666 and engine NUTS

[WORTH]

Here's one to lose some sleep over.

We know that a piston has more push when the crank is at 90 degrees from the cylinder, but we fire it right after TDC.

What if you designed a floating cylinder that was connected to a follower camshaft,

piston goes up to create compression,
cylinder follows the piston back down til the crank is at 90 degrees,
spark fires and forces piston down,
cylinder returns to top and waits for the piston to do it's exhaust and intake stroke

Rinse and repeat.

 

[88 Fox GT]

Engines usually fire before TDC, not after.

I'm not really sure what your trying to do here with a floating cylinder...

 

[WORTH]

Engines usually fire before TDC, not after.

I'm not really sure what your trying to do here with a floating cylinder...

I was talking about the explosion, not the spark.

 

[bnickel]

hey worth have you been hitting the cap'n morgans this morning?
sounds like you're trying to build some kind of rotary diesel contraption. not that it is a bad thing some of the best in the world are the craziest

 

[WORTH]

hey worth have you been hitting the cap'n morgans this morning?
sounds like you're trying to build some kind of rotary diesel contraption. not that it is a bad thing some of the best in the world are the craziest

No Morgan yet today , but I may need some for the final blueprints

 

[Skymarshal]

The plug fires several degrees BTDC, and as the combustion begins in the cylinder, the piston completes its compression stroke and begins the power stroke downward to absorb the energy from combustion.
The combustion process is not instantaneous- if it were, you would be experiencing Detonation, and that's why smacking the piston as it's still on the way up causes bent rods, cracked rings, broken pistons, etc.

 

[mustangdave]

Let me know when you design that "floating cylinder"; I gotta see that one. Interesting theory though.

 

[WORTH]

Let me know when you design that "floating cylinder"; I gotta see that one. Interesting theory though.

I'll have to do some research, but as I recall one of the car companies in the 30's or 40's had one that didn't have valves, and moved the cylinder up and down to expose the intake and exhaust ports. SO it's been done, but not this way.

I would think by optimizing the position of the crank you should get a lot more push for the same size bang. The only complication I can think of is that the outside of the cylinder would have to have some damn good seals to stop coolant leakeage.

 

[88 Fox GT]

So are you talking about something like a 2-stroke design? As in no valves. The piston reveals the intake and exhaust ports as it moves up and down.

 

[ForceFed70]

Neat idea.

Almost like 2 pistons facing each other.

You wouldn't want to fire the plug when the crank is at 90* tho... more like about 45*. So that peak pressure is exerted when the crank is indeed at 90*.

Also I don't know what the heck you guys are talking about the plug firing a "couple of degrees BTDC". Maybe when your doing your timing at idle with the vacum advance disconnected. Most ford V8's run in the neighbourhood of 36* total timing advance. They only run 10* or so when at full throttle during low engine RPM (below 1500). This is of course assuming your running the standard VAC adance/mechanical adv setup.

 

[Route666]

I only just saw this thread. OMG that's not too bad of an idea.

Having two pistons facing each other, with their crankshafts out of phase, say the top one, where the head used to be, should be at TDC when the bottom one is at 90 ATDC when the fuel starts really burning.

Or yeh, I get it now, have the top piston on a cam, so it doesn't move until after the exhaust stroke is under way.

Problems I can see are: You'd need a darn strong cam and lever to cope with the forces, you have to mount the spark plug and inlets somewhere, perhaps a two-stroke would be the key. Perhaps a diesel setup, no spark plug. Also there is extra mass and friction in the engine. Which again may be reduced because no valvetrain, etc.

One really bad thing I just thought of is you'd need ENORMOUS spring pressure to hold the top piston in position against the cam at 6000rpm or so, because it will weigh a LOT more than a valve. It would still operate at the 1/2 speed though, like a valve. This would a great design for a 4000rpm diesel. No spark plug, the fuel lubricates both sets of rings, and lower spring pressure because of low rpm. The max torque firing chamber design too lends itself to this.

You could use the top piston to open and close the intake and exhaust ports though, that would be a good thing, plus it's on a cam anyway.

I'm really starting to think this isn't as crazy of an idea as I first thought.

 

[WORTH]

So are you talking about something like a 2-stroke design? As in no valves. The piston reveals the intake and exhaust ports as it moves up and down.

Not really, I'm talking about a sliding cylinder/combustion chamber combination. The valves would be in teh combustion chamber just as if you had a head, only the rockers, pushrods, and cam would be stationary in the block. The cylinder-chamber would move up and down operated by an overhead cam that turned 1/4 crank speed. In the compression,intake and exhaust stroke the cylinder-chamber would remain up, but would move down during the first half of the power stroke.

 

[WORTH]

Neat idea.

Almost like 2 pistons facing each other.

You wouldn't want to fire the plug when the crank is at 90* tho... more like about 45*. So that peak pressure is exerted when the crank is indeed at 90*.

Also I don't know what the heck you guys are talking about the plug firing a "couple of degrees BTDC". Maybe when your doing your timing at idle with the vacum advance disconnected. Most ford V8's run in the neighbourhood of 36* total timing advance. They only run 10* or so when at full throttle during low engine RPM (below 1500). This is of course assuming your running the standard VAC adance/mechanical adv setup.

I was strictly talking theory on the timing, not real numbers. I really don't know how the timing would end up because in reality you will already have full compression when the spark is fired rather then the conventional engine that is coming up on the compression stroke when it's fired. You probubly wont need much advance at all as you'll be at optimum compression.

 

[ForceFed70]

I was strictly talking theory on the timing, not real numbers. I really don't know how the timing would end up because in reality you will already have full compression when the spark is fired rather then the conventional engine that is coming up on the compression stroke when it's fired. You probubly wont need much advance at all as you'll be at optimum compression.

Agreed!

Also.. think of how this would effect compression "leak". Since the engine will spend more time with the fuel under full compression, I would expect to see more loss caused by fuel leaking past the cylinder rings. Especially since now we'd technicaly have 2 sets to piston rings to leak through.

Also the "follower camshaft" would have to be pretty beefy. Almost like another crankshaft.

 

[BC61]

to many moving parts to be really feasible...but, continuing on with the idea...along the lines of a two stroke for int/ex but the top of the cylinder is another piston driven by a cam of sorts

 

[WORTH]

Agreed!

Also.. think of how this would effect compression "leak". Since the engine will spend more time with the fuel under full compression, I would expect to see more loss caused by fuel leaking past the cylinder rings.

actually max pressure is after the fuel is fired on the power stroke, and that would be shorter on this design.

Especially since now we'd technicaly have 2 sets to piston rings to leak through.

Nope, the cylinder and combustion chamber would be one piece. The seals for the moving assy would be on the outside in the water jacket.

Also the "follower camshaft" would have to be pretty beefy. Almost like another crankshaft. Yep

.

 

[D.Hearne]

There already has been an engine in which there was a common cylinder with two cranks, and the pistons opposed to each other. This was the Fairbanks-Morse diesel engine, used in most of the WWII subs and later after the war in railroad locomotives. It was a very successful sub power plant due to it's compact design, but the railroads didn't like it, due to the difficulty in overhauling one. In a sub, the top and bottom cranks were accessible, but in a locomotive, the whole thing needed to be pulled to access the bottom crank. It was an extremely powerful engine for it's size, which was the main reason it was so well liked in subs. The crews called em "rock crushers" .

 

[WORTH]

There already has been an engine in which there was a common cylinder with two cranks, and the pistons opposed to each other. This was the Fairbanks-Morse diesel engine, used in most of the WWII subs and later after the war in railroad locomotives. It was a very successful sub power plant due to it's compact design, but the railroads didn't like it, due to the difficulty in overhauling one. In a sub, the top and bottom cranks were accessible, but in a locomotive, the whole thing needed to be pulled to access the bottom crank. It was an extremely powerful engine for it's size, which was the main reason it was so well liked in subs. The crews called em "rock crushers" .

That is mearly a 2 stroke diesel with opposed pistons one controling intake and one controling exhaust ports. And the power stroke starts with the cranks at the top just like a conventional engine

My theory is this, if you take a heavy flywheel with a hand crank on it, and put the crank just off TDC and stand on the crank, it will not move because you are not heavy enough to move it with the leverage you have. Now move the same crank to the horizontal position and your weight will turn the flywheel. Same amount of power and more work. So it stands to reason taht if you fire your fuel load when the crank is closer to the horizontal position, you will creat more HP with the same amount of fuel.

 

[D.Hearne]

Yes, in theory, but gasoline doesn't ignite instantaniously enough to do that, that's why ignition timing is advanced so far as engine speed goes up. The fuel needs more lead time to burn and have the maximum thrust on the crank at the right time. You're theory is fine, just not practical with gasoline. The fuel/air mixture is burning the whole time the piston is traveling down the bore, as proof of this, there is the unburned fuel/air mixture in the exhaust, even in a finely tuned motor, there is still some unburned fuel in the exhaust. As proof that your theory won't hold water, if you retard the ignition to where it fires the mixture when the crank is at mid stroke, or at 90 degrees in relation to the cylinder bore, which is what you're suggesting doing, the engine simply won't run. Now go hit the showers.

 

[88 Fox GT]

Also I don't know what the heck you guys are talking about the plug firing a "couple of degrees BTDC". Maybe when your doing your timing at idle with the vacum advance disconnected. Most ford V8's run in the neighbourhood of 36* total timing advance. They only run 10* or so when at full throttle during low engine RPM (below 1500). This is of course assuming your running the standard VAC adance/mechanical adv setup.

Not even at idle with vacuum adv is the timing a "couple" degrees BTDC. Most 302s base timing are set at 10° BTDC.

WORTH, I'm starting to understand what your saying now.