Genuine AC built Cobra for replica money

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nikbj68
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Re: Genuine AC built Cobra for replica money

Post by nikbj68 »

COX5012 wrote:...Not sure where you can buy higher octane than 97 Ron?
Tesco Ultimate... 98.
My Rover Engine certainly runs better on that than the standard U/L.
Hawk 289 FiA...AT LAST!!!
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peterc
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Re: Genuine AC built Cobra for replica money

Post by peterc »

Interesting set of figures comparing CR with octane.
My engine builder quoted a max of 9.8 CR to run standard unleaded so I thought he built my engine at around 9.5.
Although I know that the octane rating has dropped since 5* disappeared I thought that the standard unleaded was around 95 octane when they built the engine. I have tried super unleaded but found no advantage in the short term.
Peter C
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Roger King
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Re: Genuine AC built Cobra for replica money

Post by Roger King »

peterc wrote:Interesting set of figures comparing CR with octane.
My engine builder quoted a max of 9.8 CR to run standard unleaded so I thought he built my engine at around 9.5.
Although I know that the octane rating has dropped since 5* disappeared I thought that the standard unleaded was around 95 octane when they built the engine. I have tried super unleaded but found no advantage in the short term.
Peter C
It's not just CR, it's other elements as well that dictate octane rating requirements - combustion chamber design, swirl, quench etc. - and experience of the engine builder/designer in what will work with what and what won't. For example, it's very difficult to get a stroked 302 (347) to pink - but it's very difficult to build a hot 351W that doesn't!
Having said that, on Pete Baldwin's rolling road my old Hawk's 289 could have the ignition timing moved right up to 42-44° total advance under load at 3,000 rpm without pinking (don't try this at home, especially if you have hypereutectic pistons) on superunleaded (9.5:1 CR). We only stopped there in deference to the piston crowns (and wound it back to 36°). But stick it on 95 and it would rattle like a box of spanners at 30° under load.
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