Longer push rods ?
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. |
Re: Longer push rods ?
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. |
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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 |
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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.
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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 |
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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. |
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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 |
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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.. |
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Danny, it's been my experience on a small block with 1.5 rockers .100 is .007 more lift.
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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 |
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I have come to the conclusion that the typical OEM mass produced, union labor assembled typical car engine is the most forgiving invention made by mankind. Almost all of them run quite well, some in the face of incredible abuse, others with almost nonexistant maintenance , and practically none of them are anywhere near right. In considering all of this, they truly are an amazing device!!
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I totally agree with you on the ability of engines to run under about any circumstance.. But I always wondered how friends could purchase 2 cars just alike and one would always out run, out perform, out gas mileage the other. And after many, many years of disassembling these engines , I finally understand why this can happen. Also I clearly understand now why some racers are always faster than others when both seemingly have identical setups and packages. Attention to detail, attention to stuffing the envelope, and more important than anything, the ability to think out side the box to details. Now I dont want to include the acid porting and those things, but I mean just attention to detail and ability to THINK. Look how long the first roller rocker built by Harland Sharp went until some man by the name of Jenkins figured out it was designed wrong. You know sumtin, even now at his age, he thinks outside the box. I just luv them tenna shoes and plaid pants he wears. Ridicule, no way. Man still exploring the world as he sees it. Thanks yall for my dissertation. PS. I would shore like to talk more about learning and thinking reed |
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Maybe its good for us. I have the idea that if I didn't learn something today,I wasted the day. Learning isn't just for the young people.
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reed |
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Setting them at zero like you do when you roll the cam to check the lift.
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I am sorry I didnt ask the question correctly. Did you set the rocker arm geometry to zero(at half lift) before you installed the longer pushrod. I have seen variations on how much lift you get with the longer pushrod and I was trying to understand why. Sorry if I didnt make my self clear. Crap I just realized you may have answered it correctly any how. Reason I was asking I have a big block I am checking now with 2 different camshafts. One picked up .009 and the other picked up .004. I just pulled both and going to graph the lobes but even then that is a large difference between the two. have you seen that before reed |
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Well , i tried the 100 longs and the car ,with weather conditions at Darlington has picked up about 5-7 hundreths.....Weather was nasty and humid and car ran times like it did in 70 degree weather and 1700 ft of air. it was over 90 degrees and over 3000 ft of air and way humid...I was very happy with the results and can't wait for some good cool weather...
Now looking for a few more tricks ,...? |
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You may also find you need to make minor tuning changes to compliment what you've found. When you make a discovery like you have, you often need to check your tune up to see if you need to make changes. |
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We have spring pressure low because engine was new and it ran so consistant we never raised the spring pressure to were we had originally checked at...Next i am going to to shim springs 30 and try that . I know this will help the flatness i have over 7200 .We already checked it for coil bind before when we had engine on stand. If this helps on the higher rpm ,we will then take the 538 gear out and go lower on it. I can only get a 28" tire under the rear(i guess because it is a 4-door and is very tight in the rear tire compartment. I run a 26" tire for the 1/8 and a 28" for the 1/4...I don't know if i want to try a 557 or a 586. I still need to make through the 1/4 mile.....Thank all of you for your help and suggestions as it has been a help to me.....I am thinking now in good weather it will run mid 7.50's in the 1/8 with the push rod change alone.... |
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Now you have really got into this tweaking thang. May I make a suggestion, pull one pushrod"either the exhaust or intake", and go back to your starting length. Find out what the motor really likes, more intake or more exhaust or both. Once you see which it likes, try even more length on the one it prefers. Once you get what you want then have you a cam grind made with the new info and start checking all over again. You can only get so much out of a puhrod tweak and then it goes backwards as the area under the curve diminishes substantially. Man u is gittin there reed |
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While spending time in the pool after eating on a really hot humid day,I had the conclusion that the improvement noted by just a pushrod change must have had way more to do with the increased duration and overlap(especially since the engine made more RPM) than with just the increase in lift. 20 or 30 thousandths in lift alone wouldn't have done that. The only two concerns that I have are that the lift may exceed legality, getting you tossed in a tear down, and the second concern is piston to valve clearance. What happens to the duration at approximately .120-.130" lift where PtoV clearance is tightest? It would be an interesting thing to compare that figure with different pushrods. Testing the car with different pushrods would be the ultimate way to determine if desired results are being achieved. After all, the only accurate dyno is the drag strip.
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Checked the lift after the 100 longs were installed and cam checked fron 385-389 and before was 374-376. that part will still pass tech.
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Danny, the cam in the car, is it advanced or retarted from where the manufacture recomended? If not then you might want to move the cam around some. I have learned if the car likes it when you advance/retard the cam more than 4deg then you need to change the profile, duration etc. Great to hear your gains. Keep up the good work.
Robert |
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It is not normal to pick up that much lift with a .100 long push rod although not unheard of. But that would normally say you may still be off on your rocker geometry and if so, you would greatly see an enhancement with a lobe redesign. I think Greg (while in the swimming pool drinking his latte) may indeed be correct, time to look at that cam design. Motor definitely wanted more cam than you were first giving it. Get you rocker arm geometry up so you can see what area under the curve you really have before you look at the next design. Also check your rockers to see what their ratio really is. Seaperated them out, 8 shortest and 8 longest and pick what you want them on exhaust or intake reed |
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Danny, In our stocker 350's every time I"ve went from a stock pushrod to .100 long I always picked up .007 to /008 lift. With a long pushrod i would also check the rocker arm contact point on the tip of the valve and make sure it"s not running too close to the outside of the valve tip. Ideally you would want the contact point of the rocker arm to be centered on the middle of the valve tip at mid lift. Hope this helps.
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This is the most interesting thread I've read on this site in a number of years. Very Nice!!!
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I hope you do not mind me adding to your input and I will apologize if I miss speak. You are indeed correct in that ideally you want the contact point in the middle of the valve, BUT that has nothing to do with proper rocker arm geometry. The camshaft creates circular motion that transfers that circular motion to a push rod that is moving vertical. It then converts back to circular motion thru the rocker arm which in tern converts back to vertical motion by pushing down on the valve. Proper rocker arm geometry will give you the shortest scrub pattern across the valve. And as a result of this shortest scrub pastern, the engine and valve train uses the least amount of force to push down the valve. I have seen people miss the geometry so bad that it took 20 ft.lbs more force to rotate the engine thru a revolution. WHERE the rocker pushes down on the valve doesnt matter as long as the scrub pattern of the rocker doesnt go off the valve or damage the valve tip. It must stay in full contact of the tip. Where it pushes down on a valve does not wear the guide any more than to be in the center. Remember you are converting circular motion to a straight line motion. But the length of the rocker scrub will wear the valve guide and or valve and generate more friction than is needed. The length of the scrub pattern is the result of geometry, so my opinion is to get it correct when possible. Dagone it Bill, I sound like a know it all. I hope I learn sumtin every day and to day is early so even at 64 I gots plenty of time to learn a lot today. You can duplicate this and you will be surprised at the forces that can be generated in the valve area. You can be surprised at the forces you can take off the cam, rocker arm, and pushrod |
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Back in the bad days of 1973-77,I worked in a few Chevy dealers,doctoring the worst cars ever built in this country when they were new, and the thing that happened a lot were valve guide and valve train failures. Seats used to disappear, guides went away a lot, camshafts went flat a lot, and it was a mess. Everybody blamed the new lead free fuels for it, and the valve face and seat erosion seemed to reflect that. Also, when you run a motor with about 22 degrees total timing and with a cam that is ground late like all those were, exhaust temperature was through the roof. Here's the good question--why didn't all those engines do that since they were operated on the same fuel?As far as the guide wear, the SBC used to shove the valve sideways as it was opening it. That would indicate side loading caused by improper rocker arm and valve train geometry.Since these were mass produced,union labor assembled engines on an assembly line with a broad range of production line tolerances, some obviously had the valve train geometry right on the money, some probably weren't even close.The comment of the extra torque needed to rotate an engine with valve train issues seemed to point that out. Stock eliminator motors are an exercise in mechanical refinement,from wall texture and accuracy, ring seal, compression, and the valve train. Add it all together right, you've got a winner. Those new cars made in that time frame were all losers for the most part.
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Well, I pulled that 327 apart and discovered some problems, so I bought a Dart block, took it and the internal parts to Greg Luneack. I'll get back a properly bored and honed short block assy ready to assemble. We'll see if the valve lift measurements are the same, or if any difference in the block dimensions exist, and have affected the valve train geometry and the valve lift figures any. I think I'll order some more push rods and see if I can fine tune the lift dimensions that way,as well. We had such an interesting thread going that it motivated me to put more time and research into this project to see what improvement and what results might occur. I'll be back with the results.
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Once you get your lift in the ballpark, try changing pushrod lengths and rotating the complete assy. minus plugs. You'll be suprised. And the more valvespring pressure you use, the bigger the difference will be. |
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There is only one push rod length that will maximize the area under the curve that was ground into the camshaft. You can shift characteristics of the camshaft by changing the length of the pushrod. You can shift the area under the curve, but it will REDUCE the total area under the curve and it will change the torque to rotate it. If you shift the characteristic by changing the length and the engine likes it, then you have an opportunity to regrind and make additional gains. What you would really want is to maximize the amount of power and reduce the engine rotation friction to a minimum. If you do that, you WILL get a double whammy on power gain. reed |
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I started this topic and have made the changes and at first i saw a gain..
Since then ,i had alifter come apart and found every part of it in lifter tray (lifter come un-locked)... I have since ordered a new set of lifters (not shubeck type). I kept the long push rod when i changed the lifters. Now i am knocking off the rocker arm in high gear in the 1/4 only.(not rollers ) Is it possible the old lifters were worn out and that is in fact why the longer push rod picked up the performance ? Is it possible now with new lifters that i have this problem because of the longer push rods? I have never had this problem til i installed the new lifters....Any suggestions or answers please ? Thanks in advance...... |
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Check the plunger height in your new lifters compared to the old ones! You just may have to start all over again.
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I put longer push rods in to try to get more lift and found that i too knocked off rockers. The reason was that the jam nut did not screw on the stud far enough. To get full lift i ended up ordering a cam with a bigger lobe and it seemed to fix the lift problem.
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Got back to trailer and removed valve cover and rocker had come off.(polly -lock still on stud) not broken either. checked push rod and it was ok .i took the polly lock loose with my fingers and hex lock had not moved so i screwed it back on til it jammed (or locked) then i checked valve ajustment and was on the money. No problem til i installed new lifters.i will check the inside height later this week.i thing the longer push rods with new lifters could be the cause. |
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So what you're saying is that the rocker jumped off of the pushrod, without the poly lock backing off?
Are you running guide plates, or self aligning rockers? With self aligning rockers, you could have enough flex to allow the rocker to pivot sideways and jump off of the pushrod, you'd be lucky not to un-key a valve. It sounds as though you have reached the point where you have problems with flex and stability. Are the pushrods good chrome moly pushrods, with the thick tube wall? For example, 5/16" x 0.100" wall, or 3/8" x 0.125" wall? |
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Yes i am running guide plates Yes it has3/8 comp push rods and comp replacement rockers Never did this happen with the old lifters and the longer pushrods |
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