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8.1 liter HD Silverado fuel economy challenge

 
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goodwrench
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PostPosted: Tue Jul 27, 2010 9:34 am    Post subject: 8.1 liter HD Silverado fuel economy challenge Reply with quote

I've purchased a 2001 HD Silverado so I can haul when I need to in comfort. The engine has 260,000 miles on it but the truck is real nice. Challenge is how can I iimprove fuel economy of about 10mpg? My 1967 F350 duelly utility bed with a 466 engine doe's that good! I can't understand how 35 years of developement, electronic engine management and fuel injection could not improve it some. Maybe I need a new o2 sensor or to remap the perameters in the computer?
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clay
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PostPosted: Thu Jul 29, 2010 1:08 pm    Post subject: Reply with quote

That's a tough one. You're going to have a tough time to overcome the basic physics of the situation. Here's my take on it. First it takes "X" amount of horsepower to push your truck down the road. Fuel injection, overdrive transmissions, etc. do nothing to affect this. Aerodynamics, rolling resistance of tires, drivetrain effeciency, etc. affect this. In this respect, your 2001 is probably not any better than your 1967. Rolling resistance is probably better as is drivetrain effeciency but frontal area is most likely the same or maybe even more. Depending on what you are hauling in the 67, your 2001 could be heavier which takes more power during acceleration to get up to speed. I say heavier because it is more complicated. More sensors, more computers, more sound deadening, probably a heavier frame, etc. that all add up. Granted this makes is much safer and nicer to drive, but it's not free. One thing I liked on the older carbureted engines is the heated intake floor. If you search around the internet, you will undoubtly come across hot vapor technology. Better vaporization leads to being better able to effectively burn gasoline completely. The heated intake floor to me helped this happen somewhat. Late model port injection systems usually try to target the back of the intake valve to do the same thing. However I don't think there is as much time for the fuel to vaporize with this method. The computer locks you into a certain air / fuel ratio unless you either by a programmer or software to let you change parameters. It was just easier to tweak a carburetor (to me). You can most likely gather I'm a carburetor guy because their utter simplicty fascinates me compared to fuel injection. It's really tough to match drivability of fuel injection though. I don't want to stop you from trying I'm just trying to tell you some of the problems you will have to deal with. I would start investigating on some of the forums what specifically deal with your truck and see what others have used as far as programmers, etc. Welcome to SmokemUp and let us know what you figure out. Clay
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Big Dave
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PostPosted: Thu Jul 29, 2010 2:14 pm    Post subject: Reply with quote

The Triton V-10 has an advantage (well two actually in that the first advantage is it is a smaller engine, at 466 cid vs the 8.1L's 496 cube displacement) in that it has a "better" combustion chamber. The 8.1 liter Vortec is a Vortec in name only. The heads are different not because of the improved Vortec combustion chamber but because GM changed the cooling passages in the head.

You have more valve surface per cube in the smaller Triton and more squish area to better mix the fuel air charge before it lights off. You also have a higher compression ratio as the Triton uses variable valve timing to keep the dynamic compression as high as possible to match the load. The Vortec by comparison has not changed much since it was first designed back in 1963. The greatest change has been in valve timing but as noted it is a single cam that is fixed in sync with the crank and not going to change under load.

As to atomization of the fuel supply with EFI you can increase the fuel pressure (there are aftermarket fuel pressure return springs) to obtain better vaporization of the fuel. This results in a shorter firing time (pulse width ) on the injector. The EFI port injection is the best thing to happen to the BBC as it suffers from having four good ports and four bad ports as far as fuel distribution goes.

I do not know if the factory took this into consideration and adjusted their location of the injector to optimize fuel distribution (point it at the back of intake valve), but they probably went with a symmetrical set up. That would be one improvement if you could move the injector's orientation.

The big block Chevy (BBC) was designed to be a high compression engine (semi-hemispherical), but emission requirements have killed that; and the BBC is now equipped with dished and not domed pistons. This is why it is very inefficient compared to most other engines (it is also the reason why most racers chose the BBC and increase the compression back up to the original design specs to dominate over other engines when racing). Unless you have access to E-85 fuel you can not increase your static compression any. If you do; a piston swap will greatly improve both your fuel economy, and your towing power.

As Clay stated your computer is programed with a very mundane program designed to minimize service problems not optimize fuel economy. If you buy a programable controller you can adjust your ignition timing curves and fuel distribution curves to run on the ragged edge of detonation with a very lean mixture.

Big Dave
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goodwrench
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PostPosted: Fri Jul 30, 2010 11:18 am    Post subject: Thanks. I should give a little more information. Reply with quote

When I stated 466 on the Ford I did so mainly as an expression of relitive cubic inches. This is a 429 from a 71 T Bird I put a 460 crank and pistons bored 30 over to 466. I suppose one unfair part of the comparison is that the 8.1 has more miles on it. I built the 460 about 14 years ago but I have not diven it 260,000 miles. I did modernize the combo with Mallory ignition, Holly 750, RV tow cam, headers and duels, 9 to 1 compression. The Ford definately weighs more because of the enclosed 9 foot duelly utility bed loaded with tools. I think it weighs at least 1000 pounds more. The bed enclosure sticks up over the cab. The Chevy I purchased from a guy you may have seen on Pass Time running a 4x4 at ZMax drag way. Ed's Deisel Performance 704- 791-0268 out of Concord NC was the name. He specializes not only in deisels but in the Chevy HD truck line. He tuned up the truck before I got it including cleaning the injectors and changing the spark plugs. He did a good job I think and was straigth up. He had the truck calibrated to run on 93 octain with some software from his laptop but I had him put the program back stock so I could run the cheep gas. He did tell me that was giving up a lot of power but I replied if I want to haul ass I'd get in my muscle car. I think I might have been better off leaving it the way he had it because I found his gas reciepts in the console that indicated 11 + mpg. It probly gets more mpg with the 93 octain calibrations. Both trucks run great. I mean endless torque. I suppose the 8.1 probably is lossing compression from all those miles. I'll give Ed a call and see what he thinks about calibration for fuel economics. Thanks for the advise and I'll keep you posted.
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