The Stovebolt Site Forums The Shop Area Engine Shop Ol 292 was smoking.....

In a good way, I needed to make a trip to Seattle today {I am in Portland OR..160miles}.
I had to take the 68 as i was to haul home quite a load, I took the truck only dreading what may fall off/break or implode on the trip. (First real road trip since I bought the truck)

Well the trip was very noisy as the roar from the cracked exhaust maifold got louder at about 65, as the truck bombed down I-5 it seemed to run better...70,75,even a burst or two to 80. The gas milage was not the best but I got up there and back on 1 3/4 tank not too bad I guess.

But the 292 was very happy at about 70mph, this has made me re think my v-8 swap.
I am leaning to a I6 rebuild now...humm we shall see.

-a happy convert to the 292

Whoa! 75-80 mph in a 20 series pickup...?!?!?! Assuming your rear end is stock you had to be turning around 4000 rpms!

If you don't have overdrive or a low 3-something rear end I don't recommend too many trips up in the high altitude rpms with an old 292. I won't even turn those kinds of revs with my newly rebuilt 292 that has light performance mods to it.

From what I've learned here running excessively high rpms for extended periods of times leads to connecting rod stretch, thereby shortening engine life. Not to mention the stress on a 73 pound crankshaft to keep up that many rpms.

Keep it around (or under) 3k and the engine will last you exponentially longer. What is your rear end ratio?

As an example my engine is happiest around 70 mph in overdrive. That's about 2300 rpms. At 80 it's still not complaining too badly, but turns just over 2600 rpms. This starts getting just out of the ideal cruise rpms recommended by the cam manufacturer and the engine begins getting fuel wasteful. And I've added a larger 4 barrel carb, exhaust headers, aftermarket cam and a more efficient HEI ignition.

-ftyler

I have no idea if anyone has ever changed anything in this truck. I would say that it is all stock.
The truck has 89k original miles on it and i got it from the second owner.
I dont think it was buzzing at 4000 rpm, but i dont have a tach...The truck wasnt struggling either it seemed real happy at 70.
The tranny is just a 4 speed [1st-granny] so I dont know about what the gearing might be.
Maybe I will go get a tach today.

A 68 C20 with a granny low 4 speed would probably have no higher than a 3.73 rear gear stock. The 20 series is a 3/4 ton truck (I believe) so it wouldn't be geared for highway driving.

I have a 3.73 in my 66 half ton. Before I swapped out the straight drive 3 speed for an overdrive it did anything but cruise at 70 mph, turning about 3100 rpms.

Good luck.

He should have 4.57 gears in a 3/4 ton of that vintage. With 30" tires, 70 mph is 3580 rpm, which is at the top of the range for the newer six.