What length pushrods do I need?
Thread Starter
Drifting
Joined: Apr 2001
Posts: 1,412
Likes: 2
From: Seneca SC
What length pushrods do I need?
Here is all necessary information (I think), I need to know what length of pushrod to order.
My heads have had the valves sunk .015" in the seat to aid in P to V clearance, and my valves are .070" longer than stock. Heads are milled <.005" (Clean up only)
By my figuring, my valves will be ~.080 taller than stock as assembled. (.015" + .070" - .005" = .080") Do I need longer or shorter pushrods than stock (7.400"), and why?
The rest of my valvetrain is as follows:
Comp "R" lifters
Yella Terra 1.7s
Comp 977 springs
--------------------
2002 M6 Z28: Absolute Speed Stg 2.5 5.3l heads, G5X3, YTs, Comp "R"s, Hooker LTs, 3" duals w/ x-pipe, pulleys, full boltons, full suspension, Wolfe rollbar, Spec S3, Moser 12 bolt w/ 4.30s, and so on, and so on, and so on.....
2002 GMC Z71, 5.3, no mods....ever....I'm serious....
My heads have had the valves sunk .015" in the seat to aid in P to V clearance, and my valves are .070" longer than stock. Heads are milled <.005" (Clean up only)
By my figuring, my valves will be ~.080 taller than stock as assembled. (.015" + .070" - .005" = .080") Do I need longer or shorter pushrods than stock (7.400"), and why?
The rest of my valvetrain is as follows:
Comp "R" lifters
Yella Terra 1.7s
Comp 977 springs
--------------------
2002 M6 Z28: Absolute Speed Stg 2.5 5.3l heads, G5X3, YTs, Comp "R"s, Hooker LTs, 3" duals w/ x-pipe, pulleys, full boltons, full suspension, Wolfe rollbar, Spec S3, Moser 12 bolt w/ 4.30s, and so on, and so on, and so on.....
2002 GMC Z71, 5.3, no mods....ever....I'm serious....
Racer
Joined: Jul 2003
Posts: 398
Likes: 0
From: Calera AL
Re: What length pushrods do I need? (SPANKY LS1)
I recently went through a pushrod dillemma. You should also all 0.005 not subtract it since any milling of the head requires a shorter pushrod.
First milling:
Milling nearly directly affects pushrod length and isn't dependent on rocker ratios so you can
subtract 0.005 from 7.400( stock length) = 7.395
Now the pushrod length for a longer valve 0.070 is affected by the rocker ratio so also subtract
this from the stock length of 7.400
0.070/1.7(rocker ratio)= 0.041
Finally the impact of the sunken valves (0.15) on the pushrod length is also affected by rocker ratio: 0.15/1.7=0.088 ... subtract this too so:
7.400 - 0.005 - 0.041 - 0.088 = 7.354
This is going to radically change your rocker geometry to where the rocker tip may not be in the
center of the valve stem. So you will likely need to shim the rockers and use a shorter pushrod at
the same time to achive both optimal lifter preload of 0.040-0.060 at the lifter and good rocker to
valve geometry. I had to use a 0.030 shim under by rockers and a 7.37 pushrod length to get mine right. You just have to try the combos out and see how they work.
First milling:
Milling nearly directly affects pushrod length and isn't dependent on rocker ratios so you can
subtract 0.005 from 7.400( stock length) = 7.395
Now the pushrod length for a longer valve 0.070 is affected by the rocker ratio so also subtract
this from the stock length of 7.400
0.070/1.7(rocker ratio)= 0.041
Finally the impact of the sunken valves (0.15) on the pushrod length is also affected by rocker ratio: 0.15/1.7=0.088 ... subtract this too so:
7.400 - 0.005 - 0.041 - 0.088 = 7.354
This is going to radically change your rocker geometry to where the rocker tip may not be in the
center of the valve stem. So you will likely need to shim the rockers and use a shorter pushrod at
the same time to achive both optimal lifter preload of 0.040-0.060 at the lifter and good rocker to
valve geometry. I had to use a 0.030 shim under by rockers and a 7.37 pushrod length to get mine right. You just have to try the combos out and see how they work.
Melting Slicks
Joined: Jun 2002
Posts: 3,060
Likes: 3
From: Dublin CA
Re: What length pushrods do I need? (SPANKY LS1)
Stock cam? Any change in base circle radius would need to be factored in also.
You might want to get a Comp Cams 'test pushrod': "Comp Cams pushrod length checker - Designed to be installed as a "test pushrod" to check what length pushrod you need for proper valvetrain geometry. Adjustable from 6.800" to 7.800" in .050" increments. -- PN: 63-7702-1 -- $19.95"
You might want to get a Comp Cams 'test pushrod': "Comp Cams pushrod length checker - Designed to be installed as a "test pushrod" to check what length pushrod you need for proper valvetrain geometry. Adjustable from 6.800" to 7.800" in .050" increments. -- PN: 63-7702-1 -- $19.95"
