Porting Question.

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Originally Posted by tango

Before any one here starts to port out a set of stock Chevy heads . Make sure you have a lot of extra time ! I have 7 Hours on one SB head and it's around 80% done . The heads that I am porting are the 305ci #601 55-58cc . I always hear how good they are when full ported . And how much power they make on the round and round 355 Claimer engines . Well good thing I have more time then money . I would say don't buy these 305 heads thinking you will port them easy and make Lots of power . When I am done they will work good . And this set of heads has screw in studs guide plates and S/S valves . Also a set of Z-28 LT-1 springs with HD retainers and Locks . Them old Fuelly heads :) never needed this much grinding :LOL:

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The only 2 real reasons to port out a set stock heads is one if you going to be running with rules that specify "stock" heads. Two, if for some reason you just have to have your stock heads. There are so many better heads that you can get for a real decent price. Heck you can even find alum. heads real cheap.

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Originally Posted by DennyW

1, I don't agree with that, cause the person may not have the money for any other heads. 2, They may want the experience of doing it, and seeing what the improvements are. 3, They may want to try another way of porting for testing their own theory. That's what I did on mine. It depends on a number of things though. Like where they want the performance at, at what rpm's. But, I will agree, if you have the money to get a pair all done, that would also be a good way to go, especially, if you didn't have the time, or tools to do them. :)

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Ya , I guess thats another way of looking at it.... You would not have to try or test anything just by looking at a set of good heads everything is tested and proven on expensive flow benches, You can learn from those. You could buy a new set better flowing for the rpm you like for maybe 300 hundred more after selling these. If its just not in the budget ,well its just not there, port away...... Dunno maybe I am just steering clear of porting since I remember how much of a pain it was.:whacked: :D

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Originally Posted by camaro_fever68

That's with any engine. Of course, the bigger the cam the worst reversion will become an issue. An 1/8" lip on the bottom of the intake runner has the most anti-reversion benefit. It's also beneficial if the headers are about an 1/8" below the bottom of the exhaust port.

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I apologize I was reading your post wrong . Makes perfect since once I read it slow:LOL:
So your saying you should have a small lip on the bottom of the intake and exhaust ports. Sides and top should be smooth???

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Originally Posted by BigTruckDriver

So your saying you should have a small lip on the bottom of the intake and exhaust ports. Sides and top should be smooth???

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Yes. You never want the bottom smooth if you can help it.

Denny That was an interesting article. They say that larger ports tend to lead to less top end power which does make sense, but the little I open mine up brought me better HP and higher RPM's. Why??

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Originally Posted by DennyW

Please explain why Ray ? :)

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At low/mid rpm with a long duration cam, the intake valve is still open as the piston starts it's travel back up. The majority of air flow travels the top of the head port on it's way to the cylinder. When the pistons starts it's travel back up it can push some air back through the intake vavle into the port. That air will travel the bottom and the 1/8" lip exposed in the intake will create an air dam of sorts to block the air flow back into the intake tract.


Joe Mondello has a really good article on this from his head porting school.

Here's a little more about it;

A common thing that porters like to do is gasket match the heads and intake. First
for this to work it assumes that the manifold fits perfect to the heads intake face. This also
assumes that the gaskets size is right for the application. Gaskets are not designed with
airflow in mind. Remember that the majority of the port flow is on the port roof not the
port floor. Therefore removing lots of extra metal from the port floor isn’t going to do
anything other then increase port volume, which will decrease port velocity. It has also
been shown that gasket matching if not done right (i.e. proper size etc) can decrease
overall flow across the board. In a wet flow manifold (i.e. Carb or TBI) it is also actually
best to leave about a .050” step from the port floor of the intake to the port floor on the
head. The port floor on the intake should be higher. This step gives the fuel which has
puddled on the port floor a chance to re-introduce itself into the air intake stream. It acts
as a fuel shear point.

All I can tell you is the EPA bumps in the intake ports top corners have to be port matched to the intake . If not the air flow going threw the intake will hit it like a wall . Over the years I have ported Lots of cylinder heads . That is true about porting the roof of the intake port and not doing a Lot to the floor . The most HP on SB Chevy heads is in the bowl area . I make good money working on trucks but it's always gone when I need car parts ? That whey I just don't go out and buy a set . But if I did they would be a bare set that I would assemble . And I do not like aluminum heads . Every set of heads I have ported worked real well :) It's just the older SB Chevy heads need Less porting done to them . The 305 heads #416 # 601 need hours of porting . I am at 10 hours on the first head at 95% done . But Like I said these head will make my 355 Rage **)

Some real nice answers to porting guys. I learned more from some of you than I did reading up on it.:)

There are a lot of theories to how it works. Some proven and some not. I've found that you do better if you do a lot of research and create your own theories. Or trust a good head porter and let him figure it out for you.

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Originally Posted by camaro_fever68

Here's a little more about it;

A common thing that porters like to do is gasket match the heads and intake. First
for this to work it assumes that the manifold fits perfect to the heads intake face. This also
assumes that the gaskets size is right for the application. Gaskets are not designed with
airflow in mind. Remember that the majority of the port flow is on the port roof not the
port floor. Therefore removing lots of extra metal from the port floor isn’t going to do
anything other then increase port volume, which will decrease port velocity. It has also
been shown that gasket matching if not done right (i.e. proper size etc) can decrease
overall flow across the board. In a wet flow manifold (i.e. Carb or TBI) it is also actually
best to leave about a .050” step from the port floor of the intake to the port floor on the
head. The port floor on the intake should be higher. This step gives the fuel which has
puddled on the port floor a chance to re-introduce itself into the air intake stream. It acts
as a fuel shear point.

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Makes since , the heavier "solids" will naturaly go to the bottom since they are heavy.......

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Originally Posted by camaro_fever68

There are a lot of theories to how it works. Some proven and some not. I've found that you do better if you do a lot of research and create your own theories. Or trust a good head porter and let him figure it out for you.

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I did the research in books photos and racing . Don't have the ca$h to burn on a Pro head porter . I am very old School carb only race cars . Have had EFI-TPI 5.7 F-body street / strip cars . Pulled all that new EFI stuff off and installed a Carburetor and High Rise intake . Every time the cars were Faster :HMMM:

Hey guys, great discussion. I am currently learning cylinder head porting. The great thing about the class is having access to a flow bench. I am able to see the changes I am making in regards to flow and velosity. I was surprised to learn that even some of the high dollar after market heads still needed porting to reach their potential.

whats the correct term for this finish??

http://www.clubhotrod.com/forums/att...lish-20006.jpg

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Originally Posted by BigTruckDriver

whats the correct term for this finish??

http://www.clubhotrod.com/forums/att...lish-20006.jpg

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I would call it "as cast"