Just a thought on Cam Theory

moparmanjames · 03-07-2006, 09:32 PM

I was thinking about your Titan engine, and I was wondering, do you have just one overhead cam per head, or is it two?
If it is a double overhead cam configuration, then you would have one cam for the intake valve timing, and one cam for the exhaust valve timing.
Now this is where it gets interesting.
Nissan probably set up the camshafts with approx. 114 to 116 degrees of lobe separation angle. I'm not sure if you guys have a belt or a chain to drive these cams, but you could find out how many cam degrees each tooth is and vary the cam timing.
In my experience with performance camshafts, if you went from a 116 degree lobe separation angle (LSA) cam to one with say, 110 degrees of separation (thus bringing the lobes closer together) your midrange torque will increase sharply, but you lose some top end torque and some down very low like at 1000 rpm due to increased overlap. But if you want a lopey idle and explosive midrange torque, I'm guessing somewhere around 450lbft up from 379, and the peak will occur slightly sooner as well.
Just some Hot Rodding thoughts from an old engine builder. I'm not sure how the slight drop in vacuum at idle would affect the engine management system either, might cause it to run rich at idle or something.

Slewis · 03-07-2006, 11:52 PM

Thats a great thought. I know Thrust would most likly be interested in this info

PrerunnerGreg · 03-08-2006, 03:47 AM

Chain drive, DOHC

**Helinut1970** · 03-08-2006, 04:52 AM

Mopar, with what you know about engines, You need buy a Titan and show us how its done!! Instead of "got torque" being our new rep YOU could take the place of the "head"

moparmanjames · 03-08-2006, 06:16 AM

Quote:

Originally Posted by Helinut1970

Mopar, with what you know about engines, You need buy a Titan and show us how its done!! Instead of "got torque" being our new rep YOU could take the place of the "head"

I would love to but I just can't bring myself to buy a new vehicle when if I spent the same money on a classic, it would be so much better!
One of you folks can try this though, it looks like the cam sprockets are around a 50 tooth sprocket, so each tooth would be about 7 degrees of cam timing. I would move the intake cams one tooth in the direction that would decrease the LSA, but I'm not sure which way the motor rotates, so you guys could try this.
I wouldn't move this more than 1 tooth since 7 degrees is not a big deal, but 14 degrees is (2teeth) regarding valve to piston clearance. I'm not sure if this is an interferance engine or not (if the timing chain breaks, will the pistons hit the valve).
But given the formula (ILCA+ELCA)/2= LSA, where ILCA = Intake lobe centerline angle, and ELCA = Exhaust lobe centerline angle, and LSA=Lobe Separation Angle, if ICLA is currently 115 and ECLA is 115, then the LSA is 115.
So if you change the Intake 7 degrees toward a reduced LSA, you would have 108. Then recalculated, 108+115= 223, divide by two and you have around 111.5 for your LSA. I wouldn't move the exhaust unless you are really
hardcore about what you want your engine to sound like because you would end up with a LSA of 108, which would give a lot of overlap and much reduced vacuum at idle, but the mid-range torque would be fantastic.
One last note, once you jump a tooth, before you put it back together slowly turn the engine over with a wratchet to make sure there is no piston to valve interference.
Have fun guys!

moparmanjames · 03-08-2006, 06:19 AM

Quote:

Originally Posted by PrerunnerGreg

Chain drive, DOHC

Thanks Greg, Excellent pics!

scr38 · 03-08-2006, 09:02 AM

When we talk about cam timing in degrees it is in reference to crank degrees. So 7 degrees at the cam will be 14 degrees at the crank. Moving one tooth on the cam is way too much change.

moparmanjames · 03-08-2006, 09:32 AM

Quote:

Originally Posted by scr38

When we talk about cam timing in degrees it is in reference to crank degrees. So 7 degrees at the cam will be 14 degrees at the crank. Moving one tooth on the cam is way too much change.

Ahh, that's right I wasn't thinking about that, good catch scr38, you are on top of it!
I guess if you changed the intake timing 14 degrees, if you started with a 115 LCA, that would give you 101, not unheard of, and 115 for the exhaust, so together you would have an LSA of 108. With the intake opening earlier and closing earlier, the cylinder pressure will have a significant increase at midrange rpms.
It might be worth a try if there are no interference issues. What do you think?
It sure would be better if someone came out with some adjustable cam sprockets. Oh well, just daydreaming.