DAPSUPRSLO

iTrader: (14)

One must remember that for every spring the cam has to push open on the opening face of the lobe there is another spring that is pushing down on the closing side of the lobe essentially pushing it forward offsetting the power loss caused by the cam trying to open springs. In other words, more pressure does not cause power losses from trying to travel up a cam lobe and open springs. The only possible power loss will come from the increased friction of the roller on the cam's surface.

DAPSUPRSLO

iTrader: (14)

The crane's will be fine with this cam as they do not have much seat pressure compared to other duals. In fact it might even be wise to shim this spring to remove some of the installed height. A spring that is shimmed will go to higher rpm's before it becomes resonant. Ofcourse you could only shim the spring if you will be within the limits of coil bind, which you will be with small shims (.050" or so). This will probably not be necessary unless you are planning spinning to 7000 or so.

Flareside

What about the rocker fulcrum, pushrod tip on the rocker, valve in the guide, inner/outer spring friction, etc.? When you increase spring pressure, friction increases everywhere in the valvetrain, not just at the lifter. Heat also increased. My LS1 is noticably harder to turn over with a wrench with stiffer springs in it.

PREDATOR-Z

The trick is to spring right and not to over or underspring. Also lifters have to be able to handle the extra spring stiffness.
If I wanted extra insurance, I would just run 918's, just 1 step over 915's. I run 918's with .581 XE-R with no problem.

DAPSUPRSLO

iTrader: (14)

Good point, those frictions will increase as well. Heat will increase too but will it be noticeable, probably not until you get into 300 seat pounds for solid roller stuff. Also notice that when you turn over the motor by hand that it can be harder but once you pass the area which is harder to turn over the ratchet almost turns itself because the heavier springs push down on the closing side of the lobe just like they do on the opening side.

transam86ta

this is joey from D C Motorsports you can never over spring a engine more is better the spring you got is the best one for the job at hand we put those spring on all are cam instills and i have not had a problem yet

slow3hoe2

iTrader: (3)

this is true to a point. yes the lifters that are on their way down are helping the cam spin...but it is not a 50/50 offset. When the valve is closing, the lobe is being taken away from the lifter...rather than running into the lifter. As rpms increase, the lifter thats on its way down will be come less and less help. I have played with many different spring pressures in my solid roller sbf....and there is definitely power left on the table when you have more spring pressure than you need.

RedHardSupra

iTrader: (1)

what are the specs for REV duals? how do they match a Z06 cam on 1.8 rocker?

DAPSUPRSLO

iTrader: (14)

Another good point. Deffinately not a 50/50 offset at high rpms. But the added benefit of reduced valve bounce will more the offset any of these issues of higher losses, especially at higher rpms where valve bounce is very very likely to occur. Once again for the orignal intent of the orignal poster none of these theories will probably hold true to an extent of actually seeing a difference between a crane dual spring verses a comp 918 style spring.

marc_w

I don't think there will be ANY problems overspringing a smaller stick.

The thought about collapsed lifters - the way I'm thinking about things, the milder stick will have a much less-likely chance of doing that even when running overkill springs. The milder lobes are not putting as much strain on the lifters as an extreme lobe would (which would actually require heavy springs).

Parasitic loss - For every valve that has to be opened, there is another that has to be shut. I don't see heavier springs as dragging down too much power. Remember this is a roller-valvetrain so it's not like you're "skidding" parts across each other. A skateboard won't roll with much more drag with a 150-pound kid on there vs a 100-pound kid.

For what it's worth, I have no idea - I ran 918's on my stock cam for a few days with no problems. I had no extra valvetrain noise what so ever. Everything was just like stock.

marc_w

Very interesting...

Naked AV

My guy at Comp told me to stay away from the 915's and do 918's for anything I would consider the 915's for.