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Old 10-14-2002, 02:06 PM
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Post porting heads?

i am going to buy the tools to port out the heads on my .080 350. i want to know what is the maximum i can go or should go. the block is an 010 casting #, 4 bolt main, .080, 450 lift 274 dur. crane cam, the heads are early to mid 70's(64cc, 1.94 1.5). i know you have to be carefull not to hit the water jackets. is there an easy way of knowing before you go to far. any measuring that can be done with common equipment. i am farely knowledgable and pretty handy with tools. the valves have already been worked and the heads have been cleaned. just looking for the extra power. i need to know everything can not afford to screw this up or pay someone else. thanks in advance.
Tony

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Old 10-14-2002, 02:39 PM
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Knowing how far you can go is really a matter of trial and error unless you get your hands on an ultrasonic thickness tester. That being said I wouldn't spend to much time porting the actual port walls, I would instead concentrate on the area just under the valve and just clean up the port walls and match the gasket. Your cam is not radical enough to require any more than this. Generally an 1/8" (per wall) is safe to remove but later smog heads make this recommendation a little iffy.

Good luck and wear eye goggles and a shield, those cast iron shards find their way into everything.
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Old 10-14-2002, 02:55 PM
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Good point 4-Jaw. This is something I have been meaning to mention to the younger forum members - those that haven't had metal slivers dug out of their eyes yet. I have had at least 6 such procedures over the years and inevitibly it was from grinding either cast iron or brass (brazing). I always wear safety glasses and most often goggles but shaving from these two metals seem to get into the eyes no matter what I try. Grinding steel has never been a problem.
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Old 10-14-2002, 03:00 PM
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It hurts flow if you match intake opening to gasket size. It doesnt need to be that wide and if it is, air has to "bend" at pushrod pinch. so make it tall but not wider than is necessary to match the intake.
Bowl porting and some valve unshrouding gives easiest results. Maybe a few books
about porting sbc heads is good to read before doing anything? Yes,i did it wrong first time but not everyone has to do.
Good luck and it helps a lot if you know what you are
doing

[ October 14, 2002: Message edited by: ceevu ]</p>
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Old 10-14-2002, 04:49 PM
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I think the best thing to do on your first set of heads would be to port the bowls, narrow the guide boss, and just clean up the ports with a roll of emery cloth. I wouldn't get too carried away trying to make a killer set of heads on your first try.
If you look at your intake port, you'll notice a very large ridge on the back side of the port, grind this down, and blend the entire bowl into the seat area. Be careful not to hack your seats up with the die grinder. {I use a carbide bur to rough it in}. Next you can narrow the valve guide boss into a "tear drop" shape. Next, you can knock all of the roughness of the casting in the port with your carbide burr, and clean up the opening of the intake port a little, but it's unnecessary to open the port opening up to the size of the gasket. Next, finish your work in the bowl and port with a coarse emery roll.
Keep the same type of work in mind with the exhaust port, and bear in mind that the roof of the exhaust port is a high flow area, and raising the roof usually nets some good results.
Keep in mind when you are porting heads without a flow bench that the factory engineers did pretty good work in designing intake and exhaust ports, you are just refining the basic shape of the port and bowl, and hand detailing the rough casting and machining operations left by the factory.
What is listed above will net positive results, if you get carried away, you can ruin your heads in a hurry. Be conservative your first time.
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Old 10-15-2002, 06:54 AM
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[quote]Originally posted by NAIRB:
<strong>I think the best thing to do on your first set of heads would be to port the bowls, narrow the guide boss, and just clean up the ports with a roll of emery cloth. I wouldn't get too carried away trying to make a killer set of heads on your first try.
If you look at your intake port, you'll notice a very large ridge on the back side of the port, grind this down, and blend the entire bowl into the seat area. Be careful not to hack your seats up with the die grinder. {I use a carbide bur to rough it in}. Next you can narrow the valve guide boss into a "tear drop" shape. Next, you can knock all of the roughness of the casting in the port with your carbide burr, and clean up the opening of the intake port a little, but it's unnecessary to open the port opening up to the size of the gasket. Next, finish your work in the bowl and port with a coarse emery roll.
Keep the same type of work in mind with the exhaust port, and bear in mind that the roof of the exhaust port is a high flow area, and raising the roof usually nets some good results.
Keep in mind when you are porting heads without a flow bench that the factory engineers did pretty good work in designing intake and exhaust ports, you are just refining the basic shape of the port and bowl, and hand detailing the rough casting and machining operations left by the factory.
What is listed above will net positive results, if you get carried away, you can ruin your heads in a hurry. Be conservative your first time.</strong><hr></blockquote>

I agree totally with. You get a cookie for a great explanation! I would add that the ridge on the intake port is when lookin from the chamber down into the vavle bowl.

Something else that can help is gasket matching the intake to the head. Just lay the gasket on the intake centered on the holes and trace the ports with a marker. Grind the port to that shape and plend the port about 1.5 inches in. Repeat for the head. Use the same procedure as on the bowl porting.

chris
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Old 10-15-2002, 07:44 AM
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i really appreciate all the help especially nairb very detailed which is exactly what i needed. i will add the valve guides have already been narrowed. the heads have had a good rebuilding i just couldn't afford anything else at the time. any more advice is still wanted and appreciated.
thanks.
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Old 10-15-2002, 01:01 PM
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I ran across this webpage, which appears to be pretty detailed for the do-it-yourselfer. Hope this helps you out some.

http://www.sa-motorsports.com/diyport.htm
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Old 10-15-2002, 07:24 PM
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Darn it crshrmn3!!! You beat me to the link! I haven't read it all yet, but it looks pretty good.
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Old 10-15-2002, 08:34 PM
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buy this book. HOW TO BUILD AND MODIFY SMALL BLOCK CHEVY V-8 CYLINDER HEADS by David Vizard. it will tell you in detail with pics exactly what to do. it is available from www.motorbooks.com for around 20 bucks.
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Old 10-15-2002, 08:41 PM
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hey guys i really appreciate the help. it is nice having a place to go for help. i will try to keep you posted and probably have more questions. this is my first hot rod so i need all the help i can get. thanks again.

Tony
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