[SeanPlunk]

Originally Posted by enkeivette

Good argument Sean.

You guys don't seem to be getting the point, different cars are geared differently. Different cars, have different motors. It's foolish to believe that 55 mph is a magical number for all cars, whether the C6 can do it or not. My motor, in my car CANNOT cruise at 55mph in 6th gear. IT CANNOT. My big duration cam motor lugs so bad at 55 mph in 6th gear that it requires so much throttle to maintain that speed that it will literally lean spit, case in point. Are you going to try to make the argument that I'd get better gas mileage in 5th gear at 55mph, (which would also lug BTW) Than in 6th gear at a higher speed?

55mph, is NOT a magical number, it is NOT where ALL cars get best gas mileage. Don't know what else to say.

Your car is atypical, the vast majority of cars would get better mileage going 55 mph than 75 mph - that's a fact.

[SeanPlunk]

Oh,and who said anything about BEST mileage? Your initial thread was just that you get BETTER gas mileage going 55. For 99% of normal vehicles, they will get BETTER mileage going 55 than 75 pure and simple.

[Vettezuki]

I got the point and basically agree. 55mph is NOT a magic number that guarantees best mpg. Though it's probably a fair marker for your average family sedan. FWIW, my best milage in the Vette before the swap was 75 mph. That was empircle testing with Excel and everything. It was also the lowest rpm in the highest gear without lugging.

[enkeivette]

POP!!!

Did anyone hear that? It must have been an intake backfire from Adam's car, trying to cruise the 57 freeway in 6th gear at 55 mph.

Sean, the thread is titled "Commercial claiming better mpg at 55mph" Then you open it and there's a BS flag...

And I will stand by my opinion that most V8 cars and trucks (with modern OD transmissions) will get better mileage going faster than 55mph. Like I said, I don't think my Dad's Avalanche will shift into OD at 55mph. And if it does, it will frequently downshift trying to maintain speed. And those V8 cars are the ones that are wasting all the gas! We should be gearing economy commericals towards them.

[SeanPlunk]

Originally Posted by enkeivette

POP!!!

Did anyone hear that? It must have been an intake backfire from Adam's car, trying to cruise the 57 freeway in 6th gear at 55 mph.

Sean, the thread is titled "Commercial claiming better mpg at 55mph" Then you open it and there's a BS flag...

And I will stand by my opinion that most V8 cars and trucks (with modern OD transmissions) will get better mileage going faster than 55mph. Like I said, I don't think my Dad's Avalanche will shift into OD at 55mph. And if it does, it will frequently downshift trying to maintain speed. And those V8 cars are the ones that are wasting all the gas! We should be gearing economy commericals towards them.

I'm pretty sure your dad's Avalanche has the exact same 4L60E that was in my Camaro - and I know for a fact that it will go into OD at 55 mph. Also, your dad would get much better mileage cruising on the freeway at 55 than he would at 75. Using your car as an example of a normal car is simply crazy. Your car is a totally purpose built car and has nothing to do with "average."

[SeanPlunk]

Oh, and FWIW, my Cobra will EASILY cruise at 55mph in 6th gear with a T56 and 3.55 gears.

[SeanPlunk]

Oh, and your dad's Avalanche probably has the 5.3 and if he was cruising at 55 would NOT need to downshift at all to maintain speed. It would be happy sitting in OD and cruising.

[BADDASSC6]

I don't think they are trying to say that 55 is a magic number. They are just trying to get people to slow down. Force balance at a car moving at a constant speed. If it's not accelerating then the forceput to the ground at the wheels is equivalent to the sum of te wind resistance and the rolling resistance of the wheels. You are absolutely correct in saying that the motor has certain RPMs that it will operate more efficiently based on its own parameters, but this is a secondary order effect when compared to the energy required to make up for the resistance losses.

I would take you up on the offer to see if te ga mileage is better at 55, but I have a hard enough time keeping it at 75.

I will try it in my dodge 1500 that thing takes forever to get going.

[enkeivette]

Did your Camaro have 265 70 17 tires stock? And no the diff ratio is not higher to compensate, it's a 3.55 (2004). They had higher ratios available for towing, but most people don't have those. 4L60E is a .696:1 right?

That would be 1445 rpm at 55mph. That rpm deserves a Lewis Black face.

[BRUTAL64]

Originally Posted by enkeivette

Wind resistance factors in to engine load/ lower vacuum. The increased wind resistance will cause your mileage to get worse not directly, but as a result of making your engine work harder. This can be seen by reading your vacuum/ boost guage. Because my car is geared so low and has such a big OD ratio, there will be more lug on the engine (at a lower rpm in 6th gear at 75mph) than at 90 mph. Once wind resistance becomes a factor again (at speeds higher than 90 mph when the vacuum guage reads less vacuum) then the engine will be working harder, and therefore be less efficient.

It's really simple, your vacuum guage takes into account EVERYTHING (excluding air to fuel ratio, but this SHOULD be constant) including wind resistance. It is simply telling you how hard your engine is working. Therefore, the more vacuum you see on the guage, the better gas mileage you will get (at the lowest rpm possible). Have you seen some new cars that display a read out of the gas mileage on the dash? Those use formulas to determine the mpg, using a reading from a vacuum guage as the variable.

With the smaller diameter tires it might be able to pull highest vacuum at 85 or so mph. I haven't been paying attention. But it's still above 80 for sure. If I were to throw Ben's tires on my car, it would go back up to 90. But, Ben's car will get the best mpg at a slightly lower speed, since he has a higher diff ratio.

Using a Vacuum gauge to judge gas milage was used WAY back in the 60s. ( maybe 50s ). They came on Pontaics, Chevy trucks and few other vehicles.

I've had one on my C2 for MANY years.

Having been driving with a Vac guage for years, I'll say this..........

Things are not as they appear....