atomic_fungus (atomic_fungus) wrote,

#4009: That was pretty much a wasted day.

I didn't go to church this morning, and I didn't do anything useful today. Now it's after 5.

Today was, however, the first day since Monday of last week that I didn't do anything at all that had to be done to schedule. I am not happy about missing church, but I didn't really make a conscious choice to skip it. When the alarm clock went off at 8 AM this morning I shut it off and reset it to noon (when Mrs. Fungus gets up) and then fell asleep while assessing my options. ("I can get up and go, or I can stay ho...zzzz....")

Mrs. Fungus got up at her usual time and left on schedule, and I fell asleep again when she did. It was four freaking thirty when I finally woke up.


Beautiful indian summer day outside; I could have gone for a ride on the bike, if nothing else--but then I remind myself that the brain requires rest after exercise, the same as any other body part does. That "full" feeling I had Friday afternoon indicated that my brain was growing fatigued, and needed rest; well, I'm getting it.

And it's hard to feel guilty about sleeping in after six days of activity, expecially when most of those days involved busting one's hump at work. I just wish I'd been able to make it to church today, is all.

* * *

I watched an episode of Horsepower TV where they rebuild a Ford 300 I6 engine, and it got me to thinking about the I6 in the Jeep and engine design in general.

There are two basic ways to design an overhead valve (OHV) cylinder head: either you have the intake and exhaust ports on the same side of the head (reverse flow head), or you have them on opposite sides (crossflow head).

Reverse flow heads are more compact when installed in the vehicle, because you don't have a bunch of piping hanging off one side and can put it arbitrarily close to things, but the proximity of exhaust to intake tends to reduce power output. Besides, there's less room for the ports, and smaller ports means lower volumetric efficiency. Crossflow heads are less compact and must be a certain distance from other things, but keep intake and exhaust separated, and there's more room for the ports so they can be larger.

A V engine (V8, V6, V4) will have crossflow heads by default, unless it's a flathead, which isn't an OHV engine and is therefore excluded from this discussion. You could build a V engine with reverse flow heads, but it would be an engineering nightmare and a waste of space--all that room in the valley between heads would go to waste if you hung the exhaust and intake on the outside of the engine, and I wouldn't even want to consider what kind of viper's nest having all that in the valley would entail. It'd be pretty tall, though.

The Jeep's I6 is an old, old design, and it's a reverse flow head. The MGB is the same way. If you look at a modern inline engine, like those in modern cars, they tend to be crossflow almost exclusively--which is to say I haven't seen a new car with a reverse-flow head on in quite a while.

Also, it seems that most cars with inline engines and crossflow heads have the intake on the firewall side, and the exhaust on the radiator side; when mounted longitudinally rather than transversely the intake is invariably on the left (driver's) side of the car, regardless of what kind of cylinder head it has.

Then I got to thinking about the valvetrains. There are three basic places to put the camshaft in an OHV engine; one is to put the camshaft above the crank (as in a V engine) or off to one side, which is pretty much the only place you can put it in an inline unless it's an overhad cam (OHC) engine. In the latter case, the cam goes over the cylinders.

The most bulletproof method is to run the cam off a gear, but it means long pushrods and a lot of mass in the valvetrain. The most efficient method is to have the cam directly actuating the valves, but that means using a belt or chain to turn the cam, which is less reliable.

...and then you start getting into what kind of performance you want to get out of the engine. The Ford 300 (and inline sixes in general) are torque monsters, which is why they were used for so long. Torque is what moves the vehicle, and trucks require motors that make torque. Torque is made low in the poweband, so a long stroke and a (relatively) massive valvetrain aren't a problem. The engine's redline may be 5,500 RPM but you won't rev it that high very often because it'll run out of steam before you get there.

If you want a high-revving engine, though, you build a short stroke and as light a valvetrain as possible. This lets you get more horsepower out of the engine, but it comes at the expense of running the engine as fast as possible because it just doesn't generate the torque of its slower-running cousin.

Interestingly enough, it turns out that a V engine produces less torque than an I engine of equivalent displacement (but more horsepower). That's why the big diesel engines offered in pickup trucks are I6s, not V6s. But V engines just weigh less. The engine in the Jeep is a massive edifice of iron; a 4 liter V6 would probably weigh about 70% of what the I6 does. That's also why there are relatively few 4 cylinder automotive engines which are not inline engines, and the decision to go with a non-inline engine is almost always due to space constraints.

But there's no doubt in my mind that if Dad's old powerboat were still here, I could haul it wherever I wanted to with the Jeep, and if I had a car dolly I could haul the Fiero with it, no problem.

Engineering is always a series of trade offs. The I6 from any manufacturer is usually a bulletproof engine because it's been the default configuration for cars since time immemorial, and all the bugs have been worked out; they're technologically mature. They're very easy to build, compared to other designs, and they have simple components--equally technologically mature--which can be made of basic materials like iron and steel. They provide good performance and are reasonably efficient, given their size.

They're only being phased out because they're so heavy.

* * *

I would love to get a spare Jeep engine and rebuild it, putting a stroker kit in it. There is (or was, anyway) a stroker kit that would bump the 4.0 to 4.7, which is damned close to 300 cubic inches and which makes that engine pull like a locomotive. I mean, it already makes gobs of torque, but "enough" isn't really "enough" when it comes to engines, if you know what I mean, and the increase of displacement would not significantly decrease fuel economy.

There are kits, of course, that let you put an LS1 into a Jeep Cherokee--but it wasn't really designed for that and anyway I like the I6. At about 65 MPH the truck rumbles along, sounding kind of like a locomotive; why would I want to lose that?

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