Thread: Best 1.7 rockers for a VS cam

What are the best 1.7 rockers to add along with my VS cam to give m an XP cam lift?

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You want lift like XP cam? Why don't you just get a XP cam instead of a vs and 1.7 set up? Would be cheaper too...

Yea but i got the vs cam real cheap a while back and just got done installing it.

The only way to get more lift is to increase your rocker arm ratio to 1.7. That will increase the lift at the valve. You won't get any change in duration or LSA. Doing the math, there isn't a ratio that is available that comes close to the XP. The XP also has a much different lift profile than a VS. The VS has 0.005" more intake lift than exhaust lift where the XP has 0.016" more exhaust lift than intake lift. There's no way to get similar numbers by changing the rockers.

Originally Posted by ExLimey

The only way to get more lift is to increase your rocker arm ratio to 1.7. That will increase the lift at the valve. You won't get any change in duration or LSA. Doing the math, there isn't a ratio that is available that comes close to the XP. The XP also has a much different lift profile than a VS. The VS has 0.005" more intake lift than exhaust lift where the XP has 0.016" more exhaust lift than intake lift. There's no way to get similar numbers by changing the rockers.

Apparently no one makes any rocker ratio more than 1.70:1 anymore?

^^Ditto.

So since typical math fails me I'm just gonna guess here...

Stock Cam: .411/.408
VS Cam: .512/.507
XP Cam: .520/.536

.512/1.6 = .320*1.7= .544
.507/1.6 = .317*1.7= .539

Now if the XP has final lift specs of .520/.536...isn't .544/.536 (which incase you didn't follow the peak intake or exhaust lift...divided by stock rocker ratio...then multiplied by the new rocker ratio) LARGER?

But apparently math doesn't work on GPF.

Apparently people said it doesn't exist so I won't argue when I said they were 1.66 years ago.

People said: Y u so dumb.

So, I left the gas off that fire.

So I agree with ZZP?

Who the **** divided by zero.

ClubGP Message Forum troubleshooting

Swiggles:

"because stock arent rollers they will actually have a variable ratio and can extend to 1.78 or something like that which is why there is power loss from 1.7s."

Tengis:

"Rollers cannot produce the same lift and power as stock rockers. Stock rockers are in effect variable ratio and will product FAR better performance than any roller. The ratio of the stock rocker increases with cam size used as well. Some people are stuck in the mod mentality tho and have to run after market parts to feel like they're doing it right."

"A rocker works by amplifying the lift of the cam. If the pushrod cup is 1" from the rocker bolt and the 'tip' of the rocker is 2" from the rocker bolt, then your rocker is a 2.0 ratio rocker. If you cam had .300 lift, you would now get .600 valve lift.

A roller rocker like this moves on top of the valve tip. So say at mid lift the 'tip' of the roller is centered on the valve. At valve close the rocker's roller tip will be further away from the center of the valve tip surface. At full open it will be closer. The distance from the center of the rocker (bolt) to the rocker tip (roller) is always the same. The rocker just changes its contact point on the valve tip but the distance from rocker center to roller tip never changes. Hence a 1.6 ratio rocker will always be exactly 1.6

A stock rocker is not like this.

Look at the tip of a used rocker. See the shiny part? You can see that the tip of the rocker is worn over maybe .250". This is because as the valve opens, the rocker changes contact point on the valve. And actually a stock rocker can be setup to be 'centered' on the valve through duration better than a roller. Anyway the rocker essentially gets longer the further you open the valve. So in my example above of 1" from pushrod cup to bolt and 2" from bolt to rocker tip. You may actually get 1.9" from bolt to tip with valve closed and 2.1" with the valve open.

Now that you understand this, how does this work in the real world? Well, the stock rocker is a low ratio when the valve is closed, this is easy on the valve springs and keeps valve float away. This is why you can run 1.9 mod'd rockers on stock springs to ~6000 but 1.9 rollers will float at ~5600rpm. It's also why cars with stock rockers make more power consistently than cars with rollers. Doesn't matter if you're talking about 1.9's on a stock cam or 1.6's, 1.7's on an aftermarket cam.

The change in ratio is actually about .3. So a stock rocker on 130# springs/cam is going to be ~1.5 ratio closed and ~1.8 open. You do lose lift from deflection tho. Probably 40+ thou on that setup which still isn't enough to be lower than a roller."

Sounds reasonable to me.

I still made great power with the 1.7s and the vs and didn't have any float issues.

I prefer roller rockers because you know just how much lift you will have.