Topic: Fuel Economy/Octane ??s
in Forum: C3 General Discussion
Already a Member?
Click Here to Login
Not yet a Member?
Click Here to Register for Free!
Loving my new vet and driving the heck out of her. I have to admit I have been driving a bit..um..agrgessive on the highway 
I just filled her up for the third time and after doing some quick math realized I am getting horrible mileage..what a shock, I know.
I plan on taming down my driving a bit, and I live in a sleepy little town with speed limits of 25-35. So I was wondering if it makes much difference which gear I drive in. At 25 mph my RPM are 1700 in 3rd and 1200 in 2nd, and at 35mph my RPM are about 1500 in 3rd and 2300 in 2nd.
Does it make sense that the engine is working harder in 3rd and therefore using more gas? Or do I have it backward?
And on another related note, what octane do you suggest. I have used both 89 and 91. Or can I get away with 87? I have a new crate engine with 5k miles on it, 350 ci/260 hp.
Sorry for the noob question.
I just filled her up for the third time and after doing some quick math realized I am getting horrible mileage..what a shock, I know.I plan on taming down my driving a bit, and I live in a sleepy little town with speed limits of 25-35. So I was wondering if it makes much difference which gear I drive in. At 25 mph my RPM are 1700 in 3rd and 1200 in 2nd, and at 35mph my RPM are about 1500 in 3rd and 2300 in 2nd.
Does it make sense that the engine is working harder in 3rd and therefore using more gas? Or do I have it backward?
And on another related note, what octane do you suggest. I have used both 89 and 91. Or can I get away with 87? I have a new crate engine with 5k miles on it, 350 ci/260 hp.
Sorry for the noob question.
SPONSOR AD:: (Our Sponsors help support C3VR)
You can try a tank of 87 octane. If the engine doesn't "ping" while accelerating or "diesel" when you shut it off then I would assume it's safe to use 87 octane.
On my trip to Ft.Wayne I tried out a tank of 89 octane in my vette to see if I could save a couple bucks. Well it didn't like it. The engine would "diesel" when I'd shut it off. So I have to stick with the 91 octane.
Is your spark timing set to manufactures specs? Sometimes if the timing is set to high it won't work well with low octane fuel.
I'm assuming the car is a manual shift.
As far as gear selection when cruz'in around town, just pick a gear that doesn't make the engine "lug" while trying to maintain a low cruz'in speed.
GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
Lifetime Member #26
Borgeson Steering Box
Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
Lifetime Member #26
I've wound up sticking with the 89 octane.
87 caused the pinging, 91 was good and so was (is) the 89.
Since I didn't notice any difference between 91 & 89, I stuck with 89.
The lower octane seemed to be more of an issue around town and less with highway driving.
Yep, bottom line is use what makes it happy, and gives the best fuel mileage. Sometimes it takes a bit of trial and error.
Seems to like the good stuff best. I havent had the heart to try the 87 yet.
Sarge, actually it is a 3 spd. I was just wondering if there was any data on fuel economy at different rpm's. A stumper for the gallery, eh?
Sarge, actually it is a 3 spd. I was just wondering if there was any data on fuel economy at different rpm's. A stumper for the gallery, eh?
Fuel economy at different RPM is too much of a variable. First, there are the differences in the engines and state of tune. Then the tire size, final drive ratio, and transmission ratios also make a difference. The load on the engine also makes a difference. You can be at light load, mid load or heavy load at the same RPM.
There are simply too many variables to make a chart.
Lifetime MemberIrving, TX - USA
Joined: 8/21/2004
Posts: 4273
Vette(s): #1 -1969 Corvette Coupe Riverside Gold, black interior,MN,A/C,350/350,PS,PB,window cranks.
#2 -2000 C5, black/black, 6 sp, Bose system & lots of buttons.
[QUOTE=madmick11]kstyer=Thanks!! That is really helpful. And it totally makes sense. Guess I am better off just not telling my right foot ANYTHING about fuel economy. [/QUOTE]
[/QUOTE]
Hey, don't feel bad.........my right foot gives me a hard time too!
�����
My Link 
MICK - C3VR Lifetime Member #113
Charting MPG's isn't any fun...drive it like you stole it!
in Forum: C3 General Discussion
SPONSOR AD: (Our Sponsors help support C3VR)