What length pushrods do I need???
07-11-2002, 01:26 PM
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What length pushrods do I need??? I'm having my heads ported .035 over for 11:1 what size pushrods do I need? also, do i need different Head gaskets (other than stock)?
thanks in advance for any info.
Devin.
thanks in advance for any info.
Devin.
07-11-2002, 02:19 PM
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Re: What length pushrods do I need??? What's the base circle of your cam? That will ulitmately determine the necessary length. However, unless it's some goofy grind (ie. not a commonly used LS1 cam), I'd bet that you will need 7.35"
07-11-2002, 02:38 PM
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Re: What length pushrods do I need??? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Willwork4mods:
<strong>I'm having my heads ported .035 over for 11:1 what size pushrods do I need? also, do i need different Head gaskets (other than stock)?
thanks in advance for any info.
Devin.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You will need 7.35 length pushrods.
<strong>I'm having my heads ported .035 over for 11:1 what size pushrods do I need? also, do i need different Head gaskets (other than stock)?
thanks in advance for any info.
Devin.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You will need 7.35 length pushrods.
07-11-2002, 05:13 PM
#4
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Re: What length pushrods do I need??? Here is my take...
1. Most high lift cams will have a smaller base circle than the scock cam. That in itself would require [longer] pushrods in order to achieve the same lifter preload as before the stock cam was replaced.
2. If the heads are milled, that would require a [shorter] pushrod in order to achieve the same lifter preload as before.
Conclusion: High lift cam [and] milled heads = Same length pushrod as stock
Not real scientific, but you will be closer to your factory lifter preload if you install a high lift cam and a set of milled heads by just useing the stock length rods since they only are avail. in plus or minus incriments of .050" (50 thousands) from Comp Cams.
Ron,
1. Most high lift cams will have a smaller base circle than the scock cam. That in itself would require [longer] pushrods in order to achieve the same lifter preload as before the stock cam was replaced.
2. If the heads are milled, that would require a [shorter] pushrod in order to achieve the same lifter preload as before.
Conclusion: High lift cam [and] milled heads = Same length pushrod as stock
Not real scientific, but you will be closer to your factory lifter preload if you install a high lift cam and a set of milled heads by just useing the stock length rods since they only are avail. in plus or minus incriments of .050" (50 thousands) from Comp Cams.
Ron,
07-11-2002, 05:33 PM
#5
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Re: What length pushrods do I need??? BTW...
The stock LS1 cam has a base circle of 1.552" across the lobe or 0.776" from the cam centerline out to the lobe heal (backside of the lobe)
That, by the way (0.776"), is 1/2 the distance of the total base circle of 1.552
That 0.776" measurment is what is important because that distance is what determines the lifter preload when the valve is not open. If the distance from centerline to lobe heal on your aftermarket cam was lets say 0.726", that would mean that its .050" less than stock (0.776"), and you then would need .050" longer pushrods in order to achieve the exact same lifter preload as you had before.
And of course, milling the heads works the other way; Take .030" inch off the heads, then you would need .030" shorter pushrods to achieve the exact same preload.
Milled Heads and Cam; More than likely will cancell each other out as far as preload is concerned.
Good news, there is a "fudge factor" built into hyd. lifters. They dont have to have the exact preload (you can give or take a little) How much? Not sure, but I would think about 30 thousands either way. Changing pushrod length or installing shims under the rockers just gets it a little closer to ideal.
Class dismissed! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
The stock LS1 cam has a base circle of 1.552" across the lobe or 0.776" from the cam centerline out to the lobe heal (backside of the lobe)
That, by the way (0.776"), is 1/2 the distance of the total base circle of 1.552
That 0.776" measurment is what is important because that distance is what determines the lifter preload when the valve is not open. If the distance from centerline to lobe heal on your aftermarket cam was lets say 0.726", that would mean that its .050" less than stock (0.776"), and you then would need .050" longer pushrods in order to achieve the exact same lifter preload as you had before.
And of course, milling the heads works the other way; Take .030" inch off the heads, then you would need .030" shorter pushrods to achieve the exact same preload.
Milled Heads and Cam; More than likely will cancell each other out as far as preload is concerned.
Good news, there is a "fudge factor" built into hyd. lifters. They dont have to have the exact preload (you can give or take a little) How much? Not sure, but I would think about 30 thousands either way. Changing pushrod length or installing shims under the rockers just gets it a little closer to ideal.
Class dismissed! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
07-12-2002, 02:13 PM
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Re: What length pushrods do I need??? Great info.. man I love this class <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
ok, so i'm wodering if I should stay with the stockers then.. the cam i'm going with is a
229/229 566/566 112 (as opposed to the B1 I had in there). ???
hmmm.. guess i'll go with the 7.35 's to be safe then right??
ok, so i'm wodering if I should stay with the stockers then.. the cam i'm going with is a
229/229 566/566 112 (as opposed to the B1 I had in there). ???
hmmm.. guess i'll go with the 7.35 's to be safe then right??
07-12-2002, 03:58 PM
#7
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Re: What length pushrods do I need??? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Willwork4mods:
<strong>Great info.. man I love this class <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
ok, so i'm wodering if I should stay with the stockers then.. the cam i'm going with is a
229/229 566/566 112 (as opposed to the B1 I had in there). ???
hmmm.. guess i'll go with the 7.35 's to be safe then right??</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Well, if your heads have never been milled, you sure don't want shorter pushrods with a cam that has a smaller base circle. Don't use 7.35" rods. They are 50 thousands shorter than the stock rods which are 7.40"
Non-milled LS1 heads with an aftermarket high lift cam will need pushrods slightly longer than stock. I don't know what the exact base circle on that cam is, but at least use stock length pushrods, certainly not shorter.
Too short of a pushrod will cause excessive valve train noise, and possably keep the valves from opening to there fullest.
Too long of a pushrod may cause the valves not not fully close which will cause a severe loss in power, and very poor idle. May not run at all.
Again, as long as your heads have not been milled, I would just stay with stock length 7.40" rods with that cam. Very slightly longer pushrods may be ideal [but] you dont know the exact base circle that cam has, unless Comp Cams can provde that info..... Its not on the cam card, although it sure should be. Stock length should be fine. Remember, there is a fudge factor (permissible variation) as far as preload goes.....
Ron,
<strong>Great info.. man I love this class <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
ok, so i'm wodering if I should stay with the stockers then.. the cam i'm going with is a
229/229 566/566 112 (as opposed to the B1 I had in there). ???
hmmm.. guess i'll go with the 7.35 's to be safe then right??</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Well, if your heads have never been milled, you sure don't want shorter pushrods with a cam that has a smaller base circle. Don't use 7.35" rods. They are 50 thousands shorter than the stock rods which are 7.40"
Non-milled LS1 heads with an aftermarket high lift cam will need pushrods slightly longer than stock. I don't know what the exact base circle on that cam is, but at least use stock length pushrods, certainly not shorter.
Too short of a pushrod will cause excessive valve train noise, and possably keep the valves from opening to there fullest.
Too long of a pushrod may cause the valves not not fully close which will cause a severe loss in power, and very poor idle. May not run at all.
Again, as long as your heads have not been milled, I would just stay with stock length 7.40" rods with that cam. Very slightly longer pushrods may be ideal [but] you dont know the exact base circle that cam has, unless Comp Cams can provde that info..... Its not on the cam card, although it sure should be. Stock length should be fine. Remember, there is a fudge factor (permissible variation) as far as preload goes.....
Ron,
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07-12-2002, 04:20 PM
#9
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Re: What length pushrods do I need??? </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>The only time I can vision using shorter pushrods would be if you were using milled LS1 heads with the stock cam (or a cam with the same base circle as stock)
Bottom line is: These higher lift aftermarket cams will have a SMALLER base circle than stock. A shorter pushrod combined with a cam that has allready a smaller base circle will only combine to make for excessive valvetrain clearance (ie: no preload on the lifter)
Now with 5.4 or 6.0 heads (non-standard heads), I dont have a clue.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">
<strong>The only time I can vision using shorter pushrods would be if you were using milled LS1 heads with the stock cam (or a cam with the same base circle as stock)
Bottom line is: These higher lift aftermarket cams will have a SMALLER base circle than stock. A shorter pushrod combined with a cam that has allready a smaller base circle will only combine to make for excessive valvetrain clearance (ie: no preload on the lifter)
Now with 5.4 or 6.0 heads (non-standard heads), I dont have a clue.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">
07-12-2002, 06:02 PM
#10
Re: What length pushrods do I need??? This poses another question I have now..
Lets say you take a stock 98 cam (202/210 .472/.479 [19.7mm base = .7462"]) and have it reground to a 222/230 .563/.570.. This would mean the top of the lobe would have to be cut down due to the durration. The difference of the base would be greater than .091. Lets say that it would come to an exact .1 difference on the base, taking in the consideration of the change on the top of the lobe. Hypathetically your base may now be .6462".
Now for my questions..
1) Is my math right?
2) You could no longer use stock rods because there would be way too much gap creating not enough lift? ( 0.1" difference ) All in all you would need longer pushrods to do this?
Something doesn't look right to me on my thoughts..
<small>[ July 12, 2002, 06:03 PM: Message edited by: LIL SS ]</small>
Lets say you take a stock 98 cam (202/210 .472/.479 [19.7mm base = .7462"]) and have it reground to a 222/230 .563/.570.. This would mean the top of the lobe would have to be cut down due to the durration. The difference of the base would be greater than .091. Lets say that it would come to an exact .1 difference on the base, taking in the consideration of the change on the top of the lobe. Hypathetically your base may now be .6462".
Now for my questions..
1) Is my math right?
2) You could no longer use stock rods because there would be way too much gap creating not enough lift? ( 0.1" difference ) All in all you would need longer pushrods to do this?
Something doesn't look right to me on my thoughts..
<small>[ July 12, 2002, 06:03 PM: Message edited by: LIL SS ]</small>
07-12-2002, 08:11 PM
#11
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Re: What length pushrods do I need??? LIL SS....
Your right in saying the LS1 base circle is 19.7 mm, but that equates to 0.7755905511811023", or simply put 0.776" as I wrote before.
You inacuratly said 19.7 mm is 0.746"
I called Comp Cams tech line today and asked what the base circle was on there aftermarket LS1 cams. The guy said it was the same as stock. Well, I can tell you, someone else here had the base circle of his Comp Cams LS1 cam measured on a Cam Doctor, and it was indeed smaller than the stock cam that came out of the engine.
I am at the point, I dont know who to believe.
Maybe someone that has a Comp Cam sitting around can have it measured with a set of calipers. That would be helpfull.
Your right in saying the LS1 base circle is 19.7 mm, but that equates to 0.7755905511811023", or simply put 0.776" as I wrote before.
You inacuratly said 19.7 mm is 0.746"
I called Comp Cams tech line today and asked what the base circle was on there aftermarket LS1 cams. The guy said it was the same as stock. Well, I can tell you, someone else here had the base circle of his Comp Cams LS1 cam measured on a Cam Doctor, and it was indeed smaller than the stock cam that came out of the engine.
I am at the point, I dont know who to believe.
Maybe someone that has a Comp Cam sitting around can have it measured with a set of calipers. That would be helpfull.
07-12-2002, 10:01 PM
#12
Re: What length pushrods do I need??? LIL SS....
Your right in saying the LS1 base circle is 19.7 mm, but that equates to 0.7755905511811023", or simply put 0.776" as I wrote before.
You inacuratly said 19.7 mm is 0.746"
You are right.. I haven't learned how to use a calculator yet.. put in 26.4 instead of 25.4.. Sorry about that..
Even then though at .7755 - the estimated .1 I figured base would be .6755. With the stock push rod I tend to think there would be issues..
<small>[ July 12, 2002, 10:02 PM: Message edited by: LIL SS ]</small>
Your right in saying the LS1 base circle is 19.7 mm, but that equates to 0.7755905511811023", or simply put 0.776" as I wrote before.
You inacuratly said 19.7 mm is 0.746"
You are right.. I haven't learned how to use a calculator yet.. put in 26.4 instead of 25.4.. Sorry about that..
Even then though at .7755 - the estimated .1 I figured base would be .6755. With the stock push rod I tend to think there would be issues..
<small>[ July 12, 2002, 10:02 PM: Message edited by: LIL SS ]</small>
07-12-2002, 10:43 PM
#13
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Re: What length pushrods do I need??? LIL SS....
I can understand where your commin from, but in real life, they dont decrease the base circle in [equal] proportion the the increase in lobe lift.
A SB chevy engine has very small cam journals in comparison to the LS1. Because of the small journals, the SB Chev cam needs a smaller base circle when lobe lift is increased so the cam will be able to literally slide into the engine without the lobes contacting the block cam journals.
Since the LS1 has such large journals, the cam lobe can be increased without interferance with the block even when the base circle is not decreased.
Again, if I was to just change cams only, I would stick with the stock length pushrods. Certainly, you would not want shorter rods.
I can understand where your commin from, but in real life, they dont decrease the base circle in [equal] proportion the the increase in lobe lift.
A SB chevy engine has very small cam journals in comparison to the LS1. Because of the small journals, the SB Chev cam needs a smaller base circle when lobe lift is increased so the cam will be able to literally slide into the engine without the lobes contacting the block cam journals.
Since the LS1 has such large journals, the cam lobe can be increased without interferance with the block even when the base circle is not decreased.
Again, if I was to just change cams only, I would stick with the stock length pushrods. Certainly, you would not want shorter rods.
07-12-2002, 11:09 PM
#14
Re: What length pushrods do I need??? I'm a little more lost now.. How would you be able to increase lift by say .1 if .1 is not removed off the bottom of the lobe? Sory just trying to figure this out as I was thinking of doing a custom grind off a 98 cam. Going from the stock 202/210 .472/.479 base 19.7mm to 224/227 .563/.569.. I'm concerned aobout stock length push rods when I think about it..
Would you have to add material to the top of the lobe?
<small>[ July 12, 2002, 11:10 PM: Message edited by: LIL SS ]</small>
Would you have to add material to the top of the lobe?
<small>[ July 12, 2002, 11:10 PM: Message edited by: LIL SS ]</small>
07-13-2002, 09:18 AM
#15
Re: What length pushrods do I need??? </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:
Maybe someone that has a Comp Cam sitting around can have it measured with a set of calipers. That would be helpfull.[/QB]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I went out and measured my Comp Cam and its 1.493 base circle. So centerline to heal would be .7465
I'm going to mill my heads .030 so I guess I will use 7.40 push rods. Before reading this post I was going to use 7.35. Thanks for the info.
Kevin
Maybe someone that has a Comp Cam sitting around can have it measured with a set of calipers. That would be helpfull.[/QB]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I went out and measured my Comp Cam and its 1.493 base circle. So centerline to heal would be .7465
I'm going to mill my heads .030 so I guess I will use 7.40 push rods. Before reading this post I was going to use 7.35. Thanks for the info.
Kevin
07-13-2002, 10:15 AM
#16
TECH Fanatic
Re: What length pushrods do I need??? NB99Z....
Your right about that....
That worked out perfect for you. That centerline to lobe heal distance on your new cam is almost [exactly] .030" less than stock.
Mill .030" off the heads, install those stock length hardened pushrods, and you my friend should have exactly the same preload as you had before changing anything from stock. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Great...
At least you will know that the increased valvetrain noise you get from your aftermarket cam with its fast ramp speed is NOT due to improper lifter preload. <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />
It's just too bad we dont have adjustable rocker arms on these engines (ala SB Chevy) <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />
Anyway, I had the same situation working for many years on Turbo Buick engines (no rocker adjustment)
<small>[ July 13, 2002, 10:27 AM: Message edited by: Kimchee and Rice ]</small>
Your right about that....
That worked out perfect for you. That centerline to lobe heal distance on your new cam is almost [exactly] .030" less than stock.
Mill .030" off the heads, install those stock length hardened pushrods, and you my friend should have exactly the same preload as you had before changing anything from stock. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Great...
At least you will know that the increased valvetrain noise you get from your aftermarket cam with its fast ramp speed is NOT due to improper lifter preload. <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />
It's just too bad we dont have adjustable rocker arms on these engines (ala SB Chevy) <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />
Anyway, I had the same situation working for many years on Turbo Buick engines (no rocker adjustment)
<small>[ July 13, 2002, 10:27 AM: Message edited by: Kimchee and Rice ]</small>
07-13-2002, 01:02 PM
#18
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Re: What length pushrods do I need??? I just rebuilt my engine with an LS6 block, Comp cam and 6.0 liter heads. I was not told if the heads were machined or not. On the initial start-up I had a dead cylinder (#2) and found that the reason was that the exhaust valve was staying open. It also showed random misfires on other cylinders. I put in the 7.350 pushrods and the car now runs fine but it clatters bad cold and at lower RPM's. I was told by the machinist at the head shop to get .027 shorter than stock pushrods which I guess will have to be custom. I would like to know what kind of tolerance these hydraulic lifters have because I'm getting tired of changing pushrods.