Longer push rods ?

[danny waters sr]

Say a 399 lift stocker cam checks between 374 and 376 lift on each cyl with stock length push rods.
Then you put a longer push rod and can check 392 to 395 lift. (with no clearance problems)
How much performance gain would i expect et wise and hp gain if any ?
Best et is 12.18 in the 1/4 and 7.65 in the 1/8 mile.

[Alan Roehrich]

You may or may not see a gain. It depends on what it does to the over all lift curve.

A rocker arm, especially a stud mounted rocker arm, is a variable ratio lever. It will never be the same ratio throughout the lift curve. Now, by getting the lift you're supposed to get, you are correcting the ratio and the geometry at maximum lift, and losing the least amount of motion there. You may have decreased the ratio elsewhere in the lift curve, for example, down around 0.100" to 0.200" lift.

The only way to know for sure exactly what you've done is to plot the curve on a graph for each pushrod length. Then try both, at the track, on the dyno, or both.

[danny waters sr]

Thanks Alan,
I have 200 longs and will try them first since that is all i have..
I am trying to reach my goal of an et in the 11 second range ,even if it is a 11.999
I am running the 896 head on the 283 right now ,but plan to fix a set of 520's

[R. Thorne]

Be careful with different lenghth pushrods (upsetting valve train geometry and attending consequences). IHRA allows roller rockers, I think, and a used set of 1.5 may get you that additional lift without too much cost. They should also help with rocker deflection. Also, consider rocker arm studs with a generous radius to combat flex there. If you decide against roller rockers, there are certain things that can be done with stock rockers to improve their function. Ron.

[Reed Granrt]

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

[Greg Reimer 7376]

Got splainin' to do, so with my limited technical expertise and comprehension skills, I'll delve into my experience and try and help.
I built a 327 Stocker motor some time back, and it took 040" off the deck of the block to get it right, and around .078' from the heads, and all this with an .017" head gasket. This, of course, brought the head down a lot, and with each chamber volumn good by a half a CC,things are just about optimal.This, however, has the effect of shortening the push rods approximately .125".When I checked valve lift, (spec calls for .390" intake,.410" exhaust) I used a stock length OEM pushrod and a test lifter shimmed to the same height as the Smith lifters the engine was to get.Lift checked out to be -.005"- +.014", clearly over on around ten valves. A set of .150" short push rods brought the max lift down around .020" consistently with all 16 valves. i used Elgin 7/16" rockers and ARP 7/16' BBC studs. A set of pushrods .100" short would bring the lifts very close to optimal.One essential item never to forget is to make sure the slot in the rocker arm has room at max lift so as not to bind up the valve train and break studs, rocker arms,and push rods. If you have an engine(like we did) that exhibited numerous valve train failures, start checking there. Try a shorter push rod and see if it loosens things up.
I have seen and used different length push rods between intake and exhaust valves in order to adjust lift specs accordingly. Stocker camshafts are ground with a higher level of precision than most other performance camshafts, but that doesn't mean you can assume ANYTHING.The numerous machining processes necessary in the construction of any stocker mother, as previously mentioned, are enough to take it WAY away from the OEM configuration.Practically nothing measures out OEM anymore,it's essential to have a plan B,C,or whatever it takes when these situations surface. Your comparison of a rocker arm to a device swinging in twin arcs at once is a good way to put it. A cylinder head guy needs to be able to visualize this in order to work with it.Your descriptions of all this indicates your level of understanding of all this is quite high. A real reminder of the degree of departure from OEM will settle in when,once the long block is assembled,will be when you try to install your intake. Sometimes, now that the engine is narrower, the intake is now too wide, and nuttin' fits, its necessary to flycut .060-.090" off both gasket surfaces in order to facilitate installation. Then,when that's over, see how much too long the distributor is. At least, aftermarket spacers are available for that.
Thanks for the mentally stimulating discussion material.I like to think once in a while.

[Reed Granrt]

Originally Posted by Greg Reimer 7376

Got splainin' to do, so with my limited technical expertise and comprehension skills, I'll delve into my experience and try and help.
I built a 327 Stocker motor some time back, and it took 040" off the deck of the block to get it right, and around .078' from the heads, and all this with an .017" head gasket. This, of course, brought the head down a lot, and with each chamber volumn good by a half a CC,things are just about optimal.This, however, has the effect of shortening the push rods approximately .125".When I checked valve lift, (spec calls for .390" intake,.410" exhaust) I used a stock length OEM pushrod and a test lifter shimmed to the same height as the Smith lifters the engine was to get.Lift checked out to be -.005"- +.014", clearly over on around ten valves. A set of .150" short push rods brought the max lift down around .020" consistently with all 16 valves. i used Elgin 7/16" rockers and ARP 7/16' BBC studs. A set of pushrods .100" short would bring the lifts very close to optimal.One essential item never to forget is to make sure the slot in the rocker arm has room at max lift so as not to bind up the valve train and break studs, rocker arms,and push rods. If you have an engine(like we did) that exhibited numerous valve train failures, start checking there. Try a shorter push rod and see if it loosens things up.
I have seen and used different length push rods between intake and exhaust valves in order to adjust lift specs accordingly. Stocker camshafts are ground with a higher level of precision than most other performance camshafts, but that doesn't mean you can assume ANYTHING.The numerous machining processes necessary in the construction of any stocker mother, as previously mentioned, are enough to take it WAY away from the OEM configuration.Practically nothing measures out OEM anymore,it's essential to have a plan B,C,or whatever it takes when these situations surface. Your comparison of a rocker arm to a device swinging in twin arcs at once is a good way to put it. A cylinder head guy needs to be able to visualize this in order to work with it.Your descriptions of all this indicates your level of understanding of all this is quite high. A real reminder of the degree of departure from OEM will settle in when,once the long block is assembled,will be when you try to install your intake. Sometimes, now that the engine is narrower, the intake is now too wide, and nuttin' fits, its necessary to flycut .060-.090" off both gasket surfaces in order to facilitate installation. Then,when that's over, see how much too long the distributor is. At least, aftermarket spacers are available for that.
Thanks for the mentally stimulating discussion material.I like to think once in a while.

Greg
This was nice to see. Most people dont want to delve into the real rocker geometries. If you install a adjustble pushrod and set the rocker arm geometry to where it really is and then take graph paper(so you can see the effect) and plot the area under the curve, there will only be one push rod length that will give you the maximum area under the lobe curve. Here is where I see many people ASSume wrongly and that is the stock pushrod was indeed at the proper geometrey before you did any machine work. Very very wrong and the reason is that even today many of our Eiganeers dont know how to get the pivots points lined up and perpendicular to the valve. Many assume where perpendicularity to the valve is. Also with a shoe style rocker(stock) versus a roller it is totally different. The rotating point on a roller rocker is at a different point. Also for a shaft rocker, it is slightly different, but the principle is the same. If you were to check each rocker arm, the geometry is slightly different on each one. AS I stated earlier, moving the pushrod length will change where the area under the curve is.
Greg thank you for helping the understanding
reed

[danny waters sr]

Don't have access to a dyno ,but will test on track. After reading all this , i am going to start with a 100 long instead of the longest..... Thanks for your input on this.
I am not very hi-tech as a lot of you guys ,so i been doing old school and have been able to pick up a few hear and there.... Thanks again..

[Greg Hill]

Danny, it's been my experience on a small block with 1.5 rockers .100 is .007 more lift.

[Reed Granrt]

Originally Posted by Greg Hill

Danny, it's been my experience on a small block with 1.5 rockers .100 is .007 more lift.

Greg
You are correct in that most of the time by lengthening the push rod will add lift because you have made the max lift to come in at a later time. You have used the extra length as a tuning aide to move the max area of the curve where you wanted it. I have seen motors actually slow down when doing this because you have moved that portion of area under the curve to a different spot and the engine may or may not like it. If it helps, then have your next can ground with that area added to the camshaft instead of the pushrod and start back at zero geometry. This is the tweaking of horsepower that us racers are so good at maximizing HP with old setups that many people have run for years and you continue to beat them because you do not mind changing things. This by all means doesnt mean that this is the gospel but you have to start some place to arrive at the end.
reed