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Old 11-10-2013, 04:57 AM
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head porting.

been reading about the basics in this matter, folks have different opinions about it.
What is better rough or smooth finish?
1. Exhaust ports, smooth or rough
2. Intake ports, smooth or rough
3. valve cups, smooth or rough

some say smooth is not better
others say it is.

what is right, will smooth intake ports make gas build up in puddles in the ports?

Dont give me no math answers or you need flow bench to be shure.

Just the basics thanks

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Old 11-10-2013, 07:04 AM
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Non polished on intake and bowls. Polish is only eye candy.
Semi-polished on upper 2/3 of exhaust.
Neither do much without knowing where to cut and no flow device.
I see lots of ruined heads. I always call them by products of a "Monkey with a die grinder"
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Old 11-10-2013, 07:19 AM
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is that it?
Is there no reason for polishing and blending?
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Old 11-10-2013, 08:01 AM
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Lots for, but without experience or flow measuring equipment. You can make a large pretty port that flows less than a port matched stocker..
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Old 11-10-2013, 08:09 AM
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yeh heard that, but what about taking rough edges and smoothing, is that useless ?
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Old 11-10-2013, 08:45 AM
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Sharp edges are taboo and smoothing always help. Air flow in general doesn't like sharp edges or turns.
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Old 11-10-2013, 09:31 AM
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well this tells me nothing about porting, guess i have to look in other places.
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Old 11-10-2013, 09:58 AM
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ehhh i already started so its no turning back.
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Old 11-10-2013, 10:12 AM
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well sir with all the respect to you i like to learn as i go along
I dont have any pictures now but this is a 4 cylinder head DOCH.
Just playing in my garage you know like the most of you kids
I am using a dremel smoothing the ports and bowls.
and taking ruff molding marks away.
Not making any thing bigger yet.
I know its a small engine but to me the exhaust ports look kinda small to me.
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Old 11-10-2013, 10:15 AM
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There are many reference books available, HP Books in particular, with motor builds, head theory and porting, etc. Barnes and Noble, Summit, JEG's all sell them.

Edit: Denny has you convered....
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Old 11-10-2013, 10:16 AM
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Flow test? not buying a flow bench for this prodject, this is a stratus
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Old 11-10-2013, 10:22 AM
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Well to me it looks like it has no problome getting air in, but to me a novice it looks like the exhaust is small.
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Old 11-10-2013, 10:45 AM
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  1. Finally we are learning, no i dont know why they are smaller, thought it would be better for the engine to get the exhaust out faster maybe i am just wrong ?
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Old 11-10-2013, 11:07 AM
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then what the hell will make this engine more powerfull, an engine swap ?
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Old 11-10-2013, 11:43 AM
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Braddi, everyone who posted an answer to you is correct as far as they know.

Making ports flow better is both a science and a black art. It's not something that a novice can do with a Dumore or a Dremel tool unless he just gets lucky and cuts in the right places. Any novice can make a port larger, but as it has been explained above, larger is not necessarily better. It's sort of like looking at a pretty girl from the rear. It's not the size that gets you excited, it's the shape. The science of how air or a mixture of air and fuel flows through a vessel is called Fluid Dynamics, so if you really want to understand it, do some reading in that title.

As an example, I know nothing about the dynamics of air flow in a cylinder head. When my son was in high school, we built him a '72 Chevy Luv pickup (Isuzu sold under the Chevy label). We bought it as a roller with a narrowed 10 1/4" Olds rear underneath, mounted on leafs and covered by a California Stepside bed and fenders. I had a bone-stock 455 Olds and TH400 sitting out back, so we made a new home for them in the Luv. First time out, the truck went low 13's at 102. Pulled the heads off the motor, stripped them down to bare and enlisted the aid of my Craftsman grinder. Leveled all the bumps and cleaned up all the slag and made 'em real pretty to look at. Reassembled 'em, torqued 'em back on the motor, went to the drag strip and ripped off a low 13's at 103. For the 26 hours I had invested in grinding and cleaning up the ports, I was rewarded with 1 lousy mile per hour difference. You see, that's why the professional porters get the big bucks, because they know where to cut and how much to cut.

Current thinking has the intake surfaces left rough, like as rough as a lady's fingernail file, while the exhaust ports work better being smoother.

As far as the difference in size/volume between the intake and exhaust ports, think about it a little. The intake charge is pushed into the cylinder by atmospheric pressure, which at sea level, is 14.7 lbs per square inch or 29.92 inches of mercury (in. hg). The piston does not suck the mixture in, it's atmospheric pressure that loads the cylinder when it sees a void created by the descending piston. "Nature abhors a vacuum". The cylinder pressure in the cylinder at the time the exhaust valve begins to open (roughly 80 degrees before bottom dead center in the power stroke) is roughly 1,000 lbs per square inch in a production motor, so it doesn't take long for the cylinder to evacuate with pressures like that. That's why you don't need a large exhaust port.

I know there is at least one individual on this forum who constantly preaches that you should port the heads for more power, but if you have little or no experience in porting and have no access to a flow bench to learn if you're cutting in the right places or not, then you could end up with a set of heads that flow less than they did stock. Not only that, but you might cut in a area that makes the head much more susceptible to cracking.

I ran into this tutorial after I wrote the above post, it tells the story better than I did I think.....
Cylinder Pressure

Last edited by techinspector1; 11-10-2013 at 12:06 PM.
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