RPM for best gas mileage???

[Carl Bauer]

I'm driving my '79 SC to NC from CO in a few weekends. What's the best RPM range in a stock 915 for optimal gas mileage over this long haul?

[Early_S_Man]

Carl,

I have found it to be around the torque peak rpm. There are other factors that would alter mileage, though!

I suppose you can experiment along the way on your trip.

[Superman]

With the new (20/21) cams my engine is different now, but before, power did not come on until 4000 rpm. I seemed to find better mileage above that than below. In other words, officer, the car is more fuel efficient at 90 than at 80 mph.

[RoninLB]

Carl...I wouldn't worry to much about fuel mileage..Warren is correct 110%, but your not in a gas boat doing 1 1/2 miles per gallon..and a quick/simple blast from N.C. to Co. is just like stretching out before a workout..I think your SC will like the exercise better if you run at 3.4k to 3.8k..avoid 3k in 5th..avoid lugging in road work areas..minimum of 1.5k in 2nd anytime...the difference of 22 mi/gal and 25 mi/gal should be meaningless to you, IMO.. avoid a quick shut down for fuel/maybe slow to 3.2k 5-10 mi. before shut down..after a full cool down wait for oil temp to rise before the 3.4k-3.8k...Enjoy..............Ron

[nostatic]

Originally posted by RoninLB
..avoid 3k in 5th..avoid lugging

The no lugging I understand and follow religiously (120K or so put on my Bugs so I'm well trained). But why avoid 3K in 5th?

[pwd72s]

WHAT??? You guys are saying that 6,000, give or take a bit, doesn't deliver the best mileage? Seriously, not sure of mileage, but with S cams, my car seems happy just loafing along at 4,000...temp gauge stays steady there as well.

[island911]

avoiding lugging up a mnt pass should help keep the temps at bay, but better milage at 90 rather than 80. . . hmmm. . .does your car speed up to 90, when you let off the gas at 80?
Anyway, off a 1981 911 P- Factory poster:

[pwd72s]

Gawd, there always has to be somebody who spoils the fun with "facts" Could you imagine anything worse than cruising a deserted & flat stretch of highway at 56 MPH, muttering to yourself, "I'm getting 35 MPG" I wonder what the guy in the YUGO, also doing 56, is getting? Perhaps a BJ? A guy has to do something to stay awake...

[RoninLB]

I'm with Paul on this one..best gas mileage = high Cyl. Head Temp.,IMO......3k in 5th shows a higher temp than 3.2...3k in 5th on a 4% road incline is caa caa/doo doo...reminds me of a time when I had this French female in my 911..somewhere in conversation she says "wee wee"..and I shout .."Not In This Car".........Ron

[pwd72s]

LOL...LOL...LOL...LOL...

[nostatic]

21mpg in the city? Not in my car...I've been running around 15-16. Tomorrow we do a San Diego run so I'll see what the freeway yields.

[scarebus]

Carl,
I would just inflate the tires couple of
psi higher than normal and cruise at 9 mph higher
than speed limit. You get tickets going over 10.

[RoninLB]

Originally posted by nostatic
21mpg in the city? Not in my car...I've been running around 15-16. Tomorrow we do a San Diego run so I'll see what the freeway yields.

,,,,,yeah, feel it out..it's more than your eyes can see when you flip the lid...different road condition/different style, not the driver.the car... what I found interesting about S. Calif. desert driving it that my oil temp rose at a faster rate than Cyl Head Temp when ambiant was over appx 100deg...that relaxed me to see CHT at a relatively cool temp in high ambiant heat... the similar oil temp rise in cooler ambiant would be a consideration in rpm selection.don't know what would happen to CHT if I added another oil cooler under left fender...soo, the 3.8k-4k ride in 112deg desert heat had great CHT, and the oil temp rise became a less limiting consideration..in my 911... the best max/logical rpm for the 911 engine is a beautiful thing...............Ron

[RoninLB]

Originally posted by pwd72s
[ Could you imagine anything worse than cruising a deserted & flat stretch of highway at 56 MPH, muttering to yourself, "I'm getting 35 MPG" I wonder what the guy in the YUGO, also doing 56, is getting? Perhaps a BJ? A guy has to do something to stay awake... [/B]

..I think you might be able to pull the tweezers from your tools and pull nose hairs for action..have any of you "best mpg" guys done that...not trying to be aggressive/only provacative.......
Love, Ron

[RoninLB]

Originally posted by scarebus
Carl,
I would just inflate the tires couple of
psi higher than normal and cruise at 9 mph higher
than speed limit. You get tickets going over 10.

I think tire wear/tire temp across the thread [3 points] becomes a consideration on big rides..otherwise do the psi that feels good/safe..tire psi affect on handling on a good ride affects driver fatigue/enjojment...party hearty...............Ron

[Erakad]

Who cares!!! Just drive it! If you get 5 mpg...who cares...you're drivin' dude...and you're drivin a Porsche!! Who cares about mpg??

[RoninLB]

Originally posted by Superman
With the new (20/21) cams my engine is different now, but before, power did not come on until 4000 rpm. I seemed to find better mileage above that than below. In other words, officer, the car is more fuel efficient at 90 than at 80 mph.

.tell you something..it took, what felt like 2 minutes to realize that Superman took his rpm/flat 6/management seriously..then it was like two long lost friends hugging each other..If Super offers a reply take it to the front..IMO, Super has the best managed 911 that I have seen on 2 diff. BB, Metro PCA, and others..cash flow/management/love of 911 turned Superman's 911 into a trophy winner...another unrecognized hero around here......Ron

[Jack Olsen]

What RPM would an SC be in at 56 mph?

[nostatic]

As I recall, 5th gear at 56 mph is around 2K...maybe 1800rpm. I've had the pleasure of hitting those parameters coasting in traffic on the I10. I remember my '87's shift light came on at stoopid low rpms so the optimal mileage (according to the factory) seems to be in the low revs.

[Early_S_Man]

Right about power peak in 2nd gear!