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73-87 Chevy _ GMC Trucks => Performance => Topic started by: cffisher on October 10, 2019, 04:56:16 PM

Title: 1977 C20 454
Post by: cffisher 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.

Title: Re: 1977 C20 454
Post by: VileZambonie on October 10, 2019, 06:39:53 PM

I'd say you need at least 3.73:1 also is it downshifting?

Title: Re: 1977 C20 454
Post by: JohnnyPopper 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

Title: Re: 1977 C20 454
Post by: Stewart G Griffin 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.........

Title: Re: 1977 C20 454
Post by: Irish_Alley 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.

Title: Re: 1977 C20 454
Post by: Stewart G Griffin on October 13, 2019, 04:14:28 PM

Quote from: Irish_Alley 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.

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

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

Title: Re: 1977 C20 454
Post by: JohnnyPopper 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.

Title: Re: 1977 C20 454
Post by: Stewart G Griffin on October 13, 2019, 08:15:57 PM

Quote from: JohnnyPopper 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.

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.......