Questions Regarding Valvetrain Modification

Just thinking out loud here. The way I see it, cam gears (+1 intake, -3 exhaust) are only extending the valve overlap (stock is 33deg.) I haven't however, been able to figure out how many degrees this modification adds.

In most discussions with small turbos (TD04 for example) a large valve overlap is generally though of as counterproductive, with the exhaust blowing back into the combustion chamber. For me, this raises questions about the validity of that statement (to an extent) as we see TD04 cars achieve good results from cam gears.

If valve overlap isn't as big of a problem as we first thought, than maybe cams like the 264 profile (48 degree overlap) would be more beneficial than adding cam gears. Other cam combos like 264 intake and 272 exhaust (52 degree overlap) and 272 all around (56 degree overlap) might also be a good choice.


We all know stock heads and cams can make great power, this is just another way of thinking. Feel free to correct me if my theory or math is wrong, I just wanted to put this out there to see what y'all thought.

Forgot to mention that this is supposed to be a discussion question, sparking debate, etc...

I have gone the 264/272 cams route, I think You have read My build thread so You will also know that I have BLE solid lash adjusters aswell as 3SX adjustable cam gears, not to mention the BLE solid cam belt Tensioner.
Only time & a dyno will tell how all this works once hopefully I get it running next week end.
Jeff

in for this discussion and quality info. cams and cam gears are a mystery to me but i do agree with your logic. i guess what you should be trying to figure out is how much overlap is desirable and how much overlap is too much. hopefully some gurus with good data chime in.

Quote:

---

Originally Posted by mb3000

Just thinking out loud here. The way I see it, cam gears (+1 intake, -3 exhaust) are only extending the valve overlap (stock is 33deg.) I haven't however, been able to figure out how many degrees this modification adds.

In most discussions with small turbos (TD04 for example) a large valve overlap is generally though of as counterproductive, with the exhaust blowing back into the combustion chamber. For me, this raises questions about the validity of that statement (to an extent) as we see TD04 cars achieve good results from cam gears.

If valve overlap isn't as big of a problem as we first thought, than maybe cams like the 264 profile (48 degree overlap) would be more beneficial than adding cam gears. Other cam combos like 264 intake and 272 exhaust (52 degree overlap) and 272 all around (56 degree overlap) might also be a good choice.


We all know stock heads and cams can make great power, this is just another way of thinking. Feel free to correct me if my theory or math is wrong, I just wanted to put this out there to see what y'all thought.

---

I think it's the other way around. Cam gears > cams because making a simple valvetrain timing adjustment can dictate where you want the power curve. For example, +I and -E valvetrain timing settings have proven to yield significant gains in an early rpm window which aid in quick spool and low end power. Whereas a -I and +E valvetrain adjustment may delay the power curve to a later RPM window.

I think the cam gear timing adjustment allows us to shrink the reversion window in given rpm operating ranges. The benefit is the adjustment will allow you to admeasure the volumetric efficiency bell curve by adjusting the valvetrain timing events closer together at operating RPM's individual drivers will predominatly drive in.

If anything, what I think's already been proven is our heads flow really really well. I belive Chris Hill proved you benefit more from the valvetrain adjustment by gears than you do from cams. What he demonstrated to me was, I dont think any of the cam profile designs currently avail for our cars are as good as what we already have. He put down 800+ hp to the wheels out of the stock valvetrain using only cog timing adjustment to the stock cam. That's 1000brake hp on that profile. When you think about it , that's damn impressive!