Pushrod length with new heads?
Thread Starter
11 Second Club
iTrader: (18)
Joined: Mar 2008
Posts: 8,358
Likes: 27
From: Northwest AR
Pushrod length with new heads? I have aquired a pair of 799 heads with a recent "valve job" (how extensive I'm unsure but the valves are snug in the seals) I am looking to put on my car.
Was going to have them ported first but it looks like that's going to be out of budget for a good while so I'm debating just getting them milled a little and putting them on with new GM mls gaskets for now since they are just going to be sitting in the corner anyway when I would much rather put them to use
Currently I have stock 853 '99 heads, felpro replacement gaskets from Parts Plus, GMPP lifters (look like stock to me but that's what I bought them as since one of mine was bad), stock rockers, comp xe lobed 230/224 111+3 cam, and comp 7.4 pushrods
I bought the 7.4 pushrods when I ordered the cam through comp as its what my rep told me to get
I'm just confused on how much to mill the heads, and how that will affect my pushrod length and intake port alignment. I can order a pushrod length checking tool but it would be nice if I could have a good guess what to expect.
The heads don't have springs so I would be moving my pac 918 equivilents over to the new heads and selling the 853s if possible.
Was going to have them ported first but it looks like that's going to be out of budget for a good while so I'm debating just getting them milled a little and putting them on with new GM mls gaskets for now since they are just going to be sitting in the corner anyway when I would much rather put them to use
Currently I have stock 853 '99 heads, felpro replacement gaskets from Parts Plus, GMPP lifters (look like stock to me but that's what I bought them as since one of mine was bad), stock rockers, comp xe lobed 230/224 111+3 cam, and comp 7.4 pushrods
I bought the 7.4 pushrods when I ordered the cam through comp as its what my rep told me to get
I'm just confused on how much to mill the heads, and how that will affect my pushrod length and intake port alignment. I can order a pushrod length checking tool but it would be nice if I could have a good guess what to expect.
The heads don't have springs so I would be moving my pac 918 equivilents over to the new heads and selling the 853s if possible.
TECH Resident
Joined: Dec 2004
Posts: 845
Likes: 0
From: K-W, Ontario
The first thing I would consider is what static and dynamic compression
the new heads will yield 'as is' based on the intake closing point of the
camshaft installed with the 3 degrees of ground in advance.
As for the pushrod length, I wouldn't accept any guess values. Do the right
thing and buy/borrow the pushrod tool and measure the length with everything
torqued down as it would be when the engine is complete.
The rocker design, spring install height, milling, lifter, etc. will all come into
account when figuring the final length.
the new heads will yield 'as is' based on the intake closing point of the
camshaft installed with the 3 degrees of ground in advance.
As for the pushrod length, I wouldn't accept any guess values. Do the right
thing and buy/borrow the pushrod tool and measure the length with everything
torqued down as it would be when the engine is complete.
The rocker design, spring install height, milling, lifter, etc. will all come into
account when figuring the final length.
You could estimate it then confirm with a measurement, but I wouldn't buy pushrods based on the estimate or any recommendations. The tool is $17, just take the measurements so you know it is correct.
The other issue is if the valves are deeper/taller, then the wipe may need correction as well. Do this prior to measuring for pushrod length.
The other issue is if the valves are deeper/taller, then the wipe may need correction as well. Do this prior to measuring for pushrod length.
On The Tree
Joined: Apr 2010
Posts: 130
Likes: 0
From: niles,mi
The recommended pushrods for my build were 7.4's. I ended up needing 7.45's. Buy a pushrod checker. Put a wrench on your underdrive pulley and turn the crank until one of your valves starts to open or close. Then on that valve, finger tighten the rocker down until it just has no lash. Then take a torque wrench set for 22ft/lbs and tighten the rocker down. If the pushrod is of the correct size you should get between 1-1/4 to 2-1/4 turns before the torque wrench clicks. Anything under you need a longer pushrod. Anything over you need a shorter pushrod. On mine, with the 7.4's I was only getting between 1/4 to 1/2 a turn. I had to go to 7.45's to get it right. You should check both intake and exhaust valves because depending on your setup you might actually need different lengths between the intake and exhaust.
You don't go by just any valve that moves either. When the exhaust opens, you check the intake since it will always be on it's base circle. When the intake closes, you check the exhaust.
