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Discussion Starter · #1 ·
OK, I have a 96 impala and I'm trying to put on these new edelbrock "lt1 performer" cylinder heads. Only I'm not sure what length pushrods I need. The instructions with the heads say "you may need .1" longer if using the stock rockers. But I'm not putting the stock rockers back on, I'm switching to the comp cams pro magnums, 1.6 ratio self-aligning.

I'm also using the recommended edelbrock cam. See http://www.edelbrock.com/automotive/2108graph.html
for more info on the heads and cam that I'm using.

Now the instructions for the Lunati pushrod length checker tool say to use the adjustable pushrod and their supplied non-moving rocker to measure the length and put it in their formula based on your camshaft specs and rocker ratio that you are going to use. But you have to know the "net lift" which they list as "gross lift" - "valve lash". Anyone know how to come up with these numbers?

Their example is a Lunati 50149 camshaft. They list the Gross lift as .679", valve lash -0.026" and net lift as .653" for this example.

Anyone know how I get these numbers for the edelbrock #2108 cam?

Is "valve lash" how much you depress the lifter? (By the way I'm using the comp cams "R" series lifters). I wonder if I used the adjustable pushrod correctly, how do I know if the lifter was "pumped up" or not? (I had soaked them in oil but about a day had passed since installing)


I know that was a long post. Sorry. Please don't recommend asking edelbrock or lunati, I'll get nowhere with them...

Any help is GREATLY appreciated!
 
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Discussion Starter · #2 ·
Yes lash is the amount you depress the plunger into the lifter.
If you are going to use say 1/2 turn, that is
.5/20=.025.
The 20 is the threads per inch on the rocker stud.
Take this number and subtract it from the gross lift of your cam.

From the link it says that the cam has .525 lift at the valve. All cams assume a 1.5 rocker unless otherwise noted.
So if you are going to use a 1.6 rocker, the lift would be .560" of lift.
So use how many turns you are going use, with Comp-R lifters they like very little, 1/8-1/4 past.

This is what I get from what you are asking.
 
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Discussion Starter · #3 ·
And i think you'll want to add the 0.025" (1/2 turn) to your gross lift since this is a hydraulic cam and the pushrod is going into...further down...into the lifter.
It looks like Lunati was thinking solid lifters and the lash is above the pushrod.
So .56O + (.01-- 1/4 turn).
Or. forget the lash and just use the cam lift...it's close enough.
or
stick in a stock pushrod that you have laying around and see if that works ok for geometry.
I bought that Lunati checker and never could figure it out.
Karl
 
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Discussion Starter · #5 ·
Frank:

This valve train geometry is hard for me as well.

I used Crane # 10621-16 push rods which are 7.178" long. I believe these are slightly shorter than stock.

I run 1.6 RR (Crane Gold) with a Comp cam .566/.547 (yes more lift on intake than exhaust). with no problems.

Anyone who knows the "formula" for my set-up, please respond.

If you are getting more "lift" with a 1.6 vs a 1.5, wouldn't you need a slightly "shorter" push rod?

BTW, Comp tech says 0-1/8 turn on the 875R's. Not 1/4-1/2 turn. They were very firm on that point. I did a very thin 1/8 turn.

good luck
 
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Discussion Starter · #6 ·
Originally posted by BALLSS:
Frank:

BTW, Comp tech says 0-1/8 turn on the 875R's. Not 1/4-1/2 turn. They were very firm on that point. I did a very thin 1/8 turn.

good luck
I said 1/8 to 1/4. I knew it was low, but not that much. Oh Well.
 
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Discussion Starter · #7 ·
Or you can do like me and buy 3 different sizes of pushrods until you get it right, and have a shelf full of wrong sized pushrods for some later project. Better stated, Do NOT do it like me, you'll save time and money.


Karl
 
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Discussion Starter · #8 ·
"stick in a stock pushrod that you have laying around and see if that works ok for geometry."


Well, I could use the adjustable pushrod from the lunati checking tool and try some different lengths, but what exactly am I looking for? Am I just looking to see that the rod isn't rubbing against the hole in the head or what? And how much do I tighten the rocker arm when doing this (don't you adjust the rocker arm when "lashing"? won't that affect the pushrod length that I need)
 
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Discussion Starter · #9 ·
I think that you'll be checking to see if the rocker tip sets on the valve tip in the ideal spot. And like you said, check for pushrod rub on the head.
They say that the checker pushrod cannot take full valve spring pressure so you'll have to get a "checking" spring to run your valve through full travel.
I'd just do it on one valve, (pick one that has the most potential pushrod interference).
Set up the rocker with normal preload and see how the rocker rides on the valve. That's my guess anyhow.
Karl
 
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Discussion Starter · #10 ·
Ok, I gave up on the lunati tool and just put the old pushrods in and used a marker to mark the top of the valve to see where the marker ink would wear off after a few revolutions.

From what I can tell (if anyone cares): with edelbrock performer lt1 heads, edelbrock 2108 cam, comp r lifters, pro magnum 1.6 roller rockers, and 0.0289 thickness head gasket- the stock pushrod length is exactly correct. The wear mark is centered exactly in the middle.

However it seems that 2 of the lifters would not "pump up" for some reason...
 
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Discussion Starter · #12 ·
lol thanks

well i went out tonight to recheck and all the lifters are easily depressed (like the ones that I thought were bad, i guess they aren't). Only I'm pretty sure when I did this check last night they stayed up even after several engine revolutions... So I think I got the right length, and I'll go ahead and order some pushrods but it looks like maybe you have to have the engine running to really adjust them properly?
 
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