Commercial claiming better MPG at 55MPH
 

:bsflag:

Depends on the OD ratio/ final drive ratio and the power band of the motor. You get the best gas mileage in the highest gear at the lowest speed (rpm) that creates the most vacuum. Correct me if I'm wrong here, but I'm not. Vacuum level is inverse to the load demand on the engine, this takes into account wind resistance, etc.

My Vette gets best gas mileage at about 90 mph, my Neon... probably 55 mph. I can cruise at a slower speed in 6th gear in the Vette, but there is more load (lug) on the engine, consequently the vacuum isn't quite as high.

Low geared V8 trucks out there proabably won't even shift into the OD gear at 55 mph. My Dad's Avalanche is around 1800 rpm at 80 mph if I remember correctly.

Not sure, but I HIGHLY doubt your Vette gets it's best mileage at 90mph. Remember wind resistance plays a hugh roll as speeds increase.

Calculating the effects of Frontal Area and COD is not trivial. However, I could say that the frontal area, COD and lighter overall weight of the Vette means it could travel at higher speed with less of an Aero penalty than a more blocky car. I'd also say that most people burn up far more fuel accelerating unnecessarily than they do cruising at too high a speed.

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.:judge:

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.

Sorry dude, but your wrong. The lug that you feel on the engine isn't because there is more load on the engine. It's because the RPMs are way way down and the motor isn't making as much torque at 1100 rpm (approximately 55 in sixth for my car) versus 2000 rpm (80 mph my car). Also take into consisderation that as speeds increase the force of wind resistance increases exponentialy. My car gets ~23 mpg average going from SD to Phoenix when I keep it at or above 90 mph. It averages about 28 if I keep it around 75 mph.

Very true, there isn't more load on the engine, my bad. But the engine is less efficient if you lug it (as you said, it's making less power) this is why the vacuum guage will read less vacuum. Semantics aside, you will not get the best gas mileage lugging your engine.

Your C6 does better as a lower speed as you have a higher diff ratio than I do. Just like Ben's C3.

Once again, mpg are calculated by using vacuum as the variable. And I'm sure there's no doubt that lugging your engine will cause the engine to make less vacuum.

BTW I've been able to get well over 20mpg at 90 mph coming back from SD, but always less than 20 at 70mph.

BTW, I could agree that your car might do better at 75 mph than at 90mph but I'm willing to bet that your C6 will get better gas mileage at 75 mph than it would at 55mph. I don't think your LS2 would be very happy with a 3.73 diff ratio and a .5 OD. :judge:

Que? My A/F is dialed in pretty good. As I recall it's 14.x:1 < 2,000 rpm and like 12:1 at >4,000. That's not a trivial difference. However, is relatively constant and lean at lower rpms if that's your point.


[QUTOE]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.:judge:[/quote]

I would imagine it's also using duty-cycle readings from the Fuel Injectors. :huh: After all, that's giving a pretty accurate reading of the actual amount of fuel that's flowing.

I bet you're wrong. I bet his car would get better mileage at 55 mph than 75 mph.

:suicide: 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.

If anyone disagrees with my understanding of the conditions that yield the best mpg, please explain why and provide your own set of conditions. Not going to play "No it's not!" "Yes it is!" Thaaat gets old.

And yes Ben, that's what I meant about the AF ratio. Obviously if the car were richer down low and leaner up top, the lowest rpm at the highest vacuum might not be the best spot to cruise. But all cars should have a consistent AF ratio at part throttle speeds.

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

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.

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.

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."

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

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.

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.

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.

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.:bigthumbsup:

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

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

Things are not as they appear....:leaving:

What the hell are you talking about, 55mph at 1445rpm is perfectly fine for cruising around at. We're talking about cruising, not racing, you get that right? I cruise around in 6th at RPM's at the level all the time.

I agree that 55 is not magical number. I would also like to agree with Ben that this probably applies to the more eco/family sedan type of car and not our muscle machines. I would also like to say comparing your old Camaro Sean to Adam's dad's Avalahce is an apples to oranges comparison. The Avalanche is heavier and less aerodynamic by far. I do not disagree with your argument but I think that your "facts" backing your argument is flawed. There Sean I made a post without having to resort to the I can kick your a$$ argument!!

How is it flawed? It has the same transmission, and even allowing for the difference in gearing and tires, it could still easily be in OD at 55mph. Given the poor aerodynamic efficiency of the Avalanche, if anything it would benefit it even MORE going 55mph rather than 75mph.

I'd be lugging bad at 1,500rpm rpm in 6th. Remember your Torque curve from the blower is totally different. I'm ok at 2,000 rpm. But the engine seems happiest at about 2,300 like it isn't working hard at all. Cams play into this a lot.

The lugging is more harmonics than the engine is actually working hard.

No. If you lug hard enough you'll actually tip into the boost, well I will. Same goes for my mom's SRT.

What the other Adam is trying to get across is that an Avalanche (being a heavier car with more wind resistance) will have more load on the engine at the same speed/ rpm. And therefore be more likely to downshift and/or make less vacuum.

BTW I checked with my Mercedes Tech friend, and yes a vacuum reading is used to determine mpg. Once again more vacuum, more efficient.

Also, noticed that my friends Jeep Grand Cherokee 4L I6 Auto will downshift trying to maintain speed at 55mph on the 15 freeway going up a slight grade.

C6 Standard Equip:

3.42 Diff
T56 .5 OD (6th)
285 35 19 = 26.85"

1177rpm @ 55mph :D Do I even need to say anything? C'mon.

Ugg, this is getting so stupid. First of all, if you're just CRUISING on the freeway, 55mph at 1177 rpm would be JUST FINE. I was cruising in the Cobra yesterday in 6th at 55mph and my RPM was about 1400. Guess what, it was no big deal. If I needed to go up a grade or something, I would downshift to do it. Otherwise, the car could quite happily cruise at that speed and RPM for hours no problem - and I would get better mileage than if I was going 75mph. Again FOR MOST CARS, going 55mph will net them better mileage than 75 and the car would have no problem doing it in overdrive. Also most cars, especially automatics (which comprise a huge percentage of cars on the road) can easily be in overdrive comfortably cruising at 55 and again would get better mileage than 75.

:leaving: :suicide:

MOST cars 55mph = Better Mileage than 75 mph, no question.

My Vette would NOT be happy cruising at 1,200rpm in 6th PERIOD . It would be lugging . . . PERIOD, which ain't so good for wear and tear. You have a 500+HP Super Charged motor. Guess what? You're making tons of torque at that RPM and therefore have plenty of power. Post your dyno sheet.

I doubt if his dyno sheet starts low enough to have a reading at 1100-1200 RPM.

Yeah, after posting I checked mine, no dice. But we might be able to infer by starting torque around 2,500rpm. I bet you his is at least 100ft lbs, more than my H&C NA LSx.

Don't know why you guys keep posting that "most cars will do better at 55mph" like you're trying to prove a point to me. In the very first post, I said that my Neon will do better at 55. I'm sure most of the Honda Civics and Nissan Sentras out there could gain a mpg or two by slowing down their speed on the freeway.

My point was, and is, that most of the bigger more powerful cars and trucks out there... you know, the one's sucking all the gas, will not do better at 55 mph. See above.

1177 is high idle speed. No motor will move a car along at that rpm without lugging. Don't know what else to say. I can explain it to ya, but I can't understand it for ya.

And I had 521 hp with a leaking intake manifold gasket (2 ports) and a leaking head gasket (2 cylinders) with a 15:1 AF ratio at only 5lbs of boost.

Prob made a lil more with 9lbs of boost all sealed up with jets 10-12 sizes bigger in the carb.

Yeah, you are WRONG. I don't care what you say. If you want me to post this on other boards to prove you wrong, I'll be happy to do it. A Yukon, Avalanche, whatever, will do better cruising in OD at 55mph than it will at higher speeds. You are wrong about lugging. The Camaro could quite happily hang at that RPM WHILE CRUISING ALONG AT 55MPH!!! The Cobra will too. I just consulted my friend with a 4.6 2V F150 and he says his will too and won't lug. Why is this so hard for you to understand? :suicide:

All further arguments are pointless. Each person who is suffeciently interested should do a 100 mile test loop at 55 and whatever speed they think will yield best mpg, log their OBSERVED mpg and report. No speculating.

My hypothesis is that *my* Vette will get its best mileage around 70-75mph but my GMC Sierra 1500 would get its best around 55-60.

Looks like I can reuse this response.

Sean, does your friend with the NA F150 happen to have a vacuum guage in the cab? Didn't think so. So how does he know whether or not he's lugging.

And why would I be swayed by the opinions of a bunch of forum sh*t talkers that have less hands on experience than I do? You could get all of LS1forum to disagree with me, I don't expect to learn anything from a bunch of checkbook tuners.

:mad: I miss you Sean. :sm_laughing:

Not talking about hardcore lugging here. Not talking about the sort of lugging that causes a deep deep tone and the catalytic converters to rattle. This is about the very tipping point where you might be getting 17" of vacuum at 55mph but 20" of vacuum at 65mph. Not everyone can feel that slight difference with their foot. I'm talking about the kind of lugging that I do everyday in my Neon because I'm used to driving a V8. And you need to consider the average rpm and vacuum at the same time. If the car does fine at 55 cruising but lugs SLIGHTLY up a grade, then you need to take that into account, maybe the car would do better at 65 at the same vacuum level because the vacuum will remain constant up a slight grade at a higher speed. You need to take into account whether the car is downshifting. This is an average, where will cars get the best average? To be honest, I don't know. Neither do you, neither does LS1forum. But if I had to bet... I'd bet a lot of money that it's not at 1177 rpm in a Vette or a Cobra. And I bet some money that it's not at 1445 rpm in a truck... AVERAGE.

I'd go make a video of this slight difference in my car, but you already casted my car out as some freak exception. So I don't know what else I can do for you.

Spin it however you want, the fact remains that on a normal highway in the United States, the average vehicle will get better mileage going 55mph than faster. That includes your dad's Avalanche. Any vacuum difference would be negated by the higher air resistance in your scenario. Going on a flat road cruising, the Cobra will do just fine at 1200rpm's and burn less gas than if I was going faster. Less fuel is being mixed, less air resistance, etc. I posted this on another board, we'll see what they say. Personally I don't know why you're still arguing about this because you're just wrong :mad:

HAHA, here is the link to the LS2 thread: http://www.ls2.com/forums/showthread...hreadid=651842

The first response sums up my thoughts on what you're saying exactly.

Omg Sean, you're wrong. You're wrong. You're wrong. You're wrong. There, no I've said it more times. Do I sound more credible?

First of all, you skewed what I said originally. I never said that MOST vehicles will do better at 55mph. I said the commercial claiming that you will get better mpg at 55mph (an absolute statement) was BS. Remember the BS flag? Now I'm just repeating myself, which is why I'm so bored of this. Secondly you made me sound like a jackass, "he thinks he gets best mpg at 90 mph." Do they know that this is a blown 600hp motor with a race carb, low gearing and an OD trans that was never made for the car? Did you tell them that my car is gear limited to 270mph?! If you were so confident, why didn't you just copy and paste my original post?

As far as the responses on LS2forum, chocolate chip cookies and he's retarded with lots of smiley faces. You see, this is why as I said earlier I realy don't give a flying f*ck what checkbook tuners (like yourself) have to say. I can't even believe that you sent me that link, how embarrassing for you.

Throughout this entire argument, you have NEVER provided your own formula for determining best mpg, or even given me any technical reasoning as to why mine is wrong. You just keep saying "you're wrong Adam!" Like, seriously? Are you 12? :blah: I will not respond again until you provide some sort of techincal argument of your own as to why you think that I'm wrong. I feel like I'm arguing with a missionary. "No these people don't have vacuum guages, but you just gotta have faith Adam."

I'm arguing with someone who has no hands on experience, no applicational knowledge. How many motors have you tuned? How many motors have you built in your garage? How many superchargers and turbos have you installed? How many people have paid you to do work on their cars? But you want to argue with me about engine dynamics? Without even a techincal argument or a decent sense of reasoning as to why my argument is flawed. Step away from the keyboard, pick up a wrench Sean, you might learn something.

I told my Mercedes tech friend (UTI graduate) that you said you think a C6 can cruise at 1177rpm without lugging, and he laughed. But no... he doesn't have an LS2forum account, so I don't know what that will be worth to you. :rolleyes:

And oh yeah, VACUUM READINGS TAKE AIR RESISTANCE INTO ACCOUNT. THE MORE AIR RESISTANCE, THE HARDER THE MOTOR WILL BE FORCED TO WORK TO MAINTAIN SPEED AND THEREFORE THE LOWER THE VACUUM WILL BE. Thought maybe if I typed it in caps that time you'd catch on.

I did post a link to the entire thread. I just gave them a summary. Also, you did state your car would get it's best mileage at 90mph which is completely laughable(or crazy and stupid if you prefer). I posted your original post so you won't be so butthurt. It doesn't make you any less wrong. My contention the entire time has been that the AVERAGE vehicle will get better mileage going 55mph cruising than at higher speeds. You have done nothing to refute that. I didn't say it was some magic MPH, but it will net you better mileage than higher speeds for MOST vehicles. I don't care what your Mercedes Tech friend said or what you say. You may know how to work on cars, but I don't give a shit. Every car I've ever driven could cruise just fine in OD at 55 including Civics, Accords, Cobalts, Aveos, Focus', etc.