In a perfect world probably yes, but it gets technical beyond my pay grade. It will take the same amount of horsepower to move the car (again, all other factors being equal) down the road at a specific speed - regardless of whether the engine is a 350 or a 455. If you slowed the RPM of the 455 down to the point that equaled the 350 swept volume, I'm not sure that it's horsepower output would equal the 350's. I'm also not sure that it wouldn't. One would have to see horsepower graphs to be absolutely sure at what RPM one would have to spin the 455. BTW: back in my flying days, I learned that the most fuel-efficient power settings were relatively low RPMs with a fairly wide throttle opening. Obviously not to the point of causing detonation. I see no reason why that wouldn't be true of an automotive engine. If it were my car, and I had the engine, I'd bolt in the 455 and not worry about it. If you drive it 10,000 miles per year, the difference in fuel used between 20 and 15 mpg is 167 gallons. That's about $384. Not to be cavalier about it, but if $384 per year is the difference between doing something that you really want and not doing it, and you can't afford the $384 (2.30/Gal), don't do it.
I dont mean the excuse they give why its in there, I mean the real reason. Less miles per gallon, less energy per gallon, more processing, more cost and not good for engines. Is the grain lobby responsible for paying the politicians to make laws forcing us to use this crap? Why not have two pumps, one with and one without for same cost and let consumers decide.
Automotive fuel efficiency is a lot different than aviation by your example. Low rpm with wide throttle opening makes sense in an aircraft as there is always a massive load on the motor, same with marine applications. Automotive applications need to run with the highest vacuum possible which means a nearly closed throttle blade and light load. The OEM's set their advertised fuel economy in modern cars by having the engine run just off idle at 55mph; it theoretically works until you hit a hill or add a passenger or actually put you foot on the pedal. My wife's '12 challenger Srt8 had a .50 overdrive and 3.90 rear ratio. You could get it to 55, put it in 6th and let the engine coast at idle speed without touching the throttle. Another way is to get the engine rpm up to where it make the highest vacuum and lightest throttle, usually near max ve which is close to max torque output.
6.4l 470hp. it got about 23-24mpg lugging it at idle speed which was close to advertised. On a trip to Vegas we got 27-28 on the interstate traveling at 85mph.
thats amazing. Whats idle speed on that car? Mine is about 800. Are you saying its crusing down the highway at 600 - 800 rpm?
Idle speed in gear was 900-1000rpm and that's what it was doing at at about 55mph. It was close to stalling out anytime it encountered a hill or you needed to touch the brakes for any reason and weren't paying attention to hit the clutch as well. I didn't like driving it that way at all, you could feel it lugging. It left it in 5th gear unless I was going over 70mph.
according to math Ive seen from guys on here, it takes very little horsepower to keep a 2 ton car going at a constand speed of 70 mph. I wonder what mileage would be on a 350 geared up to cruise at 1000 rpm at 70 like your wifes car and how much hp it woud need to make. I think maybe 80hp or so. I wonder if it could get 28mpg. many many moons ago I had a 57 chev with a saginaw 3 speed, 283 holley and 2.73 rear end. I drove from Janesville WI to Sheboygan. I filled it up in Janesville and when i got to sheboygan I filled it again and I swear it was 30mpg and figured I must have done something wrong. But yet the math said it was so. 45 to 55mph county rds not interstate.
This is true as far as it goes. The issue with cars is that cruising speed is a direct function of RPM. If your car as turning 2,000 RPM at 60 MPH, and you slow it to 1,900 RPM in the same gear, the car will go slower. The vast majority of my flight time has been in aircraft with controllable-pitch propellers. One could slow the RPM and raise the manifold pressure (more throttle) and make the same amount of horsepower with a lower swept volume. The way you could do this in a car would be to visualize a car with a six-speed manual transmission. Pick a speed in fifth gear where the car was running at (for example) 50 MPH with a very small throttle plate opening and high intake manifold vacuum. Shift it into sixth gear. You will have to open the throttle more which will result in a lower intake manifold vacuum, but if you maintain 50 MPH, I'll bet the car gets better fuel economy at the lower RPM. If this were not so, why the gradual adoption of overdrive transmissions? My wife's six-cylinder minivan has a six-speed automatic and turns 1,600 RPM at 65. It has to downshift constantly because there's just not enough power at that RPM to climb a hill. My Dodge Magnum has a five speed and two more cylinders. It runs 2,200 rpm at 70. It virtually never downshifts, and gets better mileage then the van on the highway. Seems to contradict my argument, but the magnum has a four cylinder deactivation feature, so much of the time on the highway it is cruising on four cylinders. Lower swept volume. then the always-six cylinder minivan.
No argument here, either. I'm sure that the six cylinder engine in the minivan has to make more horsepower to move it's square shape down the highway then does the V8 Magnum; that's why I said all factors being equal. In this case they are not, but I'll bet that with the minivan's engine, transmission, and gearing, the Magnum would still do worse on gasoline on the I-95 run from MA to FL and return then it does with the 4-cylinder deactivation 5.7 Hemi that can hold top gear the whole way. A month or so after we got the minivan, we received a survey from Chrysler asking us a number of questions about how we liked it. Our answers were universally positive, but when we got to the "comments" section, we wrote that if it had the 5.7 Magnum's driveline, it would be the perfect vehicle.
I dont have a direct comparison to add, just data from other platforms that may be useful, possibly interesting. 1996 Corvette M6 all stock. Got 31mpg driving fairly easy interstate from East Tennessee to Harrisburg, Pa. Same car got 28mpg same trip later with only change being a 4.09 gear, stock was a 3.45 That double overdrive really kept the rpms down. 2013 M6 Camaro SS got 27mpg from East Tennessee to Omaha, Ne. Intersting note... On the trip I reset the mpg and trip during a particularly flat and lonely stretch of interstate. I found the sweet spot of 60mph in 6th gear and got 33.1 mpg for a stretch of over 100 miles in Nebraska. My current daily driver is a 2014 Silverado double cab 4wd with the 5.3, a 6 speed auto and a 3.08 gear. The lifetime average since new is 19.6mpg over 53k miles. That includes a lot of boat towing. I have been able to get as high as 23mpg for trips as long as 200 miles. Its all about finding that sweet spot. The one that is the most difficult to believe was my GMC Sonoma. I had a witness for this one the entire trip and I was shocked. 1999 GMC Sonoma ext cab 2wd. It had the ZQ8 package which means lowered sport suspension from the factory. I really believe the front air dam and being lower helped MPG considerably by keeping air from underneath. A 4.3 vortec V6 and a 4L60 with a G80 3.42 rear end. Using a Featherlite 22' open trailer (electric brakes and I had a controller) I towed the above 96 corvette from East tennessee to Atlanta dragway and back. I never got over 65mph and had a light foot as much as possible. I got 19mpg the entire trip towing with a passenger. I later had a 2002 4wd S10 blazer with the same drivetrain as the sonoma (but was 4wd). I never got 20mpg, ever in that one.
The Magnum, on I-91 on cruise control set at 79 MPH From Bristol on the VA/TN border northeast to Harrisonburg, has achieved 28.5 MPG twice. I don't represent this as typical, but our '05 Magnum seems to have a "sweet spot" at 79. I don't understand it either, but the numbers are there.
My car with all the engine mods, a 200-4R trans and 3.73 gears gets around 12 mpg. I'm sure my driving habits don't help. Maybe if I babied it and just drove down the highway I'd get 15 mpg would be my guess. Thank God for 20 gallon gas tanks. Not like the 10-14 gallon ones in many new smaller cars.
does it shift into overdrive around town or only on the highway? It would be interesting to see what it would get on the highway only. What rpm at 70mph?
