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Old 12-13-2011, 09:57 AM
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Default Best gas mileage RPM

What RPM's will you get the best gas mileage at in a big block?
I believe I read somewhere that you want it to cruise at where your peak torque is.
I'm trying to figure out which gears to put in my dually for cruising. I don't really use it to tow (maybe once a year) since I sold the race car. So I don't need to worry about that as much now.
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Old 12-13-2011, 10:41 AM
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While the engine will be most efficient at or near the torque peak, you will get the best mileage by keeping the rpm's at the lowest level possible. That's why all the new cars/trucks have overdrive transmissions.

Furthermore, thottle position is irrelevant. WOT at 1500 rpm will give you better mileage than light throttle at 3000 rpm. This is a common argument in this part of the world because it seems like the engine isn't being worked as hard going up a mountain pass with light throttle in a lower gear.
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Old 12-13-2011, 06:27 PM
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its crazy but i get better mpg at 2700 rpm at 80mph then 65mph at 2000 rpm 15mpg @80 13mpg @65 check it twice at drag week
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Old 12-13-2011, 09:30 PM
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It will depend on a few things.
How well the fuel metering system is dialed in.
The engine build. More agressive the higher the RPM for best economy.
If the gears, carb size engine build is right with a carb set up keeping the throttle opening at cruse within the idle curcuit will get the best economy.
of course the idle circuit has to be metering correctly to do it.
Dialing in the advance curve is necessary to for any of the above to work well.
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Old 12-13-2011, 10:00 PM
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I got 4mpg lol
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Old 12-14-2011, 12:22 AM
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Quote:
Originally Posted by quick 52 View Post
its crazy but i get better mpg at 2700 rpm at 80mph then 65mph at 2000 rpm 15mpg @80 13mpg @65 check it twice at drag week
Man that would be good excuse when cop pulls you over for going 80mph. Just trying to conserve fuel! LOL

Certainly is not always cut and dry. A good FI system with data logging can go a long way to see what is going on.

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Old 12-14-2011, 02:30 AM
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A better question IMO is what MPG are you 600ISH hp BBF guys getting with your street cars. Im not interested in an E85 or race gas burning 800+hp monster. But a 550-650hp pump gas, street driven STREET motor. I had a 408 with an 850 holley and i got 6mpg if I was nice to it so im interested to see what you BBF guys are getting with another 100+cubes and 1000+cfm carbs.
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Old 12-14-2011, 07:43 AM
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Idle
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Old 12-14-2011, 08:39 AM
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Originally Posted by truebluedevil02 View Post
A better question IMO is what MPG are you 600ISH hp BBF guys getting with your street cars. Im not interested in an E85 or race gas burning 800+hp monster. But a 550-650hp pump gas, street driven STREET motor. I had a 408 with an 850 holley and i got 6mpg if I was nice to it so im interested to see what you BBF guys are getting with another 100+cubes and 1000+cfm carbs.
Seems 7 is about what a hot street build will get to me my previous 466 got 7mpg city or highway when tuned for max performance, interestingly enough a few trips with my 523 I found that it also got 7mpg city or highway.
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Old 12-14-2011, 09:02 AM
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What I'm looking at here is a gear change for my Dually.I've looked at a possible Overdrive swaps but I just don't have the money to do it right now.
I'm limited to either a 3:54 gear or 3:73 gear. I have 4:11 in it now from the factory. I don't really use it to tow anymore but possibly once a year at tops! I need to rebuild the motor but I'm in the process of doing the paint & bodywork so I don't have the funds for that till that's all done.So a gear change is the most cost effective right now.
With 3:54 gears I would be cruising at 64 mph at 2500 rpm's.
With 3:73 gears I would be cruising at 61 mph at 2500 rpm's.
I don't use the truck really on the interstate just simply because I couldn't afford the gas & I have more economical vehicle to drive for that. Most of the areas I drive in is a 55 mph speed limit so that's about that range aia drive it in.
What do you'll think?
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Old 12-14-2011, 09:55 AM
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Quote:
Originally Posted by truebluedevil02 View Post
A better question IMO is what MPG are you 600ISH hp BBF guys getting with your street cars. Im not interested in an E85 or race gas burning 800+hp monster. But a 550-650hp pump gas, street driven STREET motor. I had a 408 with an 850 holley and i got 6mpg if I was nice to it so im interested to see what you BBF guys are getting with another 100+cubes and 1000+cfm carbs.
4mpg city, 6 freeway.
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Old 12-14-2011, 10:28 AM
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Quote:
Originally Posted by Muskratt2 View Post
What I'm looking at here is a gear change for my Dually.I've looked at a possible Overdrive swaps but I just don't have the money to do it right now.
I'm limited to either a 3:54 gear or 3:73 gear. I have 4:11 in it now from the factory. I don't really use it to tow anymore but possibly once a year at tops! I need to rebuild the motor but I'm in the process of doing the paint & bodywork so I don't have the funds for that till that's all done.So a gear change is the most cost effective right now.
With 3:54 gears I would be cruising at 64 mph at 2500 rpm's.
With 3:73 gears I would be cruising at 61 mph at 2500 rpm's.
I don't use the truck really on the interstate just simply because I couldn't afford the gas & I have more economical vehicle to drive for that. Most of the areas I drive in is a 55 mph speed limit so that's about that range aia drive it in.
What do you'll think?
I would go 3.54's my grandpa had a 77 supercab dually that he used to haul hay with with 3.54's and a 460 with a C6 and it would get ~15mpg city/highway loaded/empty. He overloaded that truck everysingle time he hauled with it and it didn't even phase it. He would haul a trailer with him and between the truck and trailer would haul 125-130 bails at ~50lbs each.
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  #13  
Old 12-14-2011, 11:08 AM
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Quote:
Originally Posted by truebluedevil02 View Post
A better question IMO is what MPG are you 600ISH hp BBF guys getting with your street cars. Im not interested in an E85 or race gas burning 800+hp monster. But a 550-650hp pump gas, street driven STREET motor. I had a 408 with an 850 holley and i got 6mpg if I was nice to it so im interested to see what you BBF guys are getting with another 100+cubes and 1000+cfm carbs.
Not really up in that power range, but my 429 got 13 mpg cruising at 80 mph / 2900 rpm this past summer going to and from a race. About 750 miles round trip. 2.75 gears.

The bone stock 2bbl 360 in my 1970 F100 gets 18 mpg cruising at 70 mph with 3.50 gears.

The OP needs to install the 3.54's in my opinion.
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Old 12-14-2011, 11:58 AM
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I've been leaning towards the 3:54 gears for a while but my buddy says I need to go with the 3:73 gears in case I do any towing.
From what I've seen though with the calculators, there isn't much difference between the 4:11 & the 3:73 gears.
I feel like that once I rebuild the new motor, it will have enough torque to make up for the gear & like I said I don't hardly do any towing anymore anyway!
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Old 12-14-2011, 12:00 PM
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Quote:
Originally Posted by bigblok86ranger View Post
Seems 7 is about what a hot street build will get to me my previous 466 got 7mpg city or highway when tuned for max performance, interestingly enough a few trips with my 523 I found that it also got 7mpg city or highway.
my TFS street headed 533ci/c6 with 3.70 gears and 1150 dominator gets about 6-7mpg in my Galaxie convertible. It gets same on street as highway.
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