Increasing rocker arm ratio...Questions.

[broncoman6524]

I'm wanting to put a larger cam into my motor, (222duration, .450intake, and .460 exhaust is what is in it now) I was talking to my dad about this, and he suggested getting new rockers arms with the increased ratio. Such as these...
http://store.summitracing.com/partdetail.asp?part=CCA-1416-16&autoview=sku

As far as I'm understanding, they will lift my valves 7% more than the 1.5ratio I have now, am I correct?

If thats true, then that would make my current cam a 481.5 lift intake and 492.2 exhaust, but would keep the duration the same. Is that also true?

I was told by the local machine shop that, high lift and low duration is the best way to pick a camshaft for torque. The above would make my cam great for that right? and it would still give it the lumpy idle that i larger cam would.

Is all of that correct? Or did i mis-understand something.

Any input guys?

 

[bigblock72]

In theory the higher ratio rocker arms could be worth a little bit of horsepower but it mainly depends on the rest of the combination.
What heads are you using?
What valve springs? most stock valve springs are maxed by .470", not to mention retainer to guide clearance issues.
What intake and carb are you using?
What exhaust are you using?
The short answer is if there is still airflow potential left in the intake, heads and exhaust then you you'll probably pick up a little power as long as there is enough valve spring to take the lift and enough guide clearance. If you are still running stock parts then they are likely already maxed with your current cam and you'll likely lose power with higher ratio rockers from the additional friction.

 

[broncoman6524]

It's a gm performace 290hp crate motor...

edelbrock air-gap intake with 600cfm carb, and longtube headers into 40series flowmasters, with 2.25 pipe.

 

[broncoman6524]

I was on the way out the door this morning when i replied last.

So im guess im correct to an extent? It will act as a "bigger cam" so long as the carb that i have now can handle it? and there is enough clearence?

Dad went to a car show today and found a set, ended up buying them, so we'll see how this works out.

 

[roadnotca]

Either way, that's one of those mods that's easy to back away from if it doesn't work; as long as you have clearance to the pistons.

 

[4X4HIGH]

Increasing the rocker ratio will increase valve lift and also the net duration will be greater as well. It is impossible to use the same cam with a larger ratio rocker arm to increase valve lift without having more duration to open the valve the extra amount. The (gross) duration that was built into the camshaft is not changing but the (net)duration at the valve is.

 

[broncoman6524]

Edit....re-read it again and understood now. Basically the lift is increased, as well as the gross duration. Correct?

So I'm going to guess that the only problems that I may encounter would be the spring clearance, and piston-valve clearance.

Me and dad are going to put them in on Monday night, so as that progresses we'll be watching the springs closely, and we could definetly hear if the valve/piston are making contact. So we shall see.

 

[4X4HIGH]

As long as you're not using vortec heads you can get away with .500" lift before you need screw in studs and new springs. It would be a nice thing to have the springs that match the given cam though.