Valve Lift- Cam Lobe vs. Rocker arm

[LethalBite]

I've seen tons of web sites pushing high ratio rocker arms for the Viper engine and am wondering why there are very few selling camshafts? I have built many engines through the years (No V-10's) and have always preferred to make valve lift at the cam rather than upping the ratio at the rocker.
I understand that throwing a set of rockers arms on is a LOT less involved than a cam swap, but making lift at the cam is a lot less strenuous on the valve train over time.
Maybe I'm missing something about the Viper engine. I dunno....

 

[Martin D]

You certainly can do it that way if you want.

One thing to consider is the maximum lift you can attain with a "stock" base circle. If it gets too small, the lifters will drop below the retainers. But then you can just.......

Regards,

 

[1TONY1]

Another thought: Does anyone even make stock ratio roller rockers for a Viper. We know that roller rockers in a stock ratio are better than stamped rockers, but if no one makes the stock ratio your stuck. I don't know ????

 

[joe117]

If the stock ratio stamped rockers last many miles, and they do.
What would one gain by having roller tips at the stock ratio?

I always thought that roller tips were only needed if you increased the spring pressure or changed the cam specs.

I think in this case, perfection is the enemy of good enough.
The stamped ones are good enough for stock. They will last forever.

 

[Fast Freddy]

the stock rocker ratio on the corvettes ls1 and ls6 engines are 1.7 ratio with the aftermarket offering lifts up to a 1.9 ratio. ahy chihuahua!!!

 

[99 R/T 10]

If the stock ratio stamped rockers last many miles, and they do.
What would one gain by having roller tips at the stock ratio?

I always thought that roller tips were only needed if you increased the spring pressure or changed the cam specs.

I think in this case, perfection is the enemy of good enough.
The stamped ones are good enough for stock. They will last forever.

I believe one of the benifits of the RR is less friction on the rocker to the valve stem. By reducing the friction, you're freeing up HP. Also, by increasing the lift, more air will flow. I do have a set of Mopar RR I am selling for $850(shameless plug ).

 

[joe117]

I agree that more lift will give you some extra power but that's not what I was talking about.
The guy asked about stock ratio roller tip rockers.

I can just imagine the slug of extra power they would free up. ;-)

If the only change was the roller tips and no ratio change, I'd say don't do it because you wouldn't be gaining any real power and there would always be the chance that a piece might fall off of one of them.

Risk and expense for no improvement.

 

[99 R/T 10]

In that sense Joe, I agree with you.

 

[Tom F&L GoR]

From a lubricant point of view, the roller tips (no matter what ratio) help reduce side loads on the stem, which wear the valve guides into oval holes.

 

[LethalBite]

Perhaps my situation would clear up my original question which seems to have taken a tangent.
I plan on doing some engine modifications for better breathing in preparations for a supercharger (down the road). Plans include; reworked cylinder heads, full exhaust, maybe connecting rods(?), and a camshaft.
Part of my question was answered with the fact that the car has stamped rockers from the factory. I didn't know that. Anyway, since I plan on making a cam swap, should I make the lift at the cam or should I buy a little bit smaller cam and use higher ratio rockers?

 

[Martin D]

Here is the deal - dependant on the amount if lift you desire, you may have trouble with the stock rocker ratio. You can only have so much lift until the base circle on the cam becomes too small and requires a custom lifter OR grinding modifications to the block.

How much lift do you want?

Regards,

 

[Torquemonster]

Your hydraulic roller lifters will whimp out long before you will wear out and break top quality roller rockers of any ratio up to 2:1 (like in Pro Stock).

If you want real power from a cam - go to a solid and accept lash adjustments - then you can have both a fast action high lift cam AND 1.7 ratio rockers. You'll need custom pistons but you'd need better rods anyway so no big deal.

It is the valve spring pressure that will put the most strain on the gear - and the lifters are the weak point - not the rockers. Vipers cannot use a fast action cam without going to a solid lifter/cam. That's the trade off for using hydraulics - they are no maintenance and quiet, but they will not tolerate a fast action and/or high rpm.

The stock beehive springs are same as the Vette. Changing to a non beehive spring will increase valvetrain loading considerably.

 

[joe117]

You want to get as much of your valve lift as possible from the cam.
If you then need to move up the rocker ratio over stock in order to get the valve lift , do it.

If you are going to make the cam any more aggressive than stock or if you beef up the spring pressure, you should go to roller tip rockers, even if they are stock ratio.

For a stock cam and stock ratio rockers, I don't think the roller tips will make your valve guides last any longer than they need to last.
By that I mean that with frequent oil change and mobil1, I don't believe that guide wear from stock rockers will be the reason you rebuild the engine in a Viper.