pushrod question
Thread Starter
Melting Slicks
Joined: Nov 2003
Posts: 3,011
Likes: 9
From: Dublin GA
pushrod question
Anyone know if I will still be able to use my 7.425 pushrods when I go from stock LS1 heads to 64cc AFR heads. Since I don't know how much AFR would have milled to get them 64ccc, I wasn't sure.
I don't have a checker :bang:
I don't have a checker :bang:
Tech Contributor
Joined: Sep 2005
Posts: 1,731
Likes: 82
From: New Market AL
Buy the $20 adjustable pushrod and check after you install the AFR heads. Nobody can answer this question properly for you. And are you going to trust the opinion of a stranger on the internet to properly set up your valvetrain?
Melting Slicks
Joined: Dec 2003
Posts: 2,857
Likes: 2
From: pawleys island sc
no one can Guess rod length, regardless what a couple of hundred guys
on this Forum will tell you.
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
Aren't the stock rods 7.400"? If the heads are milled, wouldn't you need a shorter pushrod.
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
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Thread Starter
Melting Slicks
Joined: Nov 2003
Posts: 3,011
Likes: 9
From: Dublin GA
I used this method;
. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
and using my 7.425s only have between 1/2 and 3/4 turn, so it looks like I will need a 7.45-7.475 if my calculations are correct.
I will use my checker tomorrow to verify
Last edited by Blow Torch; May 28, 2011 at 08:18 AM.
Racer
Joined: Feb 2003
Posts: 418
Likes: 28
From: Evansville IN
I had my L98 block zero decked. Stock was 7.2". With TFS heads and Comp. Pro Magnum rockers I would have been guessing a long time. In the end I ended up with 7.050 to get the geometry correct. I also had a pretty radical cam with a smaller base circle so I thought I'd need a longer pushrod but that still wan't the case.
Point is, yes, measure them with an adjustable tool and yes, I did need a MUCH shorter than standard pushrod because of the decked block and aftermarket heads.
Last edited by SMaster; May 28, 2011 at 07:55 AM.
Racer
Joined: Feb 2003
Posts: 418
Likes: 28
From: Evansville IN
I had lifter pump up with the stock lifters limiting RPM's to about 54-5600 with TFS springs, Harland Sharp rockers.
After I went with Comp Cams lifters, dual 1.46 springs, Pro Magum rockers I could do 6400 which is where I needed to shift anyway. But, the lifter pump up was gone.
I've been reading about the LS1 here and preload but seems to me enough to make it run quiet should be enough.