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Old 03-05-2008, 11:44 PM   #1 (permalink)
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Hey - Young vanner here

Just saying hey to everybody, im 21, out of KY, here (finally) because I bought a giant 87 chevy van as an impulse at an as-is auction. i just wanted to put some speakers in it, but everything i did beget something else and now im building up a custom interior from pretty much scratch. Upon finding out she gets 11 mpg from an old small block (surprise!) TBI 305, im afraid the same phenomenon is happening under the hood. I dont have the capital or expertise for an engine swap, but i refuse to believe some careful tuning and the right parts cant make a roadtrip cruiser out of the 305 yet. You don't have to read anymore. Very exciting to have finally stumbled here!

For those going on, might as well kill two birds here:
Without the obvious solution of reducing displacement or going diesel, what's next best? Reducing rpm to as low as possible? Reducing throttle restriction? More power/taller gears? Lowering peak torque rpm? How much hp do i really need to keep this thing at 70 mph? What components determine rpm operating range? What's the tallest rear end I can safely put on? *sigh* so many questions, so many factors. I care about FE/gradeability at 70 mph, and only 70 mph, and for that narrow application im sure there's a hard fast answer I just havent found yet. At any rate im learning new tricks here by the minute (WAI? Boattails?? Wow!) on topics where information is ordinarily very very rare. Keep up the awesome work everyone!

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Old 03-06-2008, 12:50 AM   #2 (permalink)
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What tranny does it have? fueleconomy.gov it looks like with the 305 (5L engine) depending on your tranny your EPA mileage will range from 12-14mpg in the city and 15-18 on the highway, so I would start out getting your vehicle to stock EPA, then improve from there.
I would start out by finding the narrowest tires you can get,and I suspect that narrow (light) rims for a van like that are going to end up being steel, just because alloy rims are tend to be wider, also if you get under your van you are going to notice the whole underside is not smooth to say the least, but I suspect that with the frame of the vehicle building an under tray should be easy and that is going to help your highway mileage.
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Old 03-06-2008, 02:08 AM   #3 (permalink)
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same as ryland said make a belly pan, i have a huge list of stuff that i posted on a thread about an rv earlier, it all pretty much carries over to vans

*grill block
*belly pan (you can go to rv parts stores and buy big sheets of fiberglass)
*tire pressure
*electric radiator fan
*the skirt thing under front bumper
*skirts around sides
*new shock absorbers/ springs
*make an angled roof extension (not to sharp of an angle) along the lines of a boat tail
*get rid of useless mass
*switch to lighter materials (heavy wood counters -> fiberglass counters carpet -> vinyl)
*remove radio antenna (relocate inside of body)
* DO NOT REMOVE MIRRORS!!!!! they are extremely valuable, just make aero housings for those

i cut some of the things from my list i posted for the rv as i dont think they apply to your situation

here is the link to that post if your interested
http://forum.ecomodder.com/showthread.php?t=1051
also in that thread (i think its the 3rd or 4th post) there is a pic of a van done by nasa, it has some really good ideas.

when it comes to efficiency of the motor, remember it is one big air pump, remove as many restrictions from the intake and exhaust as possible (switch to a high flow cat, ditching it really is not all to beneficial) also do all the regular maintenance (spark plugs, fuel filter, air filter, 5w20 oil)

anyhow hope this helps some
John
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Old 03-06-2008, 03:29 AM   #4 (permalink)
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Might be more work than what its worth but there was a 305 offered with MPFI. Figure if you could get the intake, injectors, computer and the rest of the stuff required that could net you a nice gain right there vs your current TBI setup.
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Old 03-06-2008, 01:10 PM   #5 (permalink)
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A rambling response

Thanks for the quick responses, all good ideas... THM350 or THM400, either way a 3-speed with no overdrive, which will obviously have to go. I'm probably wildly short of stock mpg because of a crap air filter, crap gaskets, exhaust corrosion, and excessive drag (especially from brakes). I'm not at all worried about pulling it back up to 15 mpg, this is all to get me to 20. I do like the idea of bigger, thinner wheels, they just take a backseat to the challenge at hand. I'll have to look into whether an undertray is easier/appreciably more effective than a front air dam. Or you could tell me, haha.

Johnpr you are certainly on point with all your ideas, excellent list, and indeed I'm sure most would pay for themselves. My to-do list grows exponentially. Do you say new shocks for the lowering benefit? If so I would expect the relative benefit of a front air dam or especially an undertray to decrease.

The rest of the recommendations, intake/exhaust and EFI, highlight a particular problem I'm having with spec'ing the engine. If it's already of sufficient torque to move the van, any breathing and thus hp gains from exhaust will seemingly encourage burning more fuel with little added usefulness. Furthermore, the stock exhaust manifold lends itself to low-end torque and vans seemed plagued with ill-fitting headers. With the intake, I don't want to upgrade the carb, im sorry i meant throttle body, only to have the engine always choked off by the throttle plate anyway.

Finally, EFI is tough to justify because of the narrow application. In short I can tune the carb, im sorry throttle body, for my application and the advantages of an adaptive EFI system all but disappear, save for cold temperatures and the minor losses inherent in only using one injector.

Thanks for the thought-provoking answers, you guys are awesome! i really do try to keep these things short. If im wrong about anything, and im sure i am, do tell me. Thanks!
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Old 03-06-2008, 06:29 PM   #6 (permalink)
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on the shocks, its not because of lowering the vehicle, you are right that it would decrease the value of the airdam and undertray, the reasoning is that as shocks get older there effectiveness decrease allowing excess movement which can rob your vehicle of power (shift in weight distribution when accelerating, turning corners etc) long story short, a stable vehicle gets better mpg. as for increasing air volume in and out, it doesnt necesarily increase fuel consumption, if you were to take an air/fuel meter and check your ratio you might find that you have a rich mixture, this is very common on older american engines and can be improved by decreasing the restriction on the airfloe into the engine (also a smoother flow increases atomization of the fuel allowing a more efficient burn process) as with the exhaust it just decreases the work the engine has to do to "exhale" but the biggest thing that is an engine specific affect is the maintenance.

anyhow, try the other mods first, those are for the most part the bigger helpers, the intake / exhaust stuff is all afterthoughts
happy modding
john
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Old 03-06-2008, 07:12 PM   #7 (permalink)
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Keep in mind though, that hp gains aren't always good, most of the mods that increase horsepower do only that, and decrease efficiency for power.

There a thread with significant info about exhaust tuning. Bigger free flowing exhaust, or none at all can actually HURT your mileage. your exhaust basically gets turned into one big muffler, not in that it muffles sound, but how one causes exhaust to bounce around into other exhaust sounds, canceling the sound. too big of an exhaust actually can hurt performance AND efficiency, but in order to get the full just of what I'm trying to say, you'll have to find the thread.

Also, you only use about 20 HP going 60 down the highway. so 70 wouldn't be too much more. I don't think power and efficiency go together, and that torque is more important that Hp. generally, smaller exhaust=more low end torque, but less power, and larger exhaust=more power, but less low end torque.

your gonna wanna look HEAVILY into aero if your gonna wanna have a van do 70 and get good mpg. look up basjoos's aerocivic, you can find a lot about aero from there.

I have more, but i gotta run.
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Old 03-06-2008, 07:56 PM   #8 (permalink)
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Welcome to the community.

The best thing you could do for the van is put a water bed in the back.
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Old 03-06-2008, 08:14 PM   #9 (permalink)
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That high-top isn't doing you any favors when you're driving; it's only when you're parked and moving around inside that it is any use. If you expect to mostly use the van for going places, then consider switching it to a lower-height, smoother model, preferably one with a nice, long taper to the rear.

Look really hard at changing your axle ratio. If you're not a speed demon and willing to drive conservatively - and being here suggests you are - and don't do any towing, you could switch out to a pretty tall final ratio and really slow the engine down. Barring that, it shouldn't be too hard to find a somewhat less prehistoric 4-spd auto that'll hook up to your 305. One with a lockup torque converter if you can find it.

What part of KY? Did you go to the Farm Machinery Show?
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Old 03-06-2008, 08:31 PM   #10 (permalink)
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Quote:
Originally Posted by elhigh View Post
That high-top isn't doing you any favors when you're driving; it's only when you're parked and moving around inside that it is any use. If you expect to mostly use the van for going places, then consider switching it to a lower-height, smoother model, preferably one with a nice, long taper to the rear.

Look really hard at changing your axle ratio. If you're not a speed demon and willing to drive conservatively - and being here suggests you are - and don't do any towing, you could switch out to a pretty tall final ratio and really slow the engine down. Barring that, it shouldn't be too hard to find a somewhat less prehistoric 4-spd auto that'll hook up to your 305. One with a lockup torque converter if you can find it.

What part of KY? Did you go to the Farm Machinery Show?
I agree with the gearing. 3.08 gear would be great.

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