Gas mileage #'s

DeeVeeEight

DeeVeeEight

Fast Pedalphile
Joined
Nov 3, 2008
Messages
2,287
Location
Southern New Jersey, USA
With my old transmission and it's 1:1 final drive gear I used to get about 10 mpg, 70 mph was 3000 rpm. Now with the new overdrive gear (.82 od with a 3:25 rear) I started to get around 13 mpg, now 70 mph is 2000 rpm. Here's where I have some questions. The above numbers make sense, a 30% increase in fuel economy and approximately a 30% cruising rpm reduction. The other day after a cruise with the windows open I got around 15 mpg. A few days later with the tops off I got back to 13 mpg. Most recently with the tops on, windows rolled up and the A/C on I got 17-18 mpg. Does that sound feasible? Is the drag coefficient so adversely affected by the windows and/or the tops being open or off? Is 18 mpg achievable with the A/C on like that or am I hallucinating? I have a Holley 750 and an Edelbrock Performer Air Gap manifold.
 
DV8 my only comment is from mammories of comments past....that you get better economy with top UP.....dunno why, just heard the comment lots of times....

I DO know this, on my stock L48 (rebuilt with mild/stock cam by prev. owner) got about 12-14 at tops....14 on the freeway.....Muncie 3.36 rr

I WAS going to put a TPI on that thing, but got sidetracked with other repair issues water pump, radiator type shit....so I went with a '88 vette serp setup I had from other cars....

the thing went TO 24 mpg on the freeway....same cast rams horn headers..I cut out the heat riser valve and had a bung welded in place of that valve setup...for the O2 sensor...stock tune with all the crapola taken out...speed density,...

wish I had stayed with it....today I have a more hotrod engine and overdrive and LESS MPG....not sure why, just do....I think too much CAM, and serious thinking of going to a GM stock ZZ4 cam to cut down on the 'power' but pick up some MPG....

today it gets 18 on the freeway clocking a Garmin proven 80 mph ....that sux....

:suicide:
 
BRUTAL64 said:
I get 17 mpg with 3.55s and a M20. That was casing Vettezuki from Palm Springs to Anaheim.:friends:
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With 400 cubes and dual quads? Your gear ratio is less favorable than mine too. I am going to have to try and improve my numbers. Something don't smell right here in 'Joisey, maybe I need to take some of the lead out of my right shoe.:push:
Did you run with windows/top open or all closed up? And this one I am afraid to ask... do you have A/C on the car?
 
I have 336 with an M20. I just went through a tank and got about 15MPG varied driving with TTops off. In the late fall/winter with the tops on, I get a little bit better at 17mpg. The AC is out of commission.

I don't know if it's the aero dynamics or the cooler weather that helps my MPG.
 
I get about 6-7 mpg regardless if the windows are up or down,or if the t-tops are on or off. I f i wanted good fuel mileage i would drive a Hybrid car.
 
These Edelbrock carburetors are advertised to be "calibrated for performance rather than gas mileage" - one of the few times the advertisement is correct :bump:

After I recently installed this 800cfm carb and the air gap manifold my gas mileage dropped to somewhere around 10mpg ... burnt like a 1/4 tank on the way to Cocoa and back home, most of that was highway driving at 2200rpm, I did floor it a few times and accelerated from 60-100 .... I'm guessing I get around 7mpg in the city.... :devil::amazed::bounce::toothbrush:
 
kwplot34 said:
I get about 6-7 mpg regardless if the windows are up or down,or if the t-tops are on or off. I f i wanted good fuel mileage i would drive a Hybrid car.
Click to expand...


It's not that I wanted good fuel economy, I am starting to get it. If I drive and shift at 5000 rpm I'll be right back into the single digits again real quick, but cruising on the highway, A/C on and the car closed up gets me into the mid and upper teens. Not too bad for a 30 year old muscle car.:cool:
 
DeeVeeEight said:
BRUTAL64 said:
I get 17 mpg with 3.55s and a M20. That was casing Vettezuki from Palm Springs to Anaheim.:friends:
Click to expand...

With 400 cubes and dual quads? Your gear ratio is less favorable than mine too. I am going to have to try and improve my numbers. Something don't smell right here in 'Joisey, maybe I need to take some of the lead out of my right shoe.:push:
Did you run with windows/top open or all closed up? And this one I am afraid to ask... do you have A/C on the car?
Click to expand...

Windows open and the stereo at 3/4s. :wink:`

AC???? I don't need no stinkin AC!:lol:
 
BRUTAL64 said:
DeeVeeEight said:
BRUTAL64 said:
I get 17 mpg with 3.55s and a M20. That was casing Vettezuki from Palm Springs to Anaheim.:friends:
Click to expand...

With 400 cubes and dual quads? Your gear ratio is less favorable than mine too. I am going to have to try and improve my numbers. Something don't smell right here in 'Joisey, maybe I need to take some of the lead out of my right shoe.:push:
Did you run with windows/top open or all closed up? And this one I am afraid to ask... do you have A/C on the car?
Click to expand...

Windows open and the stereo at 3/4s. :wink:`

AC???? I don't need no stinkin AC!:lol:
Click to expand...

Gotta toss this interesting observation into the pot here....years ago when driving in various cars/vans the very LO freq vibrations from air flows...at most noteable highway speeds....~50+ mph....that really lo freq to me meant energy losses....probable not enough to actually affect fuel economy, but rather uncomfortable for any long time....Typically I would just put up the windows and turn on the HVAC having over with it....

convertibles don't suffer the same shit...dunno why, just my observations...

I LUV sunshine....

:crutches:
 
Try feedin' Ol' Red. :gurney:

I guess I'm going to have to change that- with the addition of the 77 that's also Red, I guess now it's going to be Big Red and Little Red:confused:
 
BigBlockTank said:
71 LS5 454 in my 69, 3.08 rear, I get, at best, 14.8 around town, half heavy foot.


Tank
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I hear of the fantastic MPG the new LS1-XXX series engines get, like near 30 in a new vette, and so I would like my old 25mpg figger back again...cruising at 60-80 yesterday for 220 miles or so almost burnt a tank, and that's not cool...the tank was near 3/4 when I started, gauge is fairly accurate....but that gas is pushing 3 bux/gal now on 91 octane....so

There are two approaches that are within reach of being affordable....

one is to stick with the present computer system, get yet another chip burn, and go for a milder cam.....say a stock ZZ4 and get over with it...

the other is to get a later LS computer, go for the rewire, and yet another attempt at learning automotive programming, and laptop links....

so what are you alls' thoughts....
 
A lot of these claims just don't add up. The brakes on these things drag like crazy. The coefficient of drag is not good. I'm sure there are other intrinsic reasons why these cars will never achieve some of the numbers being claimed here. You can't change the laws of physics. If you have a big block with carb and you're getting 17 mpg in town, you better check your math! I think most of you need to check your math.

My brand new mustang V6 gets around 25-28 on the hwy. There's no way guys....your getting these kinds of numbers.

I had a 283 in mine at one time and drove back and forth to work on back roads at approx 45mph which is about the most efficient speed for mileage and i got 17 mpg. The carb was running lean too. Oh, yea with the 700r4 and 3.08 gears.
 
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The mighty Caprice powered Disco Buggy with 700R is always the LAST car to fill up on a Bird Run.:noworry:
 
turtlevette said:
A lot of these claims just don't add up. The brakes on these things drag like crazy. The coefficient of drag is not good. I'm sure there are other intrinsic reasons why these cars will never achieve some of the numbers being claimed here. You can't change the laws of physics. If you have a big block with carb and you're getting 17 mpg in town, you better check your math! I think most of you need to check your math.

My brand new mustang V6 gets around 25-28 on the hwy. There's no way guys....your getting these kinds of numbers.

I had a 283 in mine at one time and drove back and forth to work on back roads at approx 45mph which is about the most efficient speed for mileage and i got 17 mpg. The carb was running lean too. Oh, yea with the 700r4 and 3.08 gears.
Click to expand...

I guess I'll have to start laying off of the mushrooms.....:huh:
 
turtlevette said:
A lot of these claims just don't add up. The brakes on these things drag like crazy. The coefficient of drag is not good. I'm sure there are other intrinsic reasons why these cars will never achieve some of the numbers being claimed here. You can't change the laws of physics. If you have a big block with carb and you're getting 17 mpg in town, you better check your math! I think most of you need to check your math.

My brand new mustang V6 gets around 25-28 on the hwy. There's no way guys....your getting these kinds of numbers.

I had a 283 in mine at one time and drove back and forth to work on back roads at approx 45mph which is about the most efficient speed for mileage and i got 17 mpg. The carb was running lean too. Oh, yea with the 700r4 and 3.08 gears.
Click to expand...

Jim/TV you rong, in winter early '97, I drove to Florida and back from DC, with my L48/L98 induction, rams horn, O2 in the heatriser, stock L98 tune, speed density engine.....serp drive, electric fan, aluminum rad....

muncie and 336 as now, had same 17x9.5 tires/rims as now....but with whatever size the C4's came with...255? 40/17 so lower profile/diameter than now.....the car got 24 mpg up and down I95 cruising at indicated 70-80 mph with traffic, no faster..... it's a 11 hours trip....

so I can't get that good even a lower speeds now with the cammed up roller engine and overdrive.....which is why I tempted to de-cam the thing....:eek:

still think with that alternate cyl/fail to fire the injector every other stroke, is the trick to so much better on a C5+......but that required sequential then the interrupt program....another computer off a LS engine....

I have had O rings forever, my brakes allow the car to coast backwards out the garage about 90% of the time....
 
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