Why DOHC and not SOHC ??

[brett_celicacoupe]

this was on the old forums.

i saved the link

sounds to good to be true


thoughts on this system...

rotary valves

[roadsailing]

the coates engine is the biggest load of snake oil ever. i saw this about 5 years ago and thought "what a great idea!" the design is fundamentally flawed.

river is on the right track with the aero engines, but this thread is going steadily off the DOHC vs SOHC track as it is.

i'd be interested enough in a 2 stroke car engine, and it would batmobile smoke out the back as well!

[Enchanter]

My father was telling me about when there were 2 stroke car engines, they were often supercharged aparently, he said they sounded awesome.
I however know zero about them.

[roadsailing]

closest i can think of to what you mention is a GM 2 stroke supercharged V8 diesel truck engine.

they do sound pretty cool!

[Nim]

How the hell would a 2 stroke supercharged engine work? Wouldn't all the pressure just escape out of the exhaust port? Or was it just to help flush exhaust gas out?
I really don't like 2 stroke motors. They just seem wrong to me.

The main problem I see with the roller valve setup is that the air doesn't have a straight path into the cylinder. It'd cause a lot of turbulance around the valve, and not give you a very good flow. Would that be one of the fundemental flaws previously mentioned? Also, I don't see how you could set up variable duration or lift on something like that.

[horse]

there is no lift in a rotary valve. if u wanted more duration i would imagine that you would just create a larger port on the rotary valve.

[myne]

Or make them electrically driven rather than belt driven. Then you could have all the variable timing in the world

[Nim]

Perhaps not lift, but you have a relative, ie, port size (on the roller valve). That's not something you could change. And sure, you could create a larger port da-horse, but how do you do that on the fly?

If you had an electric motor for each valve (which you'd need to do variable duration) then wouldn't you have the same problem with solanoid driven valves? ie, using a lot of power to run the valvetrain? (I'm just guessing here).

Also, myne, I assume when you said timing, you meant timing and duration. Just so everyone else is clear.

[The Last Streetfighter]

How the hell would a 2 stroke supercharged engine work? Wouldn't all the pressure just escape out of the exhaust port? Or was it just to help flush exhaust gas out?
I really don't like 2 stroke motors. They just seem wrong to me.

The main problem I see with the roller valve setup is that the air doesn't have a straight path into the cylinder. It'd cause a lot of turbulance around the valve, and not give you a very good flow. Would that be one of the fundemental flaws previously mentioned? Also, I don't see how you could set up variable duration or lift on something like that.

Nim. I think you'll find the Gimmy (GM detroit 2 stroke Diesel engine) had exhaust valves on top and inlet ports around the bore (a bunch of rectangles around the bore of the cylinder.) http://auto.howstuffworks.com/diesel-two-stroke1.htm

There is a little reference on this page (Do a search on Detroit on this page.) http://www.gadgetonline.com/super.htm

[oldcorollas]

How the hell would a 2 stroke supercharged engine work? Wouldn't all the pressure just escape out of the exhaust port? Or was it just to help flush exhaust gas out?
I really don't like 2 stroke motors. They just seem wrong to me.

The main problem I see with the roller valve setup is that the air doesn't have a straight path into the cylinder. It'd cause a lot of turbulance around the valve, and not give you a very good flow. Would that be one of the fundemental flaws previously mentioned? Also, I don't see how you could set up variable duration or lift on something like that.

2 stroke supercharged... perhaps you need to do a little research into BIG diesel engines... ie compound super-turbocharged 2 stroke diesels (like ship engines and stuff...) thee are a couple of sites that explain it well.

just because you don't like 2 strokes doesn't mean they are wrong they have very high power to weight ratio, but often have small power bands.. think of motorbike or model plane 2 strokes.. shit for lower half of rpm, then they come on song in a big way (something to do with the way the lubricating oil combusts?)

with roller valve, it may not have straight pat, but it has a hell of a lot of area, meaning a shitload less resistance to overcome as air enters cylinder = less velocity required to overcome the resistance and fill cylinder. a roller valve with openign the size of the port will flow more than a poppet valve with the same circumferential area. think of it like blowing thru a bendy straw, as opposed to blowing thru a straw and holding your finger partially over the end.

again with the Vtec how many F1 cars run variable lift or timing? how many race cars run variable lift or timing? variable lift and timing are (mostly, but not exclusively) good for stret engines, where you need to have a flatter torque curve and better emissions. as you keep saying, you like a high revving motor... variable lift/duration does nothing for this high rpm region, it only improves the area out of the power band (or if you are willing to sacrafice low end, it extends power band)...

the point of the roller valve was to allow very high engine speeds with lower parasitic losses, and have large area for air to enter cylinder. pity about the sealing issues.

[fuzz!]

they have very high power to weight ratio

that's always been my understanding of the 2-strokes place in the fabric of things.. chainsaws and other hand-held power tools that require a fair amount of poke, while still being light enough to carry around..

[oldcorollas]

that's always been my understanding of the 2-strokes place in the fabric of things.. chainsaws and other hand-held power tools that require a fair amount of poke, while still being light enough to carry around..

and 500cc race bikes what did they go to when they went to 4 stroke? 750?

[Nim]

2 stroke supercharged... perhaps you need to do a little research into BIG diesel engines... ie compound super-turbocharged 2 stroke diesels (like ship engines and stuff...) thee are a couple of sites that explain it well.

Someone already explained it, thanks.

just because you don't like 2 strokes doesn't mean they are wrong they have very high power to weight ratio, but often have small power bands.. think of motorbike or model plane 2 strokes.. shit for lower half of rpm, then they come on song in a big way (something to do with the way the lubricating oil combusts?)

I don't care, I still don't like 'em. Just like I don't like SR20s. You can like them. I don't mind.

with roller valve, it may not have straight pat, but it has a hell of a lot of area, meaning a shitload less resistance to overcome as air enters cylinder = less velocity required to overcome the resistance and fill cylinder. a roller valve with openign the size of the port will flow more than a poppet valve with the same circumferential area. think of it like blowing thru a bendy straw, as opposed to blowing thru a straw and holding your finger partially over the end.

Fair enough.

again with the Vtec how many F1 cars run variable lift or timing? how many race cars run variable lift or timing? variable lift and timing are (mostly, but not exclusively) good for stret engines, where you need to have a flatter torque curve and better emissions. as you keep saying, you like a high revving motor... variable lift/duration does nothing for this high rpm region, it only improves the area out of the power band (or if you are willing to sacrafice low end, it extends power band)...

We where talking about fully variable timing, lift, and duration, and a roller bearing wouldn't help this at all.
I understand how VTEC works, and what it's for. I like having a high revving engine, but I also like it to be smooth and driveable daily (for a daily car) hence I like VTEC, VVTL-i, and that crazy 3D cut cam that Ferrari uses.

[myne]

The Ferrari one is potentially the best.
Even honda cant top the potential of a 3D cam

[Nim]

The Ferrari one is potentially the best.
Even honda cant top the potential of a 3D cam

Indeed. Appart from direct solanoid valves, 3D cut is the best way to do it. 'cept it's probably expensive (or under patent) otherwise more people would be doing it.

EDIT: Whoever neg repped, why don't you just post rather than ripping at the way I write. Of course it's oppinion. So bullshit.