I've got a theory on that, that I'm currently seeking the opinion of
others on, specifically as applies to hemis. their oil pump is in a
word. sh.t. VERY prone to seizing at higher rpm, and/or if you try to
get more oil pressure out of it. I think it's so shitful that it can
lead to vicosity index improvers (if that is the right term) breaking
down). some middle of the road mineral oils will show reduced oil
pressure after 45 seconds of high rpm use (so basically by the end of a
ridiculous burnout and 1/4mile run. or more likely during circuit
racing)

Sythetics and quality mineral oils (often semi synth) tend to do better
there, but none of them last forever. And really it's an issue with the
engines oiling system (a severe one imho, and I've written about some of
the things that can be done to fix it. You can also get a new pump from
Steve Elliot who makes a new housing with ford gears that works well for
some group nc racers, perhaps the ultimate test. My personal feeling is
an even better option would be to make _yet_ another housing and convert
it to use SBchev internals, they are far less stressful to the cam drive
gear/driven gear and deliver twice as many little pulses vs 4 'jolts'
per revolution, and furthermore are imho almost impossible to seize, at
least relatively speaking. In fact, if you have a mill in your shed
still, I'd be interested in making one from a lump of alum to try)

jags - of course their aim is poor and the oil film ends up on the road
wherever the car goes, or is towed.

Some people in aus seem dead set against using anything but them in bmc
a series engines - any reason why that you can think of. I'm honestly
starting to think it's so they can get work twice as frequently.

There's guys on the jyturbo list who are engineers, and they would stake
their left testicle on the fact that the water jacketing in t03s (which
I think is in the vl, or is it a t3, whichever) ius there in name only,
and they are still oil cooled. So yes there will be an issue of sorts.
But what it really means is that you need to look at a decent mineral
oil or a synthetic, i.e. not the lowest grade bargain basement oil in
the world, as that's hardly a fair comparison.

I used to run mobil one in all the stroked turbo holden 6s I ran,
because the turbos were worth as much as the engine almost in those
days, and they were only doing around 10,000km per year, the extra cost
of the oil (and I changed it and the filter every 5,000 or every 3
months) didn't faze me whatsoever. But I never thought I 'needed' it as
much as a case of 'might as well' I did end up finding that some of my
early turbo failures (exhaust ran so hot it coked the oil in the
housing) were actually because the exhaust housing spec of the garret
kits was way too restrictive, and the cam specs originally either
supplied or suggested with the kits (I never bought a kit new, I have
found a shitload s/hand way back when, just sold my last one in 2005
with the engine it was setup for) were shitful and caused air and fuel
to be spat out the exhaust at mid/low rpms, where the heat of the turbo
ignited it. Meaning that the traditional 'cool down' idle period before
switch off was doing the bloody opposite. After tracing that and making
amends I never had a problem again, and eventually I tried using decent
mineral oil. The turbo bearing/shaft play was like new when I sold the
combo, after 12 months and 15,000km on mineral oil with the previous
change frequency (previously I was having trouble getting _to_ 5000km -
and thought the oil made a difference, but it was the issues above, and
a couple more I couldn't be bothered going into)..

So basically my take is unless there's something completely f.cked about
the engine or it's oiling system, that shows up equally on NA rb30s then
there's no evidence I can point to to suggest that a quality mineral
based oil is any concern whatsoever on an rb30t.

I will say I'm adamant that it's retarded (and then some) to stretch oil
change frequency beyond factory specs. I've had a shitload of minis over
the years, and the one thing I did differently (and I do have a few
examples of my engines in other peoples hands where they didn't follow
my advice on this issue) was changed the oil every 5000km and filter.
And my engines tended to last double the kms - often more. No oil in the
world is meant to be left in there indefinitely, and it's simply insane
to think that it will somehow act as a bandaid. I don't think _the_ most
bargain based oil changed on time will be better than synthetic changed
1,000km late, but I _definitely_ think that quality mineral or semi
synth changed on time (or a little sooner) is a country mile ahead of
thinking there's some safety net built into full synthetic. The engine
is still going to put contaminants into the oil at around the same rate
(most of which would likely be combustion related, not wear related,
though one would lead to the other) so a synthetic is still going to be
just as compromised at a given point.

I'd also add that no oil will get around a blocked or compromised oil
return line from turbo to sump. that's the source of more stuffed turbo
bearings that I could count.

exactamundo.

yep, they are much lower.

In all seriousness, the slant 6 has a stroke of 4.125" and it will
handle 5000rpm for decent extended periods, and those engines are known
to last 'forever' I seriously doubt many modern smaller capacity engines
would have near the intertial loads at tdc and bdc even pushed to their
redline all day, and yet the slants last exceptionally on mineral oil
(as they 'gained' their reputation in an era where that's all that was
available)