Rocketman442
New Member
- Joined
- Jun 11, 2003
Good day, all. I am currently rebuilding an '87 GN motor, which includes porting and flow testing of the heads. Having done the bowl work, I found that the port responded favorably the more material I removed from the pushrod pinch. Well, I found out the hard way how wide the intake ports can go. Ports are matched to a Fel-Pro 1200. Here are my findings for your perusal:
Cyl. #2-Broke through at approx. .97" width, .71" into the port.
Cyl. #4-Broke through at approx. 1.00" width, .73" into the port.
Cyl. #6-The most forgiving. Developed a paper-thin spot around the tangent point of the wall and the radius coming off the roof, about .77" into the port. Pinch width is approx. 1.075".
These heads will be run. I lined the pushrod holes with hobby shop brass tubing using 9/16" on 2 and 6, and 19/32" on cyl. 4. I passed an appropriate sized drill through the holes on 2 and 6 and touched them with a tootsie roll until the tubing was snug when pushed in by hand. Number 4 just needed some work with the tootsie roll. I used Loctite 680, and peened the top and bottom. While this is a relatively simple fix, I'd recommend that the pushrod pinch be left around .85-.90", unless you're brave. I don't feel that the extra material would make a significant difference on the flowbench. I will verify this with the other head, which is yet untouched.
As an aside: In a bid to keep rpm down for a happy shortblock, I will be staying conservative with the cam (210/205, or so) and don't expect to see even .500" lift. As such, my focus is on the .200-.400 lift #'s. Peak #'s at .500" should, hopefully, be about 200/160 @28". Currently, the heads are slated to retain the stock valves. But, I will be testing the stock and Manley's back to back. If the Manley's flow 5% or better than stock, they will be utilized.
Thank you, all for a greatly informative site.
Cyl. #2-Broke through at approx. .97" width, .71" into the port.
Cyl. #4-Broke through at approx. 1.00" width, .73" into the port.
Cyl. #6-The most forgiving. Developed a paper-thin spot around the tangent point of the wall and the radius coming off the roof, about .77" into the port. Pinch width is approx. 1.075".
These heads will be run. I lined the pushrod holes with hobby shop brass tubing using 9/16" on 2 and 6, and 19/32" on cyl. 4. I passed an appropriate sized drill through the holes on 2 and 6 and touched them with a tootsie roll until the tubing was snug when pushed in by hand. Number 4 just needed some work with the tootsie roll. I used Loctite 680, and peened the top and bottom. While this is a relatively simple fix, I'd recommend that the pushrod pinch be left around .85-.90", unless you're brave. I don't feel that the extra material would make a significant difference on the flowbench. I will verify this with the other head, which is yet untouched.
As an aside: In a bid to keep rpm down for a happy shortblock, I will be staying conservative with the cam (210/205, or so) and don't expect to see even .500" lift. As such, my focus is on the .200-.400 lift #'s. Peak #'s at .500" should, hopefully, be about 200/160 @28". Currently, the heads are slated to retain the stock valves. But, I will be testing the stock and Manley's back to back. If the Manley's flow 5% or better than stock, they will be utilized.
Thank you, all for a greatly informative site.