Longer push rods ?

Reed Granrt · 09-01-2011, 02:59 PM

Danny
If you do not mind I would like to tackle this subject with my opinion and believe me this is all it is, my opinion. Under normal camshaft lobing, proper rocker arm geometry will give you the maximum area under the curve. Stock camshaft rules doesnt always achieve that but it is still where you should start. Question from most people is how do you get proper rocker arm geometry to start with. Many theories, but I feel that is only achieved when push rod length generates a straight line thru the two rocker pivot point and at half lift is perpendicular to the valve. This will mean that as the rocker goes thru its arc, it will have maximum area under the curve as it travels too half lift and it will have maximum area under the curve after it goes thru mid point lift. If you get your mid point lift and the two pivot points lined up perpendicular to the valve, this will be your theoretical zero point of proper rocker arm geometry. From here is where you start using push rod length as a tuning aid. If you shorten the pushrod from your zero, you will move your area to a later point. If you lengthen the push rod, you will make the area come in earlier. Try doing both on a dyno. Go shorter and longer. If one way or the other changes your power curve, then tell your cam grinder what you did and how the motor responded. Now remember you cant race a dyno. The dyno curve will only be an indicator. You will need to try on the track also. With this info, the cam grinder can tell if the cam should be ground smaller or larger. If the cam is a solid lifter cam, then lash becomes another indicator that can tell if cam is too large or too small and you can tweak it on next cam grind. Do not guess at this, make sure you know the changes you have made but verify where your zero point is. Make sure you stay with only one cam grinder during this trial as swapping from one cam grinder to another is fruitless. Also pay particular attention to the O2 sensor as it will possibly change as you move the rod lengths around.
Dog gone I just backed up and reread this and I dont know if I understand it myself. If you have further questions, please PM or ask on here and I will try to splain it better.
reed

09-01-2011, 02:59 PM	#5
Reed Granrt Member Join Date: Jul 2011 Location: Murfreesboro, Tn Posts: 149 Likes: 0 Liked 1 Time in 1 Post	Re: Longer push rods ? Danny If you do not mind I would like to tackle this subject with my opinion and believe me this is all it is, my opinion. Under normal camshaft lobing, proper rocker arm geometry will give you the maximum area under the curve. Stock camshaft rules doesnt always achieve that but it is still where you should start. Question from most people is how do you get proper rocker arm geometry to start with. Many theories, but I feel that is only achieved when push rod length generates a straight line thru the two rocker pivot point and at half lift is perpendicular to the valve. This will mean that as the rocker goes thru its arc, it will have maximum area under the curve as it travels too half lift and it will have maximum area under the curve after it goes thru mid point lift. If you get your mid point lift and the two pivot points lined up perpendicular to the valve, this will be your theoretical zero point of proper rocker arm geometry. From here is where you start using push rod length as a tuning aid. If you shorten the pushrod from your zero, you will move your area to a later point. If you lengthen the push rod, you will make the area come in earlier. Try doing both on a dyno. Go shorter and longer. If one way or the other changes your power curve, then tell your cam grinder what you did and how the motor responded. Now remember you cant race a dyno. The dyno curve will only be an indicator. You will need to try on the track also. With this info, the cam grinder can tell if the cam should be ground smaller or larger. If the cam is a solid lifter cam, then lash becomes another indicator that can tell if cam is too large or too small and you can tweak it on next cam grind. Do not guess at this, make sure you know the changes you have made but verify where your zero point is. Make sure you stay with only one cam grinder during this trial as swapping from one cam grinder to another is fruitless. Also pay particular attention to the O2 sensor as it will possibly change as you move the rod lengths around. Dog gone I just backed up and reread this and I dont know if I understand it myself. If you have further questions, please PM or ask on here and I will try to splain it better. reed