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OP
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Does anyone know what I should shoot for cruise rpm to get the best gas mileage? I'm running a 292/700r4 combo and using drive around 65 mph on the freeway. According to the online calculators, I'm pulling somewhere around 1800 rpms (although my tach reads less).
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Shoot for the torque peak, or a little lower, but not low enough to be in the power enrichment circuit of your carb(s). That is where the brake specific fuel consumption will be near its lowest. The BSFC and torque curves mirror each other. The peak torque RPM is dependent on camshaft, exhaust system and other factors.
FORD 300 inline six - THE BEST KEPT SECRET IN DRAG RACING!
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What are your camshaft specs?
MBHD
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What mileage are you seeing? At 1800 rpm cruise, if the distributor has not been recurved, will not have a correct timing curve. At cruise 40-50 degrees total timing can be had.
Inliner Member 1716 65 Chevelle Wagon and 41 Hudson Pickup Information and parts www.12bolt.com
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OP
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Here are the specs:
264-H 264 duration 214 @ .050" .498" lift 110 lobe center
I put around 200 miles on the car today. When I refill tomorrow, I will calculate mpg. At this pt, I believe I'm getting 16-18 mpg. I was expecting low-mid 20s.
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Most likely run about 1800-2000 RPM.
In order to get mid 20's I would think you would need EFI,fuel injection. Even with EFI, it would be a bit hard to get mid 20's w/a 292 & your camshaft,& no real good control of the timing.I.M.O.
MBHD
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And what carburetor(s) and have you spent time tuning them?Along with the spark advance advise above.... Been my experience most guys run a far richer cruise fuel ratio mixture than necessary because they read spark plug color. Plug color is for full throttle...Cruising at 1800 rpm the carb is generally just coming onto the main jets from the off idle circuit.Lean down about two jet sizes and try that.If no lean steady speed surge or slight hesitation as you very gently feed the gas pedal at about 45 mph,lean down a bit more.Use direct drive at 45 mph.If you jet down more than 3 or 4 sizes you may have to enlarge the high speed or power valve circuit if that's possible.Your engine's spark plugs will likely be bone white at light loads,no problem if the engine responds ok and no detonation.Check it out on the hiway at speed in OD also. But always jet for the way you drive,a easy driver can run a leaner mixture than a gas pedal jabber 
70 Triumph 650 cc ECTA current record holder
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If you do not have a wide band O2 reader, get one there cheap & you do not need to take out your plugs to read them.
O2 wide bands are low in price & worth every penny to have one.
MBHD
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If you do not have a wide band O2 reader, get one, there very affordable & you do not need to take out your plugs to read them. Well,, for the most part , you do not need to read your plugs. Maybe to see if you are detonating.
O2 wide bands are low in price & worth every penny to have one.
It will really speed up the tuning process & take out the guesswork.
MBHD
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DRIVE WITH A VAC. GAUGE AND YOUR ENGINE WILL BE MOST EFFICIENT AT PEAK VAC READIING. JMO THE OLD GUY METHOD
I BELIEVE IN " JOHN 3:16 "
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If you do not have a wide band O2 reader, get one, there very affordable & you do not need to take out your plugs to read them. Well,, for the most part , you do not need to read your plugs. Maybe to see if you are detonating.
O2 wide bands are low in price & worth every penny to have one.
It will really speed up the tuning process & take out the guesswork.
MBHD The 02 sensor is a valuable tool if you know what the ideal cruise air fuel mixture is. And the way you figure that out is trial and error by road testing.Or very expensive time on a dyno that simulates road use,wind resistance and all that. I think 21-22 mpg is within reason for the OP's small car if once the engine is tuned properly.
Last edited by Tony P; 05/22/12 08:06 AM.
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