[Rovernet] P5B V8 ignition timing

[Gordon Reddy]

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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