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Old 05-05-2017, 08:40 PM   #31 (permalink)
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I ran another tank, trying to use the A/C about the same amount as the last one. MPG ended up at 13.92, compared to 13.79 the last week. This is substantially lower than before the 12 degree mod @ 14.31/14.44 for 2 ~32 gallon tankfuls. So now that I'm fairly confident of ~13.85mpg with the mod and A/C, I'm running the next tank without A/C. Hopefully that'll tell me if the aero mod is a net negative or positive.

I hadn't thought about replacing the A/C system, but I don't really use it all that much. That's either a good argument for not bothering to fix it, or that replacing it with a smaller unit would be perfectly acceptable. Conventional wisdom is that the AC compressor uses around 8hp, and is about the equivalent of a 1.5-2 ton system. At around 20,000BTU/hr that's an electric equivalent of 1500-2500 watts, or 2-3.3hp. I could probably get away with an effective A/C about 1/4 that size, since I rarely put it over "low" on the fan except in the middle of summer. Even at 100% efficiency, an electric one would need to be good for 375-625 watts, or up to ~45A. The 12V car compressors are good for around 300-400BTU/hr, which is 1/50th as big as the stock car system. Unless I'm missing something, I don't see how this could work.


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Old 05-06-2017, 07:44 PM   #32 (permalink)
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The average power drawn by the AC compressor is proportional to how much cooling you draw from the system. The compressor is clutched on and off to maintain the high side pressure. The compressor clutch is directly controlled by a pressure switch.

The compressor is sucking a lot of power when it is running, while the mileage hit is proportional to the percent of time it is running.

The more air you push through the system, the more the compressor runs. The slower the heater blower speed, the less cooling and less average power to the compressor. If the slowest setting on the heater blower is more cooling than you need, then add a resistor to slow the blower even more.

Look for ways to use less cooling. Sun shades when parked to keep the interior cooler. Interior as warm as you can comfortably tolerate. And pull the compressor fuse when running the defroster.
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Old 05-07-2017, 10:43 PM   #33 (permalink)
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I added a lighted toggle switch to control the compressor on a Suburban I had years ago. It let me run defrost functions without the compressor running.
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Old 05-30-2017, 11:51 AM   #34 (permalink)
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I'm having tint installed on Thursday, which should increase it's creepy-factor substantially! It should also help decrease the blazing sun factor in the lunch and evening drives, so hopefully I can use a lot less A/C. The two tanks when using A/C were at 13.79 and 13.92mpg, so I'm pretty confident it's around 13.85 with A/C. My last fillup was 14.36 without A/C, which is basically the same as what I saw before I fixed the A/C. I'm running through this tank to confirm, since in the last tank I did about 50 miles @ 80mph with no drafting while rushing to get to the airport. I'm sure that hurt MPG by a little bit, but I'm not sure how much.
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Old 05-30-2017, 02:31 PM   #35 (permalink)
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Quote:
Originally Posted by Daschicken View Post
If you are going for low end torque, upping the exhaust size significantly is not the best decision.
I've thought about this a lot, and done a lot of searching on exhaust performance. I haven't found a lot of actual dyno support for the "small exhaust = better low end torque." Most of the low RPM scavenging effects are related to the exhaust headers, and the free flowing mufflers seem to have better low end torque and also better high end torque (and HP). Most dynos are done above 2500rpm though, so it's hard to find a good low end comparison that isn't a turbo-diesel chart. The one advantage of the C6 transmission is that it stalls around 2000rpm, pretty much regardless of vehicle loading. So I'm really trying to optimize the 2000-3500rpm range.

For example, here's a 2.7L Tacoma dyno with headers and stock muffler/2.4" pipes (blue) and with Magnaflow 12586 straight thru muffler and 2.25" pipes (red). No significant power difference, but the richer mixture on the Magnaflow implies less scavenging of exhaust gases for the same fuel input. My guess is this is because the stock pipes are slightly less than 2.5" (measured 2.4") and the replacement 2.25" pipes are more restrictive. There may be a slight advantage to the Magnaflow system above ~3500rpm, but otherwise they are basically the same. Run 007 with stock muffler, run 010 is with the Magnaflow in the attached dyno.

https://www.tacomaworld.com/threads/....334168/page-3

His later test compared a Flowmaster #842452 delta baffled (green) vs Magnaflow #12586 straight thru (blue) vs stock baffled (red), the one that makes more power up high also makes more torque down low. The Flowmaster is slightly better than the Magnaflow across the whole band, and generally shows slighly higher AFR = higher scavenging/lower backpressure. In this case, "better flow = better low end torque and better high end HP."

https://www.tacomaworld.com/threads/...334168/page-14

The theoretical flowrates for exhaust piping is:

2.25” exhaust flowrate = 408cfm / 185hp
2.5” = 509cfm / 232hp
2.75” = 622cfm / 283hp
3” = 757cfm / 339hp

And the displacement of 4.9L at various RPMS is:

4.9L @ 1000rpm = 69CFM
4.9L @ 2000rpm = 138CFM
4.9L @ 3000rpm = 208CFM
4.9L @ 4000rpm = 277CFM

The Tacoma 2.7L is a 2.25" exhaust, using an LCE header with what looks like 1 5/8" primary tubes. It could be 1.5" though, it's hard to tell. Based on AFRs, it looks like it would benefit from a slightly less restrictive exhaust. Since my engine is 1.8x as much displacement, it should theoretically need 1.8x as much exhaust CFM. So 2.25"CFM = 408 x 1.8 = 734CFM. Based on this, the "optimum" single tube exhaust for a 4.9L is probably around 2.75"-3".

The main reason for doing a cat-back exhaust is that the stock pipe is kinda rusty, and the exit is to the right behind the passenger rear wheel. That makes a good rear wheel flare impossible, so I'm changing it to a rear exit pipe. If I decide it's an improvement in midband HP then a larger diameter is a good idea. Otherwise I'll just stick with the cheapest pipe size I can buy (probably 2.25" or 2.5") and break out the MIG welder.

If I can figure out a way to do it, I'll bring two complete exhausts and go to the local dyno shop. That would be interesting for me anyway, especially for future projects!
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Old 05-30-2017, 02:45 PM   #36 (permalink)
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As an additional point of reference, the Tacoma poster saw a significant improvement in fuel economy. His "old record best of 28.9" improved to 30.6 immediately. Others have seen the same thing, such as the attached FE log of a Ford F150 with a 4.2L V6. The guy chopped off the OEM muffler and installed a Flowmaster 50 series and basic end pipe. 1MPG is a decent improvement for just a muffler!
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Old 06-06-2017, 09:02 AM   #37 (permalink)
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I had a 90 e150 5.0 v8 and now a 2005 e150 5.4v8 . The single best thing you can do is to drive slower and accelerate slow. Cruising speed in the low 50mph range helps, Our 05 can get about 20mpg at 53mph. Just sit back in the right lane and watch others drive past.

We only drove the van when it was loaded and our smaller vehicles were not an option.

Back in the day a friend had a 77 e150 with the 300-6 and a 5 speed manual We drove it on two cross country trips loaded with motorcycles and got 20mpg,

For years we had a 3200# 4 wheel utility trailer and usually got 12 mph The gross weight was never 5000.
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Old 06-18-2017, 09:40 AM   #38 (permalink)
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So another thing I've been wanting to do is try out an electric cooling fan. I just ran across an Engine Masters Youtube video where they test various mechanical fans for power loss:

Clutch-style fan 7lbft of torque and 14hp @ 5500rpm!!!! (This is what's on my van)
Plastic flex-fan hideously bad 18lbft and 23hp loss!!!
Steel fan with stiff aluminum blades (non-flexy) still bad 12lbft 20hp loss.
Fixed non-clutch factory steel fan 19lbft and 30hp loss WOW.
Fixed non-clutch factory steel without shroud 18lbft and 22hp loss.

In perspective, my normal highway RPM is around 2400-2500, but the fan pulley is dramatically smaller than their pulley. That's because it is designed to run the same rotational speed @ 3000rpm (redline) as on a "regular V8" with a 5500rpm redline.

So now I'm thinking more about an electric fan...hmmm....

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Old 06-18-2017, 11:46 AM   #39 (permalink)
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Find an old electric fan from a 92 up crown vic or 1996 up Taurus, then put it on thermostatic switch to only turn on when reaching a set limit, and then have an override switch for ac if used
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Old 06-18-2017, 12:51 PM   #40 (permalink)
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That is 130 mph on my econoline
If the numbers are true. which they are probably not. You have forward speed pressurizing the front of the blades.

I bet the fan losses at 60 mph (2000-2500 rpm) are about 1/8th that.

I fly electric RC planes and use a watt meter to measure the power input into the electric motor. The power used is not linear for speed.

Quote:
Originally Posted by Merlyn2220 View Post
.....

Clutch-style fan 7lbft of torque and 14hp @ 5500rpm!!!! (This is what's on my van)

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