Pushrod length ?
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Pushrod length ? Why do people run .050 less pushrod even though they are only milling .025-.035. Wouldnt that make too much slack in the valvetrain? <img src="graemlins/burnout.gif" border="0" alt="[Burnout]" />
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From: Austin, TX
Re: Pushrod length ? I have ARE heads TR 226.5 114 cam and I am running 7.250 pushrods!!
To get the right geometry I needed those Pushrods. ARE heads are using longer valves, double springs, and a lash caps on top of them. Therefore, the right pushrods were 7.250.
But, I think the shorter pushrods will be stronger. No more bent pushrods. The old hardened pushrods (stock pushrods 7.400) got bent!!
All heads are different than the other. I had to test for the right pushrods length.
To get the right geometry I needed those Pushrods. ARE heads are using longer valves, double springs, and a lash caps on top of them. Therefore, the right pushrods were 7.250.
But, I think the shorter pushrods will be stronger. No more bent pushrods. The old hardened pushrods (stock pushrods 7.400) got bent!!
All heads are different than the other. I had to test for the right pushrods length.
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From: new england
Re: Pushrod length ? RUF, i like the idea of short pushrods and lash caps, but iwanted to mention different pushrod length doesnt change geometry, geometry is set by angle between valve and rocker arm, and this doesnt change with pushrod changes.
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From: new england
Re: Pushrod length ? [quote]Originally posted by LS1derfull:
<strong>RUF, i like the idea of short pushrods and lash caps, but iwanted to mention different pushrod length doesnt change geometry, geometry is set by angle between valve and rocker arm, and this doesnt change with pushrod changes.</strong><hr></blockquote> Also pushrod length requirement is affected by rocker ratio(length of change is multiplied by 1.7 to give amount affected at valve tip.)
<strong>RUF, i like the idea of short pushrods and lash caps, but iwanted to mention different pushrod length doesnt change geometry, geometry is set by angle between valve and rocker arm, and this doesnt change with pushrod changes.</strong><hr></blockquote> Also pushrod length requirement is affected by rocker ratio(length of change is multiplied by 1.7 to give amount affected at valve tip.)
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From: SW Florida
Re: Pushrod length ? Complements of Walt Donovan:
If the heads are [flat-milled] .030”, the approximate decrease in pushrod length is estimated as follows: A 1.7:1 rocker is 1 unit long from pivot to pushrod & 1.7 units long from pivot to valve (unit size is unimportant). This means the length from valve to pushrod is 2.7 units. Therefore, moving the rocker pivot down .030” moves the pushrod seat down .030” X 2.7 / 1.7 or an approximate total of .048". A .050” shorter pushrod should be perfect when the heads are flat milled .030”
If the heads are [flat-milled] .030”, the approximate decrease in pushrod length is estimated as follows: A 1.7:1 rocker is 1 unit long from pivot to pushrod & 1.7 units long from pivot to valve (unit size is unimportant). This means the length from valve to pushrod is 2.7 units. Therefore, moving the rocker pivot down .030” moves the pushrod seat down .030” X 2.7 / 1.7 or an approximate total of .048". A .050” shorter pushrod should be perfect when the heads are flat milled .030”
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From: Orlando, FL
Re: Pushrod length ? I don't understand how the pivot -> valve unit has any bearing on pushrod length when you are only milling the heads. All you are doing is bring the pushrod cup (of the rocker) closer to the cup of the lifter. Everything else is unchanged. Now if you were milling the rocker arm base 0.030 then it would have an impact but not if you are milling the head surface.
Tim
[ March 12, 2002: Message edited by: TimZ28 ]</p>
Tim
[ March 12, 2002: Message edited by: TimZ28 ]</p>
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From: new england
Re: Pushrod length ? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by WMSuperSport:
<strong>It would seem to me that if you are flat milling .030 then you would need a pushrod that is .030 shorter, not .050. Can anyone else give some info? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I would have to agree, that formula seems to be for if you change relationship of rocker fulcrum to valvestem. I also think its worth mentioning that lifter preload has a larger range of useability than some would have you believe. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
<strong>It would seem to me that if you are flat milling .030 then you would need a pushrod that is .030 shorter, not .050. Can anyone else give some info? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I would have to agree, that formula seems to be for if you change relationship of rocker fulcrum to valvestem. I also think its worth mentioning that lifter preload has a larger range of useability than some would have you believe. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
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From: Ft. Worth, TX
Re: Pushrod length ? It would seem to me that if you are flat milling .030 then you would need a pushrod that is .030 shorter, not .050. Can anyone else give some info? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
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From: Houston, Tx.
Re: Pushrod length ? If you flat mill a head you simply need that much shorter of a pushrod to keep the geometry the same. If you dropped the rocker pivot .030 without moving the valve tip then you'd move the other end .048 and you'd need a .050 shorter pushrod to be in the same ballpark preload. Since you are moving BOTH the rockers pivot and valve tip .030 down you simply run a .030 shorter pushrod all else equal.
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From: Houston, Tx.
Re: Pushrod length ? It would be no different than running a cam with .060 more base circle. You just run a .030 shorter pushrod to compensate for the .030 taller cam base circle under the lifter.
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From: Centrifugal City
Re: Pushrod length ? Also, most aftermarket Cams have smaller base circles. Anything .550+ lift should be .050 smaller or so. That means you'd want a .025 LONGER pushrod. But then you come down .030 on the milling... So.. almost dead even.
Then again, I hear diff tuners use longer valves which changes things again.
<img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
Then again, I hear diff tuners use longer valves which changes things again.
<img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
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From: Ft. Worth, TX
Re: Pushrod length ? So if I run a cam with a base circle .050 shorter and mill the heads .030 then I would need a 7.350 long pushrod?
7.4+.025-.030=7.350 ??????????
7.4+.025-.030=7.350 ??????????
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Re: Pushrod length ? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by WMSuperSport:
<strong>So if I run a cam with a base circle .050 shorter and mill the heads .030 then I would need a 7.350 long pushrod?
7.4+.025-.030=7.350 ??????????</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Generally, a 7.350" pushrod is the typical heads/cam pushrod length. As I changed cams, I went between 7.350 and 7.400" since my basecircle changed. It just all depends on the application. Comp has a pushrod length checker you can get for like $20...thunder racing sells it.
If nothing else, throw a few stock pushrods on your setup and see if you have too much preload. Too much means you need to overnight some 7.350's, if its just right, overnight some 7.400" pushrods. It'll mean one additional day of downtime, but thats no biggie if you want it done right.
<strong>So if I run a cam with a base circle .050 shorter and mill the heads .030 then I would need a 7.350 long pushrod?
7.4+.025-.030=7.350 ??????????</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Generally, a 7.350" pushrod is the typical heads/cam pushrod length. As I changed cams, I went between 7.350 and 7.400" since my basecircle changed. It just all depends on the application. Comp has a pushrod length checker you can get for like $20...thunder racing sells it.
If nothing else, throw a few stock pushrods on your setup and see if you have too much preload. Too much means you need to overnight some 7.350's, if its just right, overnight some 7.400" pushrods. It'll mean one additional day of downtime, but thats no biggie if you want it done right.
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From: SW Florida
Re: Pushrod length ? Base circle is a critical measurment in any cam. It seems odd that a manufacturer does not show the cams base circle on the cam card.
Since the majority of the folks here are using Comp Cams, has anyone ever called them to find out what the exact base circle for there cam is? Certainly they know exactly what it is.
Whether its true or not, I have read that the LS1s cam journals are fairly large in comparison to a SBC. These oversized cam bearing journals will allow for a much higher lift aftermarket cam to be installed even when the cams base circle is identical to the stock spec.
Ron,
Since the majority of the folks here are using Comp Cams, has anyone ever called them to find out what the exact base circle for there cam is? Certainly they know exactly what it is.
Whether its true or not, I have read that the LS1s cam journals are fairly large in comparison to a SBC. These oversized cam bearing journals will allow for a much higher lift aftermarket cam to be installed even when the cams base circle is identical to the stock spec.
Ron,
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Re: Pushrod length ? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Kimchee and Rice:
<strong>Base circle is a critical measurment in any cam. It seems odd that a manufacturer does not show the cams base circle on the cam card.
Since the majority of the folks here are using Comp Cams, has anyone ever called them to find out what the exact base circle for there cam is? Certainly they know exactly what it is.
Whether its true or not, I have read that the LS1s cam journals are fairly large in comparison to a SBC. These oversized cam bearing journals will allow for a much higher lift aftermarket cam to be installed even when the cams base circle is identical to the stock spec.
Ron,</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Every cam I've had was a comp cam, and every time the basecircle has been different.
In addition, it seems the top of the lobes are already going to the extent of the cam journals and that the way to add lift would indeed still be to just remove basecircle.
Basecircles most definitly still change with LS1 cams.
<strong>Base circle is a critical measurment in any cam. It seems odd that a manufacturer does not show the cams base circle on the cam card.
Since the majority of the folks here are using Comp Cams, has anyone ever called them to find out what the exact base circle for there cam is? Certainly they know exactly what it is.
Whether its true or not, I have read that the LS1s cam journals are fairly large in comparison to a SBC. These oversized cam bearing journals will allow for a much higher lift aftermarket cam to be installed even when the cams base circle is identical to the stock spec.
Ron,</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Every cam I've had was a comp cam, and every time the basecircle has been different.
In addition, it seems the top of the lobes are already going to the extent of the cam journals and that the way to add lift would indeed still be to just remove basecircle.
Basecircles most definitly still change with LS1 cams.
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From: Centrifugal City
Re: Pushrod length ? Most of the aftermarket or higher lift cams seem to be 1.490 -> 1.500.
Good enough to estimate the preload change.
Anyone see an aftermarket cam yet NOT in that range with a .545-570 lift??
Good enough to estimate the preload change.
Anyone see an aftermarket cam yet NOT in that range with a .545-570 lift??
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Re: Pushrod length ? Kimchee and Rice,
""Base circle is a critical measurment in any cam. It seems odd that a manufacturer does not show the cams base circle on the cam card.""
Some actually do but I agree with you that it would be nice if they always did! On some of the older SBC stuff they did publish it so you'd have an idea on your rod bolt clearance to the cam lobes. Unlike the LS1 which has great clearance there, the original older SBC had a problem of the rod bolts actually hitting the cam on stroker engines so they'd actually give you the base circle to let you know how far they had cut it down for extra clearance. The LS1 has HUGE clearance since the cam is raised much higher in the block comparitively.
""Base circle is a critical measurment in any cam. It seems odd that a manufacturer does not show the cams base circle on the cam card.""
Some actually do but I agree with you that it would be nice if they always did! On some of the older SBC stuff they did publish it so you'd have an idea on your rod bolt clearance to the cam lobes. Unlike the LS1 which has great clearance there, the original older SBC had a problem of the rod bolts actually hitting the cam on stroker engines so they'd actually give you the base circle to let you know how far they had cut it down for extra clearance. The LS1 has HUGE clearance since the cam is raised much higher in the block comparitively.
Re: Pushrod length ? O.K.
One more thought.
#1 The rocker arm has nothing to do with the pushrod length if you mill the head everything else being similar. So a .030" mill would need a .030" longer pushrod.(being that the pushrod is paralell to the cylinder bore, but even at 15 degrees off you would need a .027" shorter pushrod)
#2 The LS1 has Hydraulic rollers, therfore they can move .050" or more. So a .050" shorter pushrod is not to far off.
#3 The Aluminum block of the LS1 expands 3 times faster than the steel pushrod per every degree of heat, so 200 warmer makes a movement of about .025" throughout the rocker arm mounting point to the cam location. So you have to account for that too.
Basicly if you can get the pushrod close to .025" to what is optimum then you will be o.k. So going with a Comp Cams #7954 pushrod will do, unless you then change the base circle of the cam then the stock #7955 pushrod will work. This could be a good solution to the smaller base circle problem of the 2002 LS6 cam. That cam has a smaller base circle of .0275" so milling the head .030" will now get you 6cc out of the combustion chamber (Down to 59cc in a LS1 head) and make the cam work in a LS1 with the shorter valves. How about them apples!
Bret
One more thought.
#1 The rocker arm has nothing to do with the pushrod length if you mill the head everything else being similar. So a .030" mill would need a .030" longer pushrod.(being that the pushrod is paralell to the cylinder bore, but even at 15 degrees off you would need a .027" shorter pushrod)
#2 The LS1 has Hydraulic rollers, therfore they can move .050" or more. So a .050" shorter pushrod is not to far off.
#3 The Aluminum block of the LS1 expands 3 times faster than the steel pushrod per every degree of heat, so 200 warmer makes a movement of about .025" throughout the rocker arm mounting point to the cam location. So you have to account for that too.
Basicly if you can get the pushrod close to .025" to what is optimum then you will be o.k. So going with a Comp Cams #7954 pushrod will do, unless you then change the base circle of the cam then the stock #7955 pushrod will work. This could be a good solution to the smaller base circle problem of the 2002 LS6 cam. That cam has a smaller base circle of .0275" so milling the head .030" will now get you 6cc out of the combustion chamber (Down to 59cc in a LS1 head) and make the cam work in a LS1 with the shorter valves. How about them apples!
Bret
Re: Pushrod length ? O.k. one more
Whether its true or not, I have read that the LS1s cam journals are fairly large in comparison to a SBC. These oversized cam bearing journals will allow for a much higher lift aftermarket cam to be installed even when the cams base circle is identical to the stock spec.
Fairly Large! how about larger than a Big Block Chevy or a Ford.
The Small Block Jornal is 1.868" and the Big Blcok is 1.968" while the LS1 is 2.165" The problem with that is the base circle is also really big (that's why the cam lobes comp has now for the LS1 have alot less lift than the comparable small block lobes) For example lobe number 3765 which is a LS1 lobe has a rated duration of 268, a .050 Duration of 214 and a lift of .307" While lobe number 3190 is a small block chevy lobe 266 rated duration, 214 .050" duration and .353" lift. That's .046" of lift that I would like to have!
Whether its true or not, I have read that the LS1s cam journals are fairly large in comparison to a SBC. These oversized cam bearing journals will allow for a much higher lift aftermarket cam to be installed even when the cams base circle is identical to the stock spec.
Fairly Large! how about larger than a Big Block Chevy or a Ford.
The Small Block Jornal is 1.868" and the Big Blcok is 1.968" while the LS1 is 2.165" The problem with that is the base circle is also really big (that's why the cam lobes comp has now for the LS1 have alot less lift than the comparable small block lobes) For example lobe number 3765 which is a LS1 lobe has a rated duration of 268, a .050 Duration of 214 and a lift of .307" While lobe number 3190 is a small block chevy lobe 266 rated duration, 214 .050" duration and .353" lift. That's .046" of lift that I would like to have!