Pushrod length Calculation

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Mar 25, 2008 | 06:10 AM

LS2Monte

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Pushrod length Calculation

I'm gonna replace the PR when I do the cam swap for my LQ4. The heads, gaskets, deck height, and rockers are all staying stock. I'm simply changing the cam and springs right now. The cam is a small Comp 216/226 .526/.535 112+4. Its a very similar grind to the hot cam.

Anyways, could I safely pickup a set of 7.400" pushrods? I was thinking about measuring the base circle on the stock cam and the new Comp, and then splitting that difference in half, adding it to the overall pushrod length. Should I go ahead and do this or will 7.4" pushrods be fine?

Mar 25, 2008 | 06:53 AM

brad8266

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Quote:

Originally Posted by LS2Monte

You can measure the base circle like you said, that is a good way to do it. Or to be 100% sure and get a desired preload you can buy a pushrod length checker and actually measure what you need.

Mar 25, 2008 | 04:39 PM

GuitsBoy

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Yeah, you need to know teh difference in base circle radius between teh stock and new cams. Most likely itll be 1.550 to 1.450. In which case a 7.425 pushrod will be within .005 of the stock 7.380 pushrods. 7.400 will also work, but not quite as on target.

Mar 26, 2008 | 03:05 AM

Rambo06

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You need to buy a pushrod length checker to be 100% sure, don't half *** it because you can cause premature valve stem failure if you're not centered.

Mar 26, 2008 | 10:46 AM

oldmanwinter

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Correct me please if I am wrong, cuz I am near putting mine back together.
If he has stock valve train, wouldn't the rocker wipe be the same if he used the wrong lenth PR? The rocker geometry is not a variable. Wouldn't the wrong length PR just preload the improperly?

Mar 26, 2008 | 10:48 AM

GuitsBoy

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Quote:

Originally Posted by oldmanwinter

This is a greatly debated topic. Im with you on this one. I feel the wipe would only change if the rockers were shimmed to adjust for preload. Other people will disagree on this topic to the death...

Mar 26, 2008 | 12:40 PM

bsf

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Quote:

Originally Posted by oldmanwinter

IMO, no. With a near stock setup though, I do not see how you could end up with the proper preload but have the swipe pattern too off-center. I did not bother to check swipe when I did H/C. All I was concerned w/ was selecting the push rods which gave me the desired preload. Correct me if I am wrong, but if all you change are cam and pushrods, you cannot achieve proper preload without having a proper swipe pattern. This was taken into account during design of the engine and components, was it not?

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