Would I get a significant power gain if I got camshafts with only a higher profile? In other words, no modification of timing/duration, hence no overlap tuning.

As I understand it, I should notice significant gains from the added intake/exhaust travel, but I will also notice a lopey idle…true?

What causes the lopey idle?

 

The lopey idle is caused by the big cam losing intake stream velocity at low RPM.

 

When did cams come out?

 

JWT sells VQ35 cams that can be used in the VQ30 with an extra shim kit.

 

Actually, I was going get new ones made (if I can pull together a couple grand). I was going to stick with the same profile, just increase lobe height. That's why I'm curious if I'll notice significant gains at the upper end of the spectrum.

What's the upper limit on lobe height for the VQ? Can I get cams tall enough that my car won't run at <2krpms?

 

In most cases when you increase lift you also have to increase duration. The reason for this is that there is a maximum lifting and closing speed for valves. If you exceed that speed then reaction forces get large and you can have undesireable effects such as valve bounce and excessive cam wear. The lift and closing speed is determined by the amount of lift and width of the cam profile base. So if you increase lift you also need to increase the base to keep the same opening and closing speed. Increasing the base of the profile results in increased overlap.

It could be that the VQ cams are so mild that the valve speed is below the maximum speed by a healthy margin, in which case you can increase lift without increasing overlap.

 

Thanks for the info guys!

What determines the maximum valve speed? The strength of the valve/lifter/camshaft?

 

Valve speed at a particular engine speed is determined by the slope of the cam lobe. A cam with a taller lobe (i.e. more lift) will have a steeper slope and hence a faster valve speed, all other things being equal. The maximum valve speed will occur at redline, of course.

 

Right...I know that, but you said that there will be an upper limit on valve speed...is that because the stems/valves themselves/lifters/cam wears down at faster speeds?

Also, someone told me that I could wear down my camshaft if I went too high profile at too low of a speed. They said that very aggressive (low duration) cams are meant to run at high speeds. Will I need rollers if I'm to get these types of cams made?

 

Please take a few minutes and study the VQs valvetrain. Adding a roller system would mean a total redesign of the vavletrain.

 

Yes, wear becomes an issue at the higher valve speeds, because of the increased force a steep cam profile puts on the valve. But also higher valve speed results in valve float at lower rpm due to the valves inertia, so stiffer springs are needed, which further aggravates the contact force problem. The stiffer springs also slam the valve back against the head harder, which can result in the valve bouncing against the head.

Can't help you here. I dunno. Rollers are used on rocker arms, which the VQ doesn't have.

 

Unfortunately, I don't have much information to study from. Any good references? (Aside from the FSM)

Hmm...I seem to remember reading somewhere that they make roller lifters for use with normal camshafts...maybe I'm misinformed.