MPG on a 6000 pound truck

[4x4_76]

What would be the estimated mpg on Suburban with stock 350 and 700 tranny, 4.56 r&p and 33x10,5 tires (like Cooper Discoverer H/T), lifted max 3". Highway speed max 50mph.

I need some base figures for my calculations. With current fuel prices going up week after week, I'm thinking of ditching the 6.2 diesel, and replace it with 350 sb equipped with cng system. There's cng station a mile from my work, so it would be a good choice.

Diesel costs now 1/2 more than it did last christmas, from 0.98€/litre to as high as 1.5€/litre (at my station it's currently 1.38€/litre, but getting higher)! And it's estimated to get higher than a gas, which is about a 1.48€/liter (95 oct).

 

[jonathon]

My Suburban gets 13 miles per gallon, might get more but that's what I get with my city/highway driving mix. It is stock with 3.73's, tires that measure out slightly bigger than 31", and a TBI 350. I think your gears, tires, and lift won't help your mileage any..

Our rigs are not that fuel efficient... it's a trade off for a daily driver.

 

[AJMBLAZER]

Yeah, the 4.56's are a bit deep for 33's.

With a gasser Suburban you'd be lucky to see 13mpg regular. Maybe a bit higher for sustained cruising.

 

[4x4_76]

I made some calculations about the rpm's. Stock '91 Suburban with 235/85R16 (31") and 4.10 gets rpm's little over 1600 @ 50mph. Too bad that brochure didn't give mpg numbers for '91 Suburban.

Mine with 255/85R16 (33") and 4.56 gets 1720 @ 50mph. Not much of a difference.

13 sounds realistic, and true, these aren't fuel efficient. I was hoping to get somewhere between the 15-16 mpg.

 

[AJMBLAZER]

Better stick with the diesel then. You're definitely low geared for a diesel with only 33" tires. Will Finn laws let you run a taller tire?

 

[78K5Blaza]

My brother has a mid 80s burb with a 350 crate motor and 700r4 tranny on 35" tires. Don't know the gearing but he gets 8'ish MPG's around San Diego daily driving.

 

[tRustyK5]

Here is a good side by side comparison report on a CNG GMC pick-up versus it's gas powered twin.

http://www.eere.energy.gov/afdc/pdfs/gmcpickup.pdf

Personally I can't see swapping the diesel out in favor of a CNG powered small block as being the answer to anything (from a pure economic sense)

Figure the cost of the swap itself, then add the cost for the CNG re-fit, account for a 40% drop in fuel economy, figure in the cheaper cost of the CNG and to me it sounds like you're still worse off of even than if you have kept the diesel.

Rene

 

[kevin400ex]

the best i got in my K5 with a 400carb'd small block, 700r4 4.10's and 35's was 14mpg highway, city was more like 10. the overdrive and lockup conveter heled alot for highway.

 

[4x4_76]

Better stick with the diesel then. You're definitely low geared for a diesel with only 33" tires. Will Finn laws let you run a taller tire?

33" is biggest legal size which I can easily register to that. Our DMV figures that 35" is biggest you could need on a street driven vehicle. For 35" I would need to request a special permit, and that costs 360€. And I would need to have good reason, off-road as a hobby don't apply.

 

[AJMBLAZER]

Sounds like the gears are what's killing you then.

 

[tRustyK5]

It's got OD...those gears aren't that bad. Even at 65 mph it's only turning at 2100 rpm. Should be nailing down 21 mpg or better with the 6.2.

Not a ton of rolling resistance with a 33" radial either, and I don't imagine the Sub is skyed either. 6.2's don't care that much about wieght as far as highway economy goes...

Rene

 

[AJMBLAZER]

Yeah...I forget about the fact that some of you bastards have OD...lucky SOB's.

Still, never thought we'd be arguing about gears being TOO deep or not.

 

[AJMBLAZER]

Just realized he never stated what his mpg was now. 4x4_76, do you know?

 

[4x4_76]

Here is a good side by side comparison report on a CNG GMC pick-up versus it's gas powered twin.

http://www.eere.energy.gov/afdc/pdfs/gmcpickup.pdf

Personally I can't see swapping the diesel out in favor of a CNG powered small block as being the answer to anything (from a pure economic sense)

Figure the cost of the swap itself, then add the cost for the CNG re-fit, account for a 40% drop in fuel economy, figure in the cheaper cost of the CNG and to me it sounds like you're still worse off of even than if you have kept the diesel.

Rene

I would have to rebuild 6.2 anyway, so money I invest in that would easily pay cng convesion and small-block. Depends on what level cng system is used, simplest has manual switch to choose between cng and gas. More sophisticated system you can run either one or 50/50, and it switches automatically to gas if cng runs out or vise versa.

I made some quick calculations:
20mpg = 11.75 litres/100km, diesel 1.38€/litre = 16.22€/100km
14mpg = 16.78 litres/100km, gasoline 1.49€/litre = 25€/100km

Based on that GMC Sierra fact sheet, I figured cng equipped would have 13.5mpg, so I got these numbers with 50/50 setting:

13.5mpg = 17.4 litres/100km, gasoline 1.49€/litre cng 1.01€/litre = 21.76€/100km

With 100% cng it would be 17.5€/100km

It's been estimated that diesel price will go higher than gasoline, and god knows how high. But if I make a wild guess and say that it goes 0.15€ over the gasoline, diesel cost would be a 19.27€/100km.

 

[AJMBLAZER]

How come you have 4.56 gears?

Just what you have or the future plan?

 

[tRustyK5]

I would have to rebuild 6.2 anyway, so money I invest in that would easily pay cng convesion and small-block. Depends on what level cng system is used, simplest has manual switch to choose between cng and gas. More sophisticated system you can run either one or 50/50, and it switches automatically to gas if cng runs out or vise versa.

I made some quick calculations:
20mpg = 11.75 litres/100km, diesel 1.38€/litre = 16.22€/100km
14mpg = 16.78 litres/100km, gasoline 1.49€/litre = 25€/100km

Based on that GMC Sierra fact sheet, I figured cng equipped would have 13.5mpg, so I got these numbers with 50/50 setting:

13.5mpg = 17.4 litres/100km, gasoline 1.49€/litre cng 1.01€/litre = 21.76€/100km

With 100% cng it would be 17.5€/100km

It's been estimated that diesel price will go higher than gasoline, and god knows how high. But if I make a wild guess and say that it goes 0.15€ over the gasoline, diesel cost would be a 19.27€/100km.

So based on your numbers I see it being 6 of one, a half dozen of the other whether you run the 6.2 or a CNG smallblock. Seems a lot of extra effort for no real gains IMO. I also have a hard time believing you can drop in a freshly built small block, plus do a CNG conversion for less than the cost to rebuild the 6.2...

Rene

 

[4x4_76]

How come you have 4.56 gears?

Just what you have or the future plan?

Dana 60 had 4.56 when I bought it, so I figured I stuff Van 14FF with same gears. For the offroad purposes I have 37" tires.

Check out my build thread, that gives some answers

 

[4x4_76]

So based on your numbers I see it being 6 of one, a half dozen of the other whether you run the 6.2 or a CNG smallblock. Seems a lot of extra effort for no real gains IMO. I also have a hard time believing you can drop in a freshly built small block, plus do a CNG conversion for less than the cost to rebuild the 6.2...

Rene

Well, I'll see what I come up with that small block, it may be pricier than I thought. But rebuilding the 6.2 is really expensive in here, especially machining. I would have to find a good block to start with, too.

Two reasons why I'm considering this... enviroment, and taxes. First the tax. Suburbans in here are registered in three different vehicle classes; passenger car, van, and a light duty truck. If it's a gasser, no problems (for now, at least). But with diesel, you'll have to pay diesel tax, separate from the tax you pay on fuel. For passenger car registered suburban, it would be around 950€/year Vans have about 130-150€, and same with light duty registered. Tax is calculated from the vehicle class, and GVWR. Mine is registered as a van, and because of that it has 50mph speed limit, and not so comfy rear seat.

And 2010, we'll have to pay enviromental tax, based on Co2's on 2001 and newer vehicles, and older by the GVWR. And since my 'Burban is '82, I'll pay by the GVWR, about 385€/year.

I'm hoping that by the 2010, there would be a reliably way to measure emissions, and eviro tax would be based on that.

It really bugs me that even though recycling is the word the day, everywere they say that "save the world, buy a new car". Wouldn't it make more sense to keep older vehicles in good condition and drive them? It does pollute to make that new crappy car! I hell no won't buy one.

Yep, even though cost per kilometer is about the same with cng, emissions drop a little.

 

[AJMBLAZER]

Wow...dude...I have tremendous respect for Finland and some of the stuff you did fighting the Commies off in the last century and really want to visit someday...buy holy crap do your licensing and fees make me want to run the other way!

 

[Stomis]

You need to realize your true costs for this project. Just like when I came to terms with how its not worth it to swap out an nv4500 in place of my sm465 for me.

The true cost of your project is multiple years worth of diesel if you left your truck alone. And that doesnt even factor in what your time is worth to you.

Basically its like say it cost you $3000 to convert to a CNG 350. How much diesel can you buy with $3000, a whole hell of a lot. Just go mad max and throw like 4 55 gallon drums in the back of your suburban and hook them up to drain into your tank. Thats like a 300 gallon holding capacity. That way you buy alot more gas at the lower price.