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Old 11-06-2008, 10:29 PM   #1 (permalink)
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Large GMC Van, possible improvements?

I've been reading this forum for a while, and thinking about how I can help possibly restore some life into my van. It's about the antithesis of fuel economy:
'86 Vandura, so it's huge, heavy, and has a large engine in it, the 5.0L 305. That said, I've been thinking of a few things to help it. First off, I know the engine needs work, but on top of that, it was one of the few with a carb, but also a knock sensor/prevention system, so I could relativly safely amp up the compression ratio with a thinner gasket(although it already runs at a 9.5 ratio). Ideally, I would convert it to fuel injection once I get the time and money, but a gasket would help no matter what else I did to it.

Being rather poor, I've just thrown on some duct tape on the grille, which hasn't really affected the tempature at all; once it gets to about the 1/4th point, it stays there under all but the hardest driving. Getting it to the half point, and it cools back to the quarter within about 2-5 minutes.

I do have slightly larger tires(235/75/R15, as opposed to the stock 225's), which should help somewhat(and also seems to make my odometer and speedometer spot on, most of them are 2-3% fast).

The last thing that's caught my eye, is one of these: Gear Vendors Under/Overdrive Chevrolet/GMC Final Drive Ratios.


I don't know if any of you have seen them before, but it seems you can bolt on a 2 speed onto the back of some common 2-4 speed gearboxes(sorry, front engine, rear wheel drive only). I read about a Hot Rod magazine test involving one of these, it increased the FE by about 1-3 mpg, while also allowing one to stay in the powerband easily. Bolt one of those onto my van, with the stock 4 speed, means I have a total of 8 gears to play with.

Can anybody think about other possible reasonable mods I could do? I have some mechanical ability, more electrical ability, but no real fabricating knowledge, and very little money.


As for current fuel economy, I haven't really had the time or ability to test that properly(I was getting roughly 15mpg on the highway, but I was also extremely loaded down with moving things), and the stock mpg is listed as 18 on the highway, 14 or 15 on the city. I'm shooting for about 25hwy, although the lower 20's would be acceptable by the time I'm done with it, and at least 18 in the city, although I'd live with 17.(fun fact, I have a 33 gallon tank. At 25mpg, that's 750 miles on one tank, with 3 gallons reserve).

To my credit, I do also try to do some hypermiling actions(following trucks and/or a bit too closely), shifting into neutral when coasting, I even installed an aftermarket tach so I can keep better watch of my RPM's, which was probably my best add-on thus far.

One thing, just to cut down on the inevitable "trade it in" camp. I love this van. I got it in a decrepit state and barely alive to smooth and strong again. It was literally sitting around, exposed to the elements for 3 odd years, the battery drained, the tires flat, the engine extremely out of tune, and I brought it back to performing excellently. I've driven it from Missouri to Michigan to Idaho, with all of my stuff in it in. I love it, and I don't ever plan on replacing it or selling it. I will drive it till it's doors fall off, put them back on, and drive it some more. The engine has only 94,000 miles on it(the 100,000 mile odometer limit has never been reached), so it has a LOT of life in it still, any mod over the life off it will help, and I plan on driving it for a very very long time still.

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Old 11-06-2008, 10:33 PM   #2 (permalink)
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If you are poor you will NOT end up with a Gear Vendors unit.
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Old 11-06-2008, 11:20 PM   #3 (permalink)
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Gear vendors unit is a few thousand bucks. Even if it gave you 25mpg it would take years to pay it off in savings. A cheaper alternative might be to swap to a 4.3L vortec v6 engine. You can find tons of trucks with those motors and they are basically a bolt in swap for a a V8. the 96 up engines have really good power and can work pretty well for normal use Just use the 94-95 computer and wiring/sensors to keep from having to deal with the obd2 stuff if you don't want it. Also the 99 up 4l60e transmissions are stronger than the 700r4 you currently have if you can find one cheap and will work fine with the 94 up computers.

My Astro conversion van 4.3L with 4spd auto and 3.73(I think) rear end gears is getting right at 20mpg driven fast and totally stock. With a few minor mods like electric fans, synthetic oil, belly pan, and the right tires I don't see any reason why it can't be at 25mpg. It isn't as fast as the 305 engine but it has no trouble moving itself around and towing a car on a trailer as long as you are not in a hurry going up hills.
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Old 11-07-2008, 12:51 AM   #4 (permalink)
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For what it's worth, I am saving up money. I'm poor now, but I could probably afford the auxillary transmission within a year or so(probably will also go for an aluminum driveshaft at the same time, since I would need to replace it anyways, might as well go for a light one and get a few more 'free' ponies to the wheels). As for the engine swap, I'm not totally sure how one would stuff a new engine into the van, and it probably would be more complex than what I'd be willing to do. Also, it may take years to pay off, but I'm planning on keeping the van for years and years. It's really going to become a project vehicle.
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Old 11-07-2008, 11:21 AM   #5 (permalink)
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Originally Posted by Coyote X View Post
Gear vendors unit is a few thousand bucks. Even if it gave you 25mpg it would take years to pay it off in savings. A cheaper alternative might be to swap to a 4.3L vortec v6 engine. You can find tons of trucks with those motors and they are basically a bolt in swap for a a V8. the 96 up engines have really good power and can work pretty well for normal use Just use the 94-95 computer and wiring/sensors to keep from having to deal with the obd2 stuff if you don't want it. Also the 99 up 4l60e transmissions are stronger than the 700r4 you currently have if you can find one cheap and will work fine with the 94 up computers.

My Astro conversion van 4.3L with 4spd auto and 3.73(I think) rear end gears is getting right at 20mpg driven fast and totally stock. With a few minor mods like electric fans, synthetic oil, belly pan, and the right tires I don't see any reason why it can't be at 25mpg. It isn't as fast as the 305 engine but it has no trouble moving itself around and towing a car on a trailer as long as you are not in a hurry going up hills.
I've never had good luck with that 4.3, personally. It may just be the vehicles they are in, but I've used 3 different ones, and they all lacked power and economy in my eyes.

Although it might be a more expensive option, a 4.6L Northstar is a much better option. My mother's Cadillac does 30mpg on the highway, just cruise, no hypermiling at all, at 65.
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Old 11-07-2008, 01:05 PM   #6 (permalink)
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As said, I don't really want to do an engine swap, 1: because I don't know how to do one in a van, and it's a lot of work to boot, and 2: I know my engine about as well as one can know it, and I've learned and adapted hypermiling based upon it's powerband and when it shifts. With a different engine, I'd have to re-learn things like shift points and the powerband again.

Besides, with the larger, more torquey engine I have, I can power up hills in 4th gear with some throttle balance. With a smaller, weaker one, I might have to downshift due to the lesser power(it makes 250 ft-lbs of torque at 2000 rpm)(it's the LE9 engine, if that makes any difference).
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Old 11-07-2008, 01:24 PM   #7 (permalink)
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Originally Posted by Kalanco View Post
As said, I don't really want to do an engine swap, 1: because I don't know how to do one in a van, and it's a lot of work to boot, and 2: I know my engine about as well as one can know it, and I've learned and adapted hypermiling based upon it's powerband and when it shifts. With a different engine, I'd have to re-learn things like shift points and the powerband again.

Besides, with the larger, more torquey engine I have, I can power up hills in 4th gear with some throttle balance. With a smaller, weaker one, I might have to downshift due to the lesser power(it makes 250 ft-lbs of torque at 2000 rpm)(it's the LE9 engine, if that makes any difference).
I can see not wanting to do the swap, though I think it would be easier in a van than cars, since you don't really have a whole lot of hood out in front of the engine.

But the 4.3L, when it's properly tuned can make 280-300, and comes stock at 260, with an almost flat torque curve from 2K. By comparison, the 4.6L stock has 280, and it's a thoroughly nasty little beast if you have no right foot control.

Smaller definitely does NOT equate to weaker here. My father used to own a 1983 Oldsmobile Delta 88 with the 307, and it could get run over by anything either I or my parents own now, all of which have smaller engines. And it only got better FE than one of those vehicles.
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Old 11-07-2008, 01:48 PM   #8 (permalink)
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Really for the amount of work for an engine swap even a bolt in one that is free/super cheap, it probably isn't worth it for the 3mpg or so gain. But then again the gear vendors unit will get about the same mileage gain and unless you are climbing the rockies daily with a 5 speed it won't be worth it. You could drop one size in the rear end gears and get about the same gain as the GV unit for nowhere near the cost.

The easiest and cheapest things are what I would do first. So if you have a belt driven fan swap to an electric fan. Just find one from a Taurus is what I hear is a really good one to use. That by itself is good for 1-2mpg. Changing to synthetic fluids all through it next time you change them will probably get you another mpg as well as a smoother running engine. Filling in the huge open areas underneath and trying to smooth the underside as much as possible would probably be a big help but I am not sure how much mileage it would get you, probably a mpg or 3. Also if you have a roof rack you don't use take it off for another mpg.

All that stuff costs very little and can get you more mileage than a GV unit that adds weight to the drivetrain. So even though you have a gear split, when not using it you will definitely notice a drop in power. Right now if you can hold 4th going up a hill right on the edge of downshifting you will have to downshift after installing the GV unit due to the extra drag on the drivetrain. If you want a GV unit for other reasons than mileage it might be worthwhile. A 5psd with the GV unit would be a pretty good combination if you are always hauling 10,000lbs and needing to go up hills. With an automatic I am just not sure what it gives you other than a taller overdrive. The torque converter kind of makes the split gears useless if you use an underdrive unit, an overdrive unit can give you a better 4th gear rpm to use on flat ground while empty, but swapping rear end gears to a 2.73 and just using 3rd while loaded would give you even better mileage and the first and second will still use the torque converter to get rolling so they won't be much different for non race type driving.

So maybe give us an idea of what your priorities are and that will help us understand what you are really after. Are you looking for better mileage without giving up your performance? The two are not always mutually exclusive but it will greatly limit what you can do to improve your mileage. Are you just mainly wanting better mileage while still being able to haul and tow things? That means you can give up some power and just go slower while under load. Are you willing to do engine work like a swap to a smaller cam? It would help us to know what you really want that way we can give better advice.
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Old 11-07-2008, 01:54 PM   #9 (permalink)
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25 mpg is a lot to ask. Slow down A LOT. Don't go over 55, and shoot for 50 mph max. Take a different route to avoid the interstates. A lot of interstates have parallel rural routes. Air up your tires to sidewall maximum. Subject to argument, but I believe that if you use mid-grade or premium fuel AND increase the engine timing to "just before ping" then you will save money on fuel - vice using low grade and standard ignition timing. Do the standard tuneup items - spark plugs, wires, air filter, thinner motor oil. You might want to consider upgrading the ignition to a hotter coil (40 or 45k) and 9mm or better spark plug wires. The you could gap the spark plugs an extra .05 or .075.
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Old 11-07-2008, 03:18 PM   #10 (permalink)
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Quote:
So maybe give us an idea of what your priorities are and that will help us understand what you are really after.
I want to enhance the vehicle across the board, for lack of a better term. Fuel economy would be a goal, but making it perform better in general is the ultimate aim. The Gear Vendors system helps with economy constantly, notably when I'm in 3rd gear. The 3-4 shift is rather picky(it refuses to shift until 36mph, but goes back to 3rd at around 30), so I can force it into an overdrive even at the mid 30's. Also, with double the effective gears, I can haul things better by keeping the engine in the powerband. I've looked at the transmission, it would benefit greatly from a gear vendors unit, because the ratios are extremely wide: 3.06, 1.6something, 1.0, .70. That's just begging for a few more gears. Also, while I know the claims are often different than the results, GV claims that you give up an extremely small amount of power. I wouldn't be surprised that anything you lost in the GV unit, you gain back from the fact that you have a shorter driveshaft(less rotating mass, also, see bottom of post about a way to reclaim that)

Not to mention the double overdrive end result, which would bring the RPM at 75mph to a nice 2000ish RPM, which just so happens to be right at the torque peak.

Also, I think 17/25 mpg result is just on the edge of reasonable to ask, with everything I want to throw into it. I read about a car that, with a conversion to FI and a gear vendors unit, went from 11/13mpg, to 14/17.5mpg, and it only had a 3 speed. Assuming I get the same relative gains, that goes to about 17/24mpg for my van.

I'll also list the things I've thrown into it to help.
K&N air filter(whether or not it actually helps economy, I don't ever need to buy a new one again which was reason enough); aftermarket tachometer(I would honestly rate this above a fuel consumption sensor if you are deciding which one to install first); I just switched to synthetic oil, although I was told that my engine is going to leak due to it so I'll keep a close watch and switch back if so; I also use this oil additive I read about called Restore, and it did seem to help(if nothing else, it felt like it got a bit more power and torque back, and sure felt better after a few miles, but I can't exactly do an A-B-A test with it).

I would eventually like the GV unit, an FI kit(Holley seems to make one that looks pretty good and simple enough, and includes a tunable ECU, which is excellent and would allow me to get exactly what I want out of the engine, when I want it(not that I could choose for the basic ECU anyways; 4 barrel mainfold is the only option for my engine).



Also, a question. I've heard of aluminum driveshafts being used to get back some of the power to the wheels that is lost in the drivetrain, useful for sports purposes. Has anybody had any experience with using that for economy as well? I would think that if you're getting more power to the wheels without increasing the engine's power, that you could throttle back slightly and use less fuel while still making the same effective power, no?

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