<div dir="ltr"><div class="gmail_default" style="font-size:large">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.</div><div class="gmail_default" style="font-size:large">My assumption is that 100octane is the UK's "high test" and 93 or 94octane is the NA "high test".</div><div class="gmail_default" style="font-size:large">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. </div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, 12 Sept 2025 at 11:38, Jim Pile via Rovernet <<a href="mailto:rovernet@rovernet.org" target="_blank">rovernet@rovernet.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><div style="font-family:arial;font-size:16px"><div></div>
<div dir="ltr">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!</div><div><br></div>
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On Friday, September 12, 2025 at 12:13:54 AM EDT, Gordon Reddy via Rovernet <<a href="mailto:rovernet@rovernet.org" target="_blank">rovernet@rovernet.org</a>> wrote:
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<div><div id="m_-868739363161110169m_-5428827404417969173ydp570649eayiv6391056927"><div><div dir="ltr"><div style="font-size:large">Interesting, check this out.</div><div style="font-size:large"><a shape="rect" href="https://aircooledbug.co.uk/usa-versus-uk-fuel-octane/" rel="nofollow" target="_blank">https://aircooledbug.co.uk/usa-versus-uk-fuel-octane/</a></div><div style="font-size:large"><br clear="none"></div><div style="font-size:large">Gord</div><div style="font-size:large">also </div><div style="font-size:large">1972 TVR Vixen 2500</div><div style="font-size:large">...and if I am crazy enough 19?? Citroen 2CV panel van</div></div><br clear="none"><div id="m_-868739363161110169m_-5428827404417969173ydp570649eayiv6391056927yqt65703"><div><div dir="ltr">On Thu, 11 Sept 2025 at 18:05, Gordon Reddy <<a shape="rect" href="mailto:gorgowof@gmail.com" rel="nofollow" target="_blank">gorgowof@gmail.com</a>> wrote:<br clear="none"></div><blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div style="font-size:large">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. </div><div style="font-size:large"><br clear="none"></div><div style="font-size:large">Gord</div><div style="font-size:large">67 P6 TC2000</div><div style="font-size:large">66 P5 3 litre</div><div style="font-size:large"> </div></div><br clear="none"><div><div dir="ltr">On Thu, 11 Sept 2025 at 17:54, Jon Stanley via Rovernet <<a shape="rect" href="mailto:rovernet@rovernet.org" rel="nofollow" target="_blank">rovernet@rovernet.org</a>> wrote:<br clear="none"></div><blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>Hello all, <div>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. </div><div><br clear="none"></div><div>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?</div><div><br clear="none"></div><div>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. </div><div><br clear="none"></div><div>Regards, </div><div>Jon</div></div>
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