[Rovernet] P5B V8 ignition timing

[Gordon Reddy]

Interesting, check this out.
https://aircooledbug.co.uk/usa-versus-uk-fuel-octane/

Gord
also
1972 TVR Vixen 2500
...and if I am crazy enough 19?? Citroen 2CV panel van

On Thu, 11 Sept 2025 at 18:05, Gordon Reddy <gorgowof at gmail.com> wrote:

> 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.
>
> Gord
> 67 P6 TC2000
> 66 P5 3 litre
>
>
> On Thu, 11 Sept 2025 at 17:54, Jon Stanley via Rovernet <
> rovernet at rovernet.org> wrote:
>
>> Hello all,
>> 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.
>>
>> 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?
>>
>> 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.
>>
>> Regards,
>> Jon
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>
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