IMO it's because the exhaust flows as much as the intake even with the 1.3 rocker on the intake only. I don't know exactly what it would hurt to run on both the intake and exhaust though? Nor do I know how to pick between the 1.2 or the 1.3 ratio rockers. Both increase lift, but more lift is better, right.
Stout racing has the 1.3 rockers(champion style) I would like to try. Kind of pricy. But requires a 1.3 on both intake and exhaust.
Rockers
Stout racing has the 1.3 rockers(champion style) I would like to try. Kind of pricy. But requires a 1.3 on both intake and exhaust.
Rockers
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don't guess at this stuff... you have to know what your head flows on a flow bench. if your cam is not lifting the valve high enough to get the max flow from your testing on a bench then higher ratio rockers is one way to achieve that. the other way is to change the cam to a higher lift. keeping in mind what the degrees the cam opens and closes will let you know what kind of rpm range your able to run, which coinsides with having enough air flow to do that. having more lift is not always better, you can lift it to the moon if you want but if the head does not flow at those higher lifts you will make less power not more.
So what is the advantage of only running one on the intake? Does the exhaust runner always outflow the intake? In my mind increasing the lift on the intake, increasing air intake, wouldn't that same amount of air need to leave on the exhaust stroke, if not exhaust gases would still be in the chamber after the exhaust valve closes.
Is the reason only on the intake maybe due to the fact that the piston is coming up as the valve is closing?
Is the reason only on the intake maybe due to the fact that the piston is coming up as the valve is closing?
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First off Nate's answer is spot on. Next exhaust does not flow more than intake on any head I have checked and I have checked a lot. That said the exhaust on some stock heads flows almost as much as the intake and generally for a performance engine it only needs to flow around 70% of the intake. This is a approximate value and can vary depending on engine parameters and exhaust design. The larger the valve the more lift required to reach (.25 x valve diameter) at that point the valve open area is equal to the valve head area. So if you have a larger intake valve and stock exhaust size then it may make sense to have more lift on the intake than the exhaust. Adding lift via ratio rockers to the exhaust may not hurt but if it is not needed just causes more valvetrain stress and would need more spring all things being equal to prevent early valve float.
Spot on ole4 I believe the flow of exhaust should be some were in the 70-80% range with a single pattern cam. Good information. Looks like I will have to experiment with this now once I build a motor. When I had the cam ground for my street trip motor in my truck I had more duration ground in to it than what it needed on purpose. I did this for 2 reasons, #1 I plan on adding NOS to it which dose not pertain to us but 2 although it sacrifices mid range and a little low end torque it extends the RPM range and creates more top end HP were the motor would normally drop off power. I have not seen what the intake and exhaust flow on these little motors but just looking at valve size I can see how higher rocker on intake would benefit power by balancing flow. When I put the high ratio rockers on my motor I will do intake first and exhaust second and take a video of the results for you guys. I will do one of just the exhaust with the high ratio too. It will be late summer or early fall when I do this but I will do a video of the results for you all.
