Comp Cams 233/242@.050 .533/.540 w/1.5:1 RR @ 114* going into A4 w/3200 converter 150 shot
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needs 1.6 rockers

 

why?

 

Looks like good nitrous cam, shoudl work well. I disagree on the 1.6 rockers. I think they are a good way to bandaid a cam that's not ideal for the motor, but if you pick the right grind from the start you don't need them. Why add the extra force to the valvetrain? Given it's not a lot of added pressure but think about the fact that a spring with 300lbs of pressure is more like 450lbs at the cam/lifters/pushrods with a 1.5 rocker. With a 1.6 now you're at 480lbs.

Plus I believe a 1.6 can add something on the order of 3 degrees duration and can screw up an otherwise "perfect" grind.

 

Nice cam bro go with it! add 1.6 rockers too!


Timberwolf...
you need to look at a valvespring chart. Look at say a comp cams 941 spring for example...
...incressing lift by .050 takes spring pressure from 357 pounds at 1.250 height too 379 pounds at 1.200 height.

Adding 1.6 rockers to any cam that ran 1.5 rockers only adds .046 lift which incresses spring pressure by less than "22 pounds" not the 150 pounds your talking. I'm open for debate but go to comp cams site and look at spring charts first bro .

 

Nope, you missed the point man

In my example going to a 1.6 rocker increased the spring pressure 30lbs just by the change in mechanical advantage or "leverage". That's not taking into account the additional compression of a progressive rate spring.

I can see where you might have been confused, but I was not talking about the increase in seat pressure directly, I was talking about pressure on the cam/lifters/pushrods which are on the opposite (short) end of the teeter-totter (rocker arm).

When I was talking about going from 300lbs to 450lns, I meant that 300lb spring times 1.5 (the rocker ratio) equaled 450lbs at the other end of the arm, since it's the short end that's being pushed by the pushrod

So we are both right, just talking about different things

 

Um ok if you say so but never read where rocker arms multiply spring pressures?
I see where they multiply lobe lift tho.
Sorry but I'm right your wrong.
Do you have a comp catalog handy???

 

Well, it's simple physics actually.. the rocker arm ratio is 1.6 to 1 for example. Yes lobe lift is multiplied and at the same time spring pressure is divided by the same ratio.

Picture a teeter totter with one side longer than the other. The person on the short end has to exert more pressure than the person on the long end and likewise, the person on the long end is lifted higher.

If I was on one end 10 feet long, and someone of equal weight is on the other end which is 15 feet long, I will in fact have a mechanical disadvantage, correct?

 

You guys are both right.
Question for you Jeff
If the cam is custom ground to spec using a 1.5 ratio
why step up to 1.6? What's the advantage of the
increased lift ratio over having the lift ground in?
Kevin

 

Well, I'm not Jeff, but to answer your question simply; when the lobes of the cam are less agressive it is easier to control the lifters at high rpm.


Also, if somone could explain to me how switching from 1.5 rockers to 1.6 will add duration I would appreciate it.

 

Switching rocker ratios doesn't add camshaft duration but it does add valve duration. The 1.6 rockers open the valves further for a given tappet lift. Now, since the duration that is commonly quoted for a cam is rated at a certain tappet lift, that number is not affected, but the duration the engine sees (valve duration) is. Understand?

And yes, Timberwolf is most certainly right. Increasing the rocker ratio does add contact stress to the camshaft not even considering the increase in lift which increases the valve spring force. It's just a lever arm, like he says.

As far as the valve is concerned, it doesn't care if you dictate it's motion strictly through a cam profile or modify it with a rocker ratio change. What you want to control is the valve seating velocity. You can pick a lazy lobe and add some rocker ratio or pick an aggressive lobe and run a lazy rocker ratio and still hit your limits for seating velocity.

Oh, and a comment on the 233/242 cam. The cam sounds OK, but it's the combination that matters. You really should call their techline, but I can tell you that it would work a LOT better with more converter unless you launch off the line with the nitrous. If you mostly street drive the car though, you might not like more converter.

Basic questions I used to ask when I worked on their techline a few years ago:

1) What do you use the car predominantly for? If for racing see below.
2) Engine size?
3) Weight of car?
4) Gear ratio / tire size?
5) Auto or manual? If auto, what stall?
6) Headers?
7) Which intake manifold?
8) Head flow numbers?
9) CR?
10) Emissions requirements?
11) Can you reprogram the computer for this cam?

There are certainly others to ask, but by this time I pretty much knew where I was heading based on how he answered those questions.

 

So it looks like I get a thumbs up from everyone? It was a toss up between this one and a GM "847" this one looked to be more "nitrous friendly". just a little less lift.
Thanks guys

 

Nobody knows the cam better than the cam maker. Comp Cam tech support has never left me hanging, and I have never called GMPP about parts so I don't know if they could help you out with one of their cams. CALL and see what they say. 30 more people can give you a thumbs up too but at least call.

Oh and a nitrous specific cam is made by most companies. Comp and Crane had cool off the shelf pieces last time I looked. Comp's roller nitrous grinds are really aggressive like the XE line and you could probably get setup with one of those and have more lift overall while still running 1.5 rocker arms.

Is there a perfecntage of how much faster the valve accelerates off of a 1.6 vs. 1.5? Maybe a G load or something? haha

 

Heres a GREaT link that explan's rocker arms and what ratio changes effect...read on

http://www.hotrod.com/techarticles/43418/index4.html

 

Jeff, know anything about selecting a supercharger cam? I could sure use some help. I'm looking for something on the "big" side too.