Big Block C20? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bsgmcc20 · 11-23-2008, 07:51 PM

Does anyone on the site have any information on Big Block GMC C-20 or Chevy C-20 Pick up trucks? I have bought my C-20 a few months prior to finding this site. I am hoping to find more info about it. If anyone can shoot me some web sites that would be helpful.

Thanks

Rookie

71swb4x4 · 11-23-2008, 07:53 PM

Here's a website with a ton of good information: www.67-72chevytrucks.com

In all seriousness, you have found the place. What are your questions specifically?

Longhorn Man · 11-23-2008, 08:55 PM

LOL!!! I was gonna say the same thing!
Welcome to the forums!
What kinda info are you looking for on your GMC C/2500?
In 68 the 396 was introduced in the C series of pick ups
69 still offered the 396, but with badges on the fenders (chevy only, GMC never got them)
70 - 72, the 396 was dropped, but the 402 was offered. Badged as a 400 (again, chevy only) on the fenders, I believe engine stickers also said 400. On the SPID it could be called a 396, 400, or 402, depending on who was typing out the info.

bsgmcc20 · 11-24-2008, 12:21 AM

Ok I should start by some back ground
CE234ZA*****

BX2 C60 F59 G50 L47 N40 T60 V46 Z62 504
A11 B85 F52 F60 G70 M49 P03 U63 Z53 Z81 629

The truck still has the protect-O-Plate that is the info brief above. The truck was owned by a older gentlemen from the factory. He drove it for 5 years and put it up do to illness in 75, driving 60K miles. it sat for 20 years till the guy i bought it off sold it to me. he drove it less than 38k. I have only put about a hundred. olive green is the color under the black. Planing to paint it "british racing green" with a white top.

L47 lists a 396 motor

I have trouble with the "parts changer" stores for basic parts listing the motor. I havent crawled into the motor compartment to get the motor vin number off the back. " I dont trust the one on the head"

question

1. should i switch out the points for a HEI distr.?
2. what mpg should i aim for with a big block the present is 8.5 ?
3. I took the Quad-jet off and put on a holley 650, any drawbacks to the change?

Thats just a start hope its not to many to start.

Thanks for the help guys.

**68350** · 11-24-2008, 01:57 AM

I would switch to hei personally.

bb mpg prolly be 8-15 depending on mods and how well it is tuned

don't know? but i do love the quadrajet!

71swb4x4 · 11-24-2008, 04:24 PM

I too would switch to HEI.
Unsure on mileage.
I like the Quadrajets. I think they are great when tuned correctly. Holley's seem to be more like a high maintenance woman.

YellowDog2 · 11-24-2008, 10:26 PM

My C20 big block gets 12-13 mpg and has the original Qjet...I plan on switching to HEI someday

bsgmcc20 · 11-27-2008, 11:50 PM

Thanks guys for the heads up and the advice.

Longhorn Man · 11-28-2008, 07:04 AM

these trucks average 10 to 12 MPG across the board
I wouldn't even consider NOT putting HEI in it.
The quadrajet (if in good shape) is better than a holley as far as daily driver/MPG/throttle response

Tx Firefighter · 11-28-2008, 07:55 AM

Remember too that a small block HEI will fit your big block too. Some folks try to charge a premium for a big block HEI, but they are the same.

glock35ipsc · 11-28-2008, 12:08 PM

Welcome to the board!

Let me add that I would also keep theQ-jet, with a caveat. Usually the one thing wrong with an original Q-jet is the primary shaft will be worn out, actually the bore in the base plate will be worn.

I started rebuilding the carb on my Dad's 69 C20 and his was worn out BAD. There is a guy in town that will bore the base plate out and install a larger shaft for $75. It's cheaper than a new carb, and when they are tuned correctly, they run like nothing else!

For basic parts, if they can't figure out "big block", go somewhere else!

**1970cstblazer** · 11-28-2008, 01:41 PM

My MPG is almost 13mpg. It increased almost 1 mpg with the addition of my tonneau cover.

bsgmcc20 · 11-28-2008, 07:41 PM

Thanks for the second opinion on the quad vs holley. A buddy just told me about the metering blocks on a holley. I am in the process of rebuilding the quad and putting it back on. The HEI change over is a sore spot for me. I want to keep the points system in it other wise it will go into the 72 c-20 with a 400 sb gear drive.

I found a dead brand new spark plug in number 8 as well as a burnt boot. I am going to look into heat shields.

as far as the mpg i was working on getting out of the 8 mpg if i could. was hoping for double digit mpg.

I do have a question what are my chances of finding a posi 3/4 ton rear in cali?

11-23-2008, 07:51 PM	#1
bsgmcc20 Im afraid of purple hangers.. Join Date: Oct 2008 Location: Central Cal Posts: 108	Big Block C20? Does anyone on the site have any information on Big Block GMC C-20 or Chevy C-20 Pick up trucks? I have bought my C-20 a few months prior to finding this site. I am hoping to find more info about it. If anyone can shoot me some web sites that would be helpful. Thanks Rookie

11-23-2008, 07:53 PM	#2
71swb4x4 Senior Member Join Date: Nov 2003 Location: Brookings, SD Posts: 10,497	Re: Big Block C20? Here's a website with a ton of good information: www.67-72chevytrucks.com In all seriousness, you have found the place. What are your questions specifically? __________________ Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs.

11-23-2008, 08:55 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Big Block C20? LOL!!! I was gonna say the same thing! Welcome to the forums! What kinda info are you looking for on your GMC C/2500? In 68 the 396 was introduced in the C series of pick ups 69 still offered the 396, but with badges on the fenders (chevy only, GMC never got them) 70 - 72, the 396 was dropped, but the 402 was offered. Badged as a 400 (again, chevy only) on the fenders, I believe engine stickers also said 400. On the SPID it could be called a 396, 400, or 402, depending on who was typing out the info.

11-24-2008, 12:21 AM	#4
bsgmcc20 Im afraid of purple hangers.. Join Date: Oct 2008 Location: Central Cal Posts: 108	Re: Big Block C20? Ok I should start by some back ground CE234ZA***** BX2 C60 F59 G50 L47 N40 T60 V46 Z62 504 A11 B85 F52 F60 G70 M49 P03 U63 Z53 Z81 629 The truck still has the protect-O-Plate that is the info brief above. The truck was owned by a older gentlemen from the factory. He drove it for 5 years and put it up do to illness in 75, driving 60K miles. it sat for 20 years till the guy i bought it off sold it to me. he drove it less than 38k. I have only put about a hundred. olive green is the color under the black. Planing to paint it "british racing green" with a white top. L47 lists a 396 motor I have trouble with the "parts changer" stores for basic parts listing the motor. I havent crawled into the motor compartment to get the motor vin number off the back. " I dont trust the one on the head" question 1. should i switch out the points for a HEI distr.? 2. what mpg should i aim for with a big block the present is 8.5 ? 3. I took the Quad-jet off and put on a holley 650, any drawbacks to the change? Thats just a start hope its not to many to start. Thanks for the help guys. Last edited by bsgmcc20; 11-24-2008 at 12:26 AM. Reason: missed some info

11-24-2008, 01:57 AM	#5
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: Big Block C20? I would switch to hei personally. bb mpg prolly be 8-15 depending on mods and how well it is tuned don't know? but i do love the quadrajet! __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

11-24-2008, 04:24 PM	#6
71swb4x4 Senior Member Join Date: Nov 2003 Location: Brookings, SD Posts: 10,497	Re: Big Block C20? I too would switch to HEI. Unsure on mileage. I like the Quadrajets. I think they are great when tuned correctly. Holley's seem to be more like a high maintenance woman. __________________ Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs.

11-24-2008, 10:26 PM	#7
YellowDog2 Registered User Join Date: Aug 2008 Location: SW MO Posts: 21	Re: Big Block C20? My C20 big block gets 12-13 mpg and has the original Qjet...I plan on switching to HEI someday __________________ 71 Custom Camper 20 air cab, 402 BB, 8-lugger 60K original miles

11-27-2008, 11:50 PM	#8
bsgmcc20 Im afraid of purple hangers.. Join Date: Oct 2008 Location: Central Cal Posts: 108	Re: Big Block C20? Thanks guys for the heads up and the advice.

11-28-2008, 07:04 AM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Big Block C20? these trucks average 10 to 12 MPG across the board I wouldn't even consider NOT putting HEI in it. The quadrajet (if in good shape) is better than a holley as far as daily driver/MPG/throttle response

11-28-2008, 07:55 AM	#10
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Big Block C20? Remember too that a small block HEI will fit your big block too. Some folks try to charge a premium for a big block HEI, but they are the same. __________________ I'm on the Instagram- @Gearhead_Kevin

11-28-2008, 12:08 PM	#11
glock35ipsc Next project: 1970 K10 Join Date: Feb 2004 Location: Fort Collins, Colo 80524 Posts: 6,684	Re: Big Block C20? Welcome to the board! Let me add that I would also keep theQ-jet, with a caveat. Usually the one thing wrong with an original Q-jet is the primary shaft will be worn out, actually the bore in the base plate will be worn. I started rebuilding the carb on my Dad's 69 C20 and his was worn out BAD. There is a guy in town that will bore the base plate out and install a larger shaft for $75. It's cheaper than a new carb, and when they are tuned correctly, they run like nothing else! For basic parts, if they can't figure out "big block", go somewhere else! __________________ *Bob* 1970 Chevy K10 LWB "Goldie" 350/TH350 *next project!!* 1981 Chevy C10 LWB 355/TH350 - My son's truck LS SWAP FORUM! Tons of LS swap info here! PLEASE CLICK HERE TO SUPPORT THE GREATEST BOARD ON THE NET! CLICK HERE FOR THE FAQ INDEX by KRUE

11-28-2008, 01:41 PM	#12
1970cstblazer All stock and staying that way Join Date: Jul 2003 Location: Elkland, PA Posts: 1,858	Re: Big Block C20? My MPG is almost 13mpg. It increased almost 1 mpg with the addition of my tonneau cover. __________________ 1970 K/5 Blazer CST 4WD, Medium Bronze, 93k ACT. miles, 350, 4 speed, rear positraction, 16.5" x 8.25" HD wheel option, tilt, tach, vacuum, AM/FM, manual throttle...Dad ordered and purchased new 4/70. Currently frame off restoration finally getting close to completion.. 1972 Cheyenne Super 20 2WD, DK Blue/White, 90K ACT. miles, 402, TH400, 4.10 open, tilt, tach, vacuum, A/C, AM/FM, manual throttle.. A mostly original paint never rusted Texas survivor... 2017 Sierra 1500 SLT 4WD, Black, 45k miles, 5.3, 6L80E, 3.42 LS, 20" polished wheels, everything but moonroof and 6.2... 2019 Canyon SLT 4WD, White, 62k miles, 3.6, 8L45, 3.23 LS, 18" wheels

11-28-2008, 07:41 PM	#13
bsgmcc20 Im afraid of purple hangers.. Join Date: Oct 2008 Location: Central Cal Posts: 108	Re: Big Block C20? Thanks for the second opinion on the quad vs holley. A buddy just told me about the metering blocks on a holley. I am in the process of rebuilding the quad and putting it back on. The HEI change over is a sore spot for me. I want to keep the points system in it other wise it will go into the 72 c-20 with a 400 sb gear drive. I found a dead brand new spark plug in number 8 as well as a burnt boot. I am going to look into heat shields. as far as the mpg i was working on getting out of the 8 mpg if i could. was hoping for double digit mpg. I do have a question what are my chances of finding a posi 3/4 ton rear in cali?



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