Whos got the best gas mileage combo

[man-a-fre]

Going to put together an engine for my 72 blazer with a 350 th350 3.73 gears 33.12.50 15 tires and am only getting 14 mpg now want to increase it.What are you guys getting with your blazers and whats in them for a combination.

[Jtrux]

You're doing pretty good right now, I got about the same with mine with a 350, sm465, cheapo 32's and 3.07's. If you wanted to get a little better mileage you could do all sorts of things (overdrive tranny, smaller tires with 3.07's, diesel swap, fuel injection...)

You see where i'm going, but the main thing is this, how much is it gonna cost you to get just a little better fuel economy??? Sure you'll save money at the pump but if it costs 3 grand then is it really worth it?

I think your best bet if you really want better mileage is to look into an overdrive tranny (700r4 would be your best bet) and a throttle bottle injection system. This would get better mileage and not cost a ton but it won't really be that cheap. If you're pretty mechanically inclined you will save quite a bit of money doing this yourself.

Oh and I would think this cam would be an all around decent cam if mileage is your main concern.

[turp mcspray]

If I can get 14mpg I'll be doing cartwheels across the gas station lot!

[Dusty71blazer]

14 isn't anything to complain about- 40 years of technology doesn't have the new full size SUVs doing much better

[cleszkie]

I just finished installing my junk yard find Gear Vendors overdrive unit in my 72Blazer with 350/350TH/NP205 combo with 4.10 gears and 35x12.50x16.5 tires. Took it out on the highway for a test run and what a difference! 2500 at 70-75 mph. I need to take my GPS with me next time so I can get a more accurate speed (my speedo is not calibrated). I will let you know what my gas mileage is once I've determined it. BTW, the overdrive is 22%.

[ryanbenn1207]

right now i got a 2 barrel carburetor on a 350, im baout to add a gas misting trick to increase mileage as well, if it works ill tell you guys how to do it.
I have 3.73 gears in the axle, so im curious to what i get with the 2 barrel, then i might slap a 4 barrel on as well for comparison. and im going to be putting in very small steel mesh inbetween the carb plates when the gas enters the screen it starts to mist.

[vtblazer]

First thing to remember is that your pushing a huge brick down the road, the frontal offering may as well be flat like a sheet of plywood.

That being said, when fuel mileage jumped up in the early 80's it was due mainly to over-drive transmission's, not the introduction of fuel injection alone.

Then comes fuel injection, a better fuel management system will help in many more ways than just increased mileage.

Now...consider gearing, where do you do the most driving and where is your engine running 'happy'. (what rpm)

Okay, then there's tires...bigger means more turning mass & weight.

It's a long list and a rather complicated formula to figure out but IMO, the first step to better fuel mileage is getting an overdrive & slowing down those RPM's without sacrificing torque.

[ryanbenn1207]

I am guessing im going to need to get a new transmission that has a overdrive gear to even get too that point correct?

[bama51]

I would love to hear mileage estimates from some of you running GenIII/IV engine/tranny combos. I was guessing with the right gear ratio, you could possibly get 18-20 mpg, but no one has chimed in yet.

[Tom Vogel]

See #5 above. The GV gives you six forward speeds and is unbreakable. ITs WORTH the $$$ save your money if you need to.

[Cap'n Hook]

Originally Posted by Dusty71blazer

14 isn't anything to complain about- 40 years of technology doesn't have the new full size SUVs doing much better

Ya, that's why my 2005 suburban gets hand-calculated average of almost 20 mpg (19.8)! Of course it's 90% hwy mileage, but it's still 180% better than my '72 Jimmy.

14 is great! I get 9/11, city/hwy, with my 350/350/np205/33x12.50 combo. I'd also be interested in the gear vendor unit. Will it fit behind the np205 on my Jimmy?

[Dusty71blazer]

Originally Posted by Cap'n Hook

Ya, that's why my 2005 suburban gets hand-calculated average of almost 20 mpg (19.8)! Of course it's 90% hwy mileage, but it's still 180% better than my '72 Jimmy.

For every 1 out there claiming 20 mpg there are 3 complaining that they can't get 15. Not saying that you aren't getting 20, just that it is rare. Even at 20 that's only 6 mpg better than man-a-fre & your sub has fuel injection, overdrive, etc... still nothing to brag about.

[ryanbenn1207]

Has anyone atempted steam injection? I have been considering doing this for some time, theres a few things you have to do. i could understand cold water injection it would cool the gas down before being burned but steam seems to be the opposite direction. so just some ideas i have gathered in the past.

[71GMCSWEDE]

14!? lol i get 12 and i have a 350 3 spd wit a 4 barrel

[Big J]

Mine doesn't use any gas at all, or hasn't yet anyways.
Maybe eventually.

[Firebirdjones]

Considering your combo, 14 isn't bad.

I'm running a 355/350 turbo with 3.07's and 33 inch tall tires. With a 750 holley on top and a mild crane cam to boot.
I'm getting 13 mpg in stop and go driving, and it has to work pretty hard. I haven't hit the highway yet with the changes I've made, but considering the pickup in mileage from city to highway it made in the past, it should be in the 15-16 mpg range on the highway.
With this combo I can cruise at 70 mph at only 2400 rpms, so it's pretty comfy. I'm not complaining.

Considering most all of the new SUV's are lucky to tickle 14 mpg with overdrives and fuel injection I'd say we are all doing pretty darn good.

My 79 1 ton pickup with a 454/400 turbo and 3.73 gears, weighs 5,300 lbs. and has 30 inch tall tires gets 14 mpg highway. I can pull a 10,000 lbs. enclosed trailer and still get 11 mpg. It spins 2,800 rpms at 65 mph.
Pretty damn good for what it is. Considering my father has a 3/4 ton 2003 pickup with a fuel injected 6.0 and 4L80E overdrive and he only gets 13 mpg empty

[Firebirdjones]

Originally Posted by bama51

I would love to hear mileage estimates from some of you running GenIII/IV engine/tranny combos. I was guessing with the right gear ratio, you could possibly get 18-20 mpg, but no one has chimed in yet.

I'm looking to do that very same thing. And I think it's easily doable. I tune my LSx 4th gens with software, as well as played with my fathers 03 6 litre pickup. The factory tunes suck to say the least. Especially the trucks with their timing tables in the negative catagory It's one reason why mileage sucks on them. But GM has to keep warranty claims at bay, and considering what most trucks go through, (towing and hauling) it's just a safety precaution.

I've got our 4th gen camaros getting 30 mpg highway, and 22-23 around town. Stock it was more like 26/19.
I posted what I'm getting in our blazer with the current combo above, that matches what new SUV's get, and I'm doing it with 40 year old technoligy. With the 6.0 swap along with an overdrive I'm looking to better that.
With a few tuning sessions it should be no sweat.

[Blazediggity]

14mpg must be nice... I thought i was doing good at around 10mpg... 3.73's/SM465/np205/33inch tires/355ci, 750carb/ tri-y headers. I wish i could pull 14+mpg

[chevy2racr]

i get like 7MPG oh well its too much fun to let it sit!

[runpasthefence]

LQ9 - 4L80 - 3.42 (I think)

The only time I checked was when I drove her from Charleston SC to Atlanta. Left at rush hour on a Friday so I sat in traffic in both Charleston and Columbia SC. Avg moving speed was between 75-90 mph...aggressive passing...a couple of runs to 100. Averaged 18.5mpg. I'd imagine a moving avg at highway speed would be pretty close to 20mpg. I dig it.

[Firebirdjones]

Originally Posted by Blazediggity

14mpg must be nice... I thought i was doing good at around 10mpg... 3.73's/SM465/np205/33inch tires/355ci, 750carb/ tri-y headers. I wish i could pull 14+mpg

It should do better. That's nearly identical to my current setup other than the gears. And 3.73's are pretty mild. Technically you should be beating me in around town mileage, as my truck has to work pretty hard in stop and go traffic.

With my 3.07's and 33's it has to work pretty hard around town, and the part throttle shift points accur way too early, so most of the time it's pulling itself around in 3rd gear,,,and I'm still knocking down 13 mpg,,,in town.
I'm certain some highway driving would pick it up 2-3 mpg.

I tune it with the wideband. A few idle circuit tricks on the 750 holley, and some jet changes for a decent AFR got me where it's at. And it's not perfect yet. I still have some tinkering to do, but I'm waiting for warmer weather up here at 5,000 feet so the DA rises a bit. It will probably still be a bit rich when that happens.

[Firebirdjones]

Originally Posted by chevy2racr

i get like 7MPG oh well its too much fun to let it sit!

Man that's horrible. My 454 chevelle makes 638 hp,,,with 4.10 gears, 28 inch tall tires, and no overdrive I get between 10-11 mpg with that just driving around town.

[RALONG]

14 is great i have a new chevy 6.2 six speed auto seeing 11.8 - 13 hwy and my Blazer and Jimmy probably around 10 mpg lucky you.

[Bino]

23 combined city/hwy... see signature... Big loud 4WD Blazer, I'm shooting for at least 25 with it when I have time to fiddle with tuning and such.

[MLPhere]

Keep tire type/model in mind. My '07 chevy diesel went from 17 mpg to 15.4 changing from street tires to off road tires of same diameter. Gotta burn some fuel to make all that noise!