In a post last Saturday, Arch said "--Thats why I cant understand why
nobody wants to talk gears". I agree and have some comments, ($0.03) which
might provoke some responses from the collective brain trust which is
"GMCnet". Hopefully, even though I subscribe to the "digest" and am
usually a bit behind the curve, my post will still be relevant when it
makes it to GMCnet.
I believe there's more interest in this subject than Arch thinks. It's just
that most are either waiting for someone to post the answer, like me, or
they already know it and haven't noticed that others are asking. I suspect
the lack of consensus as to the "best" ratio is because the wide variation
in preferred driving speeds and typical driving terrain results in many
"right" answers. That said, it seems to me that once the decision has been
made to make a change, deciding on the new ratio should be pretty straight
forward.
The first decision to be made is where to make the change. New drive
sprockets, transmission gears, final drive gears and many combinations of
these are all available to produce a very wide range of drive ratios.
Personally, I agree that the best place to make the improvement is the
final drive with the tranny being a good second choice. Of course if a
failure provided the "opportunity" to upgrade, changing the gearing in the
failed part would be the likely choice.
IIRC these engines, if not modified with different cams, etc., produce
their most efficient power at about 2800 rpm,. So, depending on driving
patterns, picking the new ratio should be simply a matter of numbers.
We like to cruise at 60 on the flats, and we pull quite a few grades since
we live in the west. So I will choose whatever gears will come the closest
to 2800 rpm @ 60 mph in Drive, and 2800 @ 50 mph pulling grades in "S".
Since no gear set is likely to produce both ideals, selecting the set of
gears which produces the closest numbers is the only decision left to make.
When in drive, we're much more likely to be below 2800 (lugging?) than
above it, so if I can't find a gear set that hits the 2800 @ 60 target,
I'll want to miss on the low side. On the other hand, when pulling grades
in 2nd, we're more likely to be above 2800 (over revving?) so I'd be better
off missing on the high side, say 2800 @ 55. And since lugging is less
likely to cause damage and is easily corrected by up-shifting, and
over-revving can occur easily when pulling grades, I'll choose the set that
gives me the closest to 2800 @ 50 in 2nd.
Once I have my new digital tach installed, a few readings at speed will
tell me for sure what gears are in there now, and what ratio would get us
the closest to the ideals. My guess, at this point, is that I'll want
something like a 3.5 or 3.7 final drive. Complicating this whole issue for
me is knowing how many 10,000 ft. passes we've been over with, presumably,
a 3.07 final. Hmmmm
I hope this ramble didn't bore too many, and that someone will let me know
if I'm about to make a mistake.
Oh yea, I still want to hear some thoughts on the possibility that low
power steering pump output may be a secret and significant contributor to
"wander" and "wiggle".
TIA
Dave (& Dege), '76 Royale, Santa Barbara, CA
nobody wants to talk gears". I agree and have some comments, ($0.03) which
might provoke some responses from the collective brain trust which is
"GMCnet". Hopefully, even though I subscribe to the "digest" and am
usually a bit behind the curve, my post will still be relevant when it
makes it to GMCnet.
I believe there's more interest in this subject than Arch thinks. It's just
that most are either waiting for someone to post the answer, like me, or
they already know it and haven't noticed that others are asking. I suspect
the lack of consensus as to the "best" ratio is because the wide variation
in preferred driving speeds and typical driving terrain results in many
"right" answers. That said, it seems to me that once the decision has been
made to make a change, deciding on the new ratio should be pretty straight
forward.
The first decision to be made is where to make the change. New drive
sprockets, transmission gears, final drive gears and many combinations of
these are all available to produce a very wide range of drive ratios.
Personally, I agree that the best place to make the improvement is the
final drive with the tranny being a good second choice. Of course if a
failure provided the "opportunity" to upgrade, changing the gearing in the
failed part would be the likely choice.
IIRC these engines, if not modified with different cams, etc., produce
their most efficient power at about 2800 rpm,. So, depending on driving
patterns, picking the new ratio should be simply a matter of numbers.
We like to cruise at 60 on the flats, and we pull quite a few grades since
we live in the west. So I will choose whatever gears will come the closest
to 2800 rpm @ 60 mph in Drive, and 2800 @ 50 mph pulling grades in "S".
Since no gear set is likely to produce both ideals, selecting the set of
gears which produces the closest numbers is the only decision left to make.
When in drive, we're much more likely to be below 2800 (lugging?) than
above it, so if I can't find a gear set that hits the 2800 @ 60 target,
I'll want to miss on the low side. On the other hand, when pulling grades
in 2nd, we're more likely to be above 2800 (over revving?) so I'd be better
off missing on the high side, say 2800 @ 55. And since lugging is less
likely to cause damage and is easily corrected by up-shifting, and
over-revving can occur easily when pulling grades, I'll choose the set that
gives me the closest to 2800 @ 50 in 2nd.
Once I have my new digital tach installed, a few readings at speed will
tell me for sure what gears are in there now, and what ratio would get us
the closest to the ideals. My guess, at this point, is that I'll want
something like a 3.5 or 3.7 final drive. Complicating this whole issue for
me is knowing how many 10,000 ft. passes we've been over with, presumably,
a 3.07 final. Hmmmm
I hope this ramble didn't bore too many, and that someone will let me know
if I'm about to make a mistake.
Oh yea, I still want to hear some thoughts on the possibility that low
power steering pump output may be a secret and significant contributor to
"wander" and "wiggle".
TIA
Dave (& Dege), '76 Royale, Santa Barbara, CA
