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Old 10-06-2011, 09:33 AM   #1
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RPM's & MPG

While on the highway, 60 MPH is showing about 2400 rpm. At 70 MPH, the tach is showing about 3000 rpm. My other vehicles show 1600 rpm at 60 mph. Am I correct in assuming there is no overdrive on my Boxster??? The last tank of fuel showed an average of 22 mpg. This is a combination of city/highway miles. What should I expect as far as MPG and RPM's?
Thanks,
Alex

PS: My boxster is a 2000 model with the 2.7 L, 5 speed tiptronic auto trans.
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Old 10-06-2011, 11:58 AM   #2
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I also have a 2000 model with 2.7, but with a 5 speed Manual trans.

In 5th gear at 75mph, I am around 3000rpm. As far as I can tell, it is normal. I average 23 mpg mixed city/highway. I get about 400 miles or so on a full tank.

I also read that it is good to rev high in the Boxster. Babying it will kill it slowly.

I guess it also has to do with what speed it shifts gears.
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Old 10-06-2011, 12:14 PM   #3
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I think it's kind of difficult for a Tiptronic owner to drive the car in quite the same manner as one with a 5 speed manual when just cruising. It doesn't help the car to be in 5th gear at 60, but not too many people buy an automatic because they want to keep it in 4th themselves, so I'm sure plenty of Tiptronic-equipped cars get "babied" in this way simply because that's the nature of an automatic.

My mileage is on the lower end, the last three tanks have been a pretty consistent 20.5 mpg, and it's a '97 with the 2.5 and a 5 speed manual, but I also put the car through its paces when I go for a drive, so I know that has to do with it to a point.

75mph in 5th puts me right around 3000 rpms, and I rarely let the car stay below 3000rpms for a prolonged period of time unless I don't have a choice or don't want to attract the wrong kind of attention because I'm in 2nd gear at 4000rpms doing the speed limit in the city...or 4000rpms in 5th on the highway (~100mph)

Folks have said having their engine computer tuned made a significant difference in their fuel mileage for the better. That's something to consider doing even if you don't do other modifications to the car, as those extra miles per gallon will add up over time.
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Old 10-06-2011, 05:57 PM   #4
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I've got a 2001 2.7l Tip with an IPD Plenum, BMC filter and a remapped ECU (but stock exhaust). My FC is probably in the region of 18mpg (abt 12l/100 - 12.5l/100). The car is used mainly on high speed highway (4k rpm avg, going up to 6k for overtaking).

I'm sure if I keep the average speed down to 65mph, I can get about 10+l/100 (22mpg). Perhaps a free flowing exhaust will help me in this case !

These cars are not very economical to run on the high speed highway runs... My E90 does the same run at about 27-30 mpg.

The FC above is with the top up, with the top down it's even worse ! And the noise level gets really loud.... always wondered if my Lexan windstop will fly off one day !

In all fairness, for a auto box, the Tip S is pretty decent, if you are in the mood for some fun, it does sense it and shifts pretty quick and it's smart enough to not shift up immediately when u back down (eg slowing for a corner). Not as quick as a VW DSG box but good enough and definitely smoother than a DSG on downshifts. I still prefer the control of a manual box though... but manual Boxsters are very rare here and hard to re-sell.

Most of my prev cars have the ECU re-mapped and all had better FC (and power) after the re-map. I found it strange that I had no improvement in the FC on the Box after the re-map, and I made the mistake of doing the remap before all the other mods (thought I wasn't going to add any mods but then got itchy).

Last edited by shlim8; 10-06-2011 at 06:13 PM.
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Old 10-06-2011, 06:08 PM   #5
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I've got a 3.2 6spd and last week on a 240 mile highway run I got 24 mpg's at 70 to 90.
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Old 10-06-2011, 07:27 PM   #6
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The should be a speed vs rpm chart for your car in the Technical Data section of your owners manual for both tip and manual transmissions. That will tell you the expected speed in any gear at any rpm.

My 2.5L 5-spd is doing a bit over 70mph at 3,000rpm in 5th gear and I average about 21-23mpg in steady freeway driving (70-85mph).

Here is the chart from my owners manual:

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Old 10-07-2011, 12:13 AM   #7
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The answer to your question is - yes - your transmission is an overdrive transmission.
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Old 10-07-2011, 02:37 AM   #8
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What are your other vehicles that run lower RPM? Engine size will affect gearing, my Integra turned 3500 RPM @ 75. I'm also guessing a Porsche isn't geared (pun intended) towards economy.

Last edited by stephen wilson; 10-07-2011 at 11:53 AM.
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Old 10-07-2011, 06:09 AM   #9
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Thanks for the replies. It's good to know this car is performing as it should. All my previous vehicles turn about 1600 rpm at 60 mph. This includes my wife's '05 Camry, and my '08 Sport Trac Explorer (with v-8, auto trans). We get over 30 mpg highway on Camry and about 24 mpg with the Sport Trac with both running about 60 mph.

Boxster safely,
Alex
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Old 10-07-2011, 08:07 AM   #10
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I have a 3.2 and recently upgraded the exhaust. I also had some other maintenace done which presumably might improve the MPG. I measured 14.5 gallons on the last fill up. I managed to get 305 - 310 miles. So I'm guessing at 22 mpg everything stock you're probably in the area that's to be expected.
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Old 10-07-2011, 11:57 AM   #11
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According to the OBC, my 2.7 gets 29 MPG highway @ 70-75 MPH, and 23 MPG in mixed ( and often aggressive ) driving.

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Old 10-07-2011, 02:06 PM   #12
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Quote:
Originally Posted by stephen wilson View Post
According to the OBC, my 2.7 gets 29 MPG highway @ 70-75 MPH, and 23 MPG in mixed ( and often aggresive ) driving.
29??? have you ever actually reset the trip odometer after a fill up and noted the mileage when the red light came on?
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Old 10-07-2011, 09:02 PM   #13
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That sounds about right for the Tip S.

It does have an adaptive memory which can learn new shift points correlating to your driving style, but that wouldn't affect the RPM's while cruising.

23MPH is in the 'normal' range for a city/hwy mix, but there are so many other things which effect your Range (MPG), especially your right foot, that you cannot gauge this metric with the RPMs and tranny alone. Tires, Tire condition, Alignment, Load, Accessories used, all play a part.

I once recorded a pure highway cruising MPG of 34.6 as a high, but this was on a fresh oil change, properly inflated tires, using the cruise control, and on relatively flat Interstate for a full tank 400+ miles.

Cheers!
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Old 10-08-2011, 06:06 AM   #14
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I'm actually doing my first manual check of the mileage now. If that shows the OBC to be accurate, I would assume the figures I saw were realistic. I don't do enough highway driving to confirm that number.
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Old 10-09-2011, 10:55 AM   #15
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Sounds about right. My car is a 98 5spd with stock motor and no OBC so I measure it the old fashion way. Mileage varies greatly with my right foot:

Mixed driving around town 21-23 mpg
Top up highway driving to San Diego (long straight flat road) 28-30 mpg
Track day 10-12 mpg
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Old 10-09-2011, 11:36 PM   #16
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Topless, at what speeds are you cruising to get this 28-30? Holy crap! I've never seen mileage that good. I'm interested to see how this most recent tank turns out...most of the driving was highway, though it was almost always 80+ unless I got trapped behind someone who didn't understand what the "passing lane" is meant for, or had to bring it back down to say hi to a Smokey parked on the side of the higway.
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Old 10-11-2011, 07:49 AM   #17
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Quote:
Originally Posted by Overdrive View Post
Topless, at what speeds are you cruising to get this 28-30? Holy crap! I've never seen mileage that good. I'm interested to see how this most recent tank turns out...most of the driving was highway, though it was almost always 80+ unless I got trapped behind someone who didn't understand what the "passing lane" is meant for, or had to bring it back down to say hi to a Smokey parked on the side of the higway.
Cruising to SD (2hrs) from my house in light traffic at about 70 mph true. The I-15 is a long straight road. I have checked the mileage a dozen times over the years and it is pretty consistent.

I had 2 kids playing water polo at UCSD so I made the trip to catch their games a lot during the season.
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Old 04-26-2012, 12:14 PM   #18
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I've yet to fill my second tank on my '05 S, but the 1st tank with a lot of spirited driving got my 21+ mpg.

I set the cruise 60 mph with no wind, and re-set the computer. After a couple miles, I was running 29 mpg.
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Old 04-26-2012, 12:18 PM   #19
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For some reason, when I do lots of spirited highway driving on my 4 hour trips often going what is considered a very unefficient speed, I average 28-29mpg in my tank.

But mixed city/highway spirited I average 21-22mpg.
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Old 04-26-2012, 12:49 PM   #20
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Quote:
Originally Posted by Overdrive View Post
Topless, at what speeds are you cruising to get this 28-30? Holy crap! I've never seen mileage that good. I'm interested to see how this most recent tank turns out...most of the driving was highway, though it was almost always 80+ unless I got trapped behind someone who didn't understand what the "passing lane" is meant for, or had to bring it back down to say hi to a Smokey parked on the side of the higway.
I got 29.2 mpg on a 90 mile freeway drive from LA to Willow Springs Racetrack last weekend while averaging about 75mph in virtually no traffic (it was 5:30am!). Filled up before I got on the road and filled up again when I got off the freeway and did the miles divided by gallons calculation manually.
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