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Discussion Starter · #1 ·
I took the 63 Galaxie with the big engine/C6/2.75 rear gear to the ford swap meet down at Columbus, Oh today. We drove 70-75 most of the way and I got 13.1 mpg. Connie drove back doing the speed limit everywhere, 55-55, 65-65, 70-70 etc. We got 14.8 coming back. I was looking for 18mpg. The only way I'm going to get 18mpg in that car is to push it. Jim
 

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Drop your gears to 3.00:1 and I'm betting you'll get better at highway speeds.
How is that going to work Gary? With the 2.75 gears he has now, he will turn less rpm than he would with the 3.00 gears. Maybe I am missing something, just want to know.
 

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How is that going to work Gary? With the 2.75 gears he has now, he will turn less rpm than he would with the 3.00 gears. Maybe I am missing something, just want to know.
think he's getting at some engines run more efficiently at higher RPMs.
my 85 camaro got 35mpg at 85 going across the desert, about 24 doing the speed limit.
my old D150 with a slant6 4 speed got about 18 in 3rd on the highway, about half that in overdrive as the engine simply didnt pull enough torque at light throttle to pull the gear...oddly I put a 396 chevy in it, with a th400 got about 18 also.
 

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Discussion Starter · #6 ·
R.N.R.,
My 57 with the 390/300 horse gets 20mpg with the Tremec but the Tremec in 5th gear brings the overall down to about 2.40 I think. I have no idea what the other guys are talking about but the 2.75 is as high as I want to go and have any kind of acceleration from takeoff. I've just got to slow down with the Galaxie. The nice thing about the FE is it has torque as low as 1700 rpm. I just wish I could cruise around 1850 rpm at 65mph like the 57 can. I haven't got a tach on the 63 but I estimate about 2300-2400 rpm around 65-70mph. That's just too much rpm for the gas mileage I would like to have. Jim PS. I only posted this to let others know what the 2.75 did for me. Before, there were a few guys considering going to the 2.75 like the girl did that runs this website. I can tell you this, there is no engine noise to amount to anything though. That's nice not having to hear the engine roar at those speeds.
 

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I had a 79 Ford wagon that got better mileage at 80 than it did at 55. It was factory equipped with a 351 2v with 2.26 gears. If I keep my 64 at 55 60 it gets 17 with stock 352 except for 600 Holley and Edlebrock intake. and 3.0 open rear axle.
 

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Discussion Starter · #8 ·
OK, I know what you're saying now. If you lug the engine at a slower speed you'd get less gas mileage. I get it now.
My final gear ratio for the 57 Fairlane is 2.24. I run 27.1" tires also. At 70mph that's 1975 rpm.
My final gear ratio for the 63 Galaxie is 2.75. I run 26.9" tires on it. At 70 mph that's 2405 rpm. I need to keep it at around 58 mph or less to see 2000 rpm or less. Jim
 

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Have you invested any time in tuning the car for better mpg like buying a A/F ratio indicator or having it tuned by a professional? At today's fuel prices it doesn't take long to pay for itself.
 

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Discussion Starter · #10 ·
ArnoldTX,
I haven't tried something like that. I just take it cruising and check the color of the plugs. I'm running 65 jets front and back on a 600 Holley, they seem to give me good brown plug. The trouble I have with my engine is the cam I had to put in it to allow me to use 89 octane gas. The cam I have gives me a 7.8 DCR and a cam that it needs like the 268-H comp cam would give me a 8.8 DCR. The Lunati cam they made me has the intake closing at 71 ABDC with a 61 degree overlap. After decking the block and building it to race I changed my mind half way through and decided I wanted to make a show car/driver out of it. I have no significant HP until I get to 3500-4000 rpm. Jim
 

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Although this is not an old carburetor-ed car it is on topic still. A customer was complaining about mileage on his 84 F150 4x4 short bed with automatic overdrive and 300 six engine. He had me install a vacuum gauge. When normally driven in overdrive engine had no vacuum ( or very low) and gas mileage was bad. When the OD was turned off the vacuum came up- along with the mileage. I dont remember the gear ratio but you would have though Ford's engineers would have had a better handle on this . I guess the trick is finding the sweet spot.
 

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Discussion Starter · #12 ·
I'll bet you are right. When I set my idle on the 57 it idles with about 17-18 inches maniford pressure. When I give it more gas for a little bit the vacuum goes down. Then at about 2200-2700 the vacuum goes to about 25 inches manifold pressure. Now, if I was smart enough to put it all together. Jim
 

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Discussion Starter · #13 · (Edited)
This didn't show up on the website so I thought I'd post it. Good information. I told Lunati what I had and told them to make me something that would enable me to use 87 octane gas and this is what they sent me so I put it in straight-up. I'm going to run the figures on what you've told me and see how it comes out on paper. Thanks, Jim
My427stang has just replied to a thread you have subscribed to entitled - Gas mileage - in the Galaxie Pages forum of Ford Muscle Forums : Ford Muscle Cars Tech Forum.

This thread is located at:
http://www.fordmuscleforums.com/galaxie-pages/509144-gas-mileage-new-post.html

Here is the message that has just been posted:
***************
Jim,
A couple of things I found

1. On my Mustang, going from a 2.36 final to a 2.63 final increased my mileage around town significantly, and slightly on the highway. I basically was lugging the motor. I am not sure I would do a gear change just for mileage, but if you are looking for some additional stoplight torque, you'd probably be happy in the long run.

2. Plot out your ignition curve, if you are idling too low during cruise, you may need to adjust your curve and/or vacuum advance to come in at that RPM. No load cruise a 390 likes a lot of timing because there isn't much fuel there. It's a lot tougher to do with a carb'd car versus EFI, but you can tweak it once you target a specific cruise RPM and then focus on efficiency there

3. If you have a DCR of 7.8 and you have been very careful measuring everything, crank the cam forward a few degrees, it will become more efficient in cruise. Advancing it 4 degrees from where you are will probably only drive you up to 8.0 or 8.1 with a 390 and will gain you some low rpm efficiency.

Each of these things wont be dramatic, but the combination will probably buy you some MPG

Edit: You're right. The results of going from 110 CL to 106 CL increases the HP on my calculator from 420HP @ 5000 rpm to 429 HP @ 5000 rpm and the DCR is 8.09. I'm on the low end of 89 octane now. Some 87 octane fuel doesn't ping in my engine now. 8.09 would probably be on the high end of 89 octane. I've got my initial timing set at 8 degrees now. I've got 34 degrees in at 2800 now. I could shorten the gap on my mechanical easily to maintain my total advance. If I get more HP out of it I'll be getting more vacuum out of it on the low end also. Wish I'd run some numbers before installing it.
 

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Sure, just tell the trooper you have to drive that fast to get the ol' boat up to 18 mpg, he'll understand.
 

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How is that going to work Gary? With the 2.75 gears he has now, he will turn less rpm than he would with the 3.00 gears. Maybe I am missing something, just want to know.

Yep, that 390 likes a few more rpms to find it's sweet spot is what I was telling you. Looks like the others support my statement, but Ross and his cam degreeing will definitely work to make the sweet spot move closer to where you need it.

My 2000 Cherokee Sport get's 15 in city and 17 on highway going 55-75, but I get 19.5 going 95 MPH. My Falconaround get's 20 in the city but 25.5 averaging 90+ mph and only about 21 going 65.
 

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Discussion Starter · #16 ·
Sure, just tell the trooper you have to drive that fast to get the ol' boat up to 18 mpg, he'll understand.
That may work for you but I'd be lucky to stay out of jail. I think the guys got something about the cam deal though. Getting me to take it apart since it's just been finished will be a definite problem. Jim
 

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Mine is better with the 2.75 compared to the 3.00. From 12 to almost 15, could probably get 15 or 16 if i stuck to 55 or so. But mine has the old cruiso and could probably use some tuning. I think in the owners manual i wrote the mileage down back in the elate 70s and got 17 with the original engine. This one is bored 40 over and rv cam and got 6-7mpg in the truck it came out of so i'm happy with what i got. Especially after having a 3.50 rear for a while and 8-9mpg.
 

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Jim, I deleted my post because I was confusing your overdrive cars with the C-6 2.75 car

With the 2.75 C-6, I'd advance that cam to 106 with an 8.09 DCR without thinking twice. I run 89 all day long with my 489 at 8.33 with alum heads, 8.09 isn't bad at all. I wouldn't hesitate to run mine on 87 if required.

The second thing you pointed out, that curve needs some help. Get that poor FE to closer to 14 initial and 36 total all in by whatever you think it can handle, I'd shoot for 3000 because of the tall gear and the fact you'll be starting at 14 (plot the curves you'll see what I mean)....but dont ignore vacuum advance, a lean motor needs more timing and when you are cruising it should come up to the 44-48 range when you add vacuum.

WOT mechanical plus initial is only a dyno and racing tune, you want more timing in lean conditions at low load like steady cruise.

Both the increase in initial and the earlier cam timing will raise vacuum and make it more efficient. Although your peak numbers look better, the part throttle difference will be even greater, it will be nearly magical.

Matter of fact, if you didn't have compression limits, I like a 104 ICL with that motor, it would really bring the part throttle performance around.

After you get that squared away, you could also consider playing with the primary metering block for additional gains.

Reducing primary jet size as low as it can go, but adding back PVCR to give it the fuel under load can bring even more gains, but probably not worth doing until you get those cylinders filling effectively with better intake lobe timing.
 

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+1 - deeper gears could help mileage for the reasons the others already stated. :tup: Considering there are many carb and ignition adjustments that can be made for a combination of peak HP and peak MPG, I would look into at least the following three to look for noticeable gains:

  • Lean the primaries until you get 'surge' or 'hunting' and back-off one jet size.
The primaries are for low power and cruise, and should be lean for that. Not only do you flow less fuel, you gain by reducing pumping losses. When you want power, the power valve and secondaries provide the rich mix for HP.

  • Verify your power valve is not opening at any stable cruise throttle.
Your PV should only open when pushing the throttle to accelerate for passing or going uphill, etc. The PV rating should be 1-2" vac above your stable cruise vacuum for good response with compromised good mileage.

  • Verify or establish proper cruise vacuum advance.
Your effective compression ratio is very low at cruise. Unless your vacuum advance timing is correct, you will be running with effectively retarded timing, costing both HP and mileage. Secondary side-effects include added heat and valve seat recession as you blow burning fuel out the exhaust.

I have a strong feeling you will see upper teens in your future, and yet retain all your performance. It's a process, so hang in there. There's a reason pro-tuners make good money, and there is a long line of customers with gasoline at $4+ per gallon. With some homework and elbow grease, you can do it yourself.

David
 

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Discussion Starter · #20 ·
Boy, I wish I'd have given it more thought before I threw the cam in. I was raised better than that too. We used manifold pressure and rpm to determine fuel burn on our airplanes. We used the 42-45-48 rule for fuel burn. 42 was 55% power, 45 was 65% power and 48 was 75% power. By adding your RPM in hundreds to your manifold pressure you could figure fuel burn at any altitude. The higher the vacuum number was the lower RPM you could run to get the same power setting. That's how you regulate fuel burn on an airplane. Useful tool, speedometers don't work for determining fuel burn.
I designed the gear train to give me the highest mph at the lowest RPM but I never thought of designing the engine to give me the highest vacuum at that RPM. Jim
 
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