Best MPG Gear/Speed?

I just got back from a 1000 mile road trip. It was amazing. California Highway 1 is a must for any Cayman owner. I got incredible gas millage on this trip. Most of the time I was traveling at around 80mph in 6th gear (on highway 101). This was giving me around 48mpg . Shocking... I thought my readout was broken, but considering how many times I had to refuel on this trip, it was right. My average MPG for all 1002 amazing miles was 24 . This has led me to wonder (besides why anyone would buy a Prius) what is the most fuel efficient speed/gear combination on the Cayman S (and Cayman too)? Someone with Math skill could work it out I'm sure. Friction vs Speed. :cheers:

i averaged that mph for about the same length and got around 25mpg....42 is insane. Your forgot to tell us about your Prius engine swap?

42? how is that possible? I just drove 600 miles on the interstate and got about 23.5mpg. Was cruising at 100mph about 30% of the way. So what gear and mph/rpm were you going at?

Whups - Typo. While doing 80mph in 6th I was getting 48mpg. For my whole 1002 mile trip, the average was 24 (not 42).

You should see how many mpg I get in 6th at 0mph

0?

Depends on what way the wind is blowing. I'm certainly not running out of gas.

I got 7.9L / 100kms at 100-110 km/hr today for a 50km trip. Thats one bonus of mods... more efficiency! BTW, thats 30mpg in the old language. You got 48mpg? No way ho-zay, something wrong big time. Unless you were rolling down a slope with ya foot off. 24 average about sums it up, its ok but not 30!

850 miles from Colorado to St. Louis Admittedly downhill part of the time but also at less efficient altitude ~26 mpg running 80ish most of the way on 91 octane until Missouri.

Not much math skill needed: lowest rpm=lowest gas consumption, so go with your tallest gear (6th) with minimum rpm (say 2000).

I dont know guys...I just dont believe a Cayman can get anywhere near 40+ mpg anywhere..anytime. Most of my driving is shorter trips but I have never even gotten 20mpg. I did go on a long trip or two in the CS but did not calculate the mpg for that specific trip... At any rate I am at a steady 17.4 mpg for almost a year now. It does not budge....up or down.

I've gotten 27 mpg in my CS on the Reno to LA trip several times doing 5-7 over speed limit with 6th gear. This is an actual computation (miles/gallons used) and not off the car computer. I have seen the computer on mine show 38 mpg but never paid atention to it. Even a 2.7l isn't going to get over 32mpg over level ground. Craig

Try this: Just before going onto the highway or while driving on the highway, reset your mpg info. Put her into 6 and get to 80mph. See what it says...

Best for me on level interstate at steady 65 in 6th yields 30 which I always thought was AMAZIN. Can't imagine much more unless long downhill stretch.

I routinely get 18 in the city and 24-26 on the highway (at 75-80 mph) with my CS. I think this is fantastic for a car this powerful.

I have a 2007 base Cayman (2.7). I have kept careful track, and my average over 10000 miles is 25 mpg. Driving 40-50 mph in 5th I have seen the displayed mileage get to 31 or 32. 80 or 90 mph is definitely worse than 60 or 70 for mileage. I got 28 over a tank in vermont driving between 40-60 with no traffic or stops. I have found that the in-dash mileage display is 1.5 mpg or so below mileage obtained by dividing miles traveled (per the car) by gallons (per the gas stations), and that this is pretty consistent. I don't understand why.

Sounds faulty to me. The faster you go the worse the reading will be. At a certain speed it will be optimal. Something like 90km/hr. I Must test that one day... when Im not in a hurry.

Here in the UK in our gallons and on the motorway we record over 30 at 80mph. My wife claims 33 for her commute via motorway - 80miles each way. Thats on a 2.7 car with a 5 speed box. Of course we are not using the air-con - thats 10% probably.

Remember, it's not just lowest rpm that yields results. The closer you are to peak torque, the more efficient the engine is running.(better cylinder filling, reduced pumping losses) Now, I'm not suggesting you run at 4 or 5k, clearly that is wrong, What I am saying is that in any rpm range of say 1k there will be peaks and troughs in torque (efficiency). So if you are running in a trough (relatively) you mat be losing out compared to an rpm slightly higher. It's not clear cut but a torque curve can help. Regards

Nope, not broken, but I believe that reading is an instantaneous reading of the mpg at a given point. At that point you were traveling downhill and had nearly lifted completely off the gas pedal. Either that, or your readout was broken. No way any car, let alone a Cayman, gets 48 mpg at 80 mph. Unless it's falling from an airplane. I have a hard time believing anyone is averaging more than 25mpg, and your 24 mpg seems... achievable. Still, these are surprisingly fuel-frugal vehicles, particularly considering how much fun they are to drive!

Engine efficiency is not the same as best gas mileage. You are using 2-2.5 times the gas at 4-5K as 2K, regardless of whether it is all completely burned. You will not get 2-2.5 times further down the road, though. Lowest rpm dominates this equation.

Hi, I need to clarify, between any rpm range (it could be 1500 - 2500) there would be peaks and troughs in the efficiency. If you have a peak at 2000 it could be more economical than running at 1700. Using a dyno graph will help to find peaks. regards

The amount of fuel used depends on more than just engine speed. Typical fuel maps also adjust for mass air flow (MAF) readings and manifold air pressure. The map can also be adjusted to actually target different lean/rich mixtures for different conditions. There are also correction factors applied for inlet air temperature, engine temperature, etc. On a different car, I mapped my conditions for typical highway cruising, then programmed the region of the fuel map to run slightly lean and adjusted the spark to get the least fuel to maintain that speed. I ended up with a highway mpg average of 25+ in a 4000lb car with a ~575hp engine. Unfortunately I don't think we can get enough data with accurately recorded test conditions to determine the best rpm under all conditions, but for most cars it will be top gear and around 40 mph. Drag from the air goes up roughly as the square of speed and quickly becomes the dominate factor as speeds go above 40. Caymans are pretty sleek and aren't affected as much as most other cars, but the effect is still present. Without this and rolling friction a car would sustain 60, 90, or even 173 mph across level ground consuming no more gas than at idle. That being said I would go insane if I had to drive more than 5 min at 40mph. If fuel economy becomes that critical I will stay home (or at least take one of the Minis).

I think I saw about 28mpg in my '05 Boxster S while driving six hours to the beach last summer. I was quite pleased.

Encouraging to hear because for my first 500 miles I was burning through gas and began to get concerned something was wrong. Obviously in the break-in phase so wasn't ever going really fast. Gald to report last 300 miles I 've been getter better mpg.

Use this calculator Yeah, it's crazy how much speed affects your mileage. Check out MpgForSpeed.com - Fuel Efficiency Vs. Speed It has a calculator that will show you exactly how much you can save and explains why.

I went to Maryland from Pittsburgh, PA this past weekend and managed 27MPG over about 400 highway miles.

Forgot about this thread - was hoping it dissipeared. Turns out I can't actually read - I was reading mph (average) instead of mpg. 80mph in 6th gear yield me around 26.4mpg Ive been playing with the reset switch at different speeds on the highway while in cruise control. Best way to find the most efficient mpg speed.

Did a 60km trip and got a new personal best of 7L/100km or 34mpg. At one stage it was reading 6.7L/100km but the average ended up at 7L/100km. Average speed 100kph. Amazing! Anyone with some DFI economy figures yet?