Diesel milage

[JohnnyU]

...7) ultra low sulfur diesel sucks balls

 

[rangerbum]

03 Ford F-250, with 6-gun tuner, oversized intercooler, pulls 24 on highest mileage setting on the highway, 19 in town. On the other hand, when I drive it I have never pulled over 19 on the highway. And my personal low, On Setting 10, 6 Miles to the gallon.

 

[jobar]

Driving style matters a lot. A modern diesel with 300+ hp can use a hell of a lot of fuel if you use the power.

A diesels reputation for great mileage comes from the energy density of the fuel partially--it's sold and measured by volume and it quite a bit heavier than gasoline--about 20%, so there is 20% better mileage than a gasser right there. Then, a diesel doesn't have to restrict the air coming into so there are less pumping losses--that vacuum you are reading on your gauge is costing you efficency. There's probably 5% there. And since the fuel isn't compressed with the air like a gasser, the diesel runs a lot higher compression ratio which improves thermal efficiency and is probably good for another 10%. I think any diesel should whip any gas motors butt in mileage by 35%. But that means nothing if you spend all of your time with your foot down. And last is that a diesel makes more torque at low rpms because it always has too much air available and doesn't have to wait for it. That means no downshifting on hills. Having to downshift and always getting into the power circuit to gain rpms hurts your mileage a lot when you are towing. A guy with a gasser 460 knows he's going to pay a lot so he drives easier than the Cummins guy that thinks he's gaurenteed great mileage by virtue of having a diesel.

I was thinking in terms of a stock diesel that you get from a dealership, no tuners, no upgrades. Im 19 years old and supriseingly I dont have a heavy foot so thats no problem, even though I love drag racing. The only time I think I have a heavy foot is when im towing.

Thats what I figured, I thought diesels got better than 19mpg. I was talking to a guy after class last week, and he was saying that you could put tractor engines into trucks and get like 30mpg, and still be able to tow 15000 pounds no problem. Might not go fast but you can save gas.

 

[JohnnyU]

I was talking to a guy after class last week, and he was saying that you could put tractor engines into trucks and get like 30mpg, and still be able to tow 15000 pounds no problem. That might be my next project Might not go fast but you can save gas.

1) What do you think the Cummins 6B was originally designed for? Hint: It wasn't originally designed with Dodge in mind....

2) I wouldn't listen too closely to that kid...

 

[jobar]

1) What do you think the Cummins 6B was originally designed for? Hint: It wasn't originally designed with Dodge in mind....

2) I wouldn't listen too closely to that kid...

lol, I thought there was something that didnt seem right about that. I wont talk to him anymore. The conversation started when I was asking a buddy about the diesel mileage and that kid jumped in about the tractor engines.

 

[Will]

also, they can pump fuel for almost the entire power cycle, so its powering the piston well past the initial "bang" of a gasser, contributing to torque. diesels also have long crankshaft throws, which add to the torque of the motor.

Stroke though is independent of torque. Torque is dependent only on the amount of fuel burned per cycle. The fuel rate in cubic millimeters X .86 equals approximately the torque one cylinder will make if there is enough oxygen to burn all of that fuel. The stroke only relates to piston speed.

They can't efficiently pump fuel the entire power cycle. The effectiveness drops like crazy much past top dead center. It's almost stopped near the top so the injection is going to start somewhere around 20* BTDC, just like on a gasser because it takes time for the flame to grow, but as it starts down the other side the of the bore but it accelerates like damnit. The volume in the chamber is exploding open (so to speak) and the effectiveness of the fuel you are injection is rapidly going down to nothing. If you like black smoke it might be a fun thing to do. Maybe you gain a few ft-lbs by cramming in all that fuel so for some competition it might be effective, but not for very far down the bore. And the exhaust valve is going to start opening long before the exhaust stroke actually starts because it does take time to get things moving.