Rocker Arms
Thread Starter
Racer
Joined: Feb 2007
Posts: 389
Likes: 7
From: Cliffwood Beach NJ
Rocker Arms
Considering switching rocker arms from 1:5 to 1:6 (3/8 stud). The heads are AFR. Would they be a direct bolt on, or would there be any machine work needed. Found the following on Harland sharp's website and I don't know if its applicable "SB Heads with the pushrods guided in the head cannot use 1.6:1 roller rockers, unless you machine the pushrod hole to allow for it. These rockers are designed to clear up to a 1.450 diameter valvespring." Thanks in advance for the input.
Le Mans Master
Joined: Mar 2004
Posts: 7,502
Likes: 1,509
From: Little Rock AR
Arch,
Kind of surprized nobody answered you but then again, I do not click into this part of town very often.
The factory heads have an obround (oval) punched hole in the head that the pushrods ride in. This hole is needed to keep the tip of the rocker arm in line with the tip of the valve stem. Basicaly it keeps the valvetrain in alignment. This hole is not sized for aftermarket ratio rockers as it would be in the wrong place (too small). If you want to add high ratio rockers to stock heads, you can drill the hole bigger and add screw-in studs and guideplates to keep the valvetrain in alignment.
As for aftermarket heads - the ones that have screw-in studs and guideplates "as produced" will probably be fine as the holes are already bigger to start with. There are some aftermarket heads with factory style slots and those will need to be reworked if you want to add high ratio rockers. The vast majority of aftermarket heads will accept them without additional modifications.
Probably way too long an answer for a simple question.
-Mark.
Kind of surprized nobody answered you but then again, I do not click into this part of town very often.
The factory heads have an obround (oval) punched hole in the head that the pushrods ride in. This hole is needed to keep the tip of the rocker arm in line with the tip of the valve stem. Basicaly it keeps the valvetrain in alignment. This hole is not sized for aftermarket ratio rockers as it would be in the wrong place (too small). If you want to add high ratio rockers to stock heads, you can drill the hole bigger and add screw-in studs and guideplates to keep the valvetrain in alignment.
As for aftermarket heads - the ones that have screw-in studs and guideplates "as produced" will probably be fine as the holes are already bigger to start with. There are some aftermarket heads with factory style slots and those will need to be reworked if you want to add high ratio rockers. The vast majority of aftermarket heads will accept them without additional modifications.
Probably way too long an answer for a simple question.
-Mark.
NCM Grand Opening Veteran
Joined: Sep 2005
Posts: 20,979
Likes: 384
From: South of giving a damn
St. Jude Donor '11, '17
You didn't say what rockers you were considering using. Beware, on AFR heads if you try to use Comp Pro Mag rockers with 3/8 studs you will break the rocker stud. You are required to use a longer rocker stud with the 3/8 stud. IMO, if you are going to switch to 1.6 arms then also switch to 7/16 studs. Also, do you have the piston clearance to move to 1.6?
Thread Starter
Racer
Joined: Feb 2007
Posts: 389
Likes: 7
From: Cliffwood Beach NJ
Dont know if anybody cares, but have been to the track couple times since making the change. This past weekend set new personal bests of 12.21 against previous 12.24 and 116.82 against 115.95. Got five runs in 12.2s and 12.3s and all runs were between 116.82 and 116.38. Don't know if rocker arms made much difference or if it was the great weather and my experimenting with higher shift points. (previuos best figures came early in the spring with temp in 50s.
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
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Congratulations on the new bests!
You might experiment a little with the rockers. Often small blocks respond to 1.6's on intakes only...and other times on outer 4 cyliders only.
Can't hurt to play some....
JIM
You might experiment a little with the rockers. Often small blocks respond to 1.6's on intakes only...and other times on outer 4 cyliders only.
Can't hurt to play some....
JIM
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2024 C3 of the Year Finalist- Modified
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I've had a few Crane mech rollers in my 383's. You end up with .560/.579 minus the lash number of .020 ish. I just wish that Crane had more options on custom lobes
IMO - If your heads have max CFM at say .600 lift you want to get the valves somewhat above the .600 lift to get the most time at max flow possible. To do this i used rockers with 1.65 I and 1.6 exhaust. My present motor I just went for it and installed 1.7's
IMO - If your heads have max CFM at say .600 lift you want to get the valves somewhat above the .600 lift to get the most time at max flow possible. To do this i used rockers with 1.65 I and 1.6 exhaust. My present motor I just went for it and installed 1.7's
Racer
Joined: Sep 2007
Posts: 380
Likes: 1
From: Down South
You didn't say what rockers you were considering using. Beware, on AFR heads if you try to use Comp Pro Mag rockers with 3/8 studs you will break the rocker stud. You are required to use a longer rocker stud with the 3/8 stud. IMO, if you are going to switch to 1.6 arms then also switch to 7/16 studs. Also, do you have the piston clearance to move to 1.6?
