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PR length before wrong decision is made!!!

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Old Jun 23, 2007 | 04:18 PM
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Default PR length before wrong decision is made!!!

I know this has been discussed before, I've searched and read all i can about it but want to double check to be on the safe side.

I have a TR 230/236 cam, base circle is smaller than stock I've read by .030" (comp cam spec). This would require me to run a .030 longer pushrod if i'm not mistaken by my research. However, i'm swapping heads for a set of 243 LS6's that have been milled to 61cc chambers (.012-.013) and a cometic .040 gasket.

Since the heads are .012 down and the gasket is .015 thinner than the stock (.055 if i'm not mistaken) gasket then that brings me to believe head/gasket setup requires a .028 shorter pushrod.

With this setup can i run a 7.4" pushrod i have from TSP or should i go with the 7.35 i have from TR? Both PR's were bought used so neither was recommended by a shop, just curious as to which i should install to be on the safe side.

Thanks and sorry since I know this has been discussed before.
William
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Old Jun 23, 2007 | 08:15 PM
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7.400 + .030 for smaller base, - 12 for heads, -15 for gasket = 7.413. Now the question is where was your preload before?

The better way is to measure a couple of intake and exhaust valves on both heads and determine the correct length from there.
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Old Jun 23, 2007 | 10:02 PM
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7.403
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Old Jun 24, 2007 | 12:49 AM
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Yea i got it as .003 over 7.4, but wasn't sure what i should do, i'm gonna see if i can actually measure it just to be on the safe side.

William
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Old Jun 24, 2007 | 01:00 AM
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A cam with .030" smaller base circle dia. would call for a .015" longer pushrod, since the pushrod only "sees" the difference in radius.

With the head swap and gasket change, you're losing .027". So theoretically, you'd want a 7.388" pushrod.

I would use a 7.400" in your case.
A 7.375" should still work ok,
A 7.350" would be too short.

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Old Jun 24, 2007 | 03:24 AM
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Originally Posted by Thimble
A cam with .030" smaller base circle dia. would call for a .015" longer pushrod, since the pushrod only "sees" the difference in radius.


Yes you're right - I stand corrected.
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Old Jun 24, 2007 | 07:11 AM
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Originally Posted by Thimble
A cam with .030" smaller base circle dia. would call for a .015" longer pushrod, since the pushrod only "sees" the difference in radius.
Correct but TR cams have much smaller base circles. Similar to XE-R about .040 in radius

With the head swap and gasket change, you're losing .027". So theoretically, you'd want a 7.388" pushrod.

I would use a 7.400" in your case.
A 7.375" should still work ok,
A 7.350" would be too short.

Assuming all the figures are right, you should run a 7.400 p-rod for a quiet valvetrain and stockish range preload
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Old Jun 24, 2007 | 08:15 AM
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Will69
what made you decide to go with this cam? Its a revers split.Ithought they were good for stock heads intake,or am I wrong? I have Tsp 5.3 heads with a Tr224/112 and thought about swapping it out for something else and thought about this cam.What do you think,or anyone else
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Old Jun 24, 2007 | 09:29 AM
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To be honest, i bought it because it was similar in spec to the torquer v2 (which is what i initially wanted) and i got a good deal here on ls1tech. I've thought about changing cams already before this is installed but i'll see how this one does and if i dont like it i'll change it later on.

William
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