Anybody ever done this? What's the benefits?
It's pretty common. Usually set at +-4*, IIRC retarding the cam moves the powerband up and advancing it moves it down.
Jim
So is it worth messing with? I've got a simple ± 4º crank cog. From what I've read most racing applications just use neutral phasing. Perhaps I could use this to tune it to my headers or something? Do you know if there is any performance advantages? The cam is already pretty hot so I figured if anything I'd move it 4º advance to lower the powerband. I don't know...
Thanks for the help.
If you think you'll need more torque down low that would be a good move. It will decrease the top end power some. The real question, are you one of those guys who likes to wind the motor to redline, or do you always stay a few hundred (or a few thousand) rpm's below it. Let that be your guide.
Jim
Any idea how advancing or retarding the cam effects the valve to piston clearance. My cam is set on the centre slot and my timing gear has provision for 4 degrees either way but probably wouldn't change it at the moment so purely an academic question.
Kevin.
It will effect the valve clearance without a doubt. That is definitely something to consider if tolerances are tight. That will be an issue for my build. It's pretty close. For advance there is more clearance on the exhaust. For retard there is more clearance on the intake.
I wonder what factors go into changing the torque curve. Like more compression for the advance so you get more low torque? Longer intake opening ABDC for higher speed gas flow? That's my guesses.
In the not too distant history, was "Vari-Cam" and "Cam-a-go". These were devices designed to dynamically change cam adv./retard. As I recall, Var-Cam used tunable springs, somewhat like distributor advance. Cam-a-go, I believe, was manually shifted. Story is with it, dragsters would wheely at very high speed when it was "shifted". Car manufactures don't like to spend money needlessly unless they know we're going to bail them out. Point is, many OEM., "Cammer" motors have dynamic cam controls for good reasons. Kind of like having cake, eating it, and no weight gain! We "could" do similar with our push-rod motors. I think a "wet belt" would be easiest. Your thoughts-fellow motor people?? roverman.
Maybe adapt one of those servo setups on one of the VVT engines like Toyota's 2.4L camery engine...
A centrifugal advance would seem to make sense... except that you'd be fighting the valve springs. At least one of the universities was working on an electric over hydraulic valve actuation system. I doubt they ever got the speed up high enough but the same principal could give extremely good control of cam timing. Though I'm not familiar with the "wet belt" system it does make sense that a pair of tensioners shifted left to right might do the trick very well. Power them with oil pressure and control them with a governor and you're there.
Jim
Thank You. Yes I like the idea of, "rigid " pulleys, crank/cam. I suspect pushrod motors work these components more harshly than overhead cam set-ups. I envision an adjustable spring opposite end of oil pressure actuated, twin idlers on guided beam. It might be possible to "tune" the oil supply for proper travel per rpm. Of course it would have adjustable stops in both directions. I think working with "skilled" cam people to optimize cam lay-out ,since we're moving int/exh. together. To be continued. roverman.
If you used a chain drive with lots of slop and took that slop out with two tensioner idlers, one on each side, which were tied together on a common pivot that allowed the two to move as one side to side, then you could adjust distance between the idlers to remove play. Pivot the idler pair to change timing. Shift the slack to one side for advance and to the other for retard. An oil driven piston would do that easily, with pressure/direction controlled either electronically or centrifugally, or calibrated to system oil pressure.
Jim
Jim,
Thats basically how a lot of the variable valve timing systems work and I don't see why with a bit of ingenuity it couldn't be made to work as a simple cam advance and retard device, so you could maximise torque at the bottom end and peak power as the oil pressure retards the cam.
It wil;l obviousy not be as good as a full VVT system that can with twin cam heads than can have low overlap and lift at low rpm and increase lift and overlap as the revs increase.
Something like a brake or clutch slave cylinder connected tothe sliding link between the two idler gears would work and could be easily mocked up with an old timing gearset to see how much advance and retard you would get, that together with some data on how much advance and reatard would be beneficial and give you a pretty good idea of the potential, You should patent it immediately and sell the rights to one of the big US tuning companies!!
Regards,
Kevin.
If you recall that oil pressure builds with engine speed at a nominal rate of about 10psi/1000rpms it seems a simple spring and piston arrangement should control the retard quite nicely. In fact I'd be surprised to learn that it hasn't already been done.
Jim
If we look at aftermarket belt belt drives for push-rod motors, ther'e pretty pricey. Still they sell well or stores like Jeg's wouldn't keep them in their catalog. Why because belts "rule". They virtually have one moving part vs. chain at ?? with lot's of wear factor. They also absorb harmonics well. I'm going with the belt and we'll see. roverman.
The current issue of Hot Rod magazine has an article on variable valve timing/cam phasing. That's the hot setup on some of the newer cars.