Pushrod debate with the LS6 cam
05-14-2003, 01:19 PM
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Pushrod debate with the LS6 cam I'm still up in the air about which pushrod length is actually correct when installing a 2002-03 LS6 camshaft into a LS1 engine.
It is generally known that the 2002 LS6 camshaft has a 0.050" smaller base circle that technically requires a 7.427" long pushrod to have the "correct" valve train geometery in the LS1 engine. We also know 7.427" long pushrods aren't available.
We have two options the 7.400" pushrod or the 7.450" pushrod. Which would be better for the longevity of the LS1 valvetrain with the LS6 camshaft...assuming stock LS1 heads?
I guess that the 7.400" pushrod would limit total valve lift by 0.027"...this may be the safe road but with the possibility of increased valvetrain noise. The 7.450" pushrod would require the lifter to soak up 0.023" of additional valve lift...which may cause increased stress on the lifters...am I correct?
OK, one more thought...if you go with the 7.400" pushrod and you are limiting total valve lift by 0.027" because of the 0.050" base circle/pushrod mismatch...would you be better off going with the 2001 LS6 camshaft that uses the 7.400" pushrod, has the correct valvetrain geometery and has the 0.525" lift because by the time you limit the 02 LS6 lift with the shorter pushrod you are at 0.524" lift anyway (0.551" - 0.027" = 0.524")...right???
I'm just trying to make some good solid decisions to get an LS6 cam in the car and minimize the valvetrain stresses...
I'd love to hear from JPR or Jason99T/A on this one.
It is generally known that the 2002 LS6 camshaft has a 0.050" smaller base circle that technically requires a 7.427" long pushrod to have the "correct" valve train geometery in the LS1 engine. We also know 7.427" long pushrods aren't available.
We have two options the 7.400" pushrod or the 7.450" pushrod. Which would be better for the longevity of the LS1 valvetrain with the LS6 camshaft...assuming stock LS1 heads?
I guess that the 7.400" pushrod would limit total valve lift by 0.027"...this may be the safe road but with the possibility of increased valvetrain noise. The 7.450" pushrod would require the lifter to soak up 0.023" of additional valve lift...which may cause increased stress on the lifters...am I correct?
OK, one more thought...if you go with the 7.400" pushrod and you are limiting total valve lift by 0.027" because of the 0.050" base circle/pushrod mismatch...would you be better off going with the 2001 LS6 camshaft that uses the 7.400" pushrod, has the correct valvetrain geometery and has the 0.525" lift because by the time you limit the 02 LS6 lift with the shorter pushrod you are at 0.524" lift anyway (0.551" - 0.027" = 0.524")...right???
I'm just trying to make some good solid decisions to get an LS6 cam in the car and minimize the valvetrain stresses...
I'd love to hear from JPR or Jason99T/A on this one.
05-14-2003, 02:19 PM
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Re: Pushrod debate with the LS6 cam Well, i'm not JPR or Jason99T/A
The stock LS1 cam has a 'base circle' of 1.552" (across the lobe). That equals .775" (19.7mm) from 'cam centerline' to 'lobe heal'. In fact, GM states that this distance is in fact 19.7mm on the LS1 cam.
GM also states that the 2002 LS6 cam has a 'cam centerline' to 'lobe heal' distance of 19.0mm. That is exactly .748"
The simple math will tell you that the difference in 'cam centerline' to 'lobe heal' distance between the two cams is 0.7mm or .027"
To be exact, the LS6 cam would require a .027" [longer] pushrod than the LS1 cam if you wanted to maintain the exact lifter preload as you had before the cam swap.
It's up to you whether or not go with a longer pushrod or not.
I can tell you one thing.... We measured the 7.40" Thunder Racing rods and found out that they were .015" longer than the stock rod. Using those, your now only looking at 0.12" less preload than you had stock (and that's nothing at all). And to tell you the truth, I would rather has slightly less preload than slightly more. With less preload, the lifters won't pump up as quickly at high revs.
Hyd. lifters are very forgiving. The range of preload they can operate with is faily large.
If it was me, I would just use the 2002 LS6 cam and a set of Thunder 7.40" rods. You will have no valve geomety problems as long as your heads are not milled exccesivly.
BTW, Using a shorter pushrod does decrease the lifters preload, but does [not] decrease the valves total lift as long as there is still preload in the lifter.
Ron,
The stock LS1 cam has a 'base circle' of 1.552" (across the lobe). That equals .775" (19.7mm) from 'cam centerline' to 'lobe heal'. In fact, GM states that this distance is in fact 19.7mm on the LS1 cam.
GM also states that the 2002 LS6 cam has a 'cam centerline' to 'lobe heal' distance of 19.0mm. That is exactly .748"
The simple math will tell you that the difference in 'cam centerline' to 'lobe heal' distance between the two cams is 0.7mm or .027"
To be exact, the LS6 cam would require a .027" [longer] pushrod than the LS1 cam if you wanted to maintain the exact lifter preload as you had before the cam swap.
It's up to you whether or not go with a longer pushrod or not.
I can tell you one thing.... We measured the 7.40" Thunder Racing rods and found out that they were .015" longer than the stock rod. Using those, your now only looking at 0.12" less preload than you had stock (and that's nothing at all). And to tell you the truth, I would rather has slightly less preload than slightly more. With less preload, the lifters won't pump up as quickly at high revs.
Hyd. lifters are very forgiving. The range of preload they can operate with is faily large.
If it was me, I would just use the 2002 LS6 cam and a set of Thunder 7.40" rods. You will have no valve geomety problems as long as your heads are not milled exccesivly.
BTW, Using a shorter pushrod does decrease the lifters preload, but does [not] decrease the valves total lift as long as there is still preload in the lifter.
Ron,
05-14-2003, 04:44 PM
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Re: Pushrod debate with the LS6 cam Pushrods that are 0.015" oversized (7.415") would certainly eliminate my concerns.
I've seen posts from sponsors selling the LS6 cam kits and they advise to use the 7.450" long pushrod...why? I have yet to see anyone post about using the 7.450" long pushrod. I'm interested as to why they would say to use a 0.050" longer pushrod. Can the LS6 springs withstand another 0.023" of lift above the 0.551" lift the 02 LS6 cam already has?
I tend to be leaning to the 7.400" pushrod as I have seen several people use them with some success but the 0.015" oversize pushrod seems to be a good thing in this case.
At higher engine RPMs the hydraulic lifter generally doesn't have time to soak up any of the pushrod length differences, I have a hard time believing that you are not changing the valve lift with different length pushrods, especially at high RPMs where your lifters are essentially acting like solid lifters as the hydraulic action doesn't have time to react. I think we have a choice with the stock pushrod (7.400") of slightly less lift (due to the 0.050" base circle and the need for a 0.027" longer pushrod) or slightly more lift (and more valvetrain stress) with the 7.450" pushrod.
I still think the 01 LS6 camshaft and the 7.400" pushrod may be equal to the 02 LS6 camshaft and the 7.400" pushrod due to the 0.027" loss of lift. The 01 camshaft does give up a slight amount of exhaust side duration...which may be where the slight power variation occurs between the 01 and 02 LS6 camshafts.
I've seen posts from sponsors selling the LS6 cam kits and they advise to use the 7.450" long pushrod...why? I have yet to see anyone post about using the 7.450" long pushrod. I'm interested as to why they would say to use a 0.050" longer pushrod. Can the LS6 springs withstand another 0.023" of lift above the 0.551" lift the 02 LS6 cam already has?
I tend to be leaning to the 7.400" pushrod as I have seen several people use them with some success but the 0.015" oversize pushrod seems to be a good thing in this case.
At higher engine RPMs the hydraulic lifter generally doesn't have time to soak up any of the pushrod length differences, I have a hard time believing that you are not changing the valve lift with different length pushrods, especially at high RPMs where your lifters are essentially acting like solid lifters as the hydraulic action doesn't have time to react. I think we have a choice with the stock pushrod (7.400") of slightly less lift (due to the 0.050" base circle and the need for a 0.027" longer pushrod) or slightly more lift (and more valvetrain stress) with the 7.450" pushrod.
I still think the 01 LS6 camshaft and the 7.400" pushrod may be equal to the 02 LS6 camshaft and the 7.400" pushrod due to the 0.027" loss of lift. The 01 camshaft does give up a slight amount of exhaust side duration...which may be where the slight power variation occurs between the 01 and 02 LS6 camshafts.
05-14-2003, 06:01 PM
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Re: Pushrod debate with the LS6 cam Sorry to disagree, but a longer pushrod will not get you more lift or vise-versa with a short rod. The plunger in the lifter seeks a certain point in the total travel of the internal bore of the lifter. There will be oil on both ends of this plunger.
I have a hard time explaining it, but I can tell you for certain that if you installed a pushrod that was .020" longer in your engine, the valve would not open farther when the lifter was at the top of the cam's lobe. Do to the design of a hydraulic lifter, it just don't work like that.
It's your engine. Do what you want... I suggest you call Joe Prince or Jason at Thunder and see what they to say.
I have a hard time explaining it, but I can tell you for certain that if you installed a pushrod that was .020" longer in your engine, the valve would not open farther when the lifter was at the top of the cam's lobe. Do to the design of a hydraulic lifter, it just don't work like that.
It's your engine. Do what you want... I suggest you call Joe Prince or Jason at Thunder and see what they to say.
05-14-2003, 11:01 PM
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Re: Pushrod debate with the LS6 cam Tin Indian is right...running shorter or longer pushrods on a hyd. lifter DOES NOT change valvelift...period...You wont lose lift with shorter pushrods. Thats the beauty of hydraulic lifters.
05-15-2003, 07:54 AM
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Re: Pushrod debate with the LS6 cam I agree with Ron, although I have no experience with installing the 2002-03 Z06 cams. I know a couple companies that have installed them with stock heads/gaskets without any issues.
Joe.
Joe.
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05-16-2003, 09:27 AM
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Re: Pushrod debate with the LS6 cam Ok tell me if I understand this correctly. There is no need to change anything other than the cam itself, and of course gaskets. Everything else in the stock motor will work fine????????Is this correct????
05-16-2003, 10:48 AM
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Re: Pushrod debate with the LS6 cam You need the LS6 springs and chrome moly pushrods besides the cam and gaskets.
The LS6 springs you have to do, the chrome moly pushrods are a very good idea but not absolutely necessary.
The LS6 springs you have to do, the chrome moly pushrods are a very good idea but not absolutely necessary.
