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| | | | Joined: May 2005 Posts: 281 'Bolter | | 'Bolter Joined: May 2005 Posts: 281 | I have been trying to make adjustments to my engine to improve gas mileage, but with minimal success. The most recent road trip was 750 miles with about 2/3 interstate and the rest mostly good 2-lane highway. Overall on the trip was a shade under 15 mpg. I run about 75-80 on the interstate and 65-70 on 2-lanes generally with the AC. Engine is a 350 with iron vortec heads and a quadrajet. Transmission is a 700R4 with 3.73 rear gear. Likely a pretty common setup. The rpm is about 2600 at 80 mph. I'm curious if 15 is about what most of you get with a similar combination. If so, I will quit messing with jets, timing, distributor curves, etc and just go with it. Thanks for any comments.
Mark | | | | | Joined: Apr 2005 Posts: 7,440 Bolter | | Bolter Joined: Apr 2005 Posts: 7,440 |
Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
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| | | | | Joined: Feb 2004 Posts: 29,819 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,819 | Make sure the torque converter lockup clutch is engaging properly. By the way converters are designed, there's a 10% slippage built in that can only be eliminated by using a manual clutch that locks in at highway speed. If the transmission is not original to the truck, you're going to have to install a vacuum sensing switch and a brake on/off switch to make the TCC work correctly. When the TCC is functioning on a 700R4 it acts like a second overdrive ratio. Another trick is to install a vacuum gauge and get used to feather-footing the throttle to keep the main jets and metering rods running at the lean side of the power curve as much as possible.
BTW, there's nothing new about putting a lockup clutch in a torque converter- - - - -Studebaker did it in 1949. It was hydraulic rather than electronic, though!
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: May 2005 Posts: 281 'Bolter | | 'Bolter Joined: May 2005 Posts: 281 | Thanks Jerry. As far as I can determine, the lockup is working correctly. Its definitely locked up at speed and releases when I touch the brake. I have about 10-11" manifold vacuum at constant 75 mph and the power piston spring is set to start to lift the rods at around 9" vacuum. I might try a still lighter spring but its got good throttle response now. I temporarily install a vacuum gage in the cab when I do testing and it is very revealing to see how sensitive the vacuum is to small changes in the throttle. I've probably wasted more gas just doing the testing than I will ever save.
Mark | | | | | Joined: Feb 2004 Posts: 29,819 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,819 | One advantage you've probably got is location- - - - -you need to go out of state to find the nearest hill in most of the places I've been in Oklahoma!
Jerry
WWJWBD?
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Jun 2006 Posts: 693 'Bolter | | 'Bolter Joined: Jun 2006 Posts: 693 | Rather take a shot in the dark with jetting, etc., you can install a AFR meter and see that you have the correct stoichiometry at the various RPMs and loads at which you use the truck - you may wish to optimize it at your particular cruising speed instead. The literature suggests that 14.7:1 ratio is the best for light throttle cruising conditions. Driveability is better if you go a little richer. | | | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | Drop 1 size on the primary mains and compare.
14.7:1 is a science experiment, and not particularly good for any condition. | | | | | Joined: Jan 2016 Posts: 1,101 'Bolter | | 'Bolter Joined: Jan 2016 Posts: 1,101 | In my experience you get the best performance in regards to gas mileage around 2000-2300 RPMS on the engine. The higher RPMS really use the gas. | | | | | Joined: May 2005 Posts: 281 'Bolter | | 'Bolter Joined: May 2005 Posts: 281 | Thanks for all the comments. I don't have access to an air/fuel reading so will just continue to use the vacuum gage, stop watch, and "buttometer". It feels like it is close to the ragged edge of too lean so I might adjust the rods up a bit. Actually from the comments I expect 15 is about what to expect unless I decide to drive slower. Aerodynamics on the TF Fleetside is poor even with the rocket stamped in the side of the bed.
Mark | | |
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