Author Topic: 1977 C20 454  (Read 2808 times)

Offline cffisher

  • Newbie
  • Posts: 23
  • Newbie
1977 C20 454
« on: October 10, 2019, 04:56:16 PM »
As above 1977 C20 454 100230 miles 400 trans 3.21 rear 265/75/R16 tires. I'm pulling a 30' 8K# fifth wheel. Problem it doesn't like hills. It seems to not have the power I'd expect on hills. It is fine on flat ground. Any suggestions? I thinking cam and intake but not sure which ones.
Retired and loving it.

Offline VileZambonie

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 18979
Re: 1977 C20 454
« Reply #1 on: October 10, 2019, 06:39:53 PM »
I'd say you need at least 3.73:1 also is it downshifting?
,                           ___ 
                         /  _ _ _\_
              ⌠¯¯¯¯¯'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline JohnnyPopper

  • Senior Member
  • ****
  • Posts: 2526
  • Old Goof
Re: 1977 C20 454
« Reply #2 on: October 10, 2019, 07:02:04 PM »
I had a '73 version of that same truck, and 5th wheel.

I replaced the cam with what I remember as an 'rv' cam, and it made a huge difference!

Between 2500-3500 RPM it was like nothing was behind me.

Curious about VZ's question on downshifting.

On serious grades I would manually shift it and keep it in that RPM range.

Full Disclosure: I had a water injection system on it too, which if you know about, are very effective when under load.

However,

It's the reason why I had the opp to change out the cam.

I had it parked on a slope and it filled up #2 cylinder. "Hydolock" is a ugly thing...  :o
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Stewart G Griffin

  • Senior Member
  • ****
  • Posts: 3324
Re: 1977 C20 454
« Reply #3 on: October 12, 2019, 11:32:55 AM »
i was looking at the stats:  i think you got 370 ft/lbs at 2800rpm.

i think my approach would be to check, and if possible, advance timing a little.

Then, i think you need at least 3.42 to 3.73 gear.  Since 3.42 is so close to  3.21, then let's go  with 3.73 to 4.11.    Then get a Gear Vendor's overdrive/underdrive unit.  It's $3000, but that's still much cheaper than a new truck.

i would also want to go with dual wheels on the rear axle with 8K, but that's just me.........


Offline Irish_Alley

  • Tim
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 13319
  • Family is not an important thing. It's everything.
Re: 1977 C20 454
« Reply #4 on: October 12, 2019, 01:23:58 PM »
Check the specs on the gear vendor. Pretty sure they have a up/tq limit and a gcwr.
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Stewart G Griffin

  • Senior Member
  • ****
  • Posts: 3324
Re: 1977 C20 454
« Reply #5 on: October 13, 2019, 04:14:28 PM »
Check the specs on the gear vendor. Pretty sure they have a up/tq limit and a gcwr.

i think up to 1200hp and at least 25,000 lbs. gcwr:

https://www.gearvendors.com/commercial.html

Offline JohnnyPopper

  • Senior Member
  • ****
  • Posts: 2526
  • Old Goof
Re: 1977 C20 454
« Reply #6 on: October 13, 2019, 05:36:54 PM »
I've got some OEM Dually fenders if you choose to go that route!

Used but in great shape. 600.00 for both, you cover shipping from 92111.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Stewart G Griffin

  • Senior Member
  • ****
  • Posts: 3324
Re: 1977 C20 454
« Reply #7 on: October 13, 2019, 08:15:57 PM »
I've got some OEM Dually fenders if you choose to go that route!

Used but in great shape. 600.00 for both, you cover shipping from 92111.

i'd love to put a one-ton/3/4 ton springs and rear axle on the truck as well as dually fenders, the west coast mirrors and cab marker lights  :)   But that's for later.......
« Last Edit: October 13, 2019, 08:17:36 PM by Stewart G Griffin »