[thedofuss]

if i were to go on a coast to coast road trip with my brand shiny new C7, with the 7-speed MT (actually mine is AT), and had to maintain, say, 50 mph, im guessing that conventional wisdom would suggest that i would get the max gas mileage in 7th gear. and i would agree that in a vacuum (ceteris paribus), this might be the case--notwithstanding the fact that due to lack of oxygen, you car would not start. however, in a typical environment would 7th speed give you optimal fuel mileage? i think not. if im right, how would you determine at various speeds, what the most fuel efficient gear would be? apologies if by posting this query, im living up to my chosen internet name--i do that from time to time, totally unintentionally.

 

[53Vette]

People here are finding they get the best fuel mileage in 6th a normal cruising speeds. 7th is only really good a very high cruising speeds.

 

[Milliwatt Rob]

Can you even drive 50 mph in 7th gear without the engine lugging?

 

[Derrick1812]

Can you even drive 50 mph in 7th gear without the engine lugging?

Try it and let us know


Sent from my iPhone using Corvette Stingray Forum

 

[mark13]

Can you even drive 50 mph in 7th gear without the engine lugging?

I think it is highly unlikely, based on my experience.

 

[joshg]

50 is low even for 6th gear

 

[thedofuss]

update by OP: so how do you know what is most efficient gear at various speeds? there must be some formula, albeit beyond my comprehension, that would tell you , based on gear ratios, wind speed/resistance, ambient temperature, wet/dry surface, tire coefficient of friction, etc. [i know, if you cant use it, who cares?]

 

[somethincreativ]

I think the greatest factor is going to be stoichiometry. The closer the engine is to the economy-ideal air/fuel ratio, the better the mileage will be. Just because an engine is turning fewer rev's doesn't necessarily mean it is burning less fuel per unit power/time. What we are really trying to determine here is Brake Specific Fuel Consumption (BSFC), then compare BSFC at a given RPM to the vehicle drag at the respective speed through various gears.

The link below doesn't answer your question, but it will provide you with a close enough estimation of the forces at play. By the way; this wasn't a stupid question.

Part 6: Speed and Horsepower

 

[Vigilance247]

People here are finding they get the best fuel mileage in 6th a normal cruising speeds. 7th is only really good a very high cruising speeds.

This is your captain speaking. Today, we will be cruising at very high speeds.

 

[Corgidog1]

My guess is that 55 mph at 2K rpms would be pretty darn close to optimal. If I can recall, when the speed limit was reduced to 55 mph back in the 70s, there was something about 55 being the most efficient speed and I'm thinking 2K rpms for engine revs. OR one can apply the theory stoichometry and proceed accordingly.

BTW hope all is well with you.

 

[TNSQUIRE]

50 is low even for 6th gear

Agreed. At Spring Mountain we were doing 80 in 4th gear. Probably not very economical though. ?

 

[LT1xL82]

Agreed. At Spring Mountain we were doing 80 in 4th gear. Probably not very economical though. ��

Miles per gallon not so good. Smiles per gallon perfect!

 

[Jerry U]

Can you even drive 50 mph in 7th gear without the engine lugging?

Surprised with all the posts no one put in the rpm in 7th at 50 mph! It is 1050 RPM. Not only is that lugging the engine it is no doubt below the optimum mpg for the engine. I find I need to be over 65 mph on a flat road to use 7th. Probably need at least 6th or maybe even 5th to get to the best fuel economy at 50 mph. Just put it on instant mpg on a flat road and try it!

 

[ICU LQQKIN]

And we buy a C7 to get good mpg? NOT! If you are worried about how many MPG you are getting, you may have bought the wrong car. My experience at Spring Mountain was almost 120 MPH from turn 10 to 1 ... and I was not looking at the fuel gauge. I was looking for the next apex and smiling all the way!

 

[rdslon01]

And we buy a C7 to get good mpg?

Yes. Someone bugged me the other day about how I, a tree hugger, could justify buying a Corvette. I told them how fuel efficient they are. The person shut up and went away.

Fuel efficiency does matter to some of us.

 

[VietnamVet]

Surprised with all the posts no one put in the rpm in 7th at 50 mph! It is 1050 RPM. Not only is that lugging the engine it is no doubt below the optimum mpg for the engine. I find I need to be over 65 mph on a flat road to use 7th. Probably need at least 6th or maybe even 5th to get to the best fuel economy at 50 mph. Just put it on instant mpg on a flat road and try it!

When is the engine lugging? An interesting question that I have wondered about. My 2015 owner's manual on page 9-32 says "for best fuel economy . . shift from 6th to 7th at 45 mph." It also says to keep engine RPM above 900 RPM. These numbers seem quite low to me but that's what the manual says. Perhaps I am underestimating the torque of the Corvette engine. Any comments?

 

[Trevek]

I keep my RPM's between 1000-1500, shift at 2k. Seems to be the most fuel efficient for me.

 

[thrilled]

I remember when I was young,my parents would sometimes shift from 1st to 2nd it seemed like 5 MPH.And shift from 2nd to 3rd at 15.
Never heard much about engine lugging but I imagine it was.Didn't seem to hurt it.But the cars back then didn't get the miles on the cars
Like they do now.So,maybe there was something to it.

 

[Milliwatt Rob]

Don't know how many years you go back to those short shifts, but the old straight 6 and 8 engines seemed to have lots of low end torque. I learned to drive on a straight 8 Buick that I used to call the "parade car", because it pulled smoothly on flat ground in any gear at idle speed.

 

[LT1xL82]

As a kid I did yard work for a couple that would drive me to/from my house to theirs. The woman always shifted 1-3-4. One day I asked her why she doesn't use 2nd. Turns out she thought the thing was a 3-speed (with a weird shift pattern at that!)! After a lot of convincing she tried a 1-2 shift.

Oh, back to Vermont. How do you complement a beauty queen from Vermont? Answer: "Nice tooth!"

I think I best stop posting right about now. Bye.