[XtremeRevolution]

Nice! Thanks for sharing this information. You've successfully exceed what even the Prius is rated for. I'm looking forward to seeing your results when you move up to a higher octane fuel.

Do you have any results from when you inflated your tires, or have they always been at that pressure? Have you tried going any higher? Not suggesting anything here, just curious.

 

[XtremeRevolution]

The past two weeks worth of daily reports are with my tires at 38 psi cold. Yes I have entertained the idea of increasing the psi I mean im on the road all day im constantly thinking of ideas to increase efficiency. But like others I am skeptical of any cold psi above 45 for reasons im sure everyone is aware of. I do have plans to increase my psi in the near future im curious to know if I will experience enough of an increase in mpg to make it worth the added risks of being 10psi above reccomended specs. So if i dont see a substantial increase in efficiency im talkin a 4-5 mpg increase I will stay in my comfort zone for psi which is between 37-39 cold because in hot weather I know they will be in the mid to upper 40's

There aren't any risks to increasing even up to the maximum sidewall pressure. That pressure is a cold pressure and is 100% safe to use. Not only is hydroplaning resistance improved, but stopping distance remains unaltered. Tire wear is improved both with regard to life and with regard to uniformity. The only real downside is the ride stiffness when going over small bumps.

So far, people have recorded a 4mpg increase going from 35psi to near the sidewall maximum.

 

[XtremeRevolution]

Too late, you're already in it.

I run 44 in my LS. On Saturday, when the ambient temp was well north of 100F, I took her on a 55-mile highway jaunt. PSI never went over 50 hot.

It's worth noting to everyone else, as you've demonstrated, that the sidewalls of the tires will get much, much hotter due to rolling resistance when the tires are at the factory recommended pressure than at higher pressures. This will gradually shorten the life of the tire by causing irreversible heat-induced tire degradation, which can eventually lead to a blowout.

At 50psi cold, I see a variation of no more than 3psi on the front tires and 2psi on the rear tires of my Cruze Eco. Granted, those are already "low rolling resistance" tires, so I'm sure this only makes them glide even better. I have a thread in this fuel economy section of the forum where I've started measuring tread depth on all 4 tires with consistent 3,500 mile tire rotations to track both overall tire wear, and wear uniformity.

 

[XtremeRevolution]

Sorry - my point by comparing to the Prius is that you can get high mpg without spending an arm and a leg (you need two of each to drive a stick). As a friend of mine told me "you can't brag to your highbrow eco-friends that you're saving the planet by buying a hybrid". I told him I saved green.

As for Hybrids, looking at the sedans listed on hybridcars.com, only a handful of hybrids actually get better mpg than the Cruze ECO MT. A lot appear better on the EPA tests but looking at Fuelly.com, the ECO MT is far better than its EPA ratings but that the hybrids aren't.

My thoughts exactly. I know of very, very few people who drive a Cruze Eco MT that don't get better fuel economy than the EPA rating.

 

[XtremeRevolution]

91 will probably make a bigger difference as the weather gets much hotter.

 

[XtremeRevolution]

Yeah its actually been in the mid 80's here in idaho the past week I think we reached 90 once or twice. Average this time of year is 65 degrees. Still was getting impressive mpg's in the hot heat. Now that I think about it I was getting my best MPG in that heat the last 2 weeks. But yeah I need to find some pure 91 octane around here and see what it can do for me.

Keep in mind, the higher heat means your car warms up faster and spends less time in open loop as a result. Granted, that also means you may need air conditioning, but still. The hotter air is also thinner and creates less air resistance. I'm not 100% sure how much of an effect this has though...

 

[XtremeRevolution]

NO!!! Do not do this!!!!!! It has been proven in mythbusters and countless articles. If you are over 50 mph, rolling down a window in favor of air conditioning is WORSE on your fuel economy, let alone uncomfortable. You are also severely overestimating the impact of A/C on your engine. It is a minor unnoticeable load in everyday driving.

Last time I was at the drag strip, I actually did a run accidently with the air conditioning running. I did another run with it turned off and guess what... No change - both 15.8 @ 87 mph. If the load it puts on your engine was significant, it would noticeably affect horsepower. The effect would be much more pronounced on the track where any little thing will affect your time.

The reason why your times were identical with air condition on and off is because the PCM disengages the AC Compressor clutch when you hit a higher throttle position and/or RPM level, not because there's no load on the engine. This function has been around since the early 90s if not even earlier.

Go to a Chevy dealership and try driving a Cruze Eco MT, then come back and tell me that A/C has little parasitic effect on the motor. That's simply not true. I am quite used to driving my Eco MT by now, but I get thrown off every time I run the A/C because the RPMs drop significantly faster, causing me to need to shift faster. Performance is noticeably reduced.

 

[XtremeRevolution]

It won't be noticeable until you approach 100 degrees. At least, I never noticed it in last summers 90 degree heat. The hot weather MPG comparisons were in 100+ degree heat out west. 91 Octane at that point helps, but there are more important things going on at that point like heat soak causing the ECU to cut horsepower.

The problem here is that you have no way of testing this anymore. Is aid it before, and I'm saying it again, mark my words, there will be a huge rise in people joining this forum and creating threads on hesitation, "bogging" and poor performance during the hotter summer months. Just give it another month or two.

 

[XtremeRevolution]

Interesting did not know this. So to play devils advocate.. why do people bitch about lack of power with the A/C on? I mean I understand the Eco MT and Auto Transmission models have a lot of different engine features we just don't know all of them LOL.

But yeah, it's not worth sweating for no A/C. Unless your crawling in the city, the effect of windows on the aerodynamics hurts mileage more than the A/C it has been proven and documented. The Eco relies even more on aerodynamics than other models

Well, keep in mind, when people say "lack of power," they don't really know what they're talking about. To clarify what they mean, when they say "lack of power with A/C on," they really mean "lack of power for a given throttle position" with A/C on. With daily driving around town, you'll notice more sluggish acceleration with A/C on, especially if you do most of your driving in low RPMs with low boost like I do (1100-1600RPM). In those situations, the throttle position and RPMs won't be high enough to cause the PCM to disengage the A/C compressor clutch, so it will continue to rob power from the motor and the car will simply feel slower. It's those conditions that people complain about, as it's not really practical to go around town with your foot to the floor the whole time. I just happen to notice it a lot more because I generally drive in those lower RPMs where power is low to begin with, so having the A/C compressor on makes a very noticeable difference for me. I've gotten to the point where if I have to accelerate from a stop, I'll just turn the A/C off until I get moving again.

+1 on the aerodynamics. You're right, the drag on the windows will hurt your fuel economy significantly more than the A/C will once you get up to speed. That, and all that white noise isn't good for your ears either.

 

[XtremeRevolution]

As far as I know, no 6 cylinder engines have the A/C shut off when during hard acceleration. This feature appears to only be on 4 cylinder engines. Many 6's are just barely powerful enough for the vehicle size, so the A/C drag is really noticable.

As an aside, my Fiero 2M4 had the A/C cutoff feature in 1985.

Both the 3800 Series 1 and the 3800 Series 2 supercharged motors I've driven have this feature. It's not just a feature to save power when you need to accelerate, but also to save the compressor. I don't suspect the compressor likes spinning at whatever the pulley-adjusted speed is when the engine turns over 5000+rpm.