Porting school of hard knocks

[Rocketman442]

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.

 

[chris]

Can you show us some pics of your findings and handy work.

 

[Rocketman442]

Pictures

I had intended on including pictures, but my digital camera sucks. I will attempt to procure a decent camera and try to post pix in the next week.

 

[strikeeagle]

Your experience underlines why I'd leave porting to the professionals, in particular Champion.

Champion's CNC program must be set up somewhat conservatively in order to accommodate the natural variation in head castings.

I'm sure hand porting can achieve more flow. Whether this improvement matters in the real world (for us mortals - short of all out competition) is doubtful in my mind.

I wonder how many hand porters have broken through like you, or left so little metal as to invite problems?

 

[turbot2496]

I appreciate hearing about your experience and thanks for the recomendation on pushrod pinch. Saves the rest of us the trouble of finding out just how far we can go. DIYer's like yourself sharing information is invaluable to this board. Thanks for taking the time to learn something and share with the rest of us rather than just coping out and sending champion all your cash for something you could probably figure out how to do better yourself for less.

 

[87GN_70GS]

I'm assuming there's a typo and you meant .970" instead of .097" and .850-.900" vs .085-.090, unless I'm not understanding this.

 

[Rocketman442]

Thanks, 87GN_70GS. The post has been edited.

Thanks for the kind words, turbot2496. I am happy to help. You've all been of assistance to me at times. Lord knows I need all the help I can get!

 

[strikeeagle]

"...Thanks for taking the time to learn something and share with the rest of us rather than just coping out and sending champion all your cash for something you could probably figure out how to do better yourself for less."

Way harsh.

I'd call this a thinly veiled, unjustified attack on a vendor whose support of the TR community and whose product quality are widely appreciated.

Oh, and a thinly veiled attack on me for being of the opinion that money spent with Champion is money well spent.

Call it a stretch, but I choose to believe that Champion knows a little bit more about porting TR heads than any of us...

 

[turbot2496]

I'd call this a thinly veiled, unjustified attack on a vendor whose support of the TR community and whose product quality are widely appreciated. Oh, and a thinly veiled attack on me for being of the opinion that money spent with Champion is money well spent

No, you missed my point entirely. It was a ,not so thinly veiled, attack on you yourself and no one else. I'm happy your so high on champion and you love their products, but you don't mind if some of the rest of us learn a little about head porting for ourselves, do ya?? At least we know if we do make a mistake and want to share with others in the community what we did, how we fixed it and what we learned, we can count on you waiting here to rub our noses in it. Thanks for caring and contributing strike and keep on going fast with class.

 

[strikeeagle]

I simply expressed the opinion that I (emphasize I) would leave this to Champion. Nothing more, nothing less.

How you got from there to discouraging folks from doing things themselves, discouraging folks from reporting results, sabotaging the objectives of this board, and so on is between you and your psychiatrist.