Finally.... over 24 MPG on a 3.7 !
09-29-2011, 01:26 AM
#21
Originally Posted by zap
A two wheel drive Common Rail 5.9 will if it's been taken care of. Example, my father's 06, which has a 35 gallon tank which I have driven from Austin, TX to Pueblo, CO on one tank with about an 1/8 of a tank to spare. The only thing it has that is different from the factory is LT285/70-17's instead of the OE LT275/65-17's which lowers engine speed by 150 rpm at 70 mph. LSD doesn't clog the cat like standard diesel does. The truck was bought new in September of 2006, LSD became standard in Texas in October 2006.
The LB7 was considered the most efficient of the 6.6's...from the factory. When you delete the emissions on an LBZ, you have an engine with better heads, injectors, tune, and a variable vane turbo. It also got a 6 speed allison where the LLY had a 5 speed, and the LB7 had a 4 speed. The 500 horse LBZ I speak of has a fully rebuilt Allison by Sun Coast with a lock up TC (which is who Dodge went to in order to get transmissions for the 2012 HO 6.7 which puts out 415 hp and 850 lb-ft).
I understand your reasoning about the larger engine part, but that really only holds true to American built engine. Take for instance the BMW M1. Has a 320 hp 3.0L flat 6, which you haven't seen here in the states in 50 years. M1 makes 37 mpg, which is better than most the 3.7 V6's running around (not just the Fords).
The 5.9 is a great engine but will not get those mpg numbers in a HD truck. Your dad's speedometer is off from the larger tires making the odometer read slower. I would not rely on the fuel economy readout, especially since the truck is no longer stock. Hand calculate and figure out the percentage that the odometer is off. Also, the truck has a 48RFE transmission which is a 4 speed which is not great for efficiency at highway speeds.
As for the '11.5+ CTD trucks, they have 350 hp and 800 lb ft of torque. Suncoast was not contracted for the transmissions. As a matter of fact, they are having issues holding power in the aftermarket world with the 68RFE.
The LBZ is considered the best Duramax as far as reliability, but an LB7 will typically get better fuel economy since there is no EGR or cat (except for Federal fleet, Cali models and some from the northeast). The up pipes don't have the EGR cooler section on the passenger side and the heads don't have the EGR port. Also, the 01-05 Allison is a 5 speed transmission. The LB7 and LLY transmission is exactly the same (except for the 06 LLY which is actually a detuned LBZ and has the 6 speed). In 06 they changed the first 2 clutches and added a 6th gear which is actually just a different valvebody.
As for other cars, alot depends on the transmission and other factors. For example, a 430 hp Corvette is rated for 26 highway MPG because of its really tall 6th gear. I am not a car expert and I definitely know less about European vehicles, but they should still be under the same constraints as any other vehicle.
09-29-2011, 02:29 AM
#22
Senior Member
I'm sorry, but once again, your information isn't flawed.
The 5.9 is a great engine but will not get those mpg numbers in a HD truck. Your dad's speedometer is off from the larger tires making the odometer read slower. I would not rely on the fuel economy readout, especially since the truck is no longer stock. Hand calculate and figure out the percentage that the odometer is off. Also, the truck has a 48RFE transmission which is a 4 speed which is not great for efficiency at highway speeds.
As for the '11.5+ CTD trucks, they have 350 hp and 800 lb ft of torque. Suncoast was not contracted for the transmissions. As a matter of fact, they are having issues holding power in the aftermarket world with the 68RFE.
The LBZ is considered the best Duramax as far as reliability, but an LB7 will typically get better fuel economy since there is no EGR or cat (except for Federal fleet, Cali models and some from the northeast). The up pipes don't have the EGR cooler section on the passenger side and the heads don't have the EGR port. Also, the 01-05 Allison is a 5 speed transmission. The LB7 and LLY transmission is exactly the same (except for the 06 LLY which is actually a detuned LBZ and has the 6 speed). In 06 they changed the first 2 clutches and added a 6th gear which is actually just a different valvebody.
As for other cars, alot depends on the transmission and other factors. For example, a 430 hp Corvette is rated for 26 highway MPG because of its really tall 6th gear. I am not a car expert and I definitely know less about European vehicles, but they should still be under the same constraints as any other vehicle.
The 5.9 is a great engine but will not get those mpg numbers in a HD truck. Your dad's speedometer is off from the larger tires making the odometer read slower. I would not rely on the fuel economy readout, especially since the truck is no longer stock. Hand calculate and figure out the percentage that the odometer is off. Also, the truck has a 48RFE transmission which is a 4 speed which is not great for efficiency at highway speeds.
As for the '11.5+ CTD trucks, they have 350 hp and 800 lb ft of torque. Suncoast was not contracted for the transmissions. As a matter of fact, they are having issues holding power in the aftermarket world with the 68RFE.
The LBZ is considered the best Duramax as far as reliability, but an LB7 will typically get better fuel economy since there is no EGR or cat (except for Federal fleet, Cali models and some from the northeast). The up pipes don't have the EGR cooler section on the passenger side and the heads don't have the EGR port. Also, the 01-05 Allison is a 5 speed transmission. The LB7 and LLY transmission is exactly the same (except for the 06 LLY which is actually a detuned LBZ and has the 6 speed). In 06 they changed the first 2 clutches and added a 6th gear which is actually just a different valvebody.
As for other cars, alot depends on the transmission and other factors. For example, a 430 hp Corvette is rated for 26 highway MPG because of its really tall 6th gear. I am not a car expert and I definitely know less about European vehicles, but they should still be under the same constraints as any other vehicle.
A friend of mine just bought a pre release 2012 LH MegaCab which is a fancy way of Dodge saying it will probably only be a limited edition truck. Saw the brochure on it, 415 hp and 850 lb-ft with a Sun Coast kit in it. He put it on a dyno the other day and it came out at 340 rwhp and 848 ft-lbs, which is right for a 415 horse engine with a slightly modified transmission.
My bad on the transmission, I was thinking of the autos behind the Detroits. I will agree that LB7's are the most efficient from the factory. Compare a LB7 to a LBZ without emissions controls on it and the LBZ will be more efficient.
09-29-2011, 08:47 AM
#24
The only time my 5.0 sees less than 20mpg is when i drive pretty much the whole tank in-town with red lights at every intersection. I have done 10 fillups since I got it and only one was less than 20mpg. I've had as high as 22.1 in 50/50 driving and up to 24.5 on a 50mph 300 mile road-trip.
09-29-2011, 12:24 PM
#25
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What tune is that running? I know they offer an economy tune but I feel like the performance tune would help the mpg's.
I feel like I lose a lot of mileage do to the low torque of the v6 starting and maintaining speed on a hilly road.
10-01-2011, 06:54 PM
#27
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Still wondering if you get a second to post up, thanks
10-08-2011, 11:10 AM
#28
Senior Member
Well, I can tell you based on my heavy/transport truck experience hauling up to 48,000 lbs: smaller engines do get better economy! You'll have to downshift (manual stick) like crazy on hills and the driver satisfaction will be ZERO (no torque!) but a 13 L V6 turbo diesel will beat my 15 L V6 turbo diesel. Proper gearing (matching the optimum engine speed with your preferred road speed through axle ratios) is essential. I love my powerful CAT and I offset its big L by driving slow when I'm under load.
10-08-2011, 12:53 PM
#29
Originally Posted by smd5231
Well, I can tell you based on my heavy/transport truck experience hauling up to 48,000 lbs: smaller engines do get better economy! You'll have to downshift (manual stick) like crazy on hills and the driver satisfaction will be ZERO (no torque!) but a 13 L V6 turbo diesel will beat my 15 L V6 turbo diesel. Proper gearing (matching the optimum engine speed with your preferred road speed through axle ratios) is essential. I love my powerful CAT and I offset its big L by driving slow when I'm under load.
10-08-2011, 02:13 PM
#30
Senior Member
...While a 6.2 barely has the throttle plate cracked, creating say 15 inches of vacuum a smaller engine will have less vacuum to fight. That's where the EB comes in, cruising it isn't fighting any vacuum. Like the CAT's you speak of, if an EB paced a 5.0 or 3.7 towing, the fuel economy would be very similar. I feel 90% of why it may be worse is people using the power it has.