We have DOHC engines, why not TOHC engines?

[geno]

I would love to own a high performance car with 6-Valves per cylinder.

I'd love to see you design one 4 is all that's really needed, 5 provides a small gain in flow, but not enough to justify the high cost design. Until someone maximizes 5 valve setups, don't expect to see more.

As for TOHC .... do you even know what a camshaft does? There's no point to that, you have one cam timing you exhaust valves, and another doing your intake valves...why in gods name would we ever need 3?

 

[IGBT]

How about no cams and electronic/solenoid controlled valves?? Think of the possibilities. Fully optimized valve timing at all speeds.....

 

[flot]

What gino said.

Exhaust valves = 1 cam
Intake valves = 1 cam

there are no other valves to control. You could theoretically use a 3rd cam to open/close a seperate set of intake or exhaust valves, but that's pretty pointless.

 

[geno]

Originally posted by: IGBT
How about no cams and electronic/solenoid controlled valves?? Think of the possibilities. Fully optimized valve timing at all speeds.....

It's being done. Electromagnetically controlled valves have been tried, but so far they're way too expensive to even think about using just yet.

 

[Bulk Beef]

Strokers rock. Feeling the urge as it gets on the pipe, WOW!

My TZ/RZ/RD hybrid racebike will rock (if I ever finish it). Mmmm, piston port two-strokes...

 

[DurocShark]

The only reason 2 cams are useful is because of how cramped engines have become. Hard to put enough lobes on a single cam to power 4 valves per cylinder in a small engine. 2 cams allow the lobes to be spaced out better. Increasing the cams will do nothing at all unless there is again a need to space the lobes out even more.

One cam could conceivably drive 1,000 valves per cylinder if they are spaced out enough. Of course, a cylinder with a 40ft diameter probably wouldn't be very successful in a modern car.

 

[Bulk Beef]

a cylinder with a 40ft diameter probably wouldn't be very successful in a modern car.

You don't have to make the diameter bigger. Just make the piston longer.

 

[GalvanizedYankee]

Originally posted by: sward666

a cylinder with a 40ft diameter probably wouldn't be very successful in a modern car.

You don't have to make the diameter bigger. Just make the piston longer.

Very good! The "only" problem was the rings never could be made to seal properly,
for any real service time.

Note: Old man Honda made very good piston rings for aircraft engines in the 30's & 40's..:sun:

 

[Bulk Beef]

Originally posted by: galvanizedyankee

Originally posted by: sward666

a cylinder with a 40ft diameter probably wouldn't be very successful in a modern car.

You don't have to make the diameter bigger. Just make the piston longer.

Very good! The "only" problem was the rings never could be made to seal properly,
for any real service time.

Note: Old man Honda made very good piston rings for aircraft engines in the 30's & 40's..:sun:

Yeah - it was an interesting idea though, and the streetbike they wound up putting it in was pretty damn cool.

 

[cavemanmoron]

Originally posted by: galvanizedyankee

Originally posted by: cavemanmoron
why not make the engine 2 stroke,so you need No valves!



like my snowmobile,it is 700 cc and makes about 115hp,maybe 118?

lots lighter than a 4 stroke.

Pollution! I wish it wasn't so. Strokers rock. Feeling the urge as it gets on the pipe, WOW!

Honda was working with a 2 stroke that injected its fuel through a hole in the cyl wall.
Just as the piston came up and covered the ports, fuel would squirt. It never made it out of
the lab.............

:frown:

'







The next generation of lightweight performance snowmobile engines. Semi-direct injection 2-TEC mills deliver the same horsepower as a carbureted engine while reducing fuel consumption and emissions.

Features:

Two injectors per cylinder
Electronically controlled engine calibration
Electronically-controlled R.A.V.E. exhaust valves
Knock sensors
Benefits:

Same performance as a regular 600 H.O.
Industry cleanest 2-stroke engine
Improved ease of operation
Smoother performance
Crisper throttle response
Choke not required
Emissions reduced by as much as 50%






http://www.skidoo.com/docs/700/0_US.htm

 

[geno]

Originally posted by: sward666

a cylinder with a 40ft diameter probably wouldn't be very successful in a modern car.

You don't have to make the diameter bigger. Just make the piston longer.

:Q

What kind of motor is that???

 

[cavemanmoron]

Originally posted by: geno

Originally posted by: sward666

a cylinder with a 40ft diameter probably wouldn't be very successful in a modern car.

You don't have to make the diameter bigger. Just make the piston longer.

:Q

What kind of motor is that???

hmm center of the cylinder plugs,,,, Hemi? style ,4 valves per plug;
but one piston for 2 cylinders.... Hmmm... that is Different,.
might be a bummer to rering!

 

[Siddhartha]

"We have DOHC engines, why not TOHC engines?"

Because a TOHC engine would be too expensive to justify the increase in performance orefficiency.

 

[Linux23]

Originally posted by: sward666

a cylinder with a 40ft diameter probably wouldn't be very successful in a modern car.

You don't have to make the diameter bigger. Just make the piston longer.

good lord man, I want one of those.

 

[Mark R]

There is an additional problem with having more valves - the higher circumference to cross-sectional area ratio of the smaller ports means that the exhaust gasses are cooled more effectively by having multiple exhaust valves.

The colder gasses make catalytic converters less effective - several manufacturers (e.g. MB) are planning to go to back to 3Valve/cylinder designs (2intake, 1 exhaust) simply to meet upcoming new pollution requirements.

 

[Bulk Beef]

Originally posted by: cavemanmoron

Originally posted by: geno

Originally posted by: sward666

a cylinder with a 40ft diameter probably wouldn't be very successful in a modern car.

You don't have to make the diameter bigger. Just make the piston longer.

:Q

What kind of motor is that???

hmm center of the cylinder plugs,,,, Hemi? style ,4 valves per plug;
but one piston for 2 cylinders.... Hmmm... that is Different,.
might be a bummer to rering!

It's a Honda NR750. In the late 70's-early 80's, Honda wanted to race a four stroke in 500 GP (where the grids were filled almost entirely w/two strokes, including Honda 3 and 4 cylinder bikes), but the rules stipulated a four cylinder maximum. At a given rpm, to get as many power strokes out of a four stroke as you do out of a two stroke, you need twice as many cylinders, so Honda basically made a V4 out of a V8, by making the pistons oval. 8 valves, 2 plugs, 2 rods per cylinder. It didn't get very far in GP racing, but they did eventually develop a 750 streetbike out of it, but even that was more of demonstration of Honda's technical prowess than a pratical advance.

More info

 

[Evadman]

Back to the original question: why not 3 cams.

There are only 2 valves needed, intake and exaust. The valves are on oposite sides of the cyl, so unless you want ot use short pushrods, you would need one cam directly over each row of valves. one cam is for intake (towards the middle of the engine), one is for exaust (towards the outside of the engine). No matter how many valves you add, you still only need 2 cams because there are only 2 rows of valves.. Lobes would be added to the appropriate cam to actuate the valves if you add more than 1 valve for intake or exaust.

The only reason to have a 3rd cam is if you needed a seperate valve in a differet position to do something wierd. There was an idea floated around a while ago with an engine that had 3 intake valves. 2 would open under normal circumstances, but when crusing (part throttle) conditions, only the 3rd valve would open, which was smaller than the other 2, and was positioned so the air/fuel from that valve would hang around the spark plug, letting the engine fire with a very high air/fuel ratio (I seem to remember 18:1 and higher)

But even in that case, the valve was actuated by another cam lobe on the intake cam.

 

[LAUST]

Man you guys really want to make engines huge, expensive and hard as fvsk to work on don't you?

 

[Linux23]

Guys, I understand now that it would almost be mechanically impossible to add a third camshaft to an engine. Evadman pretty much got what I wanted to express, but in his post he states that the 3rd valve was actuated by the intake camshaft, so I guess my point is moot.

I never expressed that I was an automotive expert, I just asked the question of WHY Not? Thanks to those that answered my question, and to those that gave me a better understanding of this subject.

In any case, electronically controlled valves sounds really cool.

 

[WinkOsmosis]

There are quad overhead cam engines. Either Lamborghini or Ferrari uses them...

 

[CraigRT]

Originally posted by: OS
There's only an intake and exhaust valve action anyways. What would the third cam be doing?

absolutely SFA!

TOHC is not possible in a "V" configuration engine.. or any engine as far as i can gather!! unless you had a 4 valves per cylinder engine and had a CAM for each valve... then you'd have a 4OHC engine

 

[geno]

It's totally possible to have 3 cams, but I can only imagine how bulky, complex, and delicate the head would be!