They can be, but manufacturers choose to up the HP instead, thus it nullifies any gas saving DI can bring.
Is DI always more fuel efficient?
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Increasing horse power and torque, especially low-end torque, will net fuel savings. The problem is the person behind the wheel who has a lead foot and wants to take advantage of the additional power instead of the fuel savings.
Since manufacturers only provide peak HP, we can only speculate if there are any gains elsewhere on the HP/TQ curve.
Also, the MPG gains would show up in the EPA ratings. But for a lot of the models they don’t. That eliminates the “person behind the wheel” argument.
Here is a 2013 Gen IV and a 2015 Gen V in a two wheel drive Silverado with a 5.3. In this case the Gen V had worse highway gas mileage. Not sure about the AFM/DFM systems.
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Here is a Honda Odyssey DI vs MPI. The 1mpg highway advantage on the newer model is likely due to the 10 speed automatic and not the DI.
But the HP difference is 280 vs 248.
So if they can gain over 30hp and keep the mpg pretty much the same, it stands to reason that if they kept the same HP rating the fuel economy would improve.
But the HP difference is 280 vs 248.
So if they can gain over 30hp and keep the mpg pretty much the same, it stands to reason that if they kept the same HP rating the fuel economy would improve.
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Horsepower is torque times RPM. Actually, the formula looks like this:
For the Honda Odyssey:
The GDI version makes 262 lb-ft. of torque and the MPI version 250 lb-ft of torque. And that's the peak torque at around 4K RPM. That won't make a dent in fuel economy.
However, for lighter vehicles like sedans and compacts, it does. Take something like a 2008 Sonata with a 2.4L MPI vs. 2011 Sonata with a 2.4L GDI. The first will get 30~32 Highway MPG, the second will get 36~38. Go up to the revised 2.5 GDI/MPI, and real world Highway MPG is now over 40. It's not earth shattering, but the improvement is there, at the expense of long term reliability.
Please don’t try to teach me about torque and power.
Torque is the amount of rotational work and HP is the rate at which that work can be performed. Nowhere in there there is fuel consumption involved.
For you to imply that a higher TQ output will lower fuel economy means you do not fully understand the concepts of work and power.
In fact it’s the opposite, the more work the engine is capable of, or the higher the rate, the more fuel it will use. You can’t fool the laws of thermodynamics.
If I recall correctly all things being equal, power increases about 3% for every point increase in compression. So a 10:1 engine that produces 200hp will make about 206hp at 12:1. I believe efficiency increases are on the same order.
Efficiency increases, both power and decrease in fuel consumption. This is the beauty of efficiency.
A typo? From 10:1 to 11:1 will make from 200 HP to ~206 HP (3 %) and from 10:1 to 12:1 would
result an improvement from 200 HP to roughly 212 HP. Two points make 2 x 3 % = 6 % (12 HP).
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I remember that well and the hype when GDI was introduced by Mitsubishi as a game changer. I also remember the disappointment when it didn't live up to the expectations of significantly improved fuel efficiency.
More like a brain fart. Thanks for correcting.
I should say, in their current engines. Or current when I was working on them... 1.5 tgdi from eclipse cross
I think that DI engines are more versatile with other engine management systems and can create a better power curve. Fuel mileage should also be slightly better as you are directly injecting into the oxygen and can control the effect more precisely than the slight amount of pre-atomization in port injection engines.
I didn't read this thread thru- when I purchased my 2015 Honda 2.4L, DI it didn't matter at all although now I would probably favor regular injection, I run a catch can which catches all kinds of nasties and hopefully kicks any intake trouble down the road. I also steered clear of the CVT and found a MT6 because of all the Nissan issues at the time- if it was a conventional auto probably would have taken that.
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