truedualws6

I've picked up the parts to modify my valvetrain geometry and hopefully get closer to the mid-lift
"ideal" setting. Due to limitations with my rocker covers (LT4) the longest pushrod I can use is
7.30" before the locks hit the cover. The pic below shows the parts I plan on using. I already had
the 135-7101 studs on hand so I'll put a .120" washer under the TFS guideplates so the stud into
the head is about .500". This will raise the stud so that I maintain about 8-9 turns on the lock
with the rocker arm about .150" higher at the trunnion.



This pic below shows the geometry with a 7.30" pushrod on #3 intake (3rd rocker from bottom). You can
see that the 7.30" pushrod puts the roller just off center towards the exhaust side and the other rockers
with 7.05" pushrods look angled back and off center towards the intake. Beacuse the geometry is so far
off with 7.05" pushrods the roller tip has to start on the intake side and sweep across an equivalent
distance on the exhaust side for a total sweep of close to .100".



Although the sweep pattern is centered on the valve tip, it's a wide sweep and provides a lot of wasted
motion and lost camshaft information. Raising my rockers will get me half way to the "ideal" geometry and
should reduce the sweep across the valve stem tip about 50%. I'll put up some pics of the before and after
sweep once I install the parts. I'm also hoping the ARP locks give me a tad more clearance under the covers.

Thought I would share this in case anyone had more comments.

Stl94LT1

Please don't take this wrong. But, it seems like you are going through an awful lot of trouble for little or no gains. What exactly are you hoping to gain?

truedualws6

Peace of mind for the most part. You are probably right in that I will see little to no gain after all this effort.
What will take time to tell is if there are any long term effects (good or bad), but my take is that this is the
correct way to set up geometry regardless. When you think about all of the motion taking place under the rocker
covers and then consider for each valve cycle I'm eliminating .050" of wasted sweeping motion across the
valve tip, it adds up to a lot. Just in terms of wear on the valve stem tip and side loads on the valve stem it
makes it worth while, but I'll bet there is some positive gain.

joeSS97

I am curious,if you plan on using a different length pr. on the exhaust side.I know that you mentioned it before. I think what you are doing could be a worthwhile effort.Let us know the results.

cehan

Do you have some plan for measuring before and after results? If there's not more than 3 or 4 HP and a couple of ft lbs torque increase, I guess I fail to see the cost effectiveness of the effort.

It just so happens that when this thread first came up, I just ordered a set of PAC 1518 springs to replace the CC 26918 springs that I first used with my LE heads/cam/383 about 2-1/2 years ago. The only reason that I decided to change the valve springs is that at 0.600"+ lift, and with countless redline shifts, I figured that the 26918's were probably getting tired.

At the time I set up the valve train using the more common method of centering the roller tip on the valve stem, and my pushrod length ended up at 7.050 in. Well, I started disassembling the valve train this weekend and I found zero wear on my GMPP guideplates, no scuffing of the pushrods, and no observable wear (i.e., wobble) in the valve stem to valve guide fit. By the way I've also not experienced any of the 26918 valve spring failures that have plagued so many on this board.

So my question is, what significant gains (power, reliability, etc.) could I expect from pursuing the mid-lift method of determining pushrod length?

1989TransAm

He is hoping to gain some horsepower. If done correctly it might be along the lines of going from a 1.5 to a 1.6 rocker arm. Also the valve will be help open a little bit longer.

quickSS

truedualws6,
Very informative and thanks for sharing the info.
Seems to me that the more motion in the down-up direction, (and less in the rub-accross-the-valve-tip direction), the better.

Personally I would not be looking for more power but just more longevity/reliablilty and this seems to be a step in that direction.

Karl Ellwein
Ellwein Engines

cehan

Well I guess, from my own experience,and considering that my stuff looks as good as the day I put it in, it would be hard for me to improve on that.

So, you pay your money and you take your choice

truedualws6

I'm going to use 7.30" pushrods all around. Since I can't raise the rocker high enough to reach the mid-lift without new rocker covers I'm just going up as much as possible. I'll share the results. I'm working on a friend that is a math guru and trying to get him to draw this up on AutoCAD and calculate the actual sweep distance since it's difficult to measure.

I do not plan on measuring before and after results. What really turned the lights on for me was reviewing my pictures on the computer where I could see how much better the rocker with the 7.30" pushrod looked than it's neighbor with a 7.05" pushrod. Another side effect of the shorter pushrods for me was the lack of clearance to the bottom of the guideplate slot. The wear in my setup is also as you stated, but I would still like to improve/optimize it.

I agree 100% in the longevity/reliability goal. A bit more power is frosting but the key is finding the most efficient geometry for long term use.

wrd1972

Do you have an update on this?

Jazsun

If you bought new polylocks, want to sell me your old ones?