AllCammedUp

First off, I want to thank you guys for the recent posts on p-rod length and camshaft base-circle diameters. It's really cleared up a lot for me! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

However, that leaves me wondering what the allowable 'sliding window' of variance is when considering having the lifters make up for any 'slack' or lack thereof in valvetrain geometry to try to get you as close to possible to stock?

Let's say my cam BCD is .040" smaller than stock, and my heads are milled .010", so that would mean I need a p-rod .030" longer than stock, so would the stock-length p-rods be ok in this situation, or should I go to 7.450" p-rods and be .020" to long? Since 7.450" is closer (.020" difference) to the stock geometry than where I'd be at by being .030" too short, would having longer-than-stock p-rods be preferrable in this situation, or should I stick to stockers? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

Is it a rule that you should never go too long, or is it ok to go a little too long, or what? I guess we need to know the window size that, once crossed, dictates us move to the next size up or down p-rod.

Also, when should we shim and when should we not worry about it?

Thanks!

99 Black Bird T/A

iTrader: (4)

free TTT

AllCammedUp

Thanks! <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" />

LOnSLO

iTrader: (15)

Yes, theoretically. But seeing as pushrods are only made in .050" increments, he will need to use the stock ones. DBerry, you are correct on calculations.

Tin Indian

Here is a big problem with determining pushrod length now ......

We have all been told that the stock GM rod is 7.40"
Two people say they have measured a stock rod. One claims they are 5 thousands shorter than stock. The other guy says they are 25 thousands shorter than 7.40".

Since the aftermarket stock length pushrods are in fact 7.40" (maybe), you can see how this puts a monkey wrench in all this.

When I get back from Korea, I am going to actually measure the base circle of my stock cam, then my TR-220, then my stock pushrods, and go from there to figure out what length rods I [really] need.

I sure hope the stock rods aren't 25 thousands shorter than 7.40". If so, I have allready purchased the wrong length Thunder pushrods based on my new cam and milled heads.

How about someone actually measure a stock GM rod and a aftermarket 7.40" pushrod with a quality set of calipers and see for sure if they are different or not.

Anyone up to it?

Ron,

Tin Indian

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LOnSLO

iTrader: (15)

Always good to stay on the short side, so the lifter will stay in its "cushion" range. Stock length pushrods will need to be used here, and will work fine. IMO, the stock lifters have a window of around .040.

DBerry

Not sure on your answer and don't mean to nit pick. But, in your scenario of a .040" smaller BCD cam and .010 milled heads wouldn't that give you a needed pushrod length of .010" Longer?

BCD of .040 /2 = .020 Base circle radius -.010 for the heads = .010 longer pushrod

I'm kinda in the same situation and wanted to know if I was thinking correctly.

Scalpel

iTrader: (4)

Ok, here's the length of the stock pushrod measured with a 12" caliper: 7.398" It's within +/- .005" Probably the manufacturing tolerance they use for these.

AllCammedUp

Thanks for the replies, everyone! The thread helped to clear a few things up for me, so mission accomplished! The stock length ones are what I'm using.

Tin Indian

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by NastyC5:
<strong>Ok, here's the length of the stock pushrod measured with a 12" caliper: 7.398" It's within +/- .005" Probably the manufacturing tolerance they use for these.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Thanks for measuring a stock rod. Well, that puts all this back in perspective