How do you figure pushrod length using cam base circle
Thread Starter
Melting Slicks
Joined: May 2005
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From: Leon Iowa
St. Jude Donor '06-'07-'08-'09
How do you figure pushrod length using cam base circle
I have the base circle of my cam but what is the mathematical procedure for figuring the correct pushrod length using the new base circle of the cam?
Burning Brakes
Joined: Nov 2006
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From: Goose Creek SC
Hammer
Melting Slicks
Joined: Aug 2002
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From: California USA
base circles: (25.4mm = 1")
02-04Z = 19mm
01Z = 19.3mm
LS1 = 19.7mm
So, I guess the formula would be:
( CAM1 BASE DIAMETER - CAM2 BASE DIAMETER)/2
Depending on which is larger, will decide longer or shorter pushrods.
I believe most aftermarket stuff is LS1 type lobes. So, lets say you put in a LS1 aftermarket cam in a Z06.
New Pushrod = (19.7-19)/2 or 0.35mm shorter or (0.0138" shorter). From past experience, I believe 1/2 turn on lifter = 0.050".
Note also, the Z06 valve is 0.6mm longer, ie 0.6/1.7, or 0.0139" the same amount had from a different pushrod.
02-04Z = 19mm
01Z = 19.3mm
LS1 = 19.7mm
So, I guess the formula would be:
( CAM1 BASE DIAMETER - CAM2 BASE DIAMETER)/2
Depending on which is larger, will decide longer or shorter pushrods.
I believe most aftermarket stuff is LS1 type lobes. So, lets say you put in a LS1 aftermarket cam in a Z06.
New Pushrod = (19.7-19)/2 or 0.35mm shorter or (0.0138" shorter). From past experience, I believe 1/2 turn on lifter = 0.050".
Note also, the Z06 valve is 0.6mm longer, ie 0.6/1.7, or 0.0139" the same amount had from a different pushrod.
Last edited by 427CPE; Jan 6, 2007 at 04:25 AM.
Burning Brakes
Joined: Nov 2006
Posts: 1,071
Likes: 0
From: Goose Creek SC
base circles: (25.4mm = 1")
02-04Z = 19mm
01Z = 19.3mm
LS1 = 19.7mm
So, I guess the formula would be:
( CAM1 BASE - CAM2 BASE)/2
Depending on which is larger, will decide longer or shorter pushrods.
I believe most aftermarket stuff is LS1 type lobes. So, lets say you put in a LS1 aftermarket cam in a Z06.
New Pushrod = (19.7-19)/2 or 0.35mm shorter or (0.0138" shorter). From past experience, I believe 1/2 turn on lifter = 0.050".
02-04Z = 19mm
01Z = 19.3mm
LS1 = 19.7mm
So, I guess the formula would be:
( CAM1 BASE - CAM2 BASE)/2
Depending on which is larger, will decide longer or shorter pushrods.
I believe most aftermarket stuff is LS1 type lobes. So, lets say you put in a LS1 aftermarket cam in a Z06.
New Pushrod = (19.7-19)/2 or 0.35mm shorter or (0.0138" shorter). From past experience, I believe 1/2 turn on lifter = 0.050".
Hammer
Thread Starter
Melting Slicks
Joined: May 2005
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Likes: 12
From: Leon Iowa
St. Jude Donor '06-'07-'08-'09
yes, my stock cam is base circle radius of .775 with a base circle diamater of 1.550. The Comp cam I have has a base circle radius of .732 and the base circle diamater of 1.463. I had a guy on LS1 tech figure it and he said I needed 7.425 pushrods, using stock heads. I would just like to know how he got that measurment
Melting Slicks
Joined: Aug 2002
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From: California USA
Burning Brakes
Joined: Nov 2006
Posts: 1,071
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From: Goose Creek SC
Melting Slicks
Joined: Aug 2002
Posts: 2,737
Likes: 2
From: California USA
yes, my stock cam is base circle radius of .775 with a base circle diamater of 1.550. The Comp cam I have has a base circle radius of .732 and the base circle diamater of 1.463. I had a guy on LS1 tech figure it and he said I needed 7.425 pushrods, using stock heads. I would just like to know how he got that measurment
19.685mm - 18.5928mm = 1.0922mm (so, 0.043" longer pushrod needed)
So, 7.4 + 0.043 = 7.443, rounded = 7.425, IF IF the stock pushrod really is 7.4", better measure it.
(corrected, thanks hammer)
Last edited by 427CPE; Jan 6, 2007 at 04:20 AM.
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Burning Brakes
Joined: Nov 2006
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From: Goose Creek SC
yes, my stock cam is base circle radius of .775 with a base circle diamater of 1.550. The Comp cam I have has a base circle radius of .732 and the base circle diamater of 1.463. I had a guy on LS1 tech figure it and he said I needed 7.425 pushrods, using stock heads. I would just like to know how he got that measurment
Hammer
Burning Brakes
Joined: Nov 2006
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From: Goose Creek SC
Hammer
Last edited by thehammer69; Jan 6, 2007 at 04:18 AM.
Melting Slicks
Joined: Aug 2002
Posts: 2,737
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From: California USA
Based on your radius measurements...you would need a pushrod .043" longer than your stock rods to achieve an identical preload. Assuming you have 7.4's as stock....your length needed would be 7.443. Since Push rods come in .025 increments, I would use a 7.450" push rod.
Hammer
Hammer
Thread Starter
Melting Slicks
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From: Leon Iowa
St. Jude Donor '06-'07-'08-'09
Based on your radius measurements...you would need a pushrod .043" longer than your stock rods to achieve an identical preload. Assuming you have 7.4's as stock....your length needed would be 7.443. Since Push rods come in .025 increments, I would use a 7.450" push rod.
Hammer
Hammer
Melting Slicks
Joined: Aug 2002
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From: California USA
Well, if you have 0.060" preload on a stock lifter (just a guess) w/the 7.385" pushrod, then, preload will drop 0.043" by using the stock pushrod and new cam. This means, you will have a preload of 0.017" and the stock pushrod is theoretically too short.
Last edited by 427CPE; Jan 6, 2007 at 04:42 AM.
Burning Brakes
Joined: Nov 2006
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From: Goose Creek SC
And as "427" already stated, with the .043" loss in preload, you will most likely be under spec. Stock OEM lifers have a .040-.080 spec and optimally, IMHO, would be best in the .060-.080 range.
Also, the new push rods should be hardened which should minimize flex caused by the higher lift of the new cam.
Hammer
Team Owner
Joined: Sep 2001
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From: Lake Elsinore, CA
Remember that the oiling hole in the pushrod reduces the actul length because the "tip of the pushrod is missing due to the hole being there. The effective length of the stock lifter is 7.400" if you calculate the missing tip back in. Also, the effective length is relevant because the seat of the rocker for the pushrod length is hemispherical so the pushrod sits in the rocker and works as if it were solid and had a rounded end.
Here's a couple of good articles on pushrods.
http://www.compcams.com/information/Products/Pushrods/
http://compcams.com/Community/Articl...?ID=1398679009
Here's a couple of good articles on pushrods.
http://www.compcams.com/information/Products/Pushrods/
http://compcams.com/Community/Articl...?ID=1398679009
Team Owner
Joined: Mar 1999
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From: At the beach in little Rhody
Marc,
All pushrods are measured in gauge length. If I remember, you bought an adjustable pushrod. Open the adjustable pushrod to the same length as your stock pushrods and then use the two white lines on the adjustable and figure the stock length. Then add the 0.043" to it and see what you come up with. Don't measure with a vernier, use the adjustable so you are measuring gauge length to start with.
I did listen to your video, it is louder than mine.
All pushrods are measured in gauge length. If I remember, you bought an adjustable pushrod. Open the adjustable pushrod to the same length as your stock pushrods and then use the two white lines on the adjustable and figure the stock length. Then add the 0.043" to it and see what you come up with. Don't measure with a vernier, use the adjustable so you are measuring gauge length to start with.
I did listen to your video, it is louder than mine.
Thread Starter
Melting Slicks
Joined: May 2005
Posts: 3,394
Likes: 12
From: Leon Iowa
St. Jude Donor '06-'07-'08-'09
Marc,
All pushrods are measured in gauge length. If I remember, you bought an adjustable pushrod. Open the adjustable pushrod to the same length as your stock pushrods and then use the two white lines on the adjustable and figure the stock length. Then add the 0.043" to it and see what you come up with. Don't measure with a vernier, use the adjustable so you are measuring gauge length to start with.
I did listen to your video, it is louder than mine.
All pushrods are measured in gauge length. If I remember, you bought an adjustable pushrod. Open the adjustable pushrod to the same length as your stock pushrods and then use the two white lines on the adjustable and figure the stock length. Then add the 0.043" to it and see what you come up with. Don't measure with a vernier, use the adjustable so you are measuring gauge length to start with.
I did listen to your video, it is louder than mine.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Each turn of the adjustable pushrod, where the white lines coincide with each other, is 0.050" longer. If you have the one I think you do, a Comp Cams 6.800" pushrod, then you would have:
6.800 + 11 X 0.050 = 7.350
The Comp Cams I am thinking of is:
Comp Cams pushrod length checker. Adjustable from 6.800" to 7.800" in .050" increments.
So your previous post on the stockers being 7.385 may not be far off. Then if you look at 7.385" + 0.043" = 7.428"
Do you have any access to a dial indicator?
6.800 + 11 X 0.050 = 7.350
The Comp Cams I am thinking of is:
Comp Cams pushrod length checker. Adjustable from 6.800" to 7.800" in .050" increments.
So your previous post on the stockers being 7.385 may not be far off. Then if you look at 7.385" + 0.043" = 7.428"
Do you have any access to a dial indicator?
Thread Starter
Melting Slicks
Joined: May 2005
Posts: 3,394
Likes: 12
From: Leon Iowa
St. Jude Donor '06-'07-'08-'09
Each turn of the adjustable pushrod, where the white lines coincide with each other, is 0.050" longer. If you have the one I think you do, a Comp Cams 6.800" pushrod, then you would have:
6.800 + 11 X 0.050 = 7.350
The Comp Cams I am thinking of is:
Comp Cams pushrod length checker. Adjustable from 6.800" to 7.800" in .050" increments.
So your previous post on the stockers being 7.385 may not be far off. Then if you look at 7.385" + 0.043" = 7.428"
Do you have any access to a dial indicator?
6.800 + 11 X 0.050 = 7.350
The Comp Cams I am thinking of is:
Comp Cams pushrod length checker. Adjustable from 6.800" to 7.800" in .050" increments.
So your previous post on the stockers being 7.385 may not be far off. Then if you look at 7.385" + 0.043" = 7.428"
Do you have any access to a dial indicator?