1972 C20 build and adventure thread

[FLYNAVY30]

oooooo that's tempting. I really wish I had a place to put it.

[Mike C]

Glad to see you working on the 'Burb again. I know how long you battled those Corvette brakes!

[FLYNAVY30]

Originally Posted by HO455

Sounds cool! And I'm digging the plaid seats.


I just ran across this.

https://richmond.craigslist.org/pts/...102851173.html

I keep looking back at that ad....two questions:

1. what is the difference between the K10 and K20 frame/suspension?
2. what is the difference between the K10 truck frame and the K10 Suburban fame?

[Mike C]

I think the primary difference in the 10/20 frames was slightly thicker metal on the K20/C20 frames. There were differences in ball joints and other weight bearing parts.

I would have no qualms about swapping in a K10 frame with K20 drivetrain components and don't feel you would be giving up any capacity.

'72 frames are unique on the Blazer and Suburban in that the rear bumper mount is integral to the frame while it has never been on the truck nor was it that way on the 71 and earlier people movers.

[FLYNAVY30]

Originally Posted by Mike C

I think the primary difference in the 10/20 frames was slightly thicker metal on the K20/C20 frames. There were differences in ball joints and other weight bearing parts.

I would have no qualms about swapping in a K10 frame with K20 drivetrain components and don't feel you would be giving up any capacity.

'72 frames are unique on the Blazer and Suburban in that the rear bumper mount is integral to the frame while it has never been on the truck nor was it that way on the 71 and earlier people movers.

Thanks!

[HO455]

In addition to what Mike C said I believe that some of the riveted stiffeners on the frame are slightly different when going up in through the load ranges.
The picture shows what the frame at the bumper rear mounts on my Burban looked like.

[FLYNAVY30]

Thats helpful, thanks!

[FLYNAVY30]

Finally got around to installing my Dapper Lighting "OE7s". I bought these guys over a year ago when they had an introductory sale, just never got around to installing them. I've always liked their products, but never the look. They finally started offering an OE look lense with the same quality LED set up, so I snagged a pair. As you can see, you need to hog out the buckets just slightly....about 1/16 of an inch all the way around. (Please dont judge that pic....I cleaned it up with the dremel to make it perfectly round again, and then hit it with chassis black.) Ill try to get some night pics up later. The cutoff is the best I've seen from an aftermarket LED, the low beams are excellent...probably only exceeded by the JW Speaker lights, and the high beams are equally good. Overall, I'm very impressed, and this was a significant upgrade from the LED lights they sell at LMC.

[FLYNAVY30]

#$%!& lesson learned....I need to take all pics I intend to upload to this forum as a landscape shot.

[gcburdic]

Great transformation here! Nice work!

[Mike C]

looks great!

[FLYNAVY30]

Thanks, I'm really happy with them. If you look closely, they have an integrated turn signal as well. I'm thinking about wiring that to the front bumper turn signals, and using the opening in the bumper for a set of high output fog lamps.....if I can find something that will

1. Fit in the opening without cutting the bumper

2. Doesn't look out of place....some of these modern fog lights look like something out of a Michael Bay movie.

[Mike C]

That's a great idea. I've thought about putting a 71-72 Chevy bumper on my Jimmy to have a place for driving lights. It just covers a little more of the turn signals that are in the lower grill.

[FLYNAVY30]

Heres a pic of the cutoff if anyones interested....they really are a nice set up for the price.

[FLYNAVY30]

Mid summer Suburban update:

I've been daily driving the Suburban all spring/summer. With the COVID chaos, we haven't gotten much traveling in, but its afforded plenty of time to take care of a bunch of little things.

I started with cleaning up and rerouting a lot of the wiring in the engine bay. This was the first car I had ever completely wired, and while its functional, its not as clean as it could be. The addition of the Holley EFI after the car was already wired also added to the chaos. Its still far from perfect, but clean enough under the hood. I'll probably rewire the entire car a final time when I pull the body off to fix the rust...I'd like to try my hand at building a mil-spec "inspired" harness....not necessarily full mil-spec with the required strain relief, seals, etc. but something clean, with the "cannon-plug" style connectors you find in our aircraft. Anyway, here's the pics of the cleaned up engine bay:

[FLYNAVY30]

Next up was to address the brakes. The Wilwood swap a few years ago was a definitive upgrade, but the pedal feel was never what I wanted...the truck would stop fine, but you always needed far more effort than you would expect for a given level of stopping power...almost like an unboosted brake set up. I posted a more thorough thread here:

https://67-72chevytrucks.com/vboard/...d.php?t=805668

...but the short version of the story is that I swapped out the factory single diaphragm booster to a dual diaphragm booster, along with some Wilwood "E compound" pads and the additional boost along with the more aggressive brake pads have improved things drastically. It brakes like a new truck. My wife's biggest complain was always how much effort the brakes took (she's 115 lbs, soaking wet, in a denim jump suite) and even she commented the last time she drove the truck how much better the brakes felt. I did need to modify the linkage and bracket slightly, but it did not require drilling any additional holes in the fire wall....again, see the full thread above for complete details.

[FLYNAVY30]

And most recently, round 4 of my battle with the exhaust on this truck. After the LS swap, I started out with a set of Doug Thorley headers, as they were the only ones (at the time) that would clear the LS mounts needed in the 3/4 ton chassis. I used a Flowmaster exhasut kit that utilized a cross over and 40 series mufflers. I never liked those mufflers....they sounded good at idle, but droned something fierce on the highway.

Round 2 of my battle was to remove the mufflers and tail section for a set of Borlas and some turn downs in front of the axel. I decided to get rid of the over axel and tail pipes because it just complicated maintenance as it pertained to the gas tank, suspension, rear differential, etc. And I never thought the pipes sticking out behind the wheels looked particularly good anyway. The Borla's sounded great on acceleration, but they were just too loud across the RPM range.

Round 3 saw me pull the Borlas and install a set of Flowmaster Super HP-2 mufflers....the longest ones they had available, to which, I welded on a set of turn down tips. This was by far, the best the set up had sounded. Start up and idle had a proper growl, without being obnoxious. WOT was absolutely perfect. The problem was that at highway cruising RPM, there was still this 1000 PRM band of resonance and volume between 2000-3000 RPM. I've been running this set up for 2 years now, and maybe I'm getting old, but it was time to find something better...we drive this thing enough that its important to be able to carry a conversation at cruising speed.

Round 4 was completed today. I'm running a set of 14x9 MagnaFlow mufflers on my Corvette, and both the wife and I have commented on how good they sound on acceleration, and at idle, but how unobtrusive they are at highway speeds....and with a 4 speed and 3.73 gears, that car is turning 3-3.5K RPM on the highway. So I ordered up as set of 14x9 MagnaFlows for the truck, a set of 90 degree turn down extensions, and two hangers from Deeds Engineering. These hangers are terrific....a little spendy, but they are the nicest set up I've seen that doesn't require welding...and they are infinitely adjustable.

After getting everything buttoned up and installed, I fired the truck up and took a quick test drive around the neighborhood. Initial impressions:

1. Start up....sounds exactly like the Super HP-2s....people are going to know who you are, but in a good way.

2. Idle....initially, this is the biggest draw back. From outside the truck, it sounds great. The chop of the cam is exactly what you want to hear. But the resonance in the truck hits the exact pitch in your ear drum that would cause a massive head ache within 15 minutes.

3. Cruise...absolutely perfect! As soon as you get above 1000 RPM, the resonance goes away, and the exhaust tone virtually disappears. This is absolutely the muffler for highway cruising!

4. WOT...sound is exactly what you would want...loud with no resonance. Aggressive but refined.

So in the end, I'm still reserving judgment on the Magna Flow mufflers...I'm hoping that the resonance and tone at idle will mellow with use. I also think that I may shorten the tail pipe extensions and turn them to 90 degrees, pointed straight out the side of the truck as opposed to down at a 45...I think some of the resonance at idle may be sound wave bounce back off the street. More to follow.

[HO455]

Have you looked into Helmholtz chambers or J pipes? GM used them on 68 GTO Ram Air II cars. Lots of information on the web about them.

https://www.eng-tips.com/viewthread.cfm?qid=427233

[FLYNAVY30]

very interesting....going to need to do some more reading. Its also interesting the difference in sound between the LS motor in the Suburban and the SBC in my Corvette. I'm running the exact same mufflers on both and they sound drastically different....although its not a true apples to apples comparison as the Suburban has a crossover just after the headers and the Corvette does not.

[Mike C]

Cool progress. Even a balance tube can help with the droning if you don't have one. Made a huge difference on my '84 Corvette.

[LockDoc]

-
"J" pipes cured my drone. Now my wife will ride with me....

Here is a picture and a chart for length calculation. Installed right behind the mufflers. The end of the "J" pipe is just capped.

LS1 engine with Hooker cast iron headers, full length exhaust & series 40 knockoffs.

LockDoc

[FLYNAVY30]

Thanks! The irony is that now, my drone is only below 1000RPM....as I start moving, it instantly goes away. The rest of the RPM range is perfect...which is what leads me to believe its partially reverberation off the ground.

[LockDoc]

Originally Posted by FLYNAVY30

Thanks! The irony is that now, my drone is only below 1000RPM....as I start moving, it instantly goes away. The rest of the RPM range is perfect...which is what leads me to believe its partially reverberation off the ground.

That is very possible.

LockDoc

[HO455]

Here a link to a pro-touring thread with a bunch links on J-Pipes.

https://www.pro-touring.com/threads/...-Exhaust-Drone

[FLYNAVY30]

Thanks! Lots of reading for this morning's coffee!