should not change either, but it might a little due to the lesser density.

Re: Will altitude affect compression #'s?... (boostedcivicsir)
 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boostedcivicsir &raquo;</TD></TR><TR><TD CLASS="quote">compression ratios cannot be changed.....9:1 pistons dont change to 10:1 at 100 below sea level. your volumetric effeciency increases due to a higher atmospheric pressure. so far i have only seen saab or volvo have a variable compression engine.

http://popularmechanics.com/au...gine/ </TD></TR></TABLE>

NOOOOO...

The compression #'s IE, Guage hooked to spark plug hole, crank several times with TB open... capish?

Re: Will altitude affect compression #'s?... (Bryson)
 

My local machinist here in colorado springs (~6000ft) tells us that our numbers are about 20pts lower on a compression test (in reference to my b18c)... I don't konw how much I'll believe on the 20pt rule.... but....

If you think about it, the air is less dense... so the amount of 'stuff' you are compresing with each stroke is less, so it will not provide as much pressure in the cylinder with a full compression stroke..... the number will be lower. I don't know how much... I saw a post on it once a few months back...

Re: Will altitude affect compression #'s?... (servion)
 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by servion &raquo;</TD></TR><TR><TD CLASS="quote">My local machinist here in colorado springs (~6000ft) tells us that our numbers are about 20pts lower on a compression test (in reference to my b18c)... I don't konw how much I'll believe on the 20pt rule.... but....

If you think about it, the air is less dense... so the amount of 'stuff' you are compresing with each stroke is less, so it will not provide as much pressure in the cylinder with a full compression stroke..... the number will be lower. I don't know how much... I saw a post on it once a few months back...</TD></TR></TABLE>

That's exactly what I was thinking...

I have #'s around 140, but the engine still runs damn good? 9.5:1 ZC, stock internals. Yet I always see people close to sealevel getting #'s past 200, and it makes me wonder... https://honda-tech.com/forums/images...es/emdgust.gif

Re: Will altitude affect compression #'s?... (Bryson)
 

My JDM b18c (before I cracked 4 ring lands that is...) hit 170 in each cylinder (that's 10.6:1). My buddy just built his block with some 9.8:1 JE's about 3 weeks ago and he hits 150 in each cylinder... so that should give youa good idea. It sounds like your numbers are right where they should be.

Re: Will altitude affect compression #'s?... (servion)
 

!SMACK! OIC. sorry. i see what you are saying. and i think it would change. if there is more air to move. or less what ever the case may be.

Re: Will altitude affect compression #'s?... (servion)
 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by servion &raquo;</TD></TR><TR><TD CLASS="quote">My JDM b18c (before I cracked 4 ring lands that is...) hit 170 in each cylinder (that's 10.6:1). My buddy just built his block with some 9.8:1 JE's about 3 weeks ago and he hits 150 in each cylinder... so that should give youa good idea. It sounds like your numbers are right where they should be.</TD></TR></TABLE>

Actually, we just redid the compression Yesturday, and got different #'s. We think the first gauge we used was leaking.

Here's the #'s...

160-160-170-160

https://honda-tech.com/forums/images...es/emsmile.gif

Re: Will altitude affect compression #'s?... (Bryson)
 

That's much better... looks to me like you've got a healthy motor. Just curious... what is the c/r supposed to be in your motor?

Re: Will altitude affect compression #'s?... (servion)
 

9.5:1 https://honda-tech.com/forums/images...es/emsmile.gif

Re: Will altitude affect compression #'s?... (Bryson)
 

wow... my jdm b18c (10.6:1) peaked at 170 across the board up here... thats great