CAM lift-duration

[TexasPettey]

Here's a question that's sure to get the juices flowing ...

Does anyone know the time duration of the 708 CAM for each lift range? For example, is it linear such that it spends an equal time in the rotation in the .100" to .200" range as in the .400" to .500" range. Or, is it non-linear, such that it spends 2X the time in the .400" to .500" range.

I ask in the context of thinking about head flow performance over a lift range and their value to engine performance. While peak flow is nice, it would seem to only be a small part of the story. The real goal is to get maximum air volume on the intake stroke.

On the surface, one would think that CFM * time at lift is a good aproximation of intake volume in the cylinder. Added complexity is the pull generated by the exhaust valve during overlap. Although hard to estimate, it would add some weight to the CFM at low valve lift where the overlap is happening.

 

[FE 065]

Nice bunch of questions. If you had your answer, what would you do (differently) with the information?

My 99's 708 cam has 297 degrees of duration on the intake side. How long is the intake valve open at say 5000 rpm? .0099 sec?


It's said the exhaust can have 5x the influence on cylinder filling than does the downward movement of the piston. Yet most people usually concentrate on the intake side of the engine agonizing over throttle bodies and aftermarket airboxes etc.

 

[99 R/T 10]

Hey TP,
I thought I already gave you the specs via: http://ivr.viperclub.org/specifications.php

Look at the bottom of the page.

 

[TexasPettey]

In my situation, I'm largely down the path with my mods. I'd use the information to evaluate the effectiveness of other mods relative to the $ spent. $/HP is always an interesting figure, and it is an expensive experiment.

In general, I was thinking it would be useful to evaluate the effectiveness of different cyclinder head ports and value of other modifications realtive to NA vs SC.

Since the CAM specs give you open/close and duration, but not progression, it's not clear how to evaluate the flow numbers other than "bigger is better". Since we're Vipers, that isn't a bad mantra.

 

[jp]

The numbers you'r looking for are not public, but you can measure them with a rig if you realy want them.

We are right now building a NA Vipe engine were we are limited to stock valve size and intake/exhaust runner CC. I can tell you that the camshaft is not the limiting factor. The head stands and the location of lifter bores is the main issue to get serious power out of the V10.

The Stryker heads with the reworked stands and a block were you can go with a bigger cam (950-1100) and offset lifters will waken up the beast.