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Gas Guzzle, Guzzle, Gulp, Gulp!


This is a discussion on Gas Guzzle, Guzzle, Gulp, Gulp! within the Mechanic's Corner forums, part of the TMC TECHNICAL category!
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Old 04-24-2011, 08:44 AM
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Old 04-24-2011, 01:49 PM
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Dude!
That Waukesha shit just brought back many miserable memories of my life!
Cracked heads, cracked manifolds, droped valves, broken crankshafts
Oh the horror!

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Old 04-24-2011, 02:40 PM
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There's a metric ton of aerodynamic drag on a truck at highway speeds. Little things like lowering the truck and running an air dam will greatly improve front end drag characteristics.

A truck uses about 70 - 75 HP at 80 MPH just to push it through the air, but at 55 MPH it'll use half of that. Drag increases at the square of velocity.

Tonneau covers don't decrease drag. The airflow eddies behind the back glass and acts as a roller bearing for the air above it. The flow loss is due to separation because the angle is abrupt. To make it any more aerodynamic you'd need about a 10 - 13 degree diffusion angle off the back glass towards the rear of the truck.

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This is from TruckTrend.com ... you can see the low pressure separation of the airflow at the end of the cab. That air is mostly eddied and not really doing much inside the bed. The remainder of the flow is turbulent although somewhat more laminar than just a wake.

Nothing on a truck is conducive to aerodynamics. They are a utility vehicle meant for their abilities off the road and in towing / hauling.
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Old 04-24-2011, 03:00 PM
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Things I would look at would be the weight of the wheels ... wheel and tire combined. Alot of the big aftermarket wheels and steel OEM wheels weigh upwards of 25 - 30 lbs. a piece. Add a big all-terrain tire or wide tire to that and you'll get a rolling weight around 60 lbs. a piece. That's 240 lbs. of rotational weight you have to spend alot of power to spin up at highway speeds.

Going to a 15x8" aluminum wheel (OEM options out there) and a properly sized road tire (245/70/15) should cut a solid 15 lbs. off a wheel. That's 60 lbs. of weight you no longer have to haul around, and the effects of rotational weight on braking and acceleration are pretty big, especially with lower gear ratios as the engine has less leverage per pound ft. of energy (read: highway speeds and overdrive).

Plus the wheel is probably the dirtiest aerodynamic part on the truck besides the undercarriage. Choosing a more closed off and smoother wheel face will make a pretty good change in how much drag the wheels produce, but at the cost of brake cooling. That can be fixed by running air ducts from the front dam to the brakes.

A good mod you can do pretty easily is to get some 1/4" aluminum sheet and cut out an undertray to run from the bottom of the air dam to about the sump, or behind it to the flatter undercarriage. That would reduce alot of high speed lift, and increase fuel economy somewhat.
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Old 04-24-2011, 06:53 PM
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17mpg at 85 mph aint too bad. So far I still got several things to do it.
Better PCM electronics is going to be the biggest difference.

Hell no I aint lowering it either. I did that one time. Didnt like it as a everyday driver. If I can get it to 20mpg I will be plenty happy.
When im done playing with all the other little nitches, im going to put a stroked up 305 in it. Same bore but a 3.750 stroke.
Kinda thinking about putting a turbo on it too. "Lean Burn".
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Old 04-24-2011, 06:59 PM
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The only thing that's going to lean burn in a turbo V8 is the pistons.
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Old 04-24-2011, 09:21 PM
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Thats not what gets pistons.
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Old 04-25-2011, 06:12 AM
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Old 05-20-2011, 09:04 PM
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Just filled the old PU with gas again. This tank was all in town driving. Note, I didnt drive it like I was trying to save some gas for everybody else either.
Driving around town gets my pressure to the max sometimes. People getting in the way, redlights deciding to change as soon as I get there, trying to pull out of a parking lot when somebody left the gate open ect...
What get me lead footing more than anything is those people that pass you up just to get in front of you as they decide to make a left had turn. ERRRRRR!!!
This tank fill really impressed me. Considering it was all in town driving, I got 350 miles out of this tank. Use to only get about 240 or so.
I just ordered a air cleaned housing that has two air inlets. I'll move the battery to the toolbox and hook the ram air up behind the headlights. I have a 6A box I will be installing on the old truck too. I think after the latest two upgrades, and a little better " Less high blood pressure" driving, I might get close to 400 miles out of a tank of fuel.
Right now im up to 15 MPG in town. 17 to 18 might be very possible.
Oh Yea, I still haven't had the time to datalog the PCM. I know it's running too rich cause it stinks! Im waiting to get the ram air put on, then i'll do some reprogramming.

So far the only thing that I actually spent any money on was the new radiator and the air clear stuff. Everything else I already had. All the labor and equipment was just part of my everyday run of the mill.
When I get done with all the little stuff, I have a new 305 I started building. It's not a normal 305 by no means. This was one of the engines I use to sell for the Texas 305 sprints. It has a spayed cap block, ultra lite crank, oliver rods and Diamond pistons. Nobody around here runs the 305 stuff no more so im putting it in my truck.
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Old 05-29-2011, 06:22 PM
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Update on this tank of fuel. I haven't had the chance to do anything else lately but the P.U. got right at 16 MPG all in town driving with the AC going, " IT's HOT around here"...
Im pretty ticked so far. The truck use to only get 14 on the HWY. Im going to put all the MSD stuff on it tomorrow night, so we'll see how much that helps.
Im still itching to put some headers on it, but I would really rather wait till I get ready to put the new engine in it.
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