4 replies to this topic

[Guess-Works.com]

This is mainly aimed at those in countries in which 'regular' petrol is considerably lower octane than our UK 95 ron Unleaded....

 

Do you suffer with pinking, do you have to retard the ignition at the expense of 'grunt' to keep the engine running reliably, or am I just over thinking this ?

 

Basically, I'm trying to figure out if there needs to be a different engine specification in my box of tricks specifically for those countries with lower grade fuels

[Steve220]

Won't make any difference on a naturally aspirated engine. Only really starts coming into question on highly tuned turbo applications.

[ACDodd]

John, yes there is a need. If you let me know the Ron rating you will supply to I can suggest a suitable cr for the camshaft you use.

Ac

[Steve220]

It'd have to be a high compression ratio for it have an effect!

[Spider]

YES.

 

In our major cities, we generally have available 91 (some of these have 10% Ethanol), 95 and 98.

 

Out in many regional areas, we can only get 91, though some I've bought would be lucky to be 60. While on a trip a little while ago, that was all we could get, however one member in the group couldn't hear his engine was pinging on the gravel roads, it lasted about 60 km before is was smoking, and then only went about another 50 before it was fouling plugs like no tomorrow.

 

 

Bummer.

 

As we now know he's a deaf old bastard, I've fitted a Knock Alarm in his car now (though I'm not thrilled with it and still looking for a better one).

 

In 'Bush' areas we some other kinda stuff, they call it 'Opal'. In some of these remote areas, there has been an on gong problem for many years where the 'local' (Aboriginal) population have obtained petrol for the purposes of sniffing it to get a high (I wouldn't recommend it - it give me a migraine just thinking about it) I don't know a real lot about the Opal Fuel at this time, but apparently it's blended such that when sniffed, it doesn't make the sniffer 'high'. I think I did read somewhere it was equivalent to 91 RON.

 

I can't give much of an accurate guide on Static CRs as I work to Dynamic CRs. For reference, a Stock Cooper S has 8.88:1 Dynamic CR (9.75:1 Static) and a Stock 1275  has 8.03:1 Dynamic CR (8.8:1 Static CR). The shorter the duration of the Cam, the much more careful you need to be with CRs and Fuel, as it is very easy to push the Dynamic CR through the roof while having low Static CRs.

 

We can run Dynamic CRs up to at least 8.8:1(Depending on the Cam, this could be anything from 10.5 to 12:1 Static CR) on 98, maybe even a little higher, no problems at all.

 

With 91 RON Fuels and running a Dynamic CR of 8.5, on what, they will just pinging, however, not overly, just at the onset where it can be heard, but backing off a tad it goes away. I've not bothered to retard ignition timing to overcome this.

Edited by Moke Spider, 09 March 2015 - 06:58 PM.