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Old 09-15-2008, 05:37 PM
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Cylinder head "At Home" porting

Hey guys, I'm not sure if F-BIRD'88 is on here this evening, but he gave me a couple links to some different forums that had a guide on how to do an at home porting job. He gave them to me in a different thread, but Thought i might get more info If I actually title the thread for what i wanna know. So, I started this one.
The info he gave me was definitely a good start, but i'm still a little un-easy about trying to port my 416 casting 305 heads myself. I'm the type of guy who likes to get all my ducks in a row before i take action. So my question is, Do any of you guys have some sort of Photo Guided Step-By-Step tutorial on how to do good home porting job???
As I told Bird, I have never done more to a head then bolt it on and adjust the rocker arms, But i really wanna learn how. I have 2 sets of 416's just collecting dust but i wanna get some use outta them for a LOW budget 350 build with around 375-400HP and about 410 FTLB TQ. I have almost everything else ready exept the heads.

If anyone has any info at all, like old magazine articles, links to different forums, know any good books, anything that can help me, I'd really appreciate it. I am quite a "visual, hands on" learner so I need something with a lot of pictures. I can use F-Bird's forum too, but i really need more photos of the process in its entirety.
thanks to all, Danny

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Old 09-15-2008, 05:57 PM
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http://www.sa-motorsports.com/diyport.aspx
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Old 09-15-2008, 06:37 PM
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standard abrasives

Well i found the walk through on the SA website, but I alos read a mamagine article online the other day that talked pretty extensively about de-shrouding. The SA page bairly touched on deshrouding. How vital is that process??? Is there anyone else that knows what atricle I'm talking about, I thought it was Hotrod, Chevyhiperformance, or something but i can't find it now. Go figure!! Just like anything else in my life, If i don't want it, its in my way and when i need it i can't find it!!! anyone else get that feeling?
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Old 09-15-2008, 06:45 PM
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Smokey Yunick goes into detail on this subject, describing the cone of mixture as it passes the intake valve in his book Power Secrets. The second seller on this list, ETCETERA4LESS, has it available used in good condition for $10.86. If you want to learn from the best, buy and read this book.
http://www.amazon.com/gp/offer-listi...1525696&sr=1-2
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Old 09-15-2008, 07:22 PM
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Quote:
Originally Posted by eatonde
Hey guys, I'm not sure if F-BIRD'88 is on here this evening, but he gave me a couple links to some different forums that had a guide on how to do an at home porting job. He gave them to me in a different thread, but Thought i might get more info If I actually title the thread for what i wanna know. So, I started this one.
The info he gave me was definitely a good start, but i'm still a little un-easy about trying to port my 416 casting 305 heads myself. I'm the type of guy who likes to get all my ducks in a row before i take action. So my question is, Do any of you guys have some sort of Photo Guided Step-By-Step tutorial on how to do good home porting job???
As I told Bird, I have never done more to a head then bolt it on and adjust the rocker arms, But i really wanna learn how. I have 2 sets of 416's just collecting dust but i wanna get some use outta them for a LOW budget 350 build with around 375-400HP and about 410 FTLB TQ. I have almost everything else ready exept the heads.

If anyone has any info at all, like old magazine articles, links to different forums, know any good books, anything that can help me, I'd really appreciate it. I am quite a "visual, hands on" learner so I need something with a lot of pictures. I can use F-Bird's forum too, but i really need more photos of the process in its entirety.
thanks to all, Danny
Really good book perfect for Chevy's but the rules apply on other engines just as much, How to Build & Modify Chevrolet Small-Block V-8 Cylinder Heads

by David Vizard

The process really isn't that complex, there's probably two big things to keep in mind.

1. This is a subtractive process making the port bigger which has the effect of reducing velocity which will cost bottom end and mid range power while adding it to the top end. So unless you're building a race engine or have gears out the ying-yang, conservative grinding to change shapes, streamline and redirect flow is a lot better than just making 'em big.

2. Kind of goes with 1 in that there's coolant on the far side of those walls, getting carried away will get you wet. Remember, especially for street engine, that you have to retain long term reliability which even if you don't get wet making big ports, if you thin the walls too much they will crack in time.

Most of the easy gain comes in the valve pocket, especially if you're using older heads where the casting shapes are not so refined as you see happening to ports in the mid 1990s to present. This is to some degree a serendipitous event as this can be used to slow and regain pressure behind the valve. The mixture, being a gas, travels in accordance with the physical laws of gasses. Basically as velocity goes up, pressure goes down, when velocity goes down pressure goes up. This can be used to bend around corners such as has to be made around the valve and seat. Generally the port from the plenum to the valve pocket consists of convergent passages as this keeps the energy level and speed up, keeping the charge well mixed and reducing travel time. By allowing an expansion into the valve pocket, velocity is lost allowing the mixture to better make the short side turn and pressure is recovered which enhances low lift flow into the cylinder. You typically on a 2 valve wedge engine want to streamline the valve guide. When doing that, orienting the shape of the guide to assist the major flow to pass on the side adjacent to the cylinder wall will enhance swirl.

The typical two plane intake flows about 20% less on the lower than upper plane; and the flows tend to favor the opposite of the floor or roof. Flow from the carb is downward toward the floor of the plenum. On the high side the flow tends to stay there so enlarging the bottom of the mouth of the port can be beneficial, see the Vortec intake port as an example, just don't go nuts it's for a fuel injected engine. The problem is that flow from the lower plenum gets bounced up by the shape of the runner as it approaches the head's port so that when it arrives into the head, it now favors the top of the port. Here's a place where if you have the nerve to break with convention, enlarging the width at the top of these ports, some overall gains can be had without making the port so big that it slows flow velocity. Except for BTW race engines, I tend to keep such enlargements on the port wall side adjacent to the cylinder wall as this starts to position the flow for best swirl.
the consensus on wall finish is to leave it as ground, the roughness helps to remix fuel that seperates from the boundary layer flow.

On the exhaust side you're looking at inertia putting the flow to the top side and on the port wall adjacent to the cylinder wall. Here opposite to the intake, you want the port to start smaller at the valve and pocket and open up as it goes away. If this is a closed chamber head the major exhaust flow comes from the quench pad around the center of the cylinder, inertia throws this against the outside wall and the roof. On these heads this is the area to work the hardest, again as with the intake you want to streamline the guide from where it meets the back wall to it's trailing edge. On chevy heads don't get carried aways making the back wall straight, this hurts overall flow. With an open chamber, it'll have more flow relative to closed chamber on the sparkplug side. Here adding a little width on the short side turn will slow this flow and help it make the turn without obstructing the roof flow. Keep in mind these gasses are very hot so don't get crazy with thinning the walls or shortening the guide boss as wall cracking and valve failures will become too common for a street machine's normal maintenance cycle. On the exhaust I think the jury's still out on wall finish. Aero guys would want a rough wall on divergent sections of a port to help the flow break away from the wall, but a polish keeps carbon collection to a minimum. Same can be said for in the chamber a nice polish helps minimize carbon build up. Be careful to prevent sparkplug threads from showing. If you cut chamber walls too far they will, so test this to determine is you'll have to trim plug threads before their installation.

Another trick in older heads especailly where a lot of cam overlap is used and the heads do not have the beak feature of new heads, is to sink the exhuast valve a bit so the fresh charge flows over the exhaust valve on overlap instead of out it. You may find you have to run lash caps on the intakes if you do this if you want to run the same length push rod on the intakes and exhausts.

Always listening to a different drummer, when it comes to tools, I prefer an electric die grinder and stones over an air grinder and cutters. But the only recommendation I'll make for the hobbiest porter is to get an electric die grinder rather than air. Simply because it takes a mighty good compressor to keep up to the demands of an air grinder, so unless you've got 1200 dollars laying around for a big compressor, I'd stay away from an air driven grinder. As for stones or burrs try 'em both see which works for you. If you're hacking at aluminum, keep a bar of soap handy, running the cutter into the soap every few cuts will keep it from clogging. You'll find a good light, and shop vac invaluable to seeing what your doing. Ear protection, unless you want hearing like mine where they ring loudly all the time is a goal of yours. Eye protection, a must I wear a face shield and saftey glasses simply because I don't' like the grit in the face on top of needing to protect my eyes. I don't wear a breathing mask when working but certainly see the advantages of doing so.

Bogie

Last edited by oldbogie; 09-16-2008 at 01:52 PM.
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Old 09-15-2008, 07:41 PM
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Quote:
Originally Posted by oldbogie
Really good book perfect for Chevy's but the rules apply
on other engines just as much, How to Build & Modify Chevrolet Small-Block
V-8 Cylinder Heads...

by David Vizard



Bogie
Davids currently writing a series of articles on porting:

Porting School
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Old 09-15-2008, 08:11 PM
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minor language clean up

If you want to keep the torque numbers up, which is where the REAL power is, carefully lay the intake gasket over the intake ports. Scribe the ports, using the gasket as a pattern, and cut your OPENINGS to this line. Blend the openings into the port runners, and only clean up the bumps and casting crap in the runners. On the valve end of the runners, blend in the factory machining with the runners on that end. You'll want to avoid hogging out the entire runner...this is great for top end horsepower, but the loss in velocity will hurt the low end torque. You want to keep up the port velocity, but you also want to provide a smooth, unobstructed path for the air/fuel...if you're using carburetors or TBI. Port injection is just about the opposite, since you're flowing only air. You'll also want to do the same trick with the gasket/scribe on the intake manifold. Be VERY SURE that you don't open the intake port opening larger than the head port opening...

Last edited by 345 desoto; 09-16-2008 at 07:04 AM.
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Old 09-15-2008, 08:20 PM
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For what it's worth, Here is my first attempt at cleaning up my heads 2 years ago. Very time consuming but fun. Doubt i'll ever do it again though! LOL

Mark
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Old 09-15-2008, 08:27 PM
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etonde,
Everything you need to know is in the Post from JMARK. He has a fine little tutorial in "Here is my first attempt"...
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Old 09-15-2008, 08:33 PM
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Quote:
Originally Posted by 345 desoto
etonde,
Everything you need to know is in the Post from JMARK. He has a fine little tutorial in "Here is my first attempt"...
Hey! Don't give me too much credit! I may have messed it up by doing what I did! LOL
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Old 09-15-2008, 09:06 PM
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Pretty much why I never tell anyone to port heads other than a basic bowl and port clean up is because of these lines:
Head porting is a difficult art to learn, and a lot of practical experience is required before anyone can learn enough about flow and port shaping to do a really first rate porting job. unfortunately, this is not the sort of trade you can learn by reading books. A lot has been written in magazines about head porting, And I always find these articles amusing to read, but I feel much of this imformation is misleading. So in my opinion the options boil down to this: either you spend 10 years in a good porting shop learning the business or you buy your heads from someone who knows how to do it right.
I can tell you from personal experience that what looks good on the bench sometimes doesn`t work under racing conditions. -- Smokey Yunick.
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Old 09-15-2008, 09:49 PM
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Quote:
Originally Posted by automotive breath
Davids currently writing a series of articles on porting:

Porting School
AB, that link to Vizard is the s***s as they say. For the first time that I have known of, an accurate, non-electronic flow bench is available to the budget-constrained home engine builder. KUDOS to you for posting it!!!
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Old 09-15-2008, 09:52 PM
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Originally Posted by techinspector1
Looks like a link that was posted by a porting novice.
I couldn't believe that the 1st thing on the list was to widen the intake port.
This is the LAST PLACE to work since it is essentially a straight shot & only becomes a restriction in FULL RACE PORTING applications...

The other thing that floored me *laughter* was that it advised a "smoothing" of the intake. Another big hefty NO NO. Cuttered finish reduces flow zero & actually improves mixture atomization...

Like I said looks like it was posted by a novice....
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Old 09-15-2008, 09:57 PM
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Another majior NO NO is to even touch the intake port floor.

If you're serious about head porting DAVID VIZARD & DAVID HELGESSEN are who you want to learn from.

They have written many good books & deserve your money.

Helgessen even made templates years ago for the home head porter.

You may recall Vizard. He wrote the 1st "How to rebuild your small Block Chevy" book.


Don't bother learning "wives tales" on the internet. Learn porting techniques from the experts that spent many thousands of hours with flow benches & Dyno's.

Vizard's books can be found on Amazon.com
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Old 09-15-2008, 10:14 PM
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From the link.....

"DIYs are a tough crowd. Skeptics abound, so we needed a flow test of our heads before and after basic porting. We retained Valley Head Service in Northridge, California to run those tests. After our basic porting project was complete, intake port flow improved 15.3% at low valve lifts, a significant change. Average improvement, from .050 to .500-in. valve lift, was 6.3%. In the exhaust ports, gas flow at medium valve lifts improved a whopping 17%. Average improvement of exhaust flow was 7.5%. The exhaust ports showed the greatest change, which is typical of a production Chevy head. For an engine of 300 horsepower before porting, these improvements in flow would make an approximate power increase of 19hp.
Note that we did not skew the results by flowing the head after a multi-angle valve job. Our tests were done with stock valve face and seat angles. Airflow of the head after a good, high-performance valve job would improve even more."

I don't think this was ever intended to be the "end all, double throw-down" article on head porting, but I think they did a pretty good job. Could they have done better, probably, after spending 10 years in a good head porting shop like Smokey said. But for a down and dirty home porting job by an amateur, I think it was time and money well spent. And by building the simple, non-electronic flow bench outlined by Vizard, a home porter could check his work on subsequent heads and might get pretty good at it. I suspect that's how the first guys to pick up a grinder did it.
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