Ratio rockers stock cam?

Dsx_fab

Member
I’m sure it’s been discussed but i don’t know how to search a topic like this. I was looking at a cam upgrade but I was curious what results would be with 1.3:1 rockers alone, with a stock cam. This is on a Honda clone. I understand it will only increase lift and not duration, but I just wanted to hear pros and cons of a setup like this.
 

flattop1

Dawg 89
Quick and simple .
Things could possibly collide .
Spring change may be needed .
 

mike97760

Premium User
Seeing this is stock and guessing you will be making improvements in little steps I would save this for the end. Carb, flywheel with better timing or a safe stock flywheel with offset keys, valve springs and exhaust would make more sense. Then a cam, then possibly the rockers. And somewhere in there think about a better cylinder head. Oops I forgot, get a billet rod or have the stock rod properly clearanced.
 

kartboy63

Member
I’m sure it’s been discussed but i don’t know how to search a topic like this. I was looking at a cam upgrade but I was curious what results would be with 1.3:1 rockers alone, with a stock cam. This is on a Honda clone. I understand it will only increase lift and not duration, but I just wanted to hear pros and cons of a setup like this.
it will increase duration, what a lot don't understand is that a ratio rocker will increase the ratio all the way around the cam profile not just lift, think about it, your adding 30% with 1.3 rockers every where the lifter rides on the cam, it don't know just lift, if that makes any sense. It will prob need more valve spring than stock ones, and make sure not to hit the piston.
 
it will increase duration, what a lot don't understand is that a ratio rocker will increase the ratio all the way around the cam profile not just lift, think about it, your adding 30% with 1.3 rockers every where the lifter rides on the cam, it don't know just lift, if that makes any sense. It will prob need more valve spring than stock ones, and make sure not to hit the piston.
Don't know how to exactly explain it but it's called duration under the curve.
 

DynoDon

Moderator
Duration is built into the lobe. I have a hard time understanding how changing the rocker changes duration.
 
Duration is built into the lobe. I have a hard time understanding how changing the rocker changes duration.
From what i understand since a higher ratio arm accellerates the valve to total lift quicker if shown on a graph it effectivly holds the valve open a small amount longer hence the duration increase . It is a thing and it needs somebody with better explanation skills than me.
 

01ron

Member
Ratio rockers only affect life from my understanding. Lift just accelerates faster but total duration (from zero lift) is the same. Lift also decelerates faster giving you the same duration (from zero lift) as stock rockers. The only way duration would increase is if you are measuring duration at a certain lift (for instance .050 lift). Then, yes you would reach .050 lift sooner and .050 lift later with rockers that are a larger ratio then stock. Therefore, duration at .050 lift would be a greater value.
 
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DynoDon

Moderator
Sorry, I don’t see that. If there is a duration built into the cam at .050 or .200 it can’t change if you change ratio on rockers. Duration is built into the cam. I am not saying anyone is wrong but I just can’t visualize it. I will take a look at it when I get my 308 off the shelf soon just to see.
 
Sorry, I don’t see that. If there is a duration built into the cam at .050 or .200 it can’t change if you change ratio on rockers. Duration is built into the cam. I am not saying anyone is wrong but I just can’t visualize it. I will take a look at it when I get my 308 off the shelf soon just to see.
Higher ratio rockers will not change "advertised" off the seat duration. It will change duration at .050, .200, .150 or any lift point to lift point at the valve. Think of it this way. With a higher ratio rocker the valve will reach a .200 lift point at the valve sooner and it will take longer to drop back down to back down to .200 at the valve.. If i were measuring duration at the valve with a true 1:1 rocker i would reach .200 lift a the valve about when I reach .200 lift at the lifter. With a 1.3:1 rocker I would reach .200 lift at the valve when the lifter has only lifted to about somewhere near .150 lift. Using a Dyno CL3 cam as an example, duration would increase from about 82 deg duration @ .200 lift at the valve to somewhere near 140 deg duration @ .200 lift at the valve even though the lobe stays the same. The numbers i provided are based on simple math and the lift points published by dyno cams. These values are only approximate with some rounding errors and they ignore any valve train geometry. The Dyno CL3 cam reaches .200 lift at the valve somewhere near 73 deg ATDC on the opening side and somewhere near 25 deg BBDC on the closing side with 1:1 rockers. With 1.3:1 rockers on the same cam the valve reaches .200 lift at the valve somewhere near 44 deg ATDC (at or near the .150 lift point of the lobe) on the opening side and somewhere near 4 deg ABDC on the closing side. This gives a delta of about 58 deg of duration at .200 lift at the valve. Basic engine builder 101 knowledge. But I could be wrong.
 
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DynoDon

Moderator
Even though I am a “basic engine builder” that’s been doing it for 40 years, I have not played with ratio rockers so I have learned from this post. What you say makes sense.
 

DynoDon

Moderator
No problem
 
My analysis above (post #8) only applies if you are checking lift on the valve spring retainer.
To see what the rocker arm change did you would either check it on that end of the rocker or the retainer, i never check anything at the lifter side. I agree with KB63 and CH it increase duration over the whole curve, its harder to measure at low lifts .010-020 range but you would be able to see it as the numbers get greater.
 

01ron

Member
As long as you are measuring on the valve side of the rocker arm, you could measure either right on the rocker arm or the spring retainer and they should be very close. Just don't measure on the pushrod side of the rocker arm because that would be measuring only the cam profile (negating the ratio rockers). Of course, this all applies only if your definition of duration is at a measurement other than "off the seat ". At "off the seat", the ratio rockers are not affecting lift. Duration measurements taken at .020 or .050 or any other lift height, the duration will be higher (longer).
 
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