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Old 06-02-2015, 11:33 PM   #1 (permalink)
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Vw pickup MAX mpg build!

1982 vw rabbit pickup 5 speed diesel. My goal it to get the maximum mpg out of this truck without swapping a newer engine, lets start with the engine, I plan on ceramic coating everything and using ceramic bearings, I want this engine to be able to use the lightest oil possible, I think it's also worth it to change the pistons , any other recommendations to internal engine changes? Transmission changes ceramic bearings/coated input and output shafts. To finish up this minimum friction drive line ceramic wheel bearings( might be part of the stage two build because of cost lol). Now to the valve train not sure what cam is best for the low rpm range a suggestion would be helpful, also what rpm should I try to tune this engine to mostly 55 mph driving. I have had a hard time trying to find the right header 4-2-1 not sure what's the best diameter for low rpm range either. If someone to recommend one with good build quality that would help a lot. Another question is if I put a air dam under the bumper do I still need to put a belly pan under the whole car or maybe just the back half or none at all? Does anyone know of information on building a aero cap on a rabbit specifically?

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Old 06-03-2015, 08:44 AM   #2 (permalink)
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Welcome to the site. Sounds like a lot of work! What kind of mpg are you currently getting with it?
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Old 06-03-2015, 09:06 AM   #3 (permalink)
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Ultra low tension oil rings.
File fitted piston rings.
A turbocharger.
And don't run oil that is too thin.
The ceramic bearings appear to be a waste of money on anything that turns slower than a 2 pole electric motor.
In a diesel, the stock cam is likely your best choice for low RPM.
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Old 06-03-2015, 10:00 AM   #4 (permalink)
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Welcome to Ecomodder!

I found that your coefficient of drag is 0.44, which high but about right for a pickup truck.

I'm going to post a picture of a VW pickup to get an idea of what you're working with. vvvv



An air dam will help divert air from going under the truck and somewhat block the tires off from the airflow, at the expense of increased frontal area. The belly pan, while more work, provides greater gains IMO. It smooths out bottom of the vehicle, which is usually very aero-dirty. Built right, it can prevent air from collecting underneath the rear bumper and cancel its "parachute" effect. Using both in conjunction would do nothing but help

On my Escort ZX2, I noticed a big difference in coasting and the amount of throttle needed at speed when I did a front and rear pan. You might can garner some ideas from my Aero thread in my signature. I have reduced aero drag by 18.5% with my mods.

I do not have any information on an aerocap specifically for a Rabbit truck. I suggest checking out some of the members with Toyota trucks in the Aerodynamics section. There is a lot of ideas and improvising in their threads.
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Old 06-03-2015, 10:47 AM   #5 (permalink)
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The aero cap is probably where you'll get your biggest efficiency bang for the buck if you spend a lot of time at 55 mph. I'd consider starting there.

Or...





I think the tapered bed and the chopped top probably helped. But my gut says the front taper that exposed the front wheels is worse than stock in that area.

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Old 06-03-2015, 12:22 PM   #6 (permalink)
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Quote:
Originally Posted by Daox View Post
Welcome to the site. Sounds like a lot of work! What kind of mpg are you currently getting with it?
49-53 I live in southern Illinois and I am pretty strategic on the roads I pic to drive lot of flat roads gentle slopes going in the right direction. Easy to avoid towns and I barely use my breaks. I just had a injector fail, and I decided to get the motor and tranny out and go threw it all.
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Old 06-03-2015, 12:29 PM   #7 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
Ultra low tension oil rings.
File fitted piston rings.
A turbocharger.
And don't run oil that is too thin.
The ceramic bearings appear to be a waste of money on anything that turns slower than a 2 pole electric motor.
In a diesel, the stock cam is likely your best choice for low RPM.
Where do you think ceramic bearings is worth it from what I understand they can reduce friction 20-50 percent in certain places, and they last forever
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Old 06-03-2015, 12:47 PM   #8 (permalink)
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For the rear belly pan I thought about lifting the car a inch in the back and putting in fins to guide air around the rear tires, is it worth it.
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Old 06-03-2015, 01:10 PM   #9 (permalink)
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Is putting a turbo on it worth it. I might do it on the stage 2 part of the build a year down the road and a Giles pump but those two things would eat up most of my budget for the engine right now I want to put a thousand or less right now in the motor. And I don't want to chop the top I'm 6,2 and need the head room lol. Body wise I think I will make the aero back permanent and cut out the back window and move the metal back a foot or more and add cross braces to make the body stiff er. I plan on doing most of the little mods on this site. I would love to break 80 mpg in the stage one of this build, is this a realistic goal and maybe break a 100 on stage 2 after testing and fine tuning
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Old 06-03-2015, 01:27 PM   #10 (permalink)
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1) Upgrade the head bolts. That's a known problem with those engines.

2) Absolutely do anything for the aero. I think the belly pan is the better way to go but if you want to start saving money immediately the air dam will start paying dividends right away.

3) Aero reduces demands on power, and that engine never had any power to spare. It'll feel a lot better on the road with the aero treatment.

4) I think 80mpg might be achievable but only under a very specific usage envelope of steady, modest speeds on the flat. I remember Popular Science reported about 70mpg at 45mph in a Rabbit Diesel; the Caddy's longer profile will put it in a better aerodynamic position if you add the kammback aerolid.

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