MAX Update No. 62: Throttle Management

| 11/6/2010 10:57:13 AM

Tags: MAX, 100 mpg, Kubota, diesel, throttle, Jack McCornack, Jack McCornack,

I got an e-mail from a guy building his own MAX, asking about how I hooked up the throttle — which turned out not to be quite as trivial as I thought it would be back in Twenty Ought Seven, when this project began.

The problem is, diesels don't usually have throttles, and this Kubota is no exception. Oh sure, we call it a throttle, but it's not. We tend to call anything that controls power a “throttle” — my gosh, airline pilots call their jet engine power controls “throttles” and boy is that a misnomer on a jet. Throttles are usually found on spark ignition engines, such as the gasoline engines that motivate our automobiles, but throttles are not a terribly efficient way to regulate engine power output, and one of the reasons that diesel engines are more efficient than gas engines is diesels don't have throttles.

Maybe Webster's can give us a clue here. Ah yes...

Throttle \Throt"tle\, v. i.

--1. To have the throat obstructed so as to be in danger of suffocation; to choke; to suffocate.

--2. To breathe hard, as when nearly suffocated. 

We've forgotten what the word means, over the last hundred years. We talk about giving a car more throttle to make it go faster, when we mash our foot to the floor we call that ”full throttle,” but the truth is, throttling is a way to slow the engine down. If you had a spirited draft horse that pulled so hard that you had trouble jogging along behind the plow, you could make that horse ease up by partially strangling it. Well, that's how your car engine works. When you let off the gas pedal completely, the engine is so throttled that all it can do is idle, until you un-throttle it by stepping on the gas.

12/7/2010 11:52:38 PM

Late to the discussion but the reason for using a kubota engine is very simple and the same issue I had doing a similar project. Try and find an efficient computer controlled diesel engine that small in the USA. To have a fair comparison you have to take into account that its more then just the computer that makes newer computer controlled diesels more efficient

jeff dean
12/1/2010 8:21:16 AM

Used tires would work to see how a "taller" gear would "feel". You could find out if dropping 400 rpm at cruise speed caused lugging of the kubota. I found on the Cummins engine website that worn tires can be more fuel efficient than new tires,up to 7% better for otr trucks. I don't think it would be that much for passenger vehicle tires because of the tread depth. Just one more variable to consider.

Jack McCornack
11/30/2010 8:16:39 PM

Re changing wheel diameter and... > You wouldn't need new tires to try it out I think I would. I think the most we could hope for with a 4% tire diameter change is a 2% fuel economy change, and I want to keep the variables as singular as possible. Different tire designs can make an easy 5% mileage difference, even in the same size tire. I'm very fortunate that Goodyear is taking an interest in MAX, and makes high mileage tires (the aptly named "Fuel Max" line) that are identical in the 14" and 15" sizes, with the singular exception of diameter. > Did you add some framework when you added some body to max? Indeed I did, back in July. There's a pic and an explanation in... MAX Update No. 53: Taking Sides In the Impact Wars ...and you'll find a link to all the MAX Updates just below the blog post, right near where you click for Comments.

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