<div dir="auto">Turns out I had misplaced trust in the dash tachometer when trying to tune and set engine idle speeds. Turns out the tach is reading about 2x the actual RPM, it is no wonder that I couldn't get the engine to idle smoothly when it was set to below 500 RPM! Seems to run well at the real 600 RPM idle setting now. Road testing next after brakes are done. <div dir="auto"><br></div><div dir="auto">Jon</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Fri, Sep 12, 2025, 3:52\u202fPM geffandjulie--- via Rovernet <<a href="mailto:rovernet@rovernet.org">rovernet@rovernet.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div lang="EN-GB" link="blue" vlink="purple" style="word-wrap:break-word"><div class="m_-1025073254830208580WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt">Aviation 100 Octane is actually 100 LL \u2026low lead. Environmental zealots have been trying to ground general aviation, but have only succeeded in Santa Clara county, in\u2026you guessed it\u2026 California. I don\u2019t think use of 100LL would affect the engine, but I am not to be trusted on this\u2026<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt">PS: In WWII, air cooled rotary engines needed 140 Octane! I don\u2019t know about the V12 water cooled Merlin, etc. <u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt"><u></u> <u></u></span></p><p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt">Geoffrey W. McCarthy MD MBA DipAvMed Col USAFMC (ret)<u></u><u></u></span></p><p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt">677 NW Melinda Ave<u></u><u></u></span></p><p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt">Portland OR 97210<u></u><u></u></span></p><p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt">503-799-3809 (m)<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt"><u></u> <u></u></span></p><div style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Rovernet <<a href="mailto:rovernet-bounces@rovernet.org" target="_blank" rel="noreferrer">rovernet-bounces@rovernet.org</a>> <b>On Behalf Of </b>Gordon Reddy via Rovernet<br><b>Sent:</b> Friday, September 12, 2025 12:49 PM<br><b>To:</b> Rovernet <<a href="mailto:rovernet@rovernet.org" target="_blank" rel="noreferrer">rovernet@rovernet.org</a>><br><b>Cc:</b> Gordon Reddy <<a href="mailto:gorgowof@gmail.com" target="_blank" rel="noreferrer">gorgowof@gmail.com</a>><br><b>Subject:</b> Re: [Rovernet] P5B V8 ignition timing<u></u><u></u></span></p></div><p class="MsoNormal"><u></u> <u></u></p><div><div><p class="MsoNormal"><span style="font-size:18.0pt">Just found another chart which says 100octane UK equals 97.5octane NA while another site says it equals 93octane NA so it's a slippery subject.<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt">My assumption is that 100octane is the UK's "high test" and 93 or 94octane is the NA "high test".<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt">I usually run Shell Vpower 91octane in my Mazdaspeed3 (2.3L, 200psi compression, turbo/intercooled) and when I race it I sometimes change the tune to use Shell Vpower 93octane. <u></u><u></u></span></p></div></div><p class="MsoNormal"><u></u> <u></u></p><div><div><p class="MsoNormal">On Fri, 12 Sept 2025 at 11:38, Jim Pile via Rovernet <<a href="mailto:rovernet@rovernet.org" target="_blank" rel="noreferrer">rovernet@rovernet.org</a>> wrote:<u></u><u></u></p></div><blockquote style="border:none;border-left:solid #cccccc 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in"><div><div><div><p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Really good info, Gordon. I always wondered if 93 octane was sufficient for the TC, with its 100 octane sticker. Now I know that the US rating would be closer to 95. I run on 93, which is readily available on the East coast, which seems to be just fine. However, I admit to pumping in just a little racing fuel per tank (103 octane), which really perks the TC up a notch!<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><u></u> <u></u></span></p></div></div><div id="m_-1025073254830208580m_-868739363161110169m_-5428827404417969173ydp570649eayahoo_quoted_8189600378"><div><div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">On Friday, September 12, 2025 at 12:13:54 AM EDT, Gordon Reddy via Rovernet <<a href="mailto:rovernet@rovernet.org" target="_blank" rel="noreferrer">rovernet@rovernet.org</a>> wrote: <u></u><u></u></span></p></div></div><div style="border:none;border-left:solid #cccccc 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:6.0pt"><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><u></u> <u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><u></u> <u></u></span></p></div><div><div id="m_-1025073254830208580m_-868739363161110169m_-5428827404417969173ydp570649eayiv6391056927"><div><div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a">Interesting, check this out.<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><a href="https://aircooledbug.co.uk/usa-versus-uk-fuel-octane/" target="_blank" rel="noreferrer">https://aircooledbug.co.uk/usa-versus-uk-fuel-octane/</a><u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><u></u> <u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a">Gord<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a">also <u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a">1972 TVR Vixen 2500<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a">...and if I am crazy enough 19?? Citroen 2CV panel van<u></u><u></u></span></p></div></div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><u></u> <u></u></span></p><div id="m_-1025073254830208580m_-868739363161110169m_-5428827404417969173ydp570649eayiv6391056927yqt65703"><div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">On Thu, 11 Sept 2025 at 18:05, Gordon Reddy <<a href="mailto:gorgowof@gmail.com" target="_blank" rel="noreferrer">gorgowof@gmail.com</a>> wrote:<u></u><u></u></span></p></div><blockquote style="border:none;border-left:solid #cccccc 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in"><div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a">Interesting, I just returned from the UK yesterday and while there noticed octane ratings there are higher. I believe its a different rating system for octane which I was going to check on this evening. I remember my P6 TC2000 had a tag stating use 100 octane but it ran fine on 92. My P5 3 litre runs fine on 91 but its certainly not 10.5:1 more like 8.5:1 It would probably run fine on 87. More knowledgable minds will hopefully contribute. <u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><u></u> <u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a">Gord<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a">67 P6 TC2000<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a">66 P5 3 litre<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:18.0pt;font-family:"Helvetica Neue",serif;color:#26282a"> <u></u><u></u></span></p></div></div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><u></u> <u></u></span></p><div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">On Thu, 11 Sept 2025 at 17:54, Jon Stanley via Rovernet <<a href="mailto:rovernet@rovernet.org" target="_blank" rel="noreferrer">rovernet@rovernet.org</a>> wrote:<u></u><u></u></span></p></div><blockquote style="border:none;border-left:solid #cccccc 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in"><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">Hello all, <u></u><u></u></span></p><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">I'm trying to tune a stock early 67 P5B V8 with high compression 10.5:1 and is currently set to factory setting of 6 degrees BTDC. The non ethanol fuel I have access to around here in Texas is 90 octane, and adding in a boost probably pushes up to around 92, but the engine was designed and tuned for 100 octane. <u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><u></u> <u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">I'm curious if anyone here has a high compression V8 and what timing they set the engine to and what fuel? Some sources say retard the idle timing possibly all the way to TDC?<u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><u></u> <u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">Right now the engine runs poorly when cold and on choke, but eventually once warmed up seems to run well. Both carbs have been rebuilt. <u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a"><u></u> <u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">Regards, <u></u><u></u></span></p></div><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">Jon<u></u><u></u></span></p></div></div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">_______________________________________________<br>Rovernet mailing list<br><a href="mailto:Rovernet@rovernet.org" target="_blank" rel="noreferrer">Rovernet@rovernet.org</a><br><a href="http://rovernet.org/mailman/listinfo/rovernet_rovernet.org" target="_blank" rel="noreferrer">http://rovernet.org/mailman/listinfo/rovernet_rovernet.org</a><u></u><u></u></span></p></blockquote></div></blockquote></div></div></div></div><div id="m_-1025073254830208580m_-868739363161110169m_-5428827404417969173ydp570649eayqt27851"><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica Neue",serif;color:#26282a">_______________________________________________<br>Rovernet mailing list<br><a href="mailto:Rovernet@rovernet.org" target="_blank" rel="noreferrer">Rovernet@rovernet.org</a><br><a href="http://rovernet.org/mailman/listinfo/rovernet_rovernet.org" target="_blank" rel="noreferrer">http://rovernet.org/mailman/listinfo/rovernet_rovernet.org</a><u></u><u></u></span></p></div></div></div></div></div></div><p class="MsoNormal">_______________________________________________<br>Rovernet mailing list<br><a href="mailto:Rovernet@rovernet.org" target="_blank" rel="noreferrer">Rovernet@rovernet.org</a><br><a href="http://rovernet.org/mailman/listinfo/rovernet_rovernet.org" target="_blank" rel="noreferrer">http://rovernet.org/mailman/listinfo/rovernet_rovernet.org</a><u></u><u></u></p></blockquote></div></div></div>_______________________________________________<br>
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