Quote:
Originally Posted by Blu3Z3rg
I just converted to a straight pipe... i'll let ya know!
And YOU let me know about them cams!!!!
I'm looking to do underbelly pans as well, do you think this is where your most significant change is? And 3" on the intake is plenty large, 2 3/4" is what I calculated to be ideal for a 2500 power peak from flow. I won't say it has made or broke the mpgs, but I'm not going to redo it. I just have a shield I can put on or take off for the varying temps.
The problem with trucks is the weight and the huge front area, which is why letting the piston speed go a bit faster is better for trucks.
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HO cams. As for MPG, I think I lose a small amount. At least when I was puttering around the air base and in town. On I-44 however, things were different. It was obvious the truck was making more power. It did not downshift when I set the cruise and left it. Can't remember if it was at 65 or 70 mph, but I know pre-HO cams install, the tranny would downshift several times at that speed with the cruise set. Will I go back to the OEMs? No way. These are way too rewarding.
Belly panel kit. I do think this is a big area for mpg gains. This, some splitters or fairings in front of all four wheels, and blocking part of the front grill. These and the wheel covers also help things along.
--that said, the belly panel kit is about to undergo a major renovation. I did my 20.5 mpg runs with a hand-cut piece under the engine bay that barely allowed me to make normal city turns; it was so close to where the tires and wheels turned into. When I tore it up going through a huge rain puddle, I had to revert to my old 4' wide Al sheet, which left a lot of the front suspension and wheel wells hanging out in the breeze. I did have the areas covered between the frame rails and the body, which are big air catchers. I also noticed the panels were about as smooth as the Black Hills of South Dakota; didn't know I was so sloppy. Despite these shortcomings, we did manage a tank at 21.4 mpg from Oklahoma City to San Antonio this month. Nearly 450 miles with not quite a quarter tank left.
My lessons learned: #1. panels need to overlap a couple inches, end to end, so the front of one doesn't get sucked into the airstream. #2. the cleaner you make the front, the better off you are. Cover as much as you can. (I let the front wheels abrade the corroplast so I could trim it a bit at a time.) #3. Make it smooth. Look at the bottom of an F1 race car; nearly seemless and flat. #4. Make your mount brackets accessible. One of mine can only be reached from the driveshaft, not the framerail...which is a real hassle. #5. mount your panels from the inside out. I run 4' wide panels down the middle, then add the sides. #6. Make the panels removable. I can remove nearly the entire kit in an hour. #7. Use L channel for most of your brackets. Why? Flat metal strips don't offer enough rigidity to keep the panels flush. #8. Beware of what factory bolts you loosen to install stuff. I loosened two that blew my alignment and didn't know it for some time. #9. If she who must be obeyed gripes about the truck's appearance 'cuz of all the stuff you strap to it, keep going.
Wheel covers. UPDATE. I am using 3/4" wide velcro strips (thanks Ebay) to hold the 0.015" thick covers on all 4 wheels. Worked great on the above road trip. Didn't lose any, didn't tear any. I have learned not to cinch them down super tight; leaving a little slack lets them stay near perfectly flush. Brake dust does accumulate on the wheels though.
Tire fairings. Big item. I fashioned some wedge shaped fairings to mount in front of each tire. My truck has 275/60R20s; 11 inches wide, that is a LOT of tire. These definitely cut the drag...don't change my S (frontal area) 'cuz they are just as wide as the tires; maybe a couple mm more. Mine hang down about 8.5 inches from the front spoiler lip. I do need to take care in steep entrances, and avoid getting close to parking blocks.
Frontal area. In time, I plan to fabricate a slope nose (a Daytona nose for you old MOPAR fans) to block the entire front grill, and open the narrow slot in the center of my bumper. That should still give the radiator enough airflow, yet reduce the truck's parasitic drag.
Wheel balance. Not sure it affects MPG, but it does make things smoother. 51K on the tires now, and 3 of 4 wheels were out of balance. I could tell because of the dirt spots left from the old wheel weights...
Intake. I agree with you there. I still have my 3.5" steel mandrel bent pipe, but anticipate I'll soon change it to a 3" PVC pipe. PVC is quieter. Since it's 3" inside diameter, that is pretty close to what my throttle valve is (68.5mm). Future plans include repositioning the filter box right behind the radiator, getting a direct feed from it, and then straight into the throttle valve. Coming through the radiator is worth about a 5* temp rise.
Hope to make some test runs later this week. Found a good 1.1 mile stretch of flat road I can use. And it's not too far from home!