Emery:
To set the stage, I have a 78 Royale with a 403 cid engine, having
headers, Flowmaster mufflers and a 3" exhaust piping and the 3.42:1 ring
and pinion gearing. On the return trip home from the GMCMI Myrtle Beach
Convention this past March, there were four of us convoying. The other
three were all 455 cid's, with one having the Caspro Power Drive
(3.50:1) system.
On I-26 just S of Hendersonville NC, there is a long grade climb, of
several miles or more. The only one able to keep up with me was the
coach with the Power Drive, and he claimed he could have passed me.
I don't notice any difference with the 3:42:1 gearing until I'm at
highway speeds, up at the top of the torque curve. Passing ability is
definately enhanced with them as well as hill climbing ability. As
you're native to this area of Michigan, the hill on I-94 just E of the
Galesburg Exit 85, is an example of one where I no longer loose rpm's
going up as I did with the original 3.07:1.
Also, I have noticed no effect on mileage.
If I were to change the ring and pinion gearing now, I would opt for the
3.67:1 unit availble now. I know several owner's running those and they
really like them. However, I'm collecting parts now to build up a switch
pitch transmission as a prelude to replacing my original transmission.
Replacing your transmission with a switch pitch one is an option for you if
you want to keep the 2.73:1 ring and pinion gears and possibly enjoy the
features you list below in your experience with the boost in performance it
will offer you.
Paul Bartz
From: EMERYSTORA
Sent: 8/21/99 6:27 PM
Subject: GMC: Driving with a 2.73 final drive
Zack & Arch have questioned the use of a 2.73 since probably no one else
but
me has had one in their GMC. Actually it doesn't drive badly. Of
course, I
have a newly rebuilt 455 which seems to have a lot of power.
>From Santa Fe to California with my 3.07 I averaged 8.48 miles per
gallon for
about 1400 miles. This includes city driving and using the Onan a
moderate
amount. I enountered a lot of hills in Southern Calif and did quite a
bit of
city driving.
For the 2.73, I only drove about 500 miles (two tanks of gas) and got
8.75
miles per gallon. This 500 miles was from Kingman, AZ to Albuquerque, NM
on
I-40 with no city driving. This is not a very signifcant distance to
really
gauge the performance though.
The performance difference however was noticeable. The engine would lug
down
climbing hills more that the 3.07 did. Going down hills showed that
when
letting up on the pedal or even shifting into second, the engine
wouldn't
slow down the GMC as it had with the 3.07. On the level straightaway,
the
engine ran slower and quieter since it was like driving with a 12%
overdrive
on a 3.07.
I am still planning to put in a 3.07 and am trying to work with the NV
State
Attorny General's office to perhaps force the transmission shop to
cooperate.
I have found a 3.07 on a 1978 Caddillac whih the junk yard will sell me
for
$150 if I take it off myself. They also have the 425 transmission if
anyone
needs one.
I have considered going to a 3.42 Cinnibar but I haven't had problems in
the
past with my 3.07 and have even pulled a 4200 pound Jeep CJ-7 up and
down the
various mountain ranges of the west coast and all the way to New England
last
summer. I slow down some on hills but not to the point where it is
really a
major problem. I suspect that it is of more advantage to someone that
has a
403. Perhaps those that have made this swap might comment on mileage,
performance, and general feeling about their modification.
Emery Stora
77 Kingsley
Santa Fe, NM
To set the stage, I have a 78 Royale with a 403 cid engine, having
headers, Flowmaster mufflers and a 3" exhaust piping and the 3.42:1 ring
and pinion gearing. On the return trip home from the GMCMI Myrtle Beach
Convention this past March, there were four of us convoying. The other
three were all 455 cid's, with one having the Caspro Power Drive
(3.50:1) system.
On I-26 just S of Hendersonville NC, there is a long grade climb, of
several miles or more. The only one able to keep up with me was the
coach with the Power Drive, and he claimed he could have passed me.
I don't notice any difference with the 3:42:1 gearing until I'm at
highway speeds, up at the top of the torque curve. Passing ability is
definately enhanced with them as well as hill climbing ability. As
you're native to this area of Michigan, the hill on I-94 just E of the
Galesburg Exit 85, is an example of one where I no longer loose rpm's
going up as I did with the original 3.07:1.
Also, I have noticed no effect on mileage.
If I were to change the ring and pinion gearing now, I would opt for the
3.67:1 unit availble now. I know several owner's running those and they
really like them. However, I'm collecting parts now to build up a switch
pitch transmission as a prelude to replacing my original transmission.
Replacing your transmission with a switch pitch one is an option for you if
you want to keep the 2.73:1 ring and pinion gears and possibly enjoy the
features you list below in your experience with the boost in performance it
will offer you.
Paul Bartz
From: EMERYSTORA
Sent: 8/21/99 6:27 PM
Subject: GMC: Driving with a 2.73 final drive
Zack & Arch have questioned the use of a 2.73 since probably no one else
but
me has had one in their GMC. Actually it doesn't drive badly. Of
course, I
have a newly rebuilt 455 which seems to have a lot of power.
>From Santa Fe to California with my 3.07 I averaged 8.48 miles per
gallon for
about 1400 miles. This includes city driving and using the Onan a
moderate
amount. I enountered a lot of hills in Southern Calif and did quite a
bit of
city driving.
For the 2.73, I only drove about 500 miles (two tanks of gas) and got
8.75
miles per gallon. This 500 miles was from Kingman, AZ to Albuquerque, NM
on
I-40 with no city driving. This is not a very signifcant distance to
really
gauge the performance though.
The performance difference however was noticeable. The engine would lug
down
climbing hills more that the 3.07 did. Going down hills showed that
when
letting up on the pedal or even shifting into second, the engine
wouldn't
slow down the GMC as it had with the 3.07. On the level straightaway,
the
engine ran slower and quieter since it was like driving with a 12%
overdrive
on a 3.07.
I am still planning to put in a 3.07 and am trying to work with the NV
State
Attorny General's office to perhaps force the transmission shop to
cooperate.
I have found a 3.07 on a 1978 Caddillac whih the junk yard will sell me
for
$150 if I take it off myself. They also have the 425 transmission if
anyone
needs one.
I have considered going to a 3.42 Cinnibar but I haven't had problems in
the
past with my 3.07 and have even pulled a 4200 pound Jeep CJ-7 up and
down the
various mountain ranges of the west coast and all the way to New England
last
summer. I slow down some on hills but not to the point where it is
really a
major problem. I suspect that it is of more advantage to someone that
has a
403. Perhaps those that have made this swap might comment on mileage,
performance, and general feeling about their modification.
Emery Stora
77 Kingsley
Santa Fe, NM
