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1996 Fleetwood
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2,536 Posts
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It's been a while since we had a fuel economy thread, so I figured I'd bring it back from the dead.

I've currently been suffering on my fuel economy due to a bad O2 sensor. (I dropped down to 1 working sensor. Only had the 2 upstream ones still installed since my mods deleted the use for the downstream ones.)

Current stats have been with only 1 working O2 sensor, and with a failing Opti. Those have now been resolved, so I should start to regain mileage. I also tossed in a 160* thermostat as opposed to the original 180.
Mods are a 218.224 Cam, Beehive springs. 2.56 Open rear end. Transmission built with a heavy duty cooler, and a 2400 stall. RAISS cold air/ram air intake. Clear Image Auto budget headers. H pipe welded in. Class 3 trailer hitch welded on (Thing's bloody heavy).
181,000 miles on the clock.


Current: 16.4 mpg
Towing: 11.5 mpg (3500lbs worth of trailer.)

I'll report again at the end of this week with a full tank of healthy O2 sensors run through.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,737 Posts
You have at least 2 things installed which lower fuel mileage. A 160 degree thermostat delays or stops the system from going into "closed loop" so the OXY sensors never activate to tell the ECU to trim the fuel mixture. Secondly, a 2400 stall converter allows the trans to slip up to 2400 RPM wasting fuel.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,449 Posts
160 degrees is really, really bad for the engine. Regardless of "modifications", an engine runs better at its design temperatures - in this case, 185 to 210 degrees. Some emissions controls may not even change loops until over 160 degrees coolant temp.

Cool oil has significantly more internal drag than oil running at the proper 190 - 220 degrees, and cool oil never heats up enough to boil off acids and moisture for removal by the PCV system.

The mild low rpm/high torque RV cam won't hurt mileage, but the hot air intake will (and it won't "ram" one extra cubic inch into the engine). Well, with enough mouth surface area and 145 mph, maybe, just maybe. The valve springs were probably a waste - how often do you wind the thing to over 6,000 ????

Here's one of my low rpm/high torque Olds 455 engines (+.030" = 461) for marine use. Fresh water cooled, 180 degree thermostat. Built to run on 87 octane. 445 hp, 485 torque at 4,000 rpm. Nice engine. Very, very, very different from a street/towing engine.
 

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Super Moderator
2014 ELR
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9,728 Posts
The 160 isn't as bad in the LT1, sub, it had 180 stock, and unlike traditional GM V8s, it is reverse cooled. The PCM needs to be programmed for it, of course ( and with his other mods, I hope it is). The valve springs aren't a waste, either. Stock B/D cam is so mild, springs are needed with any upgrade. Even on a stock cam, stock springs float around 4500, they're bad. Beehives are great, they fit the stock pocket.
 

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1980 FBC
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980 Posts
160 degrees is really, really bad for the engine. Regardless of "modifications", an engine runs better at its design temperatures - in this case, 185 to 210 degrees. Some emissions controls may not even change loops until over 160 degrees coolant temp.

Cool oil has significantly more internal drag than oil running at the proper 190 - 220 degrees, and cool oil never heats up enough to boil off acids and moisture for removal by the PCV system.

The mild low rpm/high torque RV cam won't hurt mileage, but the hot air intake will (and it won't "ram" one extra cubic inch into the engine). Well, with enough mouth surface area and 145 mph, maybe, just maybe. The valve springs were probably a waste - how often do you wind the thing to over 6,000 ????

Here's one of my low rpm/high torque Olds 455 engines (+.030" = 461) for marine use. Fresh water cooled, 180 degree thermostat. Built to run on 87 octane. 445 hp, 485 torque at 4,000 rpm. Nice engine. Very, very, very different from a street/towing engine.
Great stuff but it's the wrong color!
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Great stuff but it's the wrong color!
Heh, heh. This/that one went into my boat - used up some old Chrysler Marine spray. The Mondello heads were the proper Olds color, but they went blue, too.

Since I sort of hijacked a "gas mileage" thread, this puppy pushes an 8-ton workboat. Running at 1750 rpm, 8.5 knots, 19", it uses 3 gallons/hour - about 2.8 NM/gallon. If you equate that rpm, manifold vacuum and load to a 60 mph car, you're talking about 20 mpg.
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
My wife's car is a 1993 Roadmaster, pretty similar to the 1993 Brougham. She gets around 17/22.
 

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1980 FBC
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980 Posts
Heh, heh. This/that one went into my boat - used up some old Chrysler Marine spray. The Mondello heads were the proper Olds color, but they went blue, too.

Since I sort of hijacked a "gas mileage" thread, this puppy pushes an 8-ton workboat. Running at 1750 rpm, 8.5 knots, 19", it uses 3 gallons/hour - about 2.8 NM/gallon. If you equate that rpm, manifold vacuum and load to a 60 mph car, you're talking about 20 mpg.
I remember that color from my 1972 340.
 
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