Phil:
> Should I feel confident about running my aluminum-engined Europa
> on unleaded fuel?
I wouldn't have any qualms about doing so. I'm not 100% certain because
everyone I know with Renault-engined Europas has dumped the
original R16 head for the Gordini crossflow head. But the stock
valve seats that Renault used on the crossflow head at the same time as
the R16 head are hard enough for no-lead, so the harder material was
certainly available to Renault at that time and I'm pretty sure they used it.
And if your motor's ever been rebuilt, harder seats and valves have almost
certainly been used because that's all that's been available for years. (Well,
from my suppliers, at least.)
> I realize that the stock compression ratio
> is 10.25/1, so I should have serious octane to prevent detonation,
> particularly when tuned for performance and driven that way. The 108 leaded
> Union racing gas would seem to be overkill, but the cheaper 104-octane Union
> racing gas is unleaded. What do you think?
I doubt you even need the 104. When I first got an R16 Europa, I ran it on
_regular_. Yup, genuine grade-A 88 PON buffalo urine. The previous owner had
the timing backed way off; when I returned it to spec it went to street premium
no lead (91 PON) without any problem.
I expect you'll be fine with street premium no-lead at 10.25. First, because I
was. Second, my Twin-Cam runs fine on street premium at 10.3, even fresh.
The compression ratio/required octane releationship is affected by cylinder
size, so these little motors can handle higher CRs than big 'murrican V8s can.
Third, because I suspect your engine has some miles on it. With a steep cam
run at high rpms with vigorous valve springs, the valves slap back down onto
the seats pretty hard. That gradually pushes the seats back into the aluminum
head, lowering the actual compression ratio and reducing intake efficiency
as well, so octane requirement goes down as the mileage piles up.
But what the heck, you don't need to take my word on octane -- experiment.
Start with pure 104, then gradually mix in more and more street gas and listen
for pinging. The best gas to use is the lowest octane that won't ping -- any
octane over that is wasted.
Dave Van Horn davevh@microsoft.com
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