MetroMPG.com mailbag: is lowest RPM really best for max MPG with big displacement? - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

DifferentPointofView · 12-06-2007, 11:21 PM

I'm pretty sure that in this automobile, that the car is more peppy while cold air is being put into the engine. The engine may be warm, but it wants that cooler air to be forced in and used. Also as with some of my Jeepin' friends have tested some things and have come to the conclusion that a cold air intake on a Jeep I6 definitely increases fuel economy by far. Also, owning a Jeep I'm sort of a nubcake with some of these terms. What's a Grille Block exactly and how does it work? Also, With the Kardboard Kammback, how well would that work with my Jeep? it slightly tapers but not by much. Also, if you had a really big long one at a slighter angle would that be a lot more effective than a smaller more angled one?

MetroMPG · 12-07-2007, 12:51 AM

Driving efficiently when nobody's looking? C'mon! :P

Cold air is good for power. The idea behind a warm air intake is to intentionally DEpower the engine, which requires a wider throttle opening to do the same amount of work. A wider throttle opening means reduced pumping losses. One of several reasons diesel engines are more efficient is because they have no throttle plate.

A grille block is just that: closing up some of the front of the vehicle ahead of the radiator. A significant amount of the total aero drag of a vehicle is airflow through the radiator. If you don't NEED the airflow, closing off that opening will help. Don't melt your engine though.

DifferentPointofView · 12-07-2007, 04:45 PM

I drive Economically all the time, I drive a lot more economically when there's no one around to pass me when oncoming traffic is too close. I've had to slow down a few times because people try to pass with not enough time. I'm not gonna drive 47 all the time.. Especially when lots of cars are behind me and it's a busy day.

I'm still thinking about that Kammback. What would be a sufficient material that's weather resistant, easy to mod, and lightweight? I also don't wanna ruin the paint job either. I wonder if I could use the Torx screws on the roof of the Jeep that used to attach the roof rack to attach the Kammback. It wouldn't require any reworking of the body to do, and it would stay on there easily. I'm wondering about visibility? Would this be legal?

MetroMPG · 12-09-2007, 10:48 PM

I can't answer the legality question - depends on your local/state situation.

Material choice for a partial Kammback is a tough one. I'm going to try making a fiberglass one myself. It'll be light, and perhaps easier to get the desired shape (by making a foam mockup).

Visibility may be an issue. You'll note that Mighty Mira used clear plastic on a metal frame partly for that reason (I'm assuming):

My kardboard kammback mockup blocked the upper 1/3 of the vertical height of the rear window, and I still had a clear view of traffic on a level road behind me in the rear view mirror.

DifferentPointofView · 12-10-2007, 11:26 PM

I was thinking about a thicker plastic, but clear as tight surran wrap. I could do thin sheet metal for framing and a layer of the clear plastic right over it. And I could rainX the thing, that way the water sheets right off of it during the rain.

MetroMPG · 12-10-2007, 11:50 PM

That could work.

Question for you: what type of driving do you do most? (urban/highway/freeway?)

DifferentPointofView · 12-10-2007, 11:56 PM

Definitely not Urban, I live in the middle of nowhere, Most of my driving is highway and some "city" with the occasional off-road adventure after it rains. But mostly the miles are highway. Freeway, not likely, maybe every 2 weeks. and that's even controversial. But yea, mostly highway.

thealterecho · 12-16-2007, 05:01 AM

Quote:

Originally Posted by MetroMPG

Driving efficiently when nobody's looking? C'mon! :P

Cold air is good for power. The idea behind a warm air intake is to intentionally DEpower the engine, which requires a wider throttle opening to do the same amount of work. A wider throttle opening means reduced pumping losses. One of several reasons diesel engines are more efficient is because they have no throttle plate.

A grille block is just that: closing up some of the front of the vehicle ahead of the radiator. A significant amount of the total aero drag of a vehicle is airflow through the radiator. If you don't NEED the airflow, closing off that opening will help. Don't melt your engine though.

Cold air is good for power cause air expands as it gets hotter. When it is cold the volume/density changes and you get more air/oxygen in the same amount of space.

MetroMPG · 12-16-2007, 03:04 PM

(K&N filter discussion moved to: Debate continues: K&N filter vs. MPG)

oldschool · 01-06-2008, 12:10 AM

well when driving my brick(67 GMC truck) I have to say I don't notice much difference in mileage between third gear and OD( yes I have a period correct borg warner 3 speed with a 30% oD). The difference I do notice is in the vacumn the engine runs in and out of OD. In 3rd gear I am usually pulling 15-16 inches of vacumn at highway speed(about 2400 rpm , in OD abnout 10 inches of vacumn( about 16-1700 rpm). I am guessing my 3.5 to 1 rear gear isn't low enough to effectively use the OD.