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aardvarcus · 06-26-2019, 03:00 PM

Freebeard,
I have measured the underbody and plotted out the points to be aware of. The 4runner has a low center belly with crossmembers dropping substantially below the frame rails, so boxing in the outer area between the tires at the frame height will still be significantly higher than the center. This is quite a bit different than other vehicles I am used to (e.g. suburban) in which the frame rails are the lowest point.

Slowmover,
I hope there is no issue with the engine beyond just sensors…

Tahoe Hybrid,
Interesting, it looks as if the widths match, I would have guessed narrower. I just replaced the front bumper though and I don’t want to mess with the crumple zone, but a novel concept nonetheless.

Aerohead,
Agreed on the suggested methodology being better, however I don’t have extra time for too awful much testing, so I just compare my tanks week to week and try to compare similar tanks/conditions to get estimates. Once I get multiple projects completed I may consider ABA for a suite of things, but I can’t do that for every change I make.
I am just surprised how much lower the “bad” tanks are from the “good” ones, it is more than I had experienced in the past.
I am not getting 10% better MPG with the kamm extension. I assume I need to fix the transition from bodywork to extension.

Everyone,
Current progress on the 4Runner has been replacing both oxygen sensors (actually air to fuel ratio sensors) on the exhaust and the throttle position sensor. Also removed the rear driveshaft and replaced the rear u-joint which was going out and vibrating at higher speeds. Carefully greased the double cardan joint to extend its life, ensuring new grease made it into each cup. Rear u-joint was a pain because the rear yoke was sloped, made it a bear to press the spider out. Eventually had to weld up custom fixtures to hold it, then it was easy.

I have done some figuring on the underbody. My current plan is to lift the vehicle a small amount (about 1”) during some upcoming suspension work, which will put the lowest parts of the underbelly about the height of the rear axle tube. From there I can run a 6 degree diffuser from behind the axle tube to the rear hitch. I picked up some materials (steel tube) for my between the tires filler panel, still doing final design on that.

06-26-2019, 03:00 PM	#28 (permalink)
aardvarcus Master EcoModder Join Date: Apr 2012 Location: Evensville, TN Posts: 676 Deep Blue - '94 GMC Suburban K2500 SLE 90 day: 23.75 mpg (US) Griffin (T4R) - '99 Toyota 4Runner SR5 90 day: 25.43 mpg (US) Thanks: 237 Thanked 580 Times in 322 Posts	Freebeard, I have measured the underbody and plotted out the points to be aware of. The 4runner has a low center belly with crossmembers dropping substantially below the frame rails, so boxing in the outer area between the tires at the frame height will still be significantly higher than the center. This is quite a bit different than other vehicles I am used to (e.g. suburban) in which the frame rails are the lowest point. Slowmover, I hope there is no issue with the engine beyond just sensors… Tahoe Hybrid, Interesting, it looks as if the widths match, I would have guessed narrower. I just replaced the front bumper though and I don’t want to mess with the crumple zone, but a novel concept nonetheless. Aerohead, Agreed on the suggested methodology being better, however I don’t have extra time for too awful much testing, so I just compare my tanks week to week and try to compare similar tanks/conditions to get estimates. Once I get multiple projects completed I may consider ABA for a suite of things, but I can’t do that for every change I make. I am just surprised how much lower the “bad” tanks are from the “good” ones, it is more than I had experienced in the past. I am not getting 10% better MPG with the kamm extension. I assume I need to fix the transition from bodywork to extension. Everyone, Current progress on the 4Runner has been replacing both oxygen sensors (actually air to fuel ratio sensors) on the exhaust and the throttle position sensor. Also removed the rear driveshaft and replaced the rear u-joint which was going out and vibrating at higher speeds. Carefully greased the double cardan joint to extend its life, ensuring new grease made it into each cup. Rear u-joint was a pain because the rear yoke was sloped, made it a bear to press the spider out. Eventually had to weld up custom fixtures to hold it, then it was easy. I have done some figuring on the underbody. My current plan is to lift the vehicle a small amount (about 1”) during some upcoming suspension work, which will put the lowest parts of the underbelly about the height of the rear axle tube. From there I can run a 6 degree diffuser from behind the axle tube to the rear hitch. I picked up some materials (steel tube) for my between the tires filler panel, still doing final design on that.