Valve Train Help needed......
Thread Starter
Joined: Oct 2002
Posts: 326
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From: Alexander City Alabama
Valve Train Help needed...... Ok cablebandit and I were talking about pushrods the other day and if mine were the right ones….I figured out that most ALL aftermarket cams have a smaller base circle than the stock cam….this is due to the design of the cam and engine block….from my research it looks like the nose (or point of highest lobe lift) of the cam is, for our discussion, the same point on either the stock cam or the aftermarket cam….so this means that all the extra lift comes from the reduced base circle diameter of the aftermarket cam….ok now to the math…..
The stock lobe lift of a stock 2002 cam is .281 and the new cam we put in has a lobe lift of .346 intake and .339 exhaust so using the intake as the example this means that the base circle of the new cam is 0.065 smaller and would require a 0.065 longer pushrod…the stock PR’s are 7.38” in length so 7.38 + 0.065 = 7.445 the closest PR to this length is 7.425…..in addition to the extra length needed by smaller base circle cam we put a thicker head gasket on which is .052….which is 0.012 thicker than the graphite head gaskets that were on there…..this puts us needing a 7.457 PR with 0 lash…..unless I’m crazy a 7.425 pushrod would put us back pretty close to the stock geometry with the preload really close to the stock settings……or would a 7.450 be a better choice....
I've been pulling my hair out trying to figure out which PR's I need....Thanks for the help....
The stock lobe lift of a stock 2002 cam is .281 and the new cam we put in has a lobe lift of .346 intake and .339 exhaust so using the intake as the example this means that the base circle of the new cam is 0.065 smaller and would require a 0.065 longer pushrod…the stock PR’s are 7.38” in length so 7.38 + 0.065 = 7.445 the closest PR to this length is 7.425…..in addition to the extra length needed by smaller base circle cam we put a thicker head gasket on which is .052….which is 0.012 thicker than the graphite head gaskets that were on there…..this puts us needing a 7.457 PR with 0 lash…..unless I’m crazy a 7.425 pushrod would put us back pretty close to the stock geometry with the preload really close to the stock settings……or would a 7.450 be a better choice....
I've been pulling my hair out trying to figure out which PR's I need....Thanks for the help....
TECH Senior Member
Joined: Mar 2004
Posts: 14,620
Likes: 17
From: BFE
Originally Posted by b1er
Ok cablebandit and I were talking about pushrods the other day and if mine were the right ones….I figured out that most ALL aftermarket cams have a smaller base circle than the stock cam….this is due to the design of the cam and engine block….from my research it looks like the nose (or point of highest lobe lift) of the cam is, for our discussion, the same point on either the stock cam or the aftermarket cam….so this means that all the extra lift comes from the reduced base circle diameter of the aftermarket cam….ok now to the math…..
The stock lobe lift of a stock 2002 cam is .281 and the new cam we put in has a lobe lift of .346 intake and .339 exhaust so using the intake as the example this means that the base circle of the new cam is 0.065 smaller and would require a 0.065 longer pushrod…the stock PR’s are 7.38” in length so 7.38 + 0.065 = 7.445 the closest PR to this length is 7.425…..in addition to the extra length needed by smaller base circle cam we put a thicker head gasket on which is .052….which is 0.012 thicker than the graphite head gaskets that were on there…..this puts us needing a 7.457 PR with 0 lash…..unless I’m crazy a 7.425 pushrod would put us back pretty close to the stock geometry with the preload really close to the stock settings……or would a 7.450 be a better choice....
I've been pulling my hair out trying to figure out which PR's I need....Thanks for the help....
The stock lobe lift of a stock 2002 cam is .281 and the new cam we put in has a lobe lift of .346 intake and .339 exhaust so using the intake as the example this means that the base circle of the new cam is 0.065 smaller and would require a 0.065 longer pushrod…the stock PR’s are 7.38” in length so 7.38 + 0.065 = 7.445 the closest PR to this length is 7.425…..in addition to the extra length needed by smaller base circle cam we put a thicker head gasket on which is .052….which is 0.012 thicker than the graphite head gaskets that were on there…..this puts us needing a 7.457 PR with 0 lash…..unless I’m crazy a 7.425 pushrod would put us back pretty close to the stock geometry with the preload really close to the stock settings……or would a 7.450 be a better choice....
I've been pulling my hair out trying to figure out which PR's I need....Thanks for the help....
So that puts you at 7.446 correct intake and 7.438 exhaust.
So the 7.425 are off shelf length.
Or you have custom length ones made with the above correct int/exhaust length.
BTW that intake diference at the cam is huge.
Last edited by PREDATOR-Z; Jun 22, 2005 at 01:46 PM.
Thread Starter
Joined: Oct 2002
Posts: 326
Likes: 0
From: Alexander City Alabama
It's not a large cam by today's standards....228/234 @ .588 in 573 exh .... plus it was free so I figured I'd try it and see how it does....
So 7.425 should be close to the right length....this is what I was hoping....
Thanks guys.....
So 7.425 should be close to the right length....this is what I was hoping....
Thanks guys.....
