p.bird wrote:
> I know in the states that you have been using unleaded for ages, but
> your cars are different to ours in many ways because of your
> enviromental laws, eg carbs not injection. I think it entirely possible
> that the cars that went to the states had different heads so they could
> run on unleaded. Here in England we were running five star petrol when
> the tr's came out and now we are already down to four star (98 ron), our
> unleaded starts at 98 ron and the usual stuff is 95 ron. If our cars
> were designed to run fuel above 98 ron (five star) leaded fuel and we
> start putting 95 ron unleaded fuel into them surely there could be the
> possibility that extra heat could be generated by the lower rated fuel
> as well as making the valve seats more vulnerable to recession. I could
> be talking pony though.
There are two different things to consider that are somewhat related,
but
also somewhat independent. These are:
*) leaded vs. unleaded
*) high octane vs. low octane
Just because the gas is being switched from leaded to unleaded
doesn't necessarily mean that the octane must be reduced, even
though this is often the case, since lead is an effective, yet
relatively inexpensive octane enhancer.
What is being said by many of the people in the states is that
the leaded vs. unleaded issue isn't a significant factor in
valve seat recession, at least not at standard operating
temperatures. My experience bears this out as well.
However, high octane vs. low octane is indeed a real issue.
For instance, I run 93 (R+M/2) octane unleaded fuel in my
1970 TR6. If I run a lower octane fuel, such as 89 (R+M/2)
then I will get moderately severe ping (knock). However,
in my lower-compression 1974 TR6, I can run on 87 (R+M/2)
octane fuel just fine, without any knock.
If you can't get high octane unleaded fuel in Europe, then
you may indeed have a problem on the higher compression heads,
in the same way that I would have a problem running less than
93 (R+M/2) octane fuel in my 1970 TR6.
Lastly, for reference, the octane ratings being talked about in
the USA and Europe are different. USA ratings are (R+M/2) where
RON is Research Octane, and MON is Motor Octane. As p. birdy
noted, the octane ratings he is looking at are RON ratings.
The difference between RON and MON is "sensitivity." With modern
fuels, this is typically around 10. What this means is that a
rough table of RON vs. R+M/2 fuel (assuming a sensitivity of 10)
can be produced. However, the sensitivity can vary significantly
according to the fuel formulation, so it can't always be assumed
to be 10. However, if it were 10, one could produce an equivalence
chart between R+M/2, RON, and MON:
R+M/2 93 = RON 98 = MON 88
R+M/2 89 = RON 94 = MON 84
R+M/2 87 = RON 92 = MON 82
This indicates that what I run in my 1970 TR6 (high compression)
is approximately equivalent to the 98 RON unleaded fuel mentioned
by p.bird above. This would mean that from my experience I would
expect his car to run fine on four star unleaded (98 RON) but to ping
on "the usual stuff" (95 RON). With a low compression TR6, I would
expect the car would run just fine on "the usual stuff." If you
are having marginal problems with pinging, you may be able to avoid
the pinging by changing timing, and/or enriching the mixture.
Finally, if you want to read more than you could have ever wanted
to know about Gasoline, take a look at Bruce Hamilton's excellent
Gasoline FAQ. You'll find a link to it from the VTR WWW site at
http://www.vtr.org/maintain
--ken
VTR WWW Maintainer -- http://www.vtr.org
--
Kenneth B. Streeter | EMAIL: streeter@sanders.com
Sanders, PTP2-A001 |
PO Box 868 | Voice: (603) 885-9604
Nashua, NH 03061 | Fax: (603) 885-0631
|