Re: What kind of gas mileage do you get with your 67-72?
 

The more I think of it, I didn't go to actual MAX, since I stopped at 2.5k. It is not that the canister is completely trashed/non-operational - it is just does not keep a vacuum when I applied my pump.

As for my cruising speed. 2.5 is about 60-ish, then 70 a bit below 30k if I recall correctly. I really don't see the point trying to cruise to 75~80. 95% of all my driving has been around town - which around here there are lots of 60 MPH roads (non-interstate). To me, it is a lot more fun going the "back way" than get on I35 in my truck.

So it seems time for some more flashy light and perhaps a friend to work the peddle for me :)

Re: What kind of gas mileage do you get with your 67-72?
 

I feed I have eaten way to many replies in this tread and have gone off topic way to much.

I have created my own thread, Timing & Gas Milage.

Hopefully you guys that have helped me so far will pivot there as I update the thread :-)

Re: What kind of gas mileage do you get with your 67-72?
 

Okay, after changing out to New Pertronix Flame-Thrower II, New Flame-Thrower Coil & Wires with 12° initial timing, ~900 RPM idle (Park) and ~640 RPM idle (Drive). Oh and I am using manifold vacuum advance, not ported.

60 Mile test drive, great mixed city and highway (Tx Farm Roads up to 70 MPH).

15 MPG!

SBC 350/TH350 and 3.07 rearend.

Re: What kind of gas mileage do you get with your 67-72?
 

update.

So after using over a half tank (well by the gauge) and adjusting the idle up for what will likely be summer "AC Idle" @500 in Drive - I am getting 13 MPG. This is still 80% if not more highway (re: Tx Farm Roads) driving. My 1st outing with the AC was not so happy, I had to keep putting her in neutral, so I upped it. I'd say it's 700~750 in neutral now. This half tank also wasn't me trying to get the best possible MPG. I wasn't dogging it all the time but I was far from being a grandpa too. Nothing like going WOT to beat a few yellow lights or passing some slow poke ;-)

I guess that is good?

PS: Last night on our drive I actually ended up being behind a 68 or so C10 on the Devil's Backbone Scenic Drive. He was very low to the ground and was either a dark blue or perhaps even purple - I couldn't tell as it was dark. Though I could tell he had the same LED backlights as me! I was really hoping he was going to stop at the bar or the rest stop but turned on a secondary road. I thought it would be weird if I had followed him to a house LOL

Re: What kind of gas mileage do you get with your 67-72?
 

The 350 4 speed Blazer would avg. 15MPG. The 402 TH400 4.10 truck gets 12 MPG no matter if empty or loaded.

Re: What kind of gas mileage do you get with your 67-72?
 

My 71 has a bone stock 350/350/Quad. On flat land at 60 MPH It gets 10 MPG.
On a downhill at 60 MPH it gets 10 MPG.
Against the wind at 60 MPH it gets 10 MPG.

My 72 is also a bone stock 350/350/Quad. Same thiAttachment 2095412ng.

Re: What kind of gas mileage do you get with your 67-72?
 

When fuel mileage doens't change depending on load or speed it is indicative of under gearing.
Exactly why a modern overdrive transmission works so well in these trucks.
I was able to get a 30% improvement with a .70 overdrive ratio in a 700R4/4L60. The 6L80 have even higher ratios with double overdrive, both 5 and 6 are overdrives, with the final ratio in Sixth is 0.67.

The wide overall ratio spread of 6.04:1 allows a “steep” first gear, as well as a very “tall” overdrive top gear for low-rpm highway cruising.

The trend is for higher differential ratios and lower first gear. This tread is nothing new and has progressed since the power-glide days.

Also a another reason to switch to a 4L60. The lower first gear if good for performance.

When in doubt "switch it out". :)
Rick