If you had a commodore 64, or the commodore 64 emulator for the pc, I
could give you a program I wrote when I was around 15 years old, that
will give you the rpm for any given mph, or diff ratio, or tyre size (in
fact you put in everything minus the missing variable, and it gives you
the last one, also allowing for slippage in a typical torque convertor
(which would be anywhere from 5-10% tops for most streeters)

It also approximates tyre size, either from a static measurement of the
diameter, or if you enter the P 225/60 14 or corresponding figures.

Based on an assumption of a 225 65 14 tyre set (fairly common fare on
the sunraysia steel rims, or whatever they were called (I've got a
chrome set free to good home if anyone wants) an auto with a fairly low
stalling convertor and the 4.11 diff (on that note, what _IS_ the exact
diff ratio for the tonners with low diff gears - I've heard anything
including 4.1 4.11 4.3 and 4.4something_?, your rpms will be
approximately (rounded off, as frankly within 5rpm is close enough, and
easier to conceptualise the spread)

at 60km/h  2120rpm
at 80km/h  2830rpm
at 100km/h 3530rpm
at 110km/h 3890rpm
at 120km/h 4240rpm

Generally speaking pushrod v8s (well as long as we don't count any pommy
or some other shitheaps) don't _mind_ higher rpms (it's all relative)
all that much, and with a stroke just over 3 inches, the 308 certainly
isn't going beserk between 3 and 4 thousand rpm. BUT, they do tend to
have known issues with cam lobe wear. One might argue that at higher rpm
there's more oil flung from the rods to the cam lobes, but the
stress/friction/wear of them (in my opinion) goes up with rpm at a rate
that 4000rpm is imho pushing things for acceptably long life for the cam
lobes if it's stuck there for hours at a time.

If it was a 202, it'd likely start using oil at some point a little too
early for my liking with that sort of rpm (assuming you do freeway runs
like me,and 120 is not exactly all that high by some standards) whereas
a 186 (not that they are technically legal) is a much better bet for
massive freeway runs at higher speeds. the 10% loss in torque and power
(approx) is an issue, but personally I'd go that way for a old holden 6
resto).

In your case, there isn't a hell of a lot of difference in the rpm
potential of the 253/308. Technically the 253 piston _is_ lighter and
might enable a few hundred rpm more, but you have more shrouded valves
and it's 55cubes down, and that means it's not making as much power so
it'd be far more likely to 'want' lower gearing than the 186 vs 202
comparison.. But in both cases 253/308 there is still the cam lobe wear
issue. I don't want to make out it's atrocious, but they're no small
block chev in the 'indestructible and still dirt cheap' stakes.

An interesting side note here is that typically the lockup convertors
will last the life of the other friction linings in the transmissions
(the 'take for granted' bits that get replaced every trans reco) so
that's not a big concern _but_ they only engage at a relatively low
throttle opening - true highway cruising, and will 'unlock' for higher
throttle inputs. This is to save them. Hypothetically if they were
overengineered, they could be engaged for higher throttle inputs). So
what it means is that for most towing duties, they might not lock up
anyway. Which means the difference in economy is (if it exists) down to
the overdrive top gear and lower overall freeway rpms, whilst towing at
least. And by towing, you could also include lugging very heavy loads on
the tray as well.

All of which tends to mean lack of a lockup convertor is no biggie, but
the diff ratio with the 3 speed auto _might_ be.

I've (unfortunately, as I now f.cking hate the bastards almost as much
as the bw35, which for the record is a decent enough auto, but should
never ever have been put in heavy cars with bigger capacity/higher
torque chrysler 6s and even the later ford 6s) had a fair bit to do with
trimatics (though I'm not sure what yours is??) esp those modified for
racing and or hard duties.

My experiences are as follows : 99% of the so called experts out there
talk a lot of sh.t, and offer the world, and sponsor a few magazine
writeups (or maybe the magazines are always on the border of being short
of articles) but when it comes down to it, when their 'grenades' go off
less than a fortnight after install (and after being told before it was
built, the kind of treatment, and the willingness to go to a th400 if
necessary to avoid trouble) they say 'tough sh.t', and charge to rebuild
the damage, then it happens again, and again.

There's two issues with trimatics (well probably 200) and the 'slightly
out of their league' autos in general. For racing or towing slow shifts
mean a lot of slip of the friction linings, and quicker wear. So you'd
typically want _slightly_ more pressure to _hold_ each clutch or band
when required. This is not the same as a harder quicker engagement. You
can apply more pressure, but route it through a restrictor (or not
enlarge the restrictor) so that it takes longer to fully buildup. This
will retain a slightly slower than 'ideal' shift but once it's engaged
the gear, it holds and resists tearing away (which will f.ck the
friction linings quicker than britney f.cked her hair).

IF you seek faster shifts, that _will_ reduce the wear on the friction
linings _BUT_ it also drastically increases the shock loading. And since
the trimatics are not all that 'well hung' in terms of planetary and
various shaft thicknesses, extra shock loading can and will break these
parts, so even _if_ the friction linings last longer, it's totally
irrelevant, as they break and that's all or nothing.

SO, the general approach is that _if_ the trans place (down the track)
offers to help out by sharpening up the shift speeds (they still shift
at the same rpm, just a more abrupt shift, no slip) thank them kindly,
and drive off (backing into their courtesy car for good measure). The
'go' is to (if they can be found) run a new heavy duty factory style
band, not a reline or otherwise manufactured band (as they typically
aren't as strong and the friction lining can peel off, which ironically
I've come across a lot with bw35s recently!) beccause it's not bonded on
as competently). If you must use a re-line, and there's a choice between
a factory band relined, or an aftermarket band and new lining, I'd go
the original.

Next, for two of the clutch packs (maybe all? I forget how many they
bloody have, but if you really want I'll re-check) the 4s have a set
number of friction clutches and shim discs. the 6s have one or two more,
and the 8s have one more again. What people used to do for tow car 6s
was run the v8 number of friction plate/discs. You _can_ go one
(actually two I think) better. What you do is get the piston from each
clutch pack (it'll make sense to any trans person, or fitter and turner)
and the corrugated (or wave shaped) spacer and turn them down in a
lathe. You don't go beserk, but it allows you to run an extra clutch
plate or two in each clutch pack. So it's like the difference between
std 6 and v8 internals, that much on top.

Aside from that don't modify the valvebody (some also do it by only
fitting half of the return springs in the clutch packs, which is imho
trouble on a long distance vehicle) to increase shift harshness. It's
possible (if unlikely) that the line pressure and so forth is a touch
down. This would be a result of the springs inside, probably one in
particular, having lost some tension due to constant compression and
thousands of heat cycles. IF (and it's a big if) test pressures were
down (*and the font pump was in proper working condition, having been
checked and addressed if necessary as part of the rebuild) then
replacing or perhaps shimming a spring might be called for. that would
not be to make the shifts harsher, but to get it back to where it was
supposed to be. From memory the 4s run lower line pressure, the 6s a
little more, and the v8 model trimatics the most (since they'd have to
counter progressively more torque/heavier vehicles. On the 4s, they are
so gutless, they'd never overpower the clutch packs etc, so it's just
wasting energy creating more line pressure for those autos in std
setups)

the other thing I'd suggest considering is the exhaust. It came up in
Trevor's query on a related matter. At those sort of rpms, even though
it wouldnt' likely be full throttle, a free flowing exhaust will make a
considerable difference to potential economy.

Another tid-bit on the dizzy, it's possible (aside from points) that the
vac advance cannister has a ruptured diaphragm, or a dodgy hose, going
into it. Maybe it's sealing ok on some days, or something like that. If
there's a stuffed hose/pipe then that could help big time. As a rough
and ready test, hook up a spare length of hose to the vac advance ont eh
dizzy (with the cap off, and such hard on teh hose, and see if the top
plate moves. Use a fairly long hose, and put a handkerchief over the end
you stick in your mouth. If it's impossible to suck in any air, or just
barely moves the dizzy top plate, it's likely actually ok. If it's
ruptured, you'll be able to keep sucking air through it. The reason for
the longer hose and hanky is if it's ruptured, the air _will_ come
through, and you'll end up inhaling a bunch of debris.

They tend to be the one thing you _won't_ have any joy sourcing from a
wrecker, as they would all be of a similar age. Such cannisters _are_
available new, but expect to pay more than $50 on average (give or take,
depending on your local area). they can make a 10% difference in fuel
usage.

last thought from the twilight zone. It's not common on the v8s, but ont
the 6s the fuel pumps could leak. Someimes into the sump, but rarely. On
the v8, it can leak fuel near the carb (not always) and end up on the
intake manifold, which then is warm enough to evaporate it, meaning it
might not be enough to notice as a smell when stopping or driving, and
will dry up by the time you look under the bonnet. Look for odd
discolouration around the carb base and inlet manifold, though I'm not
sure what colour it might be with current fuels. Still fuel related -
some of the caps on some holdens (though I concede it's the wagons
mostly, and the sedans less so, and if anything the tonners are the
least severe or non existant) that fuel can gush out the filler neck on
hard acceleration, or cornering. Perhaps very rough roads and the like.
Before I bought it off him, my mate was losing, literally, half the fuel
he put in the hk monaro, out the filler cap on right hand turns. I spent
about an hour at the local diy wreckers, and grabbed a few factory caps,
of similar diameter neck/overall. Combined what was a 2 door gemini (in
the c pillar) filler cap, and the seal rubbers from another (I forget
which) which were a _very_ secure fit/preloaded in fact, it it makes
sense) and that sorted it perfectly, until it was backed into and the
whole rear quarter, filler neck, and bloody tank, were collateral
damage.

One of the 'tricks' people used on them was to get a convertor from a 6
or a 4, then rebuilt using some bits from the v8 one (the 4 and 6cyl
convertors both fit a 6cyl trimatic, but the v8 has a bigger input
shaft, and also the torque convertor to flexplate bolts are relocated on
the v8) and you have a poor mans high stall (around 3000-3200rpm on a
308 with a 4cyl, and 2500ish with a 6cyl convertor vs 1800-2000 stock).
This would _really_ wake up a mild 253 and help it get off the line, and
likewise a 308, _but_ they are the antithesis of what you need for heavy
towing (where they'd produce so much extra heat as to cause the oil to
detiorate within a few heaving towing runs and f.ck the auto
quicksmart). In that case, you tend to need to even look at modded
convertors that drag the stall rpm even lower.

Which would probably be worth a dollar to a fair few people ou there.
You might consider swapping something like the far more common (for the
holdens of the era, but not that particular one) 3.36 or maybe 3.55 (but
imho, that might still have it revving higher than ideal). It's a hell
of a hard call to make, and tyres come into it, but I tend not to like
pushing past low 3000rpms for highway cruising. Switching to a 3.36 diff
(if that won't stuff up it's workhorse/towing potential) would pull a
good 700rpm out of it at 110-120km/h

Of course you have to weigh up all the concerns, and if it does less
than 10,000km a year, it's madness for me to even talk about diff ratio
changes, but if it was 100,000km a year, the sooner the better.

If it _is_ a holley, don't f.ck around, buy the 're-usable' gaskets.
They seal 1000 times better (maybe more, it's an estimate) and put an
end to gasket scraping sh.t. If you need to pull the fuel bowls, they'll
come off with ease for a jet change etc, and seal well after months and
even years of tweaking.

High on the list would also be the power valve. They tend to rupture the
diaphragm, with age, or after a few backfires. When they rupture, they
aren't dangerous per se, they just stay open all the time, and have the
pwoer valve enrichment all the time, costing a lot of fuel.

Holley suggest a few ways of selecting the power valve, but assuming
it's a std or nearly std cam, and that it has to pull massive freeway
rpms, I'd be making a strong case for a 55 even when a 65 is typically
called for (it won't open till higher throttle input). But to be
absolutely sure, I'd also run a manifold vac guage and see what vac you
end up with fully loaded and up an incline at 110-120, or whatever the
highest you run it to is. You absolutely _don't_ want it open for steady
state cruising short of near full throttle lugging, like towing heavy up
a steep incline.

fwiw, even _at_ full throttle, I'd be more confident of getting a holley
to not use excessive fuel than a rochester. Ironically it's their 'bug
bear' that they have no air door (which is like a temporary choke as it
opens, richening things up and working like an acc pump for the secs)
for the secs that mean they tend to run frugally at higher loads
potentially (assuming the secs weren't setup deliberately too rich to
counteract the phenomena)

let me know if I can help out. I'm fairly sure I can source a hei dizzy
locally from one of the many commodore wrecker joints, and the work
itself is like 1 minute, so if you have no luck finding one, then feel
free to email me. Failing that, I'd _definitely_ put a new set of points
and a new condenser as a matter of course before doing any longer trips,
no down side really.

I'd be checking, no scratch that, I'd be replacing the points and
condenser even if they seemed serviceable. it's possible the gaps just
closed up too. Put a tiny smear of grease on the cam (the points cam,
the octagonal thing that hits the points open.

not quite, it's a different stud pattern. The manifold _should_ have
provision for both, but you might have to lock 2 nuts together and pull
a couple of studs and put them in the other holes. If there is any
resistance, hit the area (after locking the nuts) with a propane torch
for about 30 seconds (this is with the manifold off the car and well
away from any petrol, bite the bullet and pull the inlet if the studs
for the carby won't come out.

Actually you might have to buy 2 studs come to think of it, as rear on
the quaddies is bolts rather than studs and nuts....

I'm pretty sure I could source on of these quite cheap so

I'd _absolutely_ check the points first. It won't cost much, and
considering they are a consumable, I'd not sneeze at it even if they
were ok, at least you rule it out for sure.

I'd be 100 times more likely to souce a hei dizzy and coil before
touching the carb if i was in your shoes for that matter too. Almost to
a person, when I've helped someone fit hei ignition to various early
holdens and vals, they've all said 'if I'd known the difference it made,
I woudl have fucken done this first' . And I know I'm harping, it's for
a reason.

You'd probably get away with a very lax change timetable, but still.

Without being anal about it, the amt extra it's cost in fuel would have
paid for the various fixes by now, so every trip you take without
attending to it, is costing a lot. Mind you, I can't remember the last
car I had that ever had a decent or finished paint job, so I can't
fucken talk!