Trying to get the best MPG out of my 350 olds
August 16th, 2012, 04:55 PM
#41
if it got him to 20 MPG even, it would take him 52,000 miles to brake even at $3.50 per gallon. that is if he got a continual 20 MPG but that won't happen in stop and go. i understand what you are saying but that is why i ask if he was hot roding it. if not he could get a good used one for less than $300 and go with it. don't take that long to pay for $300.
the diesel truck guys make fun of my 8.1 gas truck. i get 14 MPG and they get 18-19. they paid $4000 more at least for there truck and .50 to $1.00 more for fuel. what i am getting at is that captjim is right. if you have to pay much to increase your mileage, you are just shooting yourself in the foot.
if you don't drive this car much, it will be best to go as you are now.
the diesel truck guys make fun of my 8.1 gas truck. i get 14 MPG and they get 18-19. they paid $4000 more at least for there truck and .50 to $1.00 more for fuel. what i am getting at is that captjim is right. if you have to pay much to increase your mileage, you are just shooting yourself in the foot.
if you don't drive this car much, it will be best to go as you are now.
August 16th, 2012, 05:35 PM
#42
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Use your trans, shorten the drive shaft too. You need 3.42 or 3.55 gears, to make the most of it. I run 1800 rpm at 60 mph with a 25.5" tire with 3.42 gears, 2004r trans. You drop 2-300 rpm with the lock up converter.
August 18th, 2012, 09:57 PM
#43
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My Omega gets 21 miles to a gallon on the highway going 60 mph with 3.73 gears and 28" tall tires and a brick on the gas petal so it doesn't move and excite the double pumper Barry Grant Mighty Demon carb's accelerator pumps.
Car weighs 3460lbs with full tank of gas and 220lb driver.
Oh, when I did the highway mileage test, the wife was with me, so add 140lbs to above weight.
Car weighs 3460lbs with full tank of gas and 220lb driver.
Oh, when I did the highway mileage test, the wife was with me, so add 140lbs to above weight.
August 18th, 2012, 10:10 PM
#44
My Omega gets 21 miles to a gallon on the highway going 60 mph with 3.73 gears and 28" tall tires and a brick on the gas petal so it doesn't move and excite the double pumper Barry Grant Mighty Demon carb's accelerator pumps.
Car weighs 3460lbs with full tank of gas and 220lb driver.
Oh, when I did the highway mileage test, the wife was with me, so add 140lbs to above weight.
Car weighs 3460lbs with full tank of gas and 220lb driver.
Oh, when I did the highway mileage test, the wife was with me, so add 140lbs to above weight.
August 18th, 2012, 10:15 PM
#45
My Omega gets 21 miles to a gallon on the highway going 60 mph with 3.73 gears and 28" tall tires and a brick on the gas petal so it doesn't move and excite the double pumper Barry Grant Mighty Demon carb's accelerator pumps.
Car weighs 3460lbs with full tank of gas and 220lb driver.
Oh, when I did the highway mileage test, the wife was with me, so add 140lbs to above weight.
Car weighs 3460lbs with full tank of gas and 220lb driver.
Oh, when I did the highway mileage test, the wife was with me, so add 140lbs to above weight.
August 19th, 2012, 02:10 PM
#50
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the better way is to take a 10 mile stretch of road with mile markers. see where your odometer is at at the first mile marker and then see where it is after 10 miles (or longer if you have a good long stretch of highway). the mile markers are accurate so you can see just how far it is off over a longer distance. then just calculate the difference it is off into you MPG figures. if your odometer shows 10.5 in a 10 mile run you won't be able to tell from the speedometer but you sure will tell in the MPG figure on a tank of gas. MUCH easier to just use a GPS.
August 19th, 2012, 06:48 PM
#54
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Nah, I finger fudged the 3 and hit 2 by accident. I wish my car weighed 2750 lol! I did that in another thread too and 380 caught it...my bad.
August 19th, 2012, 07:57 PM
#55
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Stay with the dual plane manifold. A single plain hurts you in the low end. You only gain at higher RPMs in an engine that has been modified to take advantage of higher flow in the upper R's. Yours would be a dog with a single plane and it would lower your economy.
August 19th, 2012, 09:34 PM
#56
Ok thanks. Would a highrise dual plane also hurt it?
August 21st, 2012, 06:51 PM
#60
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The way I did my gas mileage calculations were point to point. I filled up @ the gas station that's closest to the interstate, had to sit at one red light after leaving gas station and paced myself to catch the next two traffic signal's while they were green. Once I reached about 65mph the wife slid the brick over onto the gas petal as I slid my foot off it and that's is where it stayed until I exited Interstate and refilled gas tank again 160 miles or so later and used a calculator and divided miles by gallons to refill the more than half full tank of gas.
Unlike speed control's that will make your car accelerate as it's going over hills, bridges down here and de-accelerate as it's going down a hill, a brick will keep that throttle position right where it's set like in an aircraft, so it slows down going up and speeds up going down and then eventually comes back to set speed.
If you can avoid exciting your accelerator pump or pumps while driving, you can squeeze every foot out of every drop of gas.
It's alot of little things that will net you decent mileage out of a performance engine, lets face it, if your engine is capable of high VE numbers, you'll be able to get decent gas mileage if you learn to drive it like hyper mileager drive their cars, light on the petal and pacing yourself so you catch lights green, instead of racing up to a red light to stop.
Unlike speed control's that will make your car accelerate as it's going over hills, bridges down here and de-accelerate as it's going down a hill, a brick will keep that throttle position right where it's set like in an aircraft, so it slows down going up and speeds up going down and then eventually comes back to set speed.
If you can avoid exciting your accelerator pump or pumps while driving, you can squeeze every foot out of every drop of gas.
It's alot of little things that will net you decent mileage out of a performance engine, lets face it, if your engine is capable of high VE numbers, you'll be able to get decent gas mileage if you learn to drive it like hyper mileager drive their cars, light on the petal and pacing yourself so you catch lights green, instead of racing up to a red light to stop.
August 21st, 2012, 07:13 PM
#61
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But does the brick on the gas give you real world numbers, or test tube numbers...like the EPA mileage. I think you should calculate it by real driving conditions, which would include keeping up with the flow of traffic, even up the hills. And it should be done over several tankfuls, otherwise, how do you know if you really filled the tank to the same level as the other time? All gas pumps aren't the same, or accurate at shutting off at the same point in the "fill".
I know you used the brick as a test to see how high you could increase the number, but why not also inflate the tires to 60 or 70 poinds. Rock hard tires also increase mileage, but like the brick, not safe or real world.
I know you used the brick as a test to see how high you could increase the number, but why not also inflate the tires to 60 or 70 poinds. Rock hard tires also increase mileage, but like the brick, not safe or real world.
August 21st, 2012, 08:00 PM
#62
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You are right, not every pump will shut off at the same point and the brick on the gas petal isn't practical but it severed to prove that even a double pumper Holley style carb is capable of decent mileage.
I have been driving for over 40 years, professionally for more than 10 years when I was younger, so driving with a brick on my gas petal isn't something that I couldn't handle.
If I was really worried about getting every mile out of every drop of gas with my hotrod, I would probably be seeking out a manual throttle control, such as those made for little people who can't reach the petals.
I have been driving for over 40 years, professionally for more than 10 years when I was younger, so driving with a brick on my gas petal isn't something that I couldn't handle.
If I was really worried about getting every mile out of every drop of gas with my hotrod, I would probably be seeking out a manual throttle control, such as those made for little people who can't reach the petals.
August 22nd, 2012, 12:11 AM
#63
But does the brick on the gas give you real world numbers, or test tube numbers...like the EPA mileage. I think you should calculate it by real driving conditions, which would include keeping up with the flow of traffic, even up the hills. And it should be done over several tankfuls, otherwise, how do you know if you really filled the tank to the same level as the other time? All gas pumps aren't the same, or accurate at shutting off at the same point in the "fill".
I know you used the brick as a test to see how high you could increase the number, but why not also inflate the tires to 60 or 70 poinds. Rock hard tires also increase mileage, but like the brick, not safe or real world.
I know you used the brick as a test to see how high you could increase the number, but why not also inflate the tires to 60 or 70 poinds. Rock hard tires also increase mileage, but like the brick, not safe or real world.
August 22nd, 2012, 12:33 AM
#64
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I have to disagree on the gas pumps. The pumps are inspected every year by the bureau of weights and measures. And if they don't meet the exact measurement then they are forced not to use the pump. Or to fix it for re inspection. Every gas pump you look at will have the government badge on it.
August 22nd, 2012, 01:49 AM
#65
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I have a 72 cutlass with the 350 rocket and a 72 quadrajet 750 cfm on it. It has the TH350 tranny. I have rebuilt the qjet myself, and have a good tall 14" air cleaner on it. Stock intake manifold. And i'm running the stock points style ignition setup. And true dual exhaust with no cats and flowmaster 40 knockoffs. Also recent tune up, and new mechanical fuel pump, fuel filter, and cap and button. What all can I do to get the best possible fuel economy? And yes I realize I will probably never see over 20mpg. But I would like to get as close to 20 as possible. Last I checked i'm getting like 15.6 mpg. Doing about 75% highway and 25% city.
August 22nd, 2012, 03:28 AM
#66
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Doing 95% city driving......
My 1970 Olds 350 & TH350 in my Cutlass I got 14 mpg using a 600cfm Holley and the 2.78 rear gear.
When I stepped up the carb to a 750cfm Edelbrock 1407 and put 3.73's in I was getting 11mpg.
That engine dyno'd out @ 300hp / 425ft lbs
SO my advice is a smaller carb and a taller highway gear.
For you to already have an overdrive transmission and only get that MPG highway, you need a smaller carb more then likely.
My 1970 Olds 350 & TH350 in my Cutlass I got 14 mpg using a 600cfm Holley and the 2.78 rear gear.
When I stepped up the carb to a 750cfm Edelbrock 1407 and put 3.73's in I was getting 11mpg.
That engine dyno'd out @ 300hp / 425ft lbs
SO my advice is a smaller carb and a taller highway gear.
For you to already have an overdrive transmission and only get that MPG highway, you need a smaller carb more then likely.
Last edited by Aceshigh; August 22nd, 2012 at 03:32 AM.
August 22nd, 2012, 08:16 AM
#68
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Doing 95% city driving......
My 1970 Olds 350 & TH350 in my Cutlass I got 14 mpg using a 600cfm Holley and the 2.78 rear gear.
When I stepped up the carb to a 750cfm Edelbrock 1407 and put 3.73's in I was getting 11mpg.
That engine dyno'd out @ 300hp / 425ft lbs
SO my advice is a smaller carb and a taller highway gear.
For you to already have an overdrive transmission and only get that MPG highway, you need a smaller carb more then likely.
My 1970 Olds 350 & TH350 in my Cutlass I got 14 mpg using a 600cfm Holley and the 2.78 rear gear.
When I stepped up the carb to a 750cfm Edelbrock 1407 and put 3.73's in I was getting 11mpg.
That engine dyno'd out @ 300hp / 425ft lbs
SO my advice is a smaller carb and a taller highway gear.
For you to already have an overdrive transmission and only get that MPG highway, you need a smaller carb more then likely.
My '72 convertible made a 190 mile trip from Austin to Houston with a 350 2bbl carburetor. The car has 2.73 gears and it got 13 miles per gallon. Once here, we did an engine swap and put in a 455 with a 750 Carter and TH400. We didn't change anything else.
On the return trip from Houston to Austin, the same car with the bigger motor and carburetor got 11.9 mpg (and that included a few ring seating punches).
While there was a difference in mpg favoring the 350 2bbl carburetor, is it worth 1.1 mpg to sacrifice the power and enjoyment that comes from having the bigger engine? IDK, I guess if you're pinching every penny it is...but I'd rather have the cubes lol!
P.S. I will give you that the 350 was a factory 40 year old engine and wasn't running to it's full potential...but tit for tat that's what we got
August 22nd, 2012, 12:38 PM
#69
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Just my opinion, but V8 powered cars average mid teens if tuned right and driven conservatively in real-world applications.
August 22nd, 2012, 02:19 PM
#70
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I wasn't going to say anything, but I also find it hard to believe. 21 mpg with a 3.73 gear and a DP? Most guys can't do that with a computer controlled 307 OD, 2.7x gears and a lock up converter. And even IF you did, that test really isn't a valid test. There are very few real world situations where you never move the throtthe for 160 miles.
Just my opinion, but V8 powered cars average mid teens if tuned right and driven conservatively in real-world applications.
Just my opinion, but V8 powered cars average mid teens if tuned right and driven conservatively in real-world applications.
September 3rd, 2012, 02:25 PM
#71
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Since you’re trying to get the best mileage possible, I would recommend fine tuning your carb and timing curve.
I agree with everyone’s comments, about adding an overdrive, and it’s mostly about driving habits and cruising speed.
One of the best methods I’ve found for squeaking the most mileage possible is with a wideband O2 sensor. Innovative Motorsports makes a few great models including their newer fast reacting MTX version that sells for about $200. I also would recommend buying or borrowing a good book on Q-Jets like the one from Cliff Ruggles, picking up a wideband 02 sensor, a vacuum gauge, a dial back timing light and plan on a lot of testing and seat time in the car. I haven’t done any fine tuning on a Q-jet before, so maybe the other guys could chime in with a good baseline/starting point for you, but I think the Q-jet probably offers the most mileage “potential” of any carb out there if you take the time to fine tune it.
My personal favorite budget carb for tuning mild cam daily drivers is the Quick Fuel Slayer Series. They are the only carb I know of at the $300 price point that has screw-in idle feed restrictors, idle air bleeds and high speed air bleeds. Every car/driver is going to experience different results. What’s worked the best for me is having the car cruise down the freeway on the idle circuit. I’ve noticed a lot of cars running Holley based carbs tend to run rich under part throttle conditions especially while mildly accelerating or pulling mild hills even after the proper power valve was installed. I usually increase the high speed air bleeds which essentially retard the mains from coming online too early, then I’ll run a looser power valve to counter act any hesitation caused from having a lean spot under harder low rpm acceleration. I’ve had great results from using DUI HEI distributors. Having the correct total timing, timing curve, and vacuum advance is essential to maximizing your mileage.
It sounds like your car runs pretty good the way it is right now. I would venture to say you’re within 20% of your max mileage potential so that may not justify the cost or labor to tune your car for mileage.
I agree with everyone’s comments, about adding an overdrive, and it’s mostly about driving habits and cruising speed.
One of the best methods I’ve found for squeaking the most mileage possible is with a wideband O2 sensor. Innovative Motorsports makes a few great models including their newer fast reacting MTX version that sells for about $200. I also would recommend buying or borrowing a good book on Q-Jets like the one from Cliff Ruggles, picking up a wideband 02 sensor, a vacuum gauge, a dial back timing light and plan on a lot of testing and seat time in the car. I haven’t done any fine tuning on a Q-jet before, so maybe the other guys could chime in with a good baseline/starting point for you, but I think the Q-jet probably offers the most mileage “potential” of any carb out there if you take the time to fine tune it.
My personal favorite budget carb for tuning mild cam daily drivers is the Quick Fuel Slayer Series. They are the only carb I know of at the $300 price point that has screw-in idle feed restrictors, idle air bleeds and high speed air bleeds. Every car/driver is going to experience different results. What’s worked the best for me is having the car cruise down the freeway on the idle circuit. I’ve noticed a lot of cars running Holley based carbs tend to run rich under part throttle conditions especially while mildly accelerating or pulling mild hills even after the proper power valve was installed. I usually increase the high speed air bleeds which essentially retard the mains from coming online too early, then I’ll run a looser power valve to counter act any hesitation caused from having a lean spot under harder low rpm acceleration. I’ve had great results from using DUI HEI distributors. Having the correct total timing, timing curve, and vacuum advance is essential to maximizing your mileage.
It sounds like your car runs pretty good the way it is right now. I would venture to say you’re within 20% of your max mileage potential so that may not justify the cost or labor to tune your car for mileage.
September 3rd, 2012, 02:34 PM
#72
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Location: Fl
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I had a friend of a friend's aquaintence, that said his brother's 3rd cousin, twice removed, who passed on that his father told him that his grandads ol 72 got better than that.
My car gets 7-8 mpg average, going uphill, downhill, headwind, tailwind, etc.. Feel Better!
My car gets 7-8 mpg average, going uphill, downhill, headwind, tailwind, etc.. Feel Better!
September 3rd, 2012, 03:42 PM
#73
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Posts: 45
Wow...worrying about MPGs on a Harley. I thought I was bad about looking for decent mileage!
I also agree, if it's not your daily driver or a car you take on long trips, why worry about mileage, build/tune for power
It sounds like the op does drive his car daily, so as long as the overall cost doesn't out weigh the benefit, it makes sense.
From strictly a mileage point of view I've often wondered if the 700R4 would help city mileage with its 3.06 first gear, helping to get the weight in motion with less load on the engine. That 1-2 shift rpm drop sure sucks for performance. PACT makes a close ratio gear set which uses 2.84, 1.56, 1, .70 which is very close to the 200 trans gear ratios, but I believe it costs around $1000, making the 200 trans a much more ideal swap.
I also agree, if it's not your daily driver or a car you take on long trips, why worry about mileage, build/tune for power
It sounds like the op does drive his car daily, so as long as the overall cost doesn't out weigh the benefit, it makes sense.
From strictly a mileage point of view I've often wondered if the 700R4 would help city mileage with its 3.06 first gear, helping to get the weight in motion with less load on the engine. That 1-2 shift rpm drop sure sucks for performance. PACT makes a close ratio gear set which uses 2.84, 1.56, 1, .70 which is very close to the 200 trans gear ratios, but I believe it costs around $1000, making the 200 trans a much more ideal swap.
September 3rd, 2012, 09:46 PM
#74
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September 4th, 2012, 02:57 PM
#75
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Man, I have a hard time believing that with 3.73s and a DP. I know FL is flat, but still. Even if it is true under perfect conditions, by the time you everage in around town driving, it is going to be low-mid teens, at best.
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