US vs UK (or European) octane ratings ...

[c4koh]

Hi,

Can anyone clarify what the situation here is; I see that octanes of 91,89 (and perhaps even 87) are used in the US, whereas in the UK we have 95, 97 or (for shell optimax) 98...

Are we using the same octane rating procedures?

Alright, on this: I doubt I'm getting any pre-detonation (knocking) from using 95 regular fuel, so is there really any benefit to using super or optimax in my ZR1? AFAIK, the only thing that makes the PROM readout different "settings" is the quality - temp and density - of the AIR...

Any ideas???

[malc350]

Hi Steve, don't know if this helps but having a turbo car makes me wonder about these things too.

Here's a link to a post I once made on Corvette Action Center's Callaway forum:

www.corvetteactioncenter.com/forums/showthread.php?s=&threadid=15082&highlight=octane

It gets pretty involved I think! There are more related topics here:

www.corvetteactioncenter.com/forums/search.php?s=&action=showresults&searchid=254956&sortby=lastpost&sortorder=descending

I have a feeling the ratings are different in the states. i.e. 87 Octane is not tyhe cr*p it sounds. It may be a higher rating. For a more informed answer may be best to ask an oil company like Esso or whatever. Personally I've never had (noticed, anyway) pinking (pinging) from any US car I've ever owned, and I've always run on regular unleaded.

Brett (Gixer) thinks he may have noticed a difference for the better running on Optimax (1990 ZR1 stock). I said I'll try it when I've got some spare money!!!

[LuS1fer]

EVO had a list of cars that actually benefitted from using Optimax and one of them was the LS1-engined HSV. What difference it actually makes is probably qualatitive rather than quantitative.

I'll certainly use it when I do the RWYB, for the possibility it might just net me a hundredth of a second (since most mods don't!) but given the minimal opportunity to use the full performance and the times being somewhat rare when a couple of hundredths of a second will make a real difference, I'll stick to the cheaper stuff. It's a con in real terms.

US fuel is poorer quality than the UK so it matters to them and they tend to use premium fuel in their test cars so no-one can say they didn't try their best. It would be interesting if they did a test to see if it made any difference at all.

[c4koh]

Lads,

Seems you're in the same sort of boat as me; I used to put Optimax in my LT-1, and I thought there seemed to be a difference... In fact, in my wife's Citroen ZX (yes, I know - I get a Cadillac and a ZR1, but hey, she's not interested in cars ) I did seem to get a racier engine from using Optimax.

But, since I guess the "bottom line" is that how much fuel is injected is governed by air flow, and as long as that doesn't cause knocking, then I really do wonder whether there's any difference in using 95 to 98! (other than 4p a litre!)

Oh - and just for any American readers in the forum: we're paying 78p a litre in the UK, which means about $5.30 per US gallon

[Gixer]

c4koh said:

Oh - and just for any American readers in the forum: we're paying 78p a litre in the UK, which means about $5.30 per US gallon

Makes ya sick dunnit ?? When we were over there for the 50th we covered 6-700 miles in a Mustang for less than $20

[KGV]

Here is a website I found that explains the US and EU octane ratings:

www.btinternet.com/~madmole/Reference/RONMONPON.html

Thanks,

Ken