Boat/Plane Tail on an SUV

[ComputernerdBD]

Hi everyone. This is my first post on this forum. I drive a 1998 GMC Jimmy 4x4 with a 4.3L V6 engine and a 4L60E automatic transmission (I live in the Hudson Valley and go to college in upstate NY where they don't cancel class JUST because there is 2 feet of snow and ice on the ground. Plus I go camping alot and I use my 4x4 alot.) and it is lightly modified to try to get better gas mileage and reliability. I have a cold air intake (MPG ^) and a transmission cooler (Reliability ^) and I used to have a throttle body spacer on the engine (MPG ^?) that I will be reinstalling next weekend now that I found a way to fit both the CAI and the spacer on this engine. I also have a Posi-Lok system, so I can not only be sure that my 4x4 locks in properly, but that it unlocks properly, so there is minimal drag. I usually use Royal Purple 5W-30 oil (weight the 4.3L calls for), minimize A/C use and use cruise control as much as possible to further save gas. I just did a tune up with a new distributor cap/rotor and AC Delco RapidFire spark plugs. Other than that, it is totally stock. I just replaced some rotting vacuum lines and I determined that at 65mph, I get between 19-21mpg (verified by factory trip computer), depending whether or not I have the aerodynamic cargo box (almost no mileage penalty) or the bike rack (some penalty because the bike wheel is in the wind). In town, depending on idle time (both waiting for traffic lights and to let the engine warm up), I get between 10 and 15mpg. For a V6 that has roots with a V8 engine design (a 4.3L is a 5.7L with 2 cylinders deleted) with 108k miles, that isn't too bad, but I am trying to increase my MPGs without sacrificing it's usefullness in the snow and offroad.


I saw on Top Gear US Death Valley challenge how one of the challengers who drove a Chevy Blazer fullsize through all the offroad challenges WON the final challenge that tested fuel economy by putting a cardboard boat tail on it and was the only one who finished without either blowing a tire or running out of gas. Just how could I build one for this truck that will not only be sturdy, but legal? I was thinking of maybe using the trailer hitch and the roof rack rear bolts as attachment points since they seem the most secure. Maybe install LED trailer lights and the license plate to the tail cone of the boat tail and plug it into the existing harness so I can remove it if I want to tow or use the bike rack. Since I like planes, maybe even put a tail fin on top of it to make the truck look like a plane? LOL JK

I have other aerodynamic mods planned like a light coating of bedliner paint (either with or without rubber texture) since this paint has alot of scratches down to metal (but no rust. Plus I keep this truck clean, so there is minimal dirt drag) and fixing damage to the front bumper (big crack/bent. Not good for aerodynamics) to try to reduce the drag coefficient. I have P235/75R15 tires (just larger than factory spec), so there are less revolutions per mile. I have been decreasing the weight of the contents of the interior, but some stuff I can't remove. I have a box of emergency equipment and spare fluids for everything among other things since this truck does enter places where there is no cell service and I might have to perform repairs myself if something happens.

Thanks

[malovich]

The cold air hurts mileage (but increases power)
The throttle body spacer doesn't help (waste of money)
Tranny cooler does help with lifetime and towing performance but I doubt it would help with mileage
The roof hauler would be detrimental to your mileage
Cruise control is detrimental to your mileage
Bedliner would be detrimental to your mileage but rust sucks more, I say go for the bedliner

There are a few things I can recommend, Pump your tires up to the sidewall max, take off anything on the roof including the cross members of the roof rack, install a grillblock, and get a scangauge II and learn how to drive efficiently. I say this in confidence because I have gotten 28mpg in a 2000 4x4 v6 s-10. You must be light on the pedal and draft semis at a safe distance whenever possible.

Then if you want to try hypermiling a blazer then you would then experiment with smoothing the undercarriage, lowering it, adding a splitter and then adding a boattail. On the newest mythbusters they did a hypermiling motorbike using 1"x1" framework covered with a semitransparent heat shrink similar to that used on boats in the winter. Good Luck

Don't add a fin it will look retarded and suck with crosswinds.

[ComputernerdBD]

The cold air hurts mileage (but increases power)

*What? I have seen 3-4 mpg more compared to before, especially after the tune up!

The throttle body spacer doesn't help (waste of money)

*I already have it from 2 years ago.


Tranny cooler does help with lifetime and towing performance but I doubt it would help with mileage

*I know it won't help with mileage. I don't tow. I just want to squeeze as much life I can out of this truck.

The roof hauler would be detrimental to your mileage

*I only have it on the truck when I am actually using it. It makes annoying noises, especially with the straps I use to secure it for safety. I don't even use it on road trips longer than 2.5 hours if I don't actually need it.

Cruise control is detrimental to your mileage
*How so?

Bedliner would be detrimental to your mileage but rust sucks more, I say go for the bedliner

*I was thinking of Grizzly Grip since they have bedliner without rubber for texture. Might make the truck smooth with it since it is easier to apply than regular paint.

There are a few things I can recommend, Pump your tires up to the sidewall max, take off anything on the roof including the cross members of the roof rack, install a grillblock, and get a scangauge II and learn how to drive efficiently.

*Tires are only 1PSI south of sidewall already. I will pump them up.
*Roof is empty right now, but I can remove the entire rack.
*Grillblock? Won't that overheat the engine and block the trans cooler?
*Would like a USB OBDII adapter work? I have a Car PC with a 7" screen. Might be more powerful than a Scangauge



I say this in confidence because I have gotten 28mpg in a 2000 4x4 v6 s-10. You must be light on the pedal and draft semis at a safe distance whenever possible.

*28MPG?! On a 4.3L?! Wow.


Then if you want to try hypermiling a blazer then you would then experiment with smoothing the undercarriage, lowering it, adding a splitter and then adding a boattail. On the newest mythbusters they did a hypermiling motorbike using 1"x1" framework covered with a semitransparent heat shrink similar to that used on boats in the winter.

*I will look into all that. I saw Mythbusters. Very cool and learned alot from it, but I was curious how I could apply that to the truck.


Good Luck

*Thanks.

Don't add a fin it will look retarded and suck with crosswinds.
*That was a joke. LOL

[Tango Charlie]

Originally Posted by ComputernerdBD

Cruise control is detrimental to your mileage
*How so?

*I was thinking of Grizzly Grip since they have bedliner without rubber for texture. Might make the truck smooth with it since it is easier to apply than regular paint.


*Grillblock? Won't that overheat the engine and block the trans cooler?

Cruise control is not detrimental to your mileage per se, it's just not as efficient as some other techniques, such as DWL or P&G. However, CC will net you better mileage than if you drive "normal" on longer trips. DWL will wear you out on longer trips, so CC becomes a second best choice. I use CC extensively. Could I get better mileage? Yup, no doubt. If I were younger, or more motivated, or more anal, I would DWL all the time instead of using CC.

Bedliner; the small amount of texture won't have any measurable affect. The boundary layer is way too thick even at highway speeds for the air to "see" it. Same goes for washing/waxing.

Grille block; I would suggest progressively blocking the grille until there's just enough cooling capability. I'm not familiar with Car PC. Does it read out coolant temperature? If it does, use that to determine how much of the grille you can block.

[ComputernerdBD]

Originally Posted by Tango Charlie

Cruise control is not detrimental to your mileage per se, it's just not as efficient as some other techniques, such as DWL or P&G. However, CC will net you better mileage than if you drive "normal" on longer trips. DWL will wear you out on longer trips, so CC becomes a second best choice. I use CC extensively. Could I get better mileage? Yup, no doubt. If I were younger, or more motivated, or more anal, I would DWL all the time instead of using CC.

Bedliner; the small amount of texture won't have any measurable affect. The boundary layer is way too thick even at highway speeds for the air to "see" it. Same goes for washing/waxing.

Grille block; I would suggest progressively blocking the grille until there's just enough cooling capability. I'm not familiar with Car PC. Does it read out coolant temperature? If it does, use that to determine how much of the grille you can block.

I use cruise mainly once I get on a straight and level interstate highway and that is when I usually get my personal best mileage.

What is DWL?

Bedliner: Ok. But I did email Grizzly Grip to ask them if they sell it without rubber so I can make the car slick smooth while protecting the truck from the elements.

Car PC is currently not interfaced with the OBDII connection. I have to get the USB adapter to hook up to the car's PCM to get the data off of it. Right now, all it does is navigation (backup since I have a dashboard GPS), music, internet (whether I tether or use Wifi) or anything that Windows XP can do. Only real "computer" that reads vehicle data is the factory trip computer that does MPG, gallons used, instant economy, temperature, compass and average speed. I normally reset it every time I fill the tank along with the trip odometer.

[malovich]

the 28 was merely from the scangauge on my most recent tank 98% highway but upon fill-up tonite (same tank as 28) I got 25 fwiw. My tires are a bit low since it's colder out and who knows how accurate my fillup was and my speedo is off (68 actual registers 70 so about 3%)

On second thought the bedliner may help a hair like a golfball if it is rough. My abs started acting up so I pulled that fuse which also kills the CC so I've been without CC for about 30K miles. It's not much strain to drive with your foot on the pedal as long as you are merely applying a constant pressure/position while allowing the speed to fluctuate, works for me.

I know the fin was a jk but the crosswinds would suck.

[Peter7307]

First up: Welcome to the place and enjoy your stay.

One item not addressed is the cruising speed.
65 is fine but your economy should be better at about 55 / 60 since this will allow you to stay in 4th. gear and keep the revs down a bit as well.

As you probably worked out already it is usually a matter of "a little bit here...a little bit there" to get to your MPG target.

Good luck and post what you find.

Peter.

[Tango Charlie]

Originally Posted by ComputernerdBD

What is DWL?

Driving With Load. Check out the "100+ Hypermilinig Tips" link at the top of the page. There's a lot of reading on this site!

Originally Posted by malovich

On second thought the bedliner may help a hair like a golfball if it is rough.

No. No, it won't. Not unless your vehicle is a 1.68" diameter spinning sphere. Did I mention that there's a lot to read on this site?!

[LUVMY02CREW]

Welcome ComputernerdBD!!

Adjusting the nut behind the wheel will make a huge difference with the 4.3 engine. And, be sure to update your fuel log regularly so you can see the improvements. I'm pretty steady at 20mpg with my crew cab.

Good Luck and happy reading here.

[orbywan]

Originally Posted by ComputernerdBD

I use cruise mainly once I get on a straight and level interstate highway and that is when I usually get my personal best mileage.

What is DWL?

Bedliner: Ok. But I did email Grizzly Grip to ask them if they sell it without rubber so I can make the car slick smooth while protecting the truck from the elements.

Car PC is currently not interfaced with the OBDII connection. I have to get the USB adapter to hook up to the car's PCM to get the data off of it. Right now, all it does is navigation (backup since I have a dashboard GPS), music, internet (whether I tether or use Wifi) or anything that Windows XP can do. Only real "computer" that reads vehicle data is the factory trip computer that does MPG, gallons used, instant economy, temperature, compass and average speed. I normally reset it every time I fill the tank along with the trip odometer.

Hi computer guy, welcome to ecomodder. I'm curious what kind of car PC you have in your Jimmy, could you post some info on that, manufacturer, cost, etc? You'll find there's a lot of things you can do to increase your mileage, many listed above are worth considering.

I built a permanent boat tail for my RV and increased the mileage easily 25% and am about to build a boat tail similar to what you described (i.e., mounting it primarily from the hitch so it is relatively easy to remove) for my Tundra. Even though it will be a challenge, you'll get by far the biggest increase in mileage from your Jimmy with a boat tail, although the truck bed will complicate that considerably. I would suggest buying a cab high shell and building the boat tail to that configuration.

If you get into this you'll find the interface for your PC to your OBD will be very useful. Good luck.