What's up dudes? My car is running like $hit now because I have a collapsed lifter or two. It happened two days ago. And the story goes like this. A year ago my buddy and I installed a set of TFS Twisted Wedge G1 heads that where stage 2 port by Total Engine Airflow in Bowling Green, KY. with a custom grind cam from Comp cams( 224,224@.050 and 528,528 liftw/112 LCA, but I had the heads mechined down to 58cc to keep the compression up because I have a ZZ4 engine and also I'm using .029 thick head gaskets to bumb the compression to 10.7 to 1. Anyway the Twisted Wedge design requires me to use two different size push rods for the int. and exh.. The stock push rod length on 87 and later blocks require you to use 7.200" length push rod for both the int. and exh. do to the factory style roller lifers, which was not all that bad for what I was doing. To make a long story short I decided to rush and I installed 7.150" push rods on both int and exh.. WELL AFTER USING THE PROPER TOOLS AND TECHNICS TO MEASURE PUSH ROD LENGTH. I realized that the exhaust push rods where TOO LONG by .300" for 12 months of driving a little over 8,000mi and what I really needed was 6.850" length push rod and the intake push rod was .150" TOO LONG and what I actually needed was 7.000" length push rod. All I do Know is that my custom ground cam has only .528" of lift on both the int. and exh., so however much more lift that gave my cam? I do not Know, But it was most definantly too much for my lifters . How much of a performance gain should I expect after I install the proper length push rod and Comp Cams heavyduty lifters for factory roller motors?The reason why I asked is because I ran a best of 12.83 @108 mph with a 1.72 60 ft., but after that run the cars performance went rock bottom at Raceway Park in New Jersy this summer at the GM High Tech Performance EFI shootout on 13 July 02 running only once with a 13.83 @ 91 mph. I also have a Mini Ram II, 58mm TB, 1 3/4 SLP headers, 3.70 rear, 3500 stall, all on a 88 Iroc sitting on a set of ZR1 wheels.

I appreciate all of your input on the topic. PEACE!

 

If you give it some thought this is quite simple.
Imagine the rocker from the side.
You´ll soon see that the point of impact for the rocker vs the valve is a tangential function.
Now..
The thing is where the rocker rests so to say,and this is very much a result of PR lenght-amongst other variables.
The thing is to use the most of the tangetial action for the first part of lifter motion.
This will assure that the valve comes off its seat fast,and thereby increase cylinder filling.
Now,this is NOT only a matter of above but very much too a Q of WHEN within the crank phasing the rocker meets these specs.
If for one live by the old adache of setting rocker lenght to maximize lift at 75deg ATDC.

How much of a difference?
Let´s just say that dry numbers won´t tell the whole story,altho torq will rise considerably from this move.
What the numbers won´t tell you is the diff in throttle response and how the engine picks up in general.
All in all getting PR lenght right is a fairly no brain deal with rather large outcome IMO.
I for one do NOT ever use the available "checkers",but instead make good use of a degree wheel and a 1" plunger dial indicator.

 

TOO LONG OF PUSHRODS

WEAR OUT YOUR VALVE GUIDES
CAUSE SPRING BIND
BEND PUSHRODS
FLATTEN HYDRO LIFTERS
CAUSE VALVE TO BE OPEN WHEN IT SHOULDNT BE...

 

explain please....why would a pushrod "checker" not work correctly. I thought the whole point of rocker arm geometry is to use the correct size pushrod so that the roller or tip of the rocker arm is constantly in the center of the valve stem throught the cycle or am i am mistaken?

 

385LT1, Racing,

Thanks for the info fellas. I guess maybe to you guys these questions are pretty dumb, but to me I'm learning something everyday thanks to web sites like this one. Again thanks for your help!!!!!

 

THAT IS 100% CORRECT...

COMP CAMS ON PUSHROD LENGTH

COMP CAMS PUSHROD LENGTH CHECKERS

CCA-7905-1 6.125" - 7.500"

 

Originally posted by 89ProchargedROC
explain please....why would a pushrod "checker" not work correctly. I thought the whole point of rocker arm geometry is to use the correct size pushrod so that the roller or tip of the rocker arm is constantly in the center of the valve stem throught the cycle or am i am mistaken?

What is 100% correct? Are you saying 100% correct that he is mistaken?

Quote: constantly in the center of the valve stem throught the cycle...

If you are implying thru the lift cycle, then yes, you are mistaken. This is not physically possible. The intent of is not to correct the poor geometry, which is not possible without hard part changes and relocating pivot points. What you attempting to accomplish with the 'checker' (or any othe form of checking) is to make the best of a bad situation. You are attempting to put the rocker tip in the center of the stem at half of the total lift. It moves/walks on either side of the center point 'thru the cycle'. This is the root of the geometry problem.

 

i just recently started posting on this board again.. now i remember why i quit...

People read too much into what i say..

He is correct in what he said, roller or tip of the rocker arm is constantly in the center of the valve stem throught the cycle) (this isnt rocket science for me, maybe for you or others i have run into recently...

i really dont think he cares how far the roller tip moves in .00000" throught a cycle.... he just wants it right...as does everyone else who doesnt have a degree in micro engineering.

But, your more than welcom to measure in hundredthousandths, the geometrical travel of the roller tip of a roller rocker arm perspectively throughout its motion throughout valve lift. That way you can call up comp cams and try an order pushrods they dont make... 7.23578" ......

comp sells push rods in increments of .005"

http://www.compcams.com/catalog/274.html

 

Secondly, what the h#$% are you talking about in the 1st place...?

to many of us "center of the valve stem" means 2 marks ,each made using machinist die, 1 mark open, 1 closed, if both are in the center (respectively, without going into rocket science)
Then your good to go...

But, im mistaken, 414 hp was mistaken..

 

Actually this has more sides to it than one would imagine.
One thing is geometry from a wear and tear view.
The other is what the geometry does as far as flow goes.
Just so happends that the maximum Cm(piston speed) coincides(sp?My english isn´t all THAT good)with around the 75 deg mark.
Ie;by taking this into effect as best we can,we will-or can-alter the effect on flow by putting "depression" into the equation.
Would i trust something as simple as a rocker arms geomtry checker out of plastic?
No sireeeee.No way.
Will i trust my own eyes and 200$ worth of measuring tools?
Yup.Every time.

 

LMAO.....

I PREFER THE COMP CAMS ADJUSTABLE PUSHROD...... LENGTH CHECKER

 

ok, well why dont you SHARE some more thoughts on this subject...and explain why you should use a degree wheel when choosing pushrod length instead of just telling us why you do it?

 

D'oh.. gotta go meet a customer for dinner... but if i have time before i hafta leave for VIR, i'll try to post some of the interesting pushrod info my buddy's learned on the spintron .

 

THE DEGREE WHEEL SHOW'S CRANKSHAFT POSITION IN DEGREES

IE: 104 DEG

USING A DIAL DIAL INDICATOR TO DETERMINE LIFT WILL HELP SHOW POINTS OF VALVE OPENING, CLOSING, MAX LIFT,AND 0 LIFT.

WITH THIS IN MIND, (IF YOU HAVE THE CORRECT PUSHROD LENGTH)
YOU SHOULD BE AT MAX LIFT ON THE INTAKE VALVE AT THE ADVERTISED INTAKE LOBE CENTERLINE.
(WHICH YOU CAN SEE ON THE DIAL INDICATOR)

IF YOU CHOOSE TO ADVANCE OR RETARD THE CAM TIMING...
YOU FIRST MUST DETERMINE THAT EVERYTHING IS CORRECT WITH ADVERTISED INTAKE CENTERLINE (STRAIGHT UP).. THEN CHANGE YOUR CENTERLINE IN THE AMOUNT OF DEGREES YOU WISH TO ADVANCE OR RETARD...

DETERMINING PUSHROD LENGTH WITH THE DEGREE KIT

IF YOUR PUSHRODS ARE TOO LONG YOU WILL BE AT MAX"ADVERTISED NOT ACTUAL, ACTUAL WILL BE TOO HIGH " LIFT BEFORE YOUR CENTERLINE,

TOO SHORT JUST THE OPPOSITE..

KNOWING WHAT YOR MAX LIFT IS , YOU CAN DETERMINE IN .000" HOW LONG OR SHORT YOUR PUSHRODS ARE BY ADDING OR SUBTRACTNG THE ACTUAL LIFT ON THE DIAL INDICATOR AT A SPECIFIED DEG. OF CENTERLINE WITH THE LIFT ON YOUR CAM CARD...

THE DIFFERENCE SHOULD GIVE YOU A BALLPARK IDEA OF YOUR PUSHROD LENGTH..

YOU CAN DOUBLE CHECK YOURSELF WITH THE COMP CAMS ADJUSTABLE PUSHROD..

USING YOUR RESULTS, ADJUST YOUR CHECKER ACCORDINGLY TO VERIFY YOUR MATH..

IE: AFTER ADJUSTMENT OF CHECKER, YOU SHOULD BE AT MAX(ADVERTISED) LIFT AT SPECIFIED INTAKE CENTERLINE...

 

Have you ever taken lite springs and actually ran the engine thru full cycle, from zero, to full lift, then back to zero B4? If you had, you'd know why roller rockers came into being. If the rocker arm tip didn't move, there would be very little friction. Talk about rocker science, LOL. But it does sound like you are not aware of the problem. It is simple math. What is pushing down on the valve stem is doing so on an arc. Do you know what that suggests?