maximising fuel economy/parasitic loads/3 cylinder ops

[jdham137]

All,
I'm so glad I found this forum. Nothing like engineers to give you a straight answer. I am modifying mt truck, a 1998 Nissan Frontier, to maximise its fuel economy (see my website at

http://www.maxmpg.org).

I started at around 23-25 combined city and highway and and now at 26-28 mpg combined and occasionally hit 30+. My biggest gain was removing the clutch driven fan and installing a 12v cooling fan and I'm currently working on a sloped cap for the bed of the truck. I'm out of town right now but when I return I'm changing all my fluids to synthetics. An electric steering pump from a 2nd generation Toyota MR2 is in the plans too. As my truck becomes more efficient and more aerodynamic the load on the engine will markedly decrease and my fuel volumetric efficiency will drop, at which point I probably won't be able to improve the mileage any further. Is there a way to modify the throttle body to reduce this effect? The first thing that comes to mind is restrictor plates used in NASCAR. Am I right in thinking along those lines? Or if I could find a more restrictive throttle body, would the truck's computer have to be reprogrammed? Thanks for any info and advice and please check out my site.

John David

 

[turbocohen]

What is fuel volumetric efficiency? Never heard that term. VE is the efficiency with which an engine of a certain displacement is able to aspirate atmospheric air. Nascar restrictor plates will do nothing to reduce greenhouse gasses of any French vehicle like a Nissan or other worldly production vehicle. period. The throttle plate of a gasoline engine controls output by starving the atmospheric pumping capacity and it will be able to starve more than enough air as needed if your modifications work. One effective way to reduce the losses from engine friction and pumping loss is to reduce rpm's at speed with taller gearing and adopting lean burn combustion strategies allowing the opening of the throttle further. If the reduced dependence on foreign oil and impact on the environment is your issue then be prepared to spend time on a chassis dyno to recalibrate fuel and spark.

Why the sloped cap? Decreased drag works with less expensive and lighter mods. Adding a belly pan, dropping the suspension, a chin spoiler and narrower tires with higher pressure will help to..

Have fun

 

[jdham137]

Maybe I'm using the wrong term. What I'm refering to is when you use too large of an engine for a certain load and efficiency drops. As I make improvements in aerodynamics and take more parasitic loads off of the engine, I'm afraid I'll hit a wall where I can no longer improve my mileage because the engine id not matched to the load. A guy I have traded e-mails with thinks this is where he might be right now because he's stuck at around 32 mpg at both 65 and 70 mph. If he weren't hitting this wall, his mileage should have dropped going from 65 to 70. And the cap is just part of my aerodynamic modifications. I plan on building a belly pan and shrouds for the wheels. Thanks and if anyone has anything else to offer in the way of advice and/or criticisms please do so.

John David

 

[globi5]

If you installed some overdrive or a different axle ratio such that you can drive 55mph at 1000 rpm (or similar). This way you could reduce your pumping losses, since you obviously need to drive at a higher throttle setting to produce enough power to keep a steady speed.