http://books.google.com/books?id=ahDbsLt1VzwC&pg=PA15&lpg=PA15&dq=engine+compression+test+at+altitude&source=web&ots=dlhnk5CTwr&sig=uvlietd1LkSleFzjcrGzRyXiMv4&hl=en&sa=X&oi=book_result&resnum=2&ct=result
I know it says its for Volkswagen Air-cooled engines but there is a nice table on it. (page 15) going by the book, mine should be 192ish psi new at sea level. ( 97 1.8l) at my altitude of 4300 feet my numbers should be right around 170 and they are after the head change earlier this spring. heres my copy of the chart. *Altitude - Factor* 1000 - .9711 2000 - .9428 3000 - .9151 4000 - .8881 5000 - .8617 6000 - .8359 7000 - .8106 8000 - .7860 I would just take what they say at sea level, whats in most books and multiply by those numbers. Hope this helps some. As for the perfect ratio, need the volume of the cylinder at the bottom of the stroke and at the top and add in the volume of area in the head to both then you should get a ratio. My dad uses a kit with a syringe to find the CCs of his VW engines. I will see if I can get the name of it from him. can't think of it off the top of my head. Mike [EMAIL PROTECTED] wrote: > > I've seen that a lot.. but it's flawed.. if all read 50psi dead one, > I'm fine? No... so at what point is it fine? 100psi? 120? 180? > > This isn't a Miata question, but an LT1 SBC question.. but it applies > to everything. If you are looking at a motor (any) how do you know > what the normal reading ought to be? Mathematically I would think it's > CR x 14.7, but that comes out very low... > > Wallyman > > > > Inactive hide details for "Keith Tanner" <[EMAIL PROTECTED]>"Keith > Tanner" <[EMAIL PROTECTED]> > > > *"Keith Tanner" <[EMAIL PROTECTED]>* > > 10/27/2008 04:06 PM > > > > To > > <[EMAIL PROTECTED]>, <[email protected]> > > cc > > > Subject > > RE: NMC - How to figure "perfect" compression for a compression check? > > > > > The easiest thing to do is check for consistency. If all four are > close, that's a good sign. > > Keith Tanner > Flyin' Miata > [EMAIL PROTECTED] > __http://www.flyinmiata.com_ <http://www.flyinmiata.com/> > 1-800-FLY-MX5s (orders) > 1-970-464-5600 (tech) > > > > ------------------------------------------------------------------------ > *From:* [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] *On Behalf Of > [EMAIL PROTECTED] > Sent:* Monday, October 27, 2008 1:15 PM* > To:* [EMAIL PROTECTED] > Subject:* NMC - How to figure "perfect" compression for a compression > check? > > Ok, so if a guy wanted to figure out what the "perfect" lossless > compression measurement is on a motor, how does one go about it? i.e. > somebody tells you to "Do a compression check"... you say "ok, what > values dictate good?".. they respond back with some arbitrary number > somewhere in the high 100's.. and that's my question: Every motor > should have an ideal reading, how do you figure that out? > > I assume you deal with bore/stroke/compression ratio/head gasket > thickness/domed-dished-flat top piston and chamber size and through > some magical formula you get a reading of xxx psi is possible? Google > is letting me down on this one... > > Wallyman > > ------------------------------------------------------------------------ > > _______________________________________________ > Miatapower mailing list > [email protected] > http://list.miatapower.net/cgi-bin/mailman/listinfo/miatapower > _______________________________________________ Miatapower mailing list [email protected] http://list.miatapower.net/cgi-bin/mailman/listinfo/miatapower
