Answers about my 17 mpg in my Burb.

[68 Suburban]

I have had a few people PM me about how I am getting 17 mpg in my burb. I posted the following to a question on my Gas tank for sale post. I thought I would post it here so it would be easier to find:

L-48 350, HEI, Plugs gapped at 60, Timing set by ear, 1406 Edelbrock carb leaned 2 steps on the chart in the book, 5w30 motor oil, turbo 400 Trans, 3.08 rear end, Accel 2 stage oil charged air cleaner. 55 lbs of air in the tires that don't have an agressive profile.

Things that I am going to try next: 0w30 ynthetic motor oil, syntetic gear lube. Fumigating the fuel with propane. Vortec Heads.

Huck has basically the same set up as me, but has a 5 speed stick and is getting 20 mpg.

Here is a link to jku72 post. He is getting over 18 mpg:
http://67-72chevytrucks.com/vboard/s...threadid=53670


__________________

[jimfulco]

link didn't work

[68 Suburban]

The link should work now.

[jku72]

If you swap a Quadrajet in instead of the Edelbrock 1406, you will likely see better results. The Quadrajet, if it can be made to operate correctly, has small primaries, which give superior mileage than the rather large primaries on the edelbrock. The Edelbrock has a maximum of 600 CFM, the Q-jet, with secondaries, is 750, for better max power flow as well.


What exhaust are you running?

[68 Suburban]

I down sized the primary jets on my 1406. My exhaust is ram horns with regular dual and a cross over. Please dont tell me headers I absolutly will not have headers on a daily driver ever again

[jku72]

I think that the crossover helps a good deal. Did your headers leak? That is a common problem, which I think I solved in an unapproved, unscientific way.(on my longhorn) I just took the header bolts, and with a single sharp blow, hammered the threads, so that they were peened on one side. They haven't loosened in 2 years of operation. My burb has a junk puny single exhaust, and am thinking of a new system. I am thinking of trying small tube headers, crossover, and 2" twice pipes.

I mentioned the edelbrock thing because no matter how you jet it down, you can never achieve the venturi velocity with a higher primary CFM carb like the edelbrock. The drawback to the Qjet is that it can be a big Pain in the butt if it isnt right, whereas the edelbrock is way easier to work with.

Do you think a cold air induction is worth the hassle?

Any idea of the effects of using a little extra of the methanol based drygas? I'd like to see if it affects things in a positive way. I run my burb on the highway as well, and am keen to boost the mileage to the max. I even contemplate 2.76 gears, since I have a low first gear that I never use.

What Torque converter are you using? A really tight one should help a little as well.

[JimKshortstep4x4]

68 Suburban,

That is great mileage for a Burb. I can see that you are doing fundamental things to get the mileage up there and I am glad to see it working out.


My son is hoping that is Burb will get 16 mpg, (72 with 350/350 and 4x4.

Jim

[68 Suburban]

I hate headers because they do losen up, but more so, because of the under hood heat that is generated. Screws up staters, wires, my hands....lol. I really dont think the benifits are there for a daily driver. Im not driving a high performance sports car here :p

I think cooler air can help, I don't know how much though.

And yes I like the edelbrock for its simplicity. I can adjusted or change things in under 3 minutes. It is nice to be able to make these adjustments when I need to tow something.

[68 Suburban]

Originally posted by JimKshortstep4x4
68 Suburban,

That is great mileage for a Burb. I can see that you are doing fundamental things to get the mileage up there and I am glad to see it working out.


My son is hoping that is Burb will get 16 mpg, (72 with 350/350 and 4x4.

Jim

The turbo 350 should get better mpg than a turbo 400. I don't know what you will lose with the 4x4. Rear end plays a big part.

[tommie]

what type of gears do you have in the rear end for this gas mileage?

[68 Suburban]

Originally posted by tommie
what type of gears do you have in the rear end for this gas mileage?

3.08

[landon4421]

I hate headers because they do losen up, but more so, because of the under hood heat that is generated. Screws up staters, wires, my hands....lol.

68 Suburban, you could always have the headers coated. Just an idea. I am trying to get my wifes 71 C-10 350/350 to get better fuel milage also. I would like to get 18MPG. Good job. Landon

[Project1970]

0w30 in Phoenix would scare me...but then again, it is Mobil1.

You need overdrive, man.

[68 Suburban]

Originally posted by Project1970
0w30 in Phoenix would scare me...but then again, it is Mobil1.

You need overdrive, man.

Actually, 20w50 is more scary...lol

[Alexis]

have you thought about a MSD?

[Project1970]

Originally posted by 68 Suburban
Actually, 20w50 is more scary...lol

Ya gots a point there, heh. Way things are going, though, I'll have to make that 350 last at least one more year before I can rebuild it / drop in a 383 / drop in a 406...

I think the bottom end is pretty good aside from liking 20w50 to keep the pressure normal. I used to have to dump in a quart every hundred or two miles; turns out the heads must've been sucking it through the valveguides or something, because since the Vortecs, it's down to a quart every 1000 or so.

[Blue68]

I always thought that an O2 sensor in the exhaust stream (and the resultant data you can aquire) would be the way to tune for mileage, that way you can get even closer to the optimal mix for your style of driving.

[Ackattack]

That's it, I'm going to rejet my edlebrock. I've been thinking of jetting down (was thinking just one step though) since christmas. I just haven't gotten around to it. I'm getting like 11 mpg on the highway.

Good thing my truck isn't my daily driver. I'll post my results when I get them.

I too have thought of the O2 sensor to tune, both for performance and economey. It wouldn't be that hard. Hmmmm

[jku72]

A vaccuum guage works nearly as well.

[bpmcgee]

Holley has an O2 sensor that they sell as an add-on kit to their TBI systems.

The interface is very simple -- it acts as a variable resistor. Should be a piece of cake to hook it up to a small voltmeter.

Brian

[Gee_Emm]

You could probably double that number if you porpoise :p

[Baradium]

You guys ever check the owner's manual chart for oil?

For hot climates, like the desert in the summer, it calls for 20W-50, and this was for the brand new engines when these trucks were new. In fact, it says you can use straight 30W motor oil in some temps (small range). The one that gives you the best temp range is 10W-40 (covers all 10W-30 ranges because of the 10W when cold and also covers more upper temp ranges than 10W-30). With synthetics a 0W-40 or 5W-50 or so would seem to be a good combo. A thinner oil might slightly help your economy, but these engines weren't designed for it and it can hurt engine life.


I'm wanting to try amsoil in the scout once I get my dual drain plug pan in, and then in the '70 later. (amsoil gives you a longer drain interval, you just check the oil and I've heard of upwards of 100,000 miles with just changing the filter and putting that extra quart back in). I've seen reports that amsoil can reduce oil consumption too, don't see how but I'm curious about that.

[68 Suburban]

Originally posted by Baradium
You guys ever check the owner's manual chart for oil?

Since the owners manual was written 35 years ago before the advancement and research that goes into todays motor oil was known, I think I will trust what I have research about todays motor oil.

Show me one car or truck today that calls for 20w50, or even 10w40 for that matter?

You seem to be a big believer in amsoil, why not read about their 0w30?

http://www.amsoil.com/products/tso.html

[Baradium]

Originally posted by 68 Suburban
Since the owners manual was written 35 years ago before the advancement and research that goes into todays motor oil was known, I think I will trust what I have research about todays motor oil.

Show me one car or truck today that calls for 20w50, or even 10w40 for that matter?

You seem to be a big believer in amsoil, why not read about their 0w30?

http://www.amsoil.com/products/tso.html

Don't know about amsoil, I just want to try it. I've heard a lot of good things though.

The call for the lower weight oil to get higher fuel economy numbers, that is all. Show me one car or truck today that will last for as long as our trucks will. IIRC my dad's 91 Z71 w/ 350 still calls for 10W-40 in higher temps.

[68 Suburban]

Your not serious? Todays trucks and cars engines will last a lot longer than any car and truck engine from the 60's if the all conditions are the same.

You mean to tell me that you would rather run dino 10w40 rather than synthetic 5w30? If you think that 10w40 is giving you better protection, go for it.

By the way the new Corvette calls for Synthetic 5w30.