Longer push rods ? - Page 3

Reed Granrt · 09-05-2011, 05:06 PM

Quote:

Originally Posted by danny waters sr

I usually shift at 6500 and now i shift at 6900 and still pulled good . Before it would slow at 7000 shift..
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....

Danny
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

Greg Reimer 7376 · 09-06-2011, 08:55 AM

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.

danny waters sr · 09-06-2011, 01:01 PM

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.

Robert Simpson · 09-06-2011, 01:37 PM

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

Reed Granrt · 09-06-2011, 02:13 PM

Quote:

Originally Posted by danny waters sr

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.

Danny
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

Bill Bogues · 09-06-2011, 09:51 PM

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.

Greg Reimer 7376 · 09-07-2011, 08:51 AM

Quote:

Originally Posted by danny waters sr

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.

I think I would be tempted to try a .150" long pushrod before moving the cam around. That would bring the lift near to optimal . Do that, race the car, then try moving the cam around. Good luck again!

mannymen · 09-07-2011, 10:01 AM

This is the most interesting thread I've read on this site in a number of years. Very Nice!!!

Reed Granrt · 09-07-2011, 11:15 AM

Quote:

Originally Posted by Bill Bogues

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.

Bill
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

Greg Reimer 7376 · 09-07-2011, 12:05 PM

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.

09-06-2011, 08:55 AM	#22
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,136 Likes: 172 Liked 705 Times in 219 Posts	Re: Longer push rods ? 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.

09-06-2011, 01:01 PM	#23
danny waters sr VIP Member Join Date: Apr 2007 Location: lagrange,nc Posts: 2,224 Likes: 1 Liked 0 Times in 0 Posts	Re: Longer push rods ? 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. __________________ Danny Waters, Sr / 73 Duster "340"

09-06-2011, 01:37 PM	#24
Robert Simpson Senior Member Join Date: Aug 2004 Location: Jacksonville, Florida Posts: 808 Likes: 7 Liked 20 Times in 12 Posts	Re: Longer push rods ? 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

09-06-2011, 09:51 PM	#26
Bill Bogues Member Join Date: Apr 2005 Location: Bethany La. Posts: 323 Likes: 96 Liked 169 Times in 53 Posts	Re: Longer push rods ? 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. __________________ Bill Bogues 4696 STK

09-07-2011, 10:01 AM	#28
mannymen Senior Member Join Date: Apr 2003 Posts: 728 Likes: 5 Liked 13 Times in 7 Posts	Re: Longer push rods ? This is the most interesting thread I've read on this site in a number of years. Very Nice!!! __________________ N/A

09-07-2011, 12:05 PM	#30
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,136 Likes: 172 Liked 705 Times in 219 Posts	Re: Longer push rods ? 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.