90-95 D21 4x4 fuel mileage and aerodynamics thread

[SpudWhitman]

Now I see what you're referring to with the hoods. You could always try the dimpling effect on whatever surfaces you're brave and OCD enough to set to work on. They tested it on Mythbusters, and you don't see a golfball without dimples. Minimal gains for a whole lot of time and effort.

 

Moondiscs or pizza trays on the wheels? Wheelwell skirts? More undertraying and sideskirting? Granted, some of that would not too handy for offroading.

[HRH]

I'll just update this thread also, rather a double post of sorts, but hey, have to get the information out there. Currently have NOT re-geared, and have decided not to though I will be installing the LSD into the current diff. The new KAZ24 has plenty of power to push the higher effective ratio of 1.2" taller tires.

 

After getting less than stellar mileage at Canby, I have been kicking around cam timing ideas in my head. We originally had mistakenly come to the conclusion that milling the head would advance the cam by .5 degrees. In actuality, milling the head retards the cam. Reason being is the tension side stays the same, the slack side (with tensioner) is the only side that can pick up the chain slack from the .030 clearance of head. Thus, cam gear rotates counter-clockwise, and if this is at TDC, then the cam lobes will be further away and will come down after TDC, thus retarding the cam.

 

Consequently, the fix is to advance the cam via the #2 or #3 hole. I had it on #2 to begin with and mileage wasn't that great, though it had plenty of torque and I drove it to Canby that way with no issues. However, on #3, the truck still has plenty of power, but it definitely shifted the powerband up. 3500 rpm and above has excellent pull now. The other good thing is that lessens the hp at lower rpm and lets you take advantage of the torque. As a result, the latest mileage was 22.26 vs 20.5 average on Canby 2011 trip.

 

So in other words, at 60-65 mph, I'm getting the same mileage as I used to in my 2wd standard cab D21. Booyah!!!! ;) That includes very little in-town driving, but one high speed run of 60-95 mph (passed a Mercedes, hehe) and some general screwing around after I put the cam gear on #3 to test. Ran it to 6000 rpm so far, no issues. Starts a little differently in the morning and idles a smidge lower, but other than that no ill effects and still 100% for driveability. I'm really tempted to build another one for the 510.

 

 

[wildmaninid]

remember when and if you change your rear gear ratio, you need to change your fronts too!!!

[HRH]

Yep, have both diffs, but I'm just going to yank the LSD out and put in the rear of the D21, then return the diffs and get my money back! Haha! :D They're too dumb to know it's not LSD and it doesn't say on the receipt!

[Spades]

honestly, if you wanted a milage rig for 4x4ing...i would have recommended a small turbo diesel engine and having a machine shop build the parts to bolt everything together. I would be concerned that by the time and money spent on swapping the KA to the naps, and then on the other planned modifications, you could have found a totaled low mileage car or truck and put in a high torque, good mpg, and efficient motor that would get you the 25 mpg right off the bat.

 

more work and time without a truck, but you are asking for a 4x4 with bigger tires than it came with from the factory to have more power to turn the bigger tires and still get better milage than most people do with stockers...either way, good updates so far. keep us updated!

[Sealik]

/

[HRH]

The funny thing is I would love to put a turbo diesel in it, and have thought of many options. However, the problem I run into is it would have to get substantially better mileage to offset the cost of diesel fuel. Interestingly enough, it hasn't been as expensive lately.

 

And yes, there are much better options for getting better mileage. But we all like what we like. While I can drive the NX and get 30 mpg, I much prefer the hardbody. Consequently, I'd like it to get as good of mileage as possible.

 

Now, on the diesel option, the KAZ24 was actually much less involved and cost-effective than installing a turbo diesel. With the added cost of a 4 cylinder turbo diesel (even one purchased cheaply) the conversion would have been quite expensive. Figure fuel lines, lift pumps, fuel tank conversion to run diesel, etc. Also consider oil changes and maintenance with diesel tend to add up quickly. Were I towing most of the time, diesel torque wins hands down. However, for regular duty and light off-roading, gas makes more sense. If I could have gotten the motor to around 175 or 200 hp with the less rotating mass of a 4 cylinder, I could take even more advantage of mileage when not in the throttle.

 

With iridium plugs, a good set of wires/cap/rotor, I won't have to do anything other than clean the K&N in the next 50,000 miles or more. Oil changes are oil 4.5 quarts, not 13 like a Cummins, of course a 4 cyl Cummins would be less.

 

All in all, it doesn't matter what I drive, I would prefer it to get maximum mileage. Except the 510, it's a play toy, I'm not concerned, plus it gets 24 mpg at 4000 rpm sustained, so I really can't complain. And it's damn quick. The D21 now is quicker than my old '87 B2000, which was slow. I would imagine it's about an 18-19 second quarter mile rig. So dirt slow comparatively. But here's something funny. I watched stock Dodge Cummins pickups run 18 seconds in the quarter mile all night long when I lived in Phoenix. And my 2wd D21 was only getting 17.75 in the quarter. Best time I ever ran. :D

 

I'm pretty stinkin' happy with the results, and realistically this was a cheap project. I probably have less than $1000 into the motor. The 510 motor cost $1500 to build.

[Spades]

meh, you and I are thinking of different diesel motors...if you are thinking cummins and not buying a wrecked donor car or truck with low miles and BUYING each individual part, then yes, the naps KA is a way better option cost wise.

 

I personally would have found a wrecked TDI for a few hundred bucks, and built it up a bit, then swiped EVERYTHING from the wrecked car...but that is just me.

 

If you want a bread truck diesel (like a cummins 4bt) then you will pay a fortune, especially if you are buying all the parts.

 

Most diesels are very high torque and efficient at low RPM, and are not built for high RPM power, and when a turbo is set up properly, you can build a turbo with a compressor wheel designed for low RPM efficiency, which will give you BETTER mileage than a N/A 4cylinder or normal diesel.

 

At any rate, keep up with the modifications, I bet once you have your timing and all the electrical stuff dialed in you should be able to get better mileage than what you have now, and even now 20mpg (for a p/u)is pretty good!

[HRH]

Yeah, I thought about a TDI, but I have this problem of despising Volkswagen. The old transporters are cool, the real beetles are at least rear drive, but I just hate VW with a passion. All their retarded door lock ideas, vacuum tubes, multi pin connectors, f. I just don't like German engineering. I don't mind BMW as much but I still can't stand working on any of them. Japan makes sense, Germany does not. I won't even let German bolts touch any of my cars. When I gather bolts in the wrecking yard it's Japan only (no Toyotas either). No bullshit 13mm head German bolts for me! :) In case you're wondering, I don't like VW.

 

And while the TDI is impressive, I've heard some minor maintenance items are a giant pain in the ass. Granted, you wouldn't have to screw with them much, but I also don't think I'd get the 50 mpg in the new Beetle since the aerodynamics are much less. I think the timing belt change is like 9 book hours though and requires some funky stuff/procedures/expensive parts? Can't remember what it was exactly.

 

Anyway, I'm happy with 22 mpg in a heavy 4x4. Hit some headwinds and only got 21.36 this last tank, but still not bad really. I need to start working on the 510 so I can drive that to work. It's more fun, but also tend to speed in it vs. the truck.

[Spades]

Yeah, I thought about a TDI, but I have this problem of despising Volkswagen. The old transporters are cool, the real beetles are at least rear drive, but I just hate VW with a passion. All their retarded door lock ideas, vacuum tubes, multi pin connectors, f. I just don't like German engineering. I don't mind BMW as much but I still can't stand working on any of them. Japan makes sense, Germany does not. I won't even let German bolts touch any of my cars. When I gather bolts in the wrecking yard it's Japan only (no Toyotas either). No bullshit 13mm head German bolts for me! :) In case you're wondering, I don't like VW.

 

And while the TDI is impressive, I've heard some minor maintenance items are a giant pain in the ass. Granted, you wouldn't have to screw with them much, but I also don't think I'd get the 50 mpg in the new Beetle since the aerodynamics are much less. I think the timing belt change is like 9 book hours though and requires some funky stuff/procedures/expensive parts? Can't remember what it was exactly.

 

Anyway, I'm happy with 22 mpg in a heavy 4x4. Hit some headwinds and only got 21.36 this last tank, but still not bad really. I need to start working on the 510 so I can drive that to work. It's more fun, but also tend to speed in it vs. the truck.

 

 

In most cases I would rather get hit with a baseball bat than work on a VW, the TDI's are a bit better. Be prepared to shell out some cash on the proper tools for doing a timing belt job, but other than that it isn't bad. You have to remember, the Jetta is a FWD car, and that is what makes them such a PITA to work on. Mounted in a 4WD or RWD truck would not be that bad. I have seen it done in Toyotas with good results, and even in a ford ranger, but never in a Nissan product. But I agree with you on one thing, German engineering sucks ass on almost every occasion. Also, 22mpg for a 4x4 with larger tires is still pretty good, and I definitely would not be disappointed with the results.

[HRH]

22.53 mpg this last tank. 2500 rpm - 2600 rpm really helps. 57-62 mph. Don't think I can squeeze out 23, but I'm damn close. ;)

[mike]

Just for shits and giggles try taping up all the drag areas and removing your mirrors (if its not too much of a PITA) for better aerodynamics and see what you get...

 

I put an old aluminum canopy on the yota last weekend and dropped to 16.5, broke out the duct tape and went between the cab/canopy and got 22.7 freeway (70 - 80 mph)

 

Have you tried different fuel grades? I went with a tank of premium and noticed no difference on mileage and marginally better power on smoothness/power but it wasnt worth the price. Theres a place in Cda that sells the unoxygenated premium and I think Im going to give it a shot next time Im over that way just to see.

 

Nissans are cool but I dig the 2.7... I want one in a KC 620 4x4 :cool:

 

VW TDIs are *fucking* cool in little rigs. I had a buddy in AK that has a built 1.9 in a stretched sammy with 39.5 boggers on yota axles... It literally floats across most soupy mud holes/tundra that swallow bigger rigs and its got enough power to smoke the tires. I think he gets 35ish MPG fully loaded (winch and full of gear) Id like to see one of these in a 620 too but the 1.9s are spendy little bastards.

[HRH]

Yeah, I'm not going to go to quite that amount of trouble. I'm pretty happy right now. If I were able to utilize a wide-band O2 sensor or even a 3 wire, that would be a much better idea. Except upgrading to a 96 ish ECU would be a giant pain in the ass. Thought about adding a separate heater circuit but don't know how I would control it.

[HRH]

Update on the D21 mileage! From the KAZ24 build thread, I bypassed the EGR valve due to not being able to fit the tube since the KA block vent tube goes around where the EGR tube was. (KA was vented through timing cover) Went scrounging through the FSM and found that the EGR is actually controlled by the ECU on the hardbody.

 

There is a ported vacuum switch near the end of the fuel rail that goes to the EGR BPT valve, which then goes to the EGR. ECU sends a signal to switch the valve which opens one, then in response to vacuum opens the EGR appropriately. So considering I have the EGR bypassed and sealed, this seemed as though it might cause driveability issues.

 

As Father Wild said though, the neat thing about Nissan systems is once you disconnect it, often time the computer ignores it and it runs fine anyway. So disconnected the EGR controlling ported vacuum switch, and noticed perhaps a smidgen better mileage and a little less hiccup in certain running conditions. Very minor anyway.

 

At the same time (thus negating measuring the effects of the ECU controlled switch) I installed a Pacesetter header. Noticeable difference in the header with the additional compression. Previous stock hardbody I didn't notice much with the header. In this case, with the roughly 9.3:1 compression there was a very pleasant mid-range increase in torque (butt-dyno of course, but probably due to these being fairly long-tube headers.) and the upper end was much less restricted. Going to 5500 rpm is much easier now.

 

The best difference was noticed today when I filled up. I have achieved the best mileage thus far with mostly highway back and forth to work driving, but with some city driving also of 22.79 mpg. I had headwinds going to work for two days, so without those, I very likely would have broke into the 23 mpg range.

 

This 22.79 trumps the previous record of 22.53 mpg. There you go, food for thought. :)

[Creepy Cruiser]

Nice!

 

That's way better than the 16mpg that I'm getting in mine right now, lol. (time for a tune up)

[HRH]

16, yuck! Is yours Z24 or KA24 Todd, I forget?

[Creepy Cruiser]

250k+ mile z24 that has had a very hard life, lol.

 

I think my wife actually did the last tuneup on it about 4-5 years ago, lol, so it's about time. I have all the parts just sitting here, just need to find the time.

[HRH]

Thread revival again!  The D21 is getting shit mileage.  Again.  Trying to figure it out, computer says everything's fine, went through all the common issues.  I'm getting anywhere from 16.5-17.5 on a fairly regular basis.  Also getting a backfire every now and again, most prominently after mid throttle acceleration through second, then when the liftoff for third comes, just a little bark.  Been over the exhaust, it's good, 02 is new, temp sensor has been replaced.

 

Anyone else have any oddball hardbody fixes involving mileage?  Right now the Z24 tbi in the chump truck is looking like the better option.  It at least stays above 18 mpg!

[Draker]

Thread revival again!  The D21 is getting shit mileage.  Again.  Trying to figure it out, computer says everything's fine, went through all the common issues.  I'm getting anywhere from 16.5-17.5 on a fairly regular basis.  Also getting a backfire every now and again, most prominently after mid throttle acceleration through second, then when the liftoff for third comes, just a little bark.  Been over the exhaust, it's good, 02 is new, temp sensor has been replaced.

 

Anyone else have any oddball hardbody fixes involving mileage?  Right now the Z24 tbi in the chump truck is looking like the better option.  It at least stays above 18 mpg!

 

 

Vacuum readings?

[Sealik]

Wide band.

Would be curious about the A/F ratios when the engine... barks.....etc.

[HRH]

What kind of vacuum readings?

[HRH]

Well interestingly enough, this week has been foggy.  Really foggy.  Which means all my drives to and from work have had zero winds across the high plains.  I also filled up the truck with 92 octane this last tank which shouldn't matter, it's not smart enough to sense fuel temp and doesn't have a knock sensor.  I think the lack of wind is the major factor in the better mileage.  I'm at half tank right now at 100 miles, which isn't great, but it's in the 18-19 range, which is at least acceptable.  110-115 is about 20-21 mpg.

 

Tomorrow I'm planning on going after the solder joint for the ground for the IAC and MAF which is in the harness near the front of the air cleaner.  I read that TSB a while back and never did do anything about it as the truck still ran pretty well.  Lately though, I'm wondering if it's just crappy enough to cause an issue.  Besides digging into the wiring harness and re-soldering the connector, I'm going to run an additional ground strap from the valve cover and/or the efi harness ground down to the frame.

 

If I manage to change mileage to any degree, I'll let you guys know!

[HRH]

So I started going through the harness today, and realized my truck doesn't suffer from the harness issue of the 94+ trucks as the way they wired the harness was different then.  Looks like there's a junction way at the end of the harness near the firewall, but after unearthing quite a bit of loom, I found no junctions to repair.  Furthermore, I read more into that TSB and the spikes of idle were drastic, like 300 rpm change.  It also pointed out that manipulating the wire could make or alleviate the problem.  So I started her up and moved the wiring this way and that with no change.

 

What I DID do, however, was clean the IAC valve by means of the bypass opening.  Basically filled it fill of throttle body cleaner a few times and let it sit, then burned it out.  Did some while it was running too.  Also opened up the throttle plate with it open and washed out the runners, which you think wouldn't have much on them, but seemed to have quite a bit of residue.  Aside from that, I ran a redundant ground strap from where the ECU harness grounds attach on the manifold, down to the upper shock mount, which is attached to the frame.  Connected it to a bolt that holds the power steering line, or fuel line, or something.  Anyway, a bolt that was already there.

 

Fucking photophucket is not working right now, trying to upload pics, aaaiiggggghhh!!

 

Okay, here we go.

 

 

 

 

Here's where to clean out the IAC valve without removing it (real pain on the D21 location, have to remove throttle body assy.)  Check out the air bypass hole in the middle of the throttle housing.

 

 

Oh yeah, and there will be lots of little brittle wire tap bits.

 

 

 

Here we are with the new ground strap.  It's pretty blue from the 510, covered up with loom now, but should provide a bit of extra ground.