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Variable Valve Timing

420ATTAK

420ATTAK

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Joined
Sep 26, 2007
Messages
155
Location
Ingersoll, Ontario
comming from an automotive backgroung i got to thinking some of the high performance 4 cyl cars have VVT and we have high performance 4cyl snowmobiles that might help with a bit more top end that everyone wants from time to time but the great thing about VVT is that it adjusts with the RPM so it wouldnt be like putting in "big cams" and sacraficing trailability and reliability. maby just a pipe dream i dunno i would like to hear other thoughts and ideas good bad what ever i havnt seen it discussed on the site so i thioght i would bring it up

RyGuy
 

Dont you think it would be less effective in a sled since our clutching lets motor run in optimum rpm range anyway?
 
You'll notice that these engines idle pretty fast (compared to a car). The standard cams don't allow for a particularly low idle speed, but with an engagement over 3000 rpm, its not such a big deal that the idle is a bit higher. vvt would allow you to get the idle speed down to a nice strong 400-ish rpms, and would allow a lower and stronger engagement. Thing is that you don't really want a lower and stronger engagement - it'll end up shredding belts too easily. Plus, adding on everything you need for vvt and you'll add more weight and complexity than its worth (for little to no tangible benefit). What you have to gain up top is really not much -- its already good for top end.
 
How 'bout instead of a cam to drive the valve, actuate them using solenoids. You could then program the solenoids when to open an close the valves based on a pre-determined map, using inputs of rpm, engine load, throttle position, engine temp, etc. etc.

Thing of the weight savings .... no more cam shafts, valve springs, timing chains, etc. The only thing spinning would be the crankshaft.

I think an automaker messed around with this a few years ago. And (someone please correct me if I'm wrong) I think they had a idle speed of around 200rpm. I don't know what happened with it's development, but it sounds pretty cool.
 
The main reason MOST production cars have VVT is emission related.

Back in 82 we had them on Alfa Romeo 2 litre engines. It was a very simple lightweight system consisting of a flyweight on the intake cam sprocket that opened an oil passage, the oil pressure then advanced the cam timing via a helical ramp.
We had lots of problems with the early production versions... seemed the Italians on the assembly line liked Loc-Tite and used so much it clogged the oil passage in the cam and it would either not advance or get stuck in the advance position then the car would not idle. :o|
Once we figgured out the problem the system worked pretty well.
 
i like the idea of the solonoid idea ive heard about that and that would be the best way to do it however complex and prolly hard to get around the patens too, this is the kind of conversation i was looking to get started keep it comming!!
 
I think the solenoid idea would be fairly straight-forward. Even if it wasn't programmed to be variable, at least look at the mechanical friction and weight you can eliminate from the engine. I bet you could get 5-10hp alone just from eliminating friction from all the moving parts that were removed.

And if a solenoid went bad, you could design it so that those valves would then stay open on the faulty solenoid (provided they don't hit the piston) so that you could at least limp the engine home.
 
gade-thrasher said:
I think the solenoid idea would be fairly straight-forward. Even if it wasn't programmed to be variable, at least look at the mechanical friction and weight you can eliminate from the engine. I bet you could get 5-10hp alone just from eliminating friction from all the moving parts that were removed.

And if a solenoid went bad, you could design it so that those valves would then stay open on the faulty solenoid (provided they don't hit the piston) so that you could at least limp the engine home.
Click to expand...

If it was designed 1 solenoid per valve, then having multiple intake and exhaust valves would allow you to limp home by leaving faulty valves CLOSED. Valves would hit if left open, and the spring would return the valve to the closed position anyways. If the solenoid failed, there would be no way to open the valve. Just gotta keeps the rpms low to allow sufficient gas to flow past the remaining valves.
 
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