I think the guy who told you that was either f-ing with you or didn't know **it. Octane translates into the fuel's ability to resist knock. Depending on the technology and engineering (and bhp/liter), you may need a higher octane in a 4 cylinder than in an 8 cylinder. Knock, an uncontrolled explosion in the engine, can be caused by high boost pressure, high compression, advanced timing, intake temperature, hot spots in the cylinder, and a couple other things. Some if you might have heard of "turbo pistons". In high compression engines, they are not only stronger, but more importantly differently shaped so that the compression ratio is lower. I've recently done the math, an engine with a CR of 10:1 can only be boosted 5psi before needing a higher octane to control knock, whereas a 8.5:1 can do about 10 psi before being at the same "danger level" So when push comes to shove, basically the more power per liter that an engine can make, the higher octane is necessary to avoid knock. The honda s2000's inline 4 (120hp/liter) needs higher octane than the PRV (47hp/liter). Technology (ie, vtec) helps span this disparity as well. Of course, these are mostly just rules of thumb... Every engine is different and may be more (or less) prone to detonation. Apparently the volumetic efficiency (effiency of the output power to the displacement of the engine) of the s2000 is almost 100%. I guess this metric was determined many years ago, when american engines couldn't manage 80%. Jim On Tue, 19 Aug 2003 12:31:17 -0500 Farrar Hudkins <fhudkins@xxxxxxx> writes: > I was told a rule of thumb by my old mechanic that 87 octane is good > enough for four cylinders, 89 for six, and 93 for eight cylinders. > That's probably wrong, though, so I'd like some clarification. > However, > I've used 89 Octane fuel in all my six-cylinder engines after trying > > both ends of the spectrum and believe that it's a good match for > fuel > economy and efficient burning. > > Off-topic note: Happy birthday to Gene Roddenberry, author of the > most > famous split infinitive of all time. ;) > > Farrar > > cruznmd wrote: > > Do you guys all really put 93 octane in your cars, or have you > found > > that it doesn't really matter? > > > > The manual says "91 octane only" but all the pumps in my area only > > > sell 87, 89, & 93 octane. I would think that 89 would be close > enough > > but..... > > > > Anyone notice any adverse performance or mileage from the lower > > octane fuels? > > > > Rich > > > > > > > > To unsubscribe from this group, send an email to: > > DMCForum-unsubscribe@xxxxxxxxxxxxxxx > > > > > > > > Your use of Yahoo! Groups is subject to > http://docs.yahoo.com/info/terms/ > > > > > > > > > > > > -- > Farrar Hudkins > Announcer/Producer > 89.9 WWNO FM New Orleans / 90.5 KTLN FM Thibodaux-Houma > Live audio stream @ www.wwno.org > > > ------------------------ Yahoo! Groups Sponsor > > To unsubscribe from this group, send an email to: > DMCForum-unsubscribe@xxxxxxxxxxxxxxx > > > > Your use of Yahoo! Groups is subject to > http://docs.yahoo.com/info/terms/ > > > ________________________________________________________________ The best thing to hit the internet in years - Juno SpeedBand! Surf the web up to FIVE TIMES FASTER! Only $14.95/ month - visit www.juno.com to sign up today! Yahoo! Groups Sponsor ADVERTISEMENT <http://rd.yahoo.com/M=244522.3707890.4968055.1261774/D=egroupweb/S=170512 6215:HM/A=1595053/R=0/SIG=124gf29oe/*http://ashnin.com/clk/muryutaitakenat togyo?YH=3707890&yhad=1595053> Click Here! <http://us.adserver.yahoo.com/l?M=244522.3707890.4968055.1261774/D=egroupm ail/S=:HM/A=1595053/rand=489618664> To unsubscribe from this group, send an email to: DMCForum-unsubscribe@xxxxxxxxxxxxxxx Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> .
<<attachment: winmail.dat>>
Back to the Home of PROJECT VIXEN