A Real F-Head! (1 Viewer)

[Dizzy]

https://www.curbsideclassic.com/automotive-histories/automotive-history-the-curious-f-head-engine/ (Yes, I'm plotting on getting a CJ-3B, if you happen to know of one, PM me.)

So, if I'm picking up what they are putting down, you have a proportion of bore-to-stroke. Ideally, more stroke than bore for low end torque, like pounds per square inch - less area of piston to push is like tiny tires sinking the truck to the frame rails in snow.

Could it be that the Land Cruiser's F actually has more low-end torque with a bore of 90mm to the 94 of the 2F?

 

[65swb45]

I’ve always considered the extra rotating mass of the earlier flywheel beneficial to the crawl-torque of the LC. I currently have one behind the 2F in the karma cruiser, and I really like the way I can and have wheeled that combo.

 

[Steamer]

Wiki say more torque with the 2F. "WIKI"
My friend has a jeep F-head engine running his swamp buggy. I always wondered why Willys decided on that valve configuration. I also never new why they called it the F head. But I just now found out. The shaded letter "F" on the diagram shows it. Thanks for the link Dizzy.

 

[Dizzy]

Wiki say more torque with the 2F. "WIKI"

Yes, but torque is usually measured at a higher rpm for internal combustion engines?

I think that the comparison is at low-end, torque and how piston stroke relates to cylinder bore - or, at least that was my understanding of the engine designs that place valves in awkward configurations.

 

[flee]

Great link, Dizzy.
To answer your question, increasing stroke is what would possibly increase torque, not decreasing bore. The 2F has the same stroke + more bore.
What matters more is the resulting volumetric efficiency - how effectively the fuel/air mixture enters and exhaust exits.
Engine designers seem to have figured out how to get good torque at low rpms and still get good horses at high rpms with ever shorter strokes.

 

[1911]

Increasing the stroke increases torque, because it makes more leverage on the crankshaft from the rods and pistons. But it also increases the piston speed, which brings it's own problems including not being able to reach as high of rpm. Increasing the stroke also complicates valve timing and efficiency (as @flee pointed out), since the intake and exhaust strokes are longer so the valve duration needs to be longer, but too much overlap will reduce dynamic compression. Everything in four-stroke engine design and tuning is a compromise; at best you can design and tune for a good powerband at a desired rpm range. The F and 2F were designed to have good torque over a fairly wide powerband at low rpm. They make 80% of peak torque from just off of idle to 1800 rpm, which is pretty ideal for 4-wheeling.

The 3F (and later) engines reduced the stroke so as to be able to make more rpm, which by itself increases hp since hp = torque x rpm. Toyota engineers knew they were giving up some torque and low-end powerband for more hp on the top end, to make it more useful on the highway.

 

[Dizzy]

Doing a little research...

What is Engine Torque? It's Characteristics & Formula

Torque is ‘Twisting or Turning Force’. In automotive, engine torque is the measure of rotational effort applied on the crankshaft by a piston.

carbiketech.com

The thing that keeps coming up is the 'square,' 'over-square,' 'under-square,' terms. It is as if proportion has something to do with it, and not relative stroke length - in this case, they remain the same for the F and 2F.

It all kinda sheds new light on the J30. And, it makes me wonder if those over-square Chevy 230 or 250 swaps have some merit for today's highway speeds.

 

[Dizzy]

Hoping that some carb gurus can shed some light regarding the 'undersquare' proportion and how it might affect carburetor design.

I hear folks talk about a 'tractor,' quite a bit, but what does that imply?

Bump.

 

[1911]

The thing that keeps coming up is the 'square,' 'over-square,' 'under-square,' terms. It is as if proportion has something to do with it, and not relative stroke length - in this case, they remain the same for the F and 2F.

Don't over-think this, it's just one way of identifying a "stroker" motor. Square motors are just where the diameter of the cylinder bore equals the length of the stroke. Over-square motors have a bigger cylinder diameter than the length of the stroke; as previously discussed, this yields lower piston speed and hence enables more rpm and hence more hp. Under-square (or "stroker") motors have the cylinder bore smaller than the stroke length. As has been said, longer stroke = more leverage of the pistons and con rods on the crankshaft, thus more torque, but with the resultant faster piston speed it limits rpm.

Hoping that some carb gurus can shed some light regarding the 'undersquare' proportion and how it might affect carburetor design.

I'm no carb guru, but I've built more than a few (but mostly motorcycle) motors including stroker motors in my day.

Under-square designs are used to rev high. high-revving motors need very efficient intake, valves, and exhaust systems, hence the development of overhead cams, efficient squish-design combustion chambers, multiple valves per cylinder, and modern fuel injection systems. Carbs are too much of a compromise and can't be efficient at all rpm's, they can only be efficient in a relatively narrow rpm and volumetric range. Carb designers tried to address this over the years by going from single-barrel large venturi carbs to two smaller venturi barrels, then to four even smaller (relatively) venturis. But they were never as efficient as a good FI system.

I hear folks talk about a 'tractor,' quite a bit, but what does that imply?

A farm tractor has some similar design goals to a 4WD off-road truck, namely high torque at slow steady speed and low to moderate rpm. Both have used stroker motors, heavy flywheels, and low gearing to accomplish this. Both were originally reliable and repairable in the field with commonly-available tools. Horsepower, highway speed, and efficiency were much less important considerations. The F and 2F motors are good examples of this, hence the comparison to tractor motors.

 

[rkymtnflyfisher]

By the title of this thread i thought you met my boss.

 

[franklin40]

lol i was thinking it was another PO screw up thread!!

 

[Dizzy]

Engine Specifications: Off-Road.com

Gas Land Cruiser engines are manufactured by Toyota. The F and 2F engines were also used in Toyota Forlifts. The F engine is supposed to be based on the Chevy 225 I-6 "Cast Iron Wonder" and some of the bottom end of the engine is rumored to be interchange

www.off-road.com