It's even more complicated. That graph is for a static compression ratio with no heat transfer. In a real engine, there is heat loss to the cold cylinder/head/piston plus leakage past the piston and an intake valve that's still partially open at the beginning of the compression stroke. After an engine is running compression is much higher (less heat loss, less time to leak past piston, and less valve loss because of the the momentum of incoming chatge)
> -----Original Message----- > From: Mercedes [mailto:mercedes-boun...@okiebenz.com] On Behalf Of > Larry Turner via Mercedes > Sent: Tuesday, June 19, 2018 7:44 PM > To: mercedes@okiebenz.com > Cc: Larry Turner <l02tur...@comcast.net> > Subject: Re: [MBZ] Compression numbers they are bragging about seem low to > me > > Thanks, > > That certainly makes sense. So my math method appears to be off by a factor > of 1.75 or so? I kept mulling that over and came to the [wrong] conclusion > about multiplying the stated compression time the atmospheric pressure and > failed to consider the heat needed? Now that you mention it, there are so > many variables at play it must be a much more complex formula than I tried to > make it.. > > Thanks for the explanation.... > > Larry --- > > > On 06/19/2018 2:04 PM, G Mann via Mercedes wrote: > > Diesel engine is a "compression ignition" engine, so to fire the > > fuel/air charge it must raise the temperature of the charge to a point > > at or above the flash point of the fuel/air charge, so the engine "lights > > off". > > > > Typical compression charge temps necessary to hit flash point for > > diesel is > > 400 degrees F. > > Ambient air temp plays a part in reaching that flash point, thus, glow > > plugs. > > Crank speed is another factor.. thus, the need for a strong battery. > > Next is compression condition of the engine. > > > > You can put a hair dryer in the intake, add a booster battery... but > > if you have low compression... very hard to start.. > > > > >From my experience, the magic happens best between 390 and 420 psi on > > >a hot > > engine compression test. > > > > On Tue, Jun 19, 2018 at 10:49 AM, Larry Turner via Mercedes < > > mercedes@okiebenz.com> wrote: > > > >> Speaking of what an engines compression should be, I always thought > >> it was the compression ration X atmospheric pressure. So a engine > >> with 18:1 (as a diesel might be) would look for 18X14.7 (approx) = > >> 264psi or so. While a gas engine at 7:1 would be ~103. Is this logical? > >> > >> LarryT > >> > >> 91 300D (RIP ??) > >> > >> 06 E350 (POS also dead) > >> > >> 06 Ford Explorer > >> > >> 74 911 > >> > >> 66 MGB > >> > >> > >> On 06/18/2018 1:51 PM, Andrew Strasfogel via Mercedes wrote:Speaking > >> of > >> > >>> Seller seems WAY too enthusiastic. Buyer beware. > >>> 264 > >>> On Mon, Jun 18, 2018 at 10:33 AM, Frederick Moir via Mercedes < > >>> mercedes@okiebenz.com> wrote: > >>> > >>> Depends on cranking speed amongst other criteria. > >>>> Fred. > >>>> > >>>> On Mon, Jun 18, 2018 at 10:18 AM, Kaleb C. Striplin via Mercedes < > >>>> mercedes@okiebenz.com> wrote: > >>>> > >>>> Closer to 400 or over in my mind > >>>>> Sent from my iPhone > >>>>> > >>>>> On Jun 17, 2018, at 9:49 PM, Dwight Giles <dwight.gi...@gmail.com> > >>>>> wrote: > >>>>> > >>>>>> What should they be? > >>>>>> > >>>>>> Dwight Giles Jr. > >>>>>> Wickford RI > >>>>>> > >>>>>> On Jun 17, 2018 10:21 PM, "Kaleb C. Striplin via Mercedes" < > >>>>>> mercedes@okiebenz.com> wrote: > >>>>>> 1979 Mercedes-Benz 300SD **VERY CLEAN** > >>>>>>> https://albuquerque.craigslist.org/cto/d/1979- > >>>>>>> > >>>>>> mercedes-benz-300sd-very/ > >>>>> 6612681421.html > >>>>> > >>>>>>> Sent from my iPhone > >>>>>>> > >>>>>>> _______________________________________ > >>>>>>> http://www.okiebenz.com > >>>>>>> > >>>>>>> To search list archives http://www.okiebenz.com/archive/ > >>>>>>> > >>>>>>> To Unsubscribe or change delivery options go to: > >>>>>>> http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > >>>>>>> > >>>>>>> _______________________________________ > >>>>> http://www.okiebenz.com > >>>>> > >>>>> To search list archives http://www.okiebenz.com/archive/ > >>>>> > >>>>> To Unsubscribe or change delivery options go to: > >>>>> http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > >>>>> > >>>>> > >>>>> > >>>> -- > >>>> Fred Moir > >>>> Lynn MA > >>>> Diesel preferred > >>>> _______________________________________ > >>>> http://www.okiebenz.com > >>>> > >>>> To search list archives http://www.okiebenz.com/archive/ > >>>> > >>>> To Unsubscribe or change delivery options go to: > >>>> http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > >>>> > >>>> > >>>> _______________________________________ > >>> http://www.okiebenz.com > >>> > >>> To search list archives http://www.okiebenz.com/archive/ > >>> > >>> To Unsubscribe or change delivery options go to: > >>> http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > >>> > >>> > >>> > >> _______________________________________ > >> http://www.okiebenz.com > >> > >> To search list archives http://www.okiebenz.com/archive/ > >> > >> To Unsubscribe or change delivery options go to: > >> http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > >> > >> > > _______________________________________ > > http://www.okiebenz.com > > > > To search list archives http://www.okiebenz.com/archive/ > > > > To Unsubscribe or change delivery options go to: > > http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > > > > > > > _______________________________________ > http://www.okiebenz.com > > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com _______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
