When improving HP does that naturally decrease MPG or is it actually more efficient?
But the heavy foot is the cause of any loss of MPG?

 

I’m not an expert engine builder, or expert in thermodynamics, but it takes fuel to make power. How efficiently the engine turns the heat into power determines the fuel economy. It doesn’t take big power to propel a car at typical interstate speeds. At the same time, the faster you drive, the more power it takes, which in turn takes more fuel. The key would be to find the best balance of speed/power, then do whatever you can to improve the efficiency in that sweet spot.

 

Top Gear did a hilarious bit where they had a Prius drive around the track at full tilt and Jezzer simply followed it in a BMW. Naturally, the BMW got better gas mileage than the Prius.
So your driving style has a major impact on mileage. A more powerful engine might encourage you to use less throttle. e.g., when I was driving a 2000 Altima I would regularly just keep the pedal on the floor. No reason not to. Didn't really accelerate much regardless of what you did, so why not? Of course, that wastes gas. Now driving a 450 hp car I'm much more careful with the go pedal.

 

Improving HP by doing these things improves MPG (increases efficiency):
- increasing compression ratio
- decreasing exhaust back pressure (exhaust headers, dual exhaust)

Improving HP by doing these things decreases MPG:
- increasing the size of the intake passages
- richening fuel-air mixture
- installing a longer-duration cam

And, yes, a heavy foot decreases MPG because that causes the carburetor or fuel injection to richen the mixture.

 

A new Camaro SS makes 455 HP and gets WAAAAY better gas mileage than any Olds I own.

 

Plus if you drive a rig like mine with the arodermatics of a loaf of bread you will embarrass yourself at the gas pump but who cares that the only place I'm embarrassed with that car..... Tedd

 

My Challenger weighs 4100 pounds and gets around 30 US, 35 Imperial Highway with 305 HP. Even with OD it is near impossible to compete with efficient, modern design multi port and direct injection motors with 8 and 10 speed transmissions. I figure with the 200+ HP and 300 ft/lbs Olds 350, 2004R and 3.42 gears with 225/70R14 tires might eek out 25 mpg Imperial.

 

Unfortunately, today’s engine management makes a apples to apples comparison impossible. With the DOD (Displacement on Demand) at cruise you are basically driving a puny 4 cylinder engine. Add in the aerodynamics and the playing field is no longer level.

 

Horsepower is not a good measurement to discuss this as it is merely your torque times your engine speed and a few oddball units conversions. Some HP adds can decrease cruise fuel consumption, some have no effect, and some can increase it.

Low end torque seems to be inverse to mileage, more torque, less mpg. Modern engines seem to be as small as they can get them to give max HP that is needed (not that is wanted, just needed) and using many, many gears so that the engine stays at cruise RPM the most it can. This is why a lot of companies are dropping a cylinder or two and going turbo. I will miss instant power in the gear I am in already, for sure.

 

I know what you mean. At a 50 mph cruise in my Mazda, if I back off the throttle and slowly roll it back on, it actually kicks down two gears. Even when I'm going downhill. Drives me up the wall.

 

I hated the 8 and 9 speed transmissions when the first came out. My wife’s Chrysler 200 would shift 3 times crossing an intersection, and would going into top gear until about 65mph. Maybe most people wouldn’t notice, but since I have an extensive transmission background I’m tuned into those things.

 

True. My '16 Silverado with 355 5.3 knocked down 26 mpg when we took it back from FL in January, with the cruise set to ~70 mph. That is pretty impressive for a crew cab, 4x4, 3 ton brick no matter how it's sliced, considering the power it makes. I'm no fluid dynamics engineer, but I don't think that truck is more aerodynamic than a '50s-'70s car. Power band comes into play as well; the engine will get the most mpg, and operate most efficiently, in its powerband. My X3 gets much better fuel economy at 80 mph than at 65-70 mph, the old rule of thumb speed for best fuel economy, despite the engine turning faster, making more power, and punching harder through the air. VANOS/VVT is why.

We just had a new ship built, and went from ~800 hp inline 6 Luggers to ~1300-1500 hp V8 or V12 Cats (I forget which, I haven't worked that boat). Where as the 4 x 6 cyl boats burn 100 gal/hr cruising in the mid 20 knots, the new one maxes out at 18 knots and burns 250 gallons/hr. As mentioned above, you gotta feed them horses! They key is the "type" (in a basic sense) of horse you're feeding, some make better use of the "hay."

No matter what the vehicle, I seem to get better fuel economy if I accelerate briskly up to speed from a stop sign when pulling out onto a road or highway, rather than slowly accelerating up to speed and risking a rear end collision.

 

Kinda off the subject, but I think the myth of running the A/C killing mileage is a bit dated. Maybe the A/C did drop mileage on older cars (especially GM cars with the massive overkill A/6 compressor. Had a college instructor tell us that compressor has enough capacity to cool a small house) but I firmly believe the windows down has a much bigger impact on economy. I’m guessing the windows down disrupts that carefully sculpted vehicle profile. Enough that the aerodynamic drag is far worse than the puny compressors used today.

 

That may be true for cars built in the last 20 years or so, but I'm not convinced that the aerodynamics of a 1960s car are impacted that much with the windows up or down. Be careful about mixing too many variables. For an example, try driving in a newer car with only the front windows open - you can't. The buffeting becomes painfully annoying in short order. Crack the rear windows open even a little and that problem goes away. Try the same thing in a 1960s car (like my 62 F85) and you have no problem driving at speed with only the driver's door window open. There's clearly a big difference in airflow around those two shapes.

 

That was the point I was trying to make. I’m guessing the A/C hurting fuel economy started with old iron, designed before the CAFE crisis, no concern of aerodynamics, and massive compressors. I bet with today’s cars A/C has little impact on highway mileage.

 

I hated the GM truck 6 SPD programming, slow shifts and never in the 5.3's power band. I like how quick and unoticeable both our Challenger and the GM 8 speed trucks I have drove.

 

Yeah, I was impressed with the mileage of my BIL's 17 GMC when we borrowed it but can't stomach the price tag of new trucks. I gained two to three MPG on the Challenger going from 117 km/hr to 118 or 119 km/hr. And yeah, the newer the diesel's, tons of emissions failures and horrid mileage. At least Frieghtliner shrunk the fuel tanks on their new tandem trucks.

 

I really don’t understand the thinking the EPA has when it comes to the diesel engines. My first Cummins powered truck (2001 ram 4x4 2500) got about 19 mph highway stock, 21-22 after some tuning. My 2006 MegaCab got 16-17stock, after some tuning it will occasionally get 19. Anytime the EPA tightens emissions standards, the mileage drops. Look at the Volkswagen lawsuits, the OEM gives them a tune so the performance and mileage is acceptable, and the EPA nails them. Forces a recall for a reflash, then owners bitch their cars have the same mileage and performance capabilities of a bulldozer. I think Jeep has the same issue with their small diesel engine, I have heard of people taking their cars in for the reflash, and then taking the money that was reimbursed and buying a aftermarket tuner to get back the performance and mileage, while pocketing the difference. I’m all for being able to breath, but until other countries decide to stop polluting with zero regard for anyone else it’s time to back off on this country regulations. Seems like the EPA keeps adding restrictions here to offset 3rd world nations. All while costing the manufacturers money in research and development, which gets passed on in the sticker price.

 

Well, duh, if you protest in China they take your organs and sell them, then burn what's left of you.

 

Not all emissions are created equal. CO2 (i.e. increasing mileage) is certainly a concern for climate change, but it isn't the worst thing for human health that comes out of a tailpipe - particularly a diesel tailpipe. Diesel exhaust is extremely toxic to humans. Goal #1: don't kill people now. Goal #2: don't kill people in the future.

The US is the second highest producer of CO2 in the world (behind China and ahead of India) and the third highest producer of CO2 per capita (behind Saudi Arabia and Australia). China is 12th per capita. India is 20th per capita. So yes, we're producing more than our fair share of emissions.

 

You're mixing your stats up a bit.

 

No I'm not.

https://www.ucsusa.org/resources/eac...-co2-emissions

 

Please move to China or India. Permanently. They're clearly an environmental paradise. You'll love it there.

 

Ok, you didn't grasp my point.

This is an absolute.
This is a per capita
As is this.
And, this, is an unfounded conclusion.
You literally parroted that website in order of its findings, which makes you a talking-point-recycler. There's a word for people that present data in the worst way for a particular conclusion, and that is biased.
Either talk absolute terms, or talk per capita, and, either way, don't ignore pertinent stuff like landmass and percent development and please, learn to read a graph.

 

And may I add one more .
Increasing spark advance .

 

Again, I did not mix up anything. I have no idea why you think I did, as I was pretty explicit at calling out which were raw numbers and which were per capita - using the same countries in both examples. Presenting both raw numbers and per capita is how you show more of the complete story of what is happening. It's called "accounting for key variables" and it is something that scientists do to isolate things. NOT showing the complete picture is how statistics get twisted to show unfounded conclusions. Your recommendation to use one or the other is what manipulators do to try to push an agenda.

I'm done - not derailing the thread to satisfy your BS agenda.

 

Dude, you have 73 posts and most of them are you talking about pollution and electric motors. I'm not the one with the agenda. Please don't be done with the thread, be done with the site.

 

I did not read all the replies but sometimes yes and sometimes no. A 1991 Quad 442 got in the high 20's MPG. The 1991 Quad 442 W-41 had more power and torque in the same car and got 30 to 31 MPG. The W-41 had higher compression, a different cam and a special computer chip. It also had lower gears than the standard Quad but better mpg. I got better MPG with the A?C on in my W-41 then I did with the A/C off. I never figured that one out