Re: [Tech Article] Porting & Matching Heads & Manifolds (Mega-Long)

["Chris DeLong" <green536@hotmail.com>]

Dude! You must not be gettin any ore somethin man cause thats a long ASS 
email. I think you exceeded the quota.

Chris DeLong
ICQ#45030867
Seattle, WA USA
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'91 GLi 2.0 16V
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'91 Vanagon
'78 Rabbit
'78 Rabbit (for sale)
'87 GTi 16V



>From: Shawn C Meze <skerocdriver@juno.com>
>To: scirocco-L@scirocco.org
>Subject: [Tech Article] Porting & Matching Heads & Manifolds (Mega-Long)
>Date: Thu, 29 Nov 2001 22:02:26 EST
>
>I got this from Underhood Service, November 2001. Pretty cool and
>explains alot of stuff for all you youngins. The Science of Horsepower:
>Porting & Matching Heads & Manifolds, Larry Carley.
>
>
>Air flow makes horsepower. The more cubic feet per minute (cfm) of air
>that flows through the intake ports and into the combustion chambers,
>the more horsepower the engine makes.
>
>A larger carburetor or throttle body, bigger valves, a high-lift,
>long-duration camshaft, three-angle valve job and exhaust headers are
>all performance enhancements that increase air flow for more power. Add
>a turbocharger or supercharger and even more air is forced through the
>engine. But bolt-ons can accomplish only so much. To realize the utmost
>performance potential from a given combination of cubic inches and
>mechanical modifications, you also have to optimize the ports in the
>cylinder heads and match the ports to the runners in the intake
>manifold.
>
>There are two ways to port and match cylinder heads: The right way and
>the wrong way. The right way is to refine the flow characteristics of
>the head and manifold so as much air as possible enters the cylinders at
>the engine’s peak power curve. Every engine is different so there’s no
>"standard" port configuration that is guaranteed to deliver maximum air
>flow on every application. The port profile that works best will be
>limited by the physical dimensions of the cylinder head.
>
>Limiting factors include the size, position and angle of the stock
>ports; the size, configuration and angle of the valves; the thickness of
>the casting around the ports; and the location of the water jackets,
>head bolts and other valvetrain components. But other factors must be
>taken into account, too, such as engine displacement (big block versus
>small block), the engine’s bore and stroke, the shape of the combustion
>chambers, compression ratio, the depth and angles on the valve seats,
>total valve lift, camshaft profile (duration, overlap, etc.), and type
>of intake manifold and induction system.
>
>Porting can unleash hidden horsepower by increasing air flow - but it
>requires know-how, a flow bench and special tools to successfully pull
>it off.
>
>
>Opening Up:
>One of the basic goals of head porting is to minimize obstructions so
>air can flow relatively unimpeded from the throttle plate to the valves.
>Two things that get in the way are the valve guides and valve guide
>bosses. Cutting down the length of the valve guide stem and narrowing
>the valve guide boss can improve air flow past these obstacles. So too
>can using smaller diameter valve stems or valves that are necked down
>just above the valve head.
>
>Bolt bosses that protrude into ports also create bumps in the ports that
>disrupt air flow. Grinding these flush with the surrounding port surface
>can also smooth out the route, provided you don’t run out of metal and
>grind all the way through the boss or dangerously weaken the head.
>
>Transition areas in the port also need to be reworked so air will flow
>more easily around corners with a sharp radius and into the seat throat
>just above the valves. Sharp edges and rough castings also need to be
>smoothed and blended to eliminate turbulence and improve air flow.
>
>The cross-sectional area of most intake ports becomes gradually smaller
>as the air moves toward the valve. This causes the air to accelerate as
>it approaches the valve, and actually helps ram more air past the valve
>into the cylinder when the valve opens. Any sudden changes in the
>cross-section of the port can disrupt this effect and restrict air flow.
>That’s why port modifications that are made in the area just above the
>valve must not upset the normal increase in air velocity. The same goes
>for the exhaust side, too, except here the cross-section of the ports
>gets larger as the exhaust gases flow away from the valves. Again, the
>secret to maximizing flow is to have a smooth transition and as few
>obstructions as possible.
>
>The joint where the intake manifold and cylinder head meet also is a
>critical area. If the runners in the intake manifold are not perfectly
>aligned with the ports in the head, sharp edges can interrupt normal air
>flow and impair performance. Matching up the ports so there’s a smooth
>transition from manifold to head will ensure maximum air flow. The same
>goes for exhaust ports. The head ports must be aligned with the header
>openings so the exhaust gases can pass freely out of the engine without
>encountering any sharp edges or obstacles.
>
>The right way to improve air flow is to locate the best places to remove
>metal (or in some cases, to even add metal). This takes experience
>(knowing what kind of changes work and what ones don’t), using the right
>tools (properly shaped cutters for reworking the various portions of the
>ports, valve pockets and manifold), and a flow bench to measure the
>changes in air flow produced by the various changes that have been made.
>
>The wrong way to go at it is to grab a die grinder and start hogging out
>the intake and exhaust ports with no idea of where you’re going or what
>you’re trying to accomplish other than to open up the ports.
>
>Bigger is not always better. Grind away too much metal and you may end
>up ruining the casting if you cut into a water jacket. But even if you
>don’t grind all the way through, removing metal in the wrong places can
>actually end up hurting air flow more than it helps. Here’s why: The
>secret to maximizing air flow and engine performance is maximizing
>volumetric efficiency and air flow velocity.
>
>Big ports with lots of volume will obviously flow more air than a
>smaller port with less volume - but only at higher rpm. A lot of people
>don’t know that. At lower rpm and mid-range, a smaller port actually
>flows more efficiently and delivers better torque and performance
>because the air moves through the port at higher speed. This helps push
>more air and fuel into the cylinder every time the valve opens. At
>higher rpm, the momentum of the air helps ram in more air, so a larger
>port can flow more air when the engine needs it.
>
>The ultimate port would actually be one with a variable cross-section
>that’s small at low rpm for high air flow velocity and gradually opens
>up for more air flow as engine speed increases. That’s sort of the idea
>behind staged split-plenum intake manifolds that open up and feed more
>air into the engine at higher rpm.
>
>The bottom line is this: To realize the most power and performance out
>of an engine, air flow has to match the breathing requirements of the
>engine within the engine’s rpm range where it is designed to make the
>most power.
>
>A set of killer aftermarket heads with huge ports and valves that are
>engineered to flow more than 500 cfm with a 0.800" valve lift at 8,000
>rpm may be the hot setup for a 585-cubic-inch Pro Stock engine, but
>would be overkill on a street-driven, big-block Chevy that has a less
>radical cam, gearing and a redline of only 5,500 rpm. That’s why
>big-block Chevy heads with smaller oval ports work better on the street,
>and big-block heads with larger rectangular ports perform better on the
>strip.
>
>Therefore, when choosing either an OEM cylinder head or an aftermarket
>head, you should try to match the port size with the engine’s power
>curve and rpm range. Don’t waste your money bolting a set of high-flow
>heads onto an engine that can never realize the head’s full performance
>potential because of limitations in gearing, the valvetrain, cam
>specifications or carburetion. Likewise, if you’re going all out, then
>start with the highest flowing heads you can find and try to add even
>more cfm potential by massaging the ports and manifold.
>
>Kevin Self of Self Racing Heads & Engines, Durant, OK, said CNC
>(computer numeric controlled) machined aftermarket heads are a great
>place to start because the port configurations are based on designs that
>have already been proven to deliver maximum air flow. Even so, there’s
>always some room for improvement. Self said he can usually find an
>additional 25 to 30 cfm improvement in air flow in many CNC heads by
>tweaking the head on a flow bench.
>
>"One of the advantages of CNC heads is that they all have very
>consistent flow characteristics. But, because they’re all the same, you
>don’t necessarily gain any advantage over a competitor if he buys the
>exact same set of heads as you. If you can’t improve the head, you’ll
>have to find more horsepower someplace else, otherwise you’re not going
>to go any faster than the next guy."
>
>CNC machining is much faster than hand grinding, and produces ports that
>have uniform profiles. But someone still has to develop the initial
>profile by hand and then prove it works on a dyno and on the track.
>
>As for port alignment, Self said the runners in the intake manifold
>should be about .050" smaller than the port opening in the cylinder head
>to allow for any misalignment that occurs during engine assembly.
>
>"We’ve developed a special ‘Port Intruder’ kit that allows you to narrow
>the thickness of the wall between the intake ports on small-block Chevy
>heads without increasing the risk of cracking the manifold or deck area
>of the head. The kit allows the use of a shorter head bolt between the
>ports, eliminating the need for a head bolt or bolt sleeve between the
>ports. The head must be machined to accept the Port Intruder plugs. This
>change alone can increase air flow up to 30 cfm," said Self.
>
>Bob Irvin of M2 Race Systems, Farmingdale, NJ, said his company
>specializes in CNC-machined cylinder heads. "We use outsiders to develop
>the port configurations, then digitize the ports for reproduction on
>customers’ cylinder heads."
>
>Irvin said he charges a one-time fee of $2,000 to digitize and program a
>port configuration, and $1,200 to $1,500 to CNC machine a pair of
>cylinder heads (which includes valve seat and guide work, too).
>
>"CNC is foolproof and is much faster than trying to port a set of heads
>by hand from scratch. But there’s no reason why you can’t do additional
>finishing on the heads after they’ve been CNC machined to find some
>extra power," said Irvin.
>
>Where It Counts:
>As a rule, the roof of an intake or exhaust port has much more influence
>on air flow than the floor or sides of the port. The greatest gains in
>air flow can often be realized by removing metal from the top of the
>port only and leaving the sides and floor relatively untouched. This can
>have the same effect as using a different head casting or an aftermarket
>head that has the ports relocated slightly higher to give a straighter
>shot at the valves.
>
>Additional gains in air flow can often be found by carefully smoothing
>and blending the short-side radius in the port floor where the port
>bends toward the valve seat. This helps air round the corner more easily
>for improved air flow.
>
>In the area where the intake manifold and head are bolted together,
>using a template to scribe alignment marks on the head and manifold can
>serve as a guide for hand grinding and smoothing this area.
>
>Mr. Gasket Company’s plastic "UltraSeal Port Gauge" templates for
>small-block and big-block Chevys can be used for this purpose, and are
>much more accurate than using a gasket as a template.
>
>Expert Advice:
>Joe Mondello, who’s name has long been synonymous with high-performance
>cylinder heads, said a lot of people who don’t really know what they’re
>doing jump into head porting and make big mistakes.
>
>"They take out metal where they shouldn’t be taking out metal and end up
>with ports that are too big and don’t flow as well as they should. The
>shape of the port is far more critical than the overall size of the
>port," stated Mondello.
>
>Mondello, who teaches the secrets of building, porting and flow testing
>high-performance cylinder heads at his Mondello Technical School in Paso
>Robles, CA, said he also sells special porting tools that are designed
>for every part of the cylinder head.
>
>"When you’re doing the short-side radius of a port, you don’t want to
>take out too much metal. You just want it to be nice and smooth,"
>instructed Mondello. "Trying to get around the short-side radius bend is
>difficult unless you use a cutter that’s designed for that purpose.
>
>"When cleaning up the bowl area, blending alone won’t improve flow
>unless you also remove some metal to increase volume. Many people don’t
>do valve bowls properly. You have to blend everything from the base of
>the valve guide to the base of the primary valve seat, and then do a
>3-angle valve job. Otherwise you’re just scratching the valve bowl and
>ports, and aren’t really gaining anything."
>
>As for matching ports, Mondello said not to use gaskets as a guide
>because there’s too much variation in gaskets and most aftermarket
>gaskets have openings that are up to 1/8" larger than the port runners.
>If the port is enlarged to match the gasket, it can reduce air velocity
>and hurt performance.
>
>"We teach port matching, not gasket matching. I pick the largest port,
>match all the others to it, then do all the work inside the port to
>maximize air flow around the pushtube turn because that’s where the
>biggest restriction is in the port," said Mondello.
>
>"The largest gains in horsepower are found on the intake side by raising
>the roof of the port (the side closest to the valve cover) by .100" to
>.175". The amount of metal in the top of the intake manifold runner will
>determine how high you can raise the roof.
>
>"On late-model Chevy Vortec heads, you don’t want to change the shape of
>the port much. The best advice here is to clean up and equalize the
>ports so they have the same height and width. On small-block heads,
>there’s a large pocket right below the rocker arm stud in the roof of
>the port. This should be filled in with epoxy to improve air flow. Doing
>that will give you an extra 15 cfm.
>
>"On exhaust ports, if you tried to match the port to a header gasket
>you’d probably destroy the port. The secret of exhaust porting today is
>not how big the port is, but the shape of the port and the velocity of
>the exhaust flowing through it. We don’t even flow test exhaust ports
>anymore because most heads have plenty of flow capacity as is. All we
>care about is velocity and pressure.
>
>"Nearly every single exhaust port today, except for Ford 302, 5.0L and
>351 heads, are big enough. The only thing we do to enhance air flow is
>raise the roof of the port about 0.100", depending on the headers used.
>We don’t touch the floor of the exhaust port or the sides unless we have
>to get rid of a hook, seam or rough area in the casting," said Mondello.
>"Any time you start making the ports bigger on the exhaust side, you
>usually end up killing air flow in the head. I’m talking a reduction of
>25 to 30 cfm. All you need to do is clean up the valve bowl, blend the
>short-side radius, and raise the roof slightly. Don’t touch the floor or
>walls."
>
>Mondello explained that CNC machining and hand grinding are two
>different techniques for porting heads. "Everybody says CNC is the way
>to go. But you first need someone who can take a raw casting and rework
>it so it has good air velocity and flows well. Then you can digitize it
>and reproduce it with CNC tooling on other heads. There are a lot of CNC
>profiles being sold today, but I think most have some room for
>improvement. Additional hand grinding can usually pick up another 10 to
>12 or more cfm."
>
>As for polishing, Mondello said a smooth finish is great for exhaust
>ports, but a rougher finish flows better on the intake side. He
>recommends using 300- or 400-grit paper followed by a Cross Buff for
>polishing exhaust ports, and 50- or 60-grit paper for the intake ports.
>A slightly rough surface texture in the intake ports and intake manifold
>runners creates a boundary layer of air that keeps the rest of the air
>column flowing smoothly and quickly through the port.
>DIY Porting:
>Though the greatest gains in horsepower will be realized only when heads
>are flow tested and professionally ported, do-it-yourselfers who are
>racing on a limited budget can still do some basic porting themselves to
>improve air flow and increase the performance potential of their
>engines.
>
>The technical staff at Standard Abrasives (www.sa-motorsports.com) have
>an online DIY Cylinder Head Porting Guide complete with photos that
>provides detailed step-by-step instructions for head porting and
>manifold matching.
>
>All you need are a basic porting kit (which includes various grinding
>stones and abrasive rolls), some common tools and some free time
>(typically 10 to 12 hours to port a pair of V8 heads).
>
>A basic DIY port job should focus on reducing restrictions caused by
>steps that may obstruct intake air flow as it transitions from the
>intake manifold to a smaller intake port entry in the head. These
>restrictions could be casting bumps, ridges or other marks, such as
>those on port floors or roofs, sharp edges, such as those around the
>valve guide bosses at the top of the valve pockets, and the area where
>the intake port floor curves down to the valve seat.
>
>The job itself consists of six steps:
>
>1. Enlarging and matching the intake port entrances;
>
>2. Smoothing the intake short-side radii, valve guides and valve
>pockets;
>
>3. Smoothing the exhaust short-side radii, valve guides and bowls;
>
>4. Polishing the exhaust ports and bowls;
>
>5. Polishing the combustion chambers (to reduce carbon buildup); and
>
>6. Matching the intake manifold ports to the head.
>
>Some porting suggestions offered by Standard Abrasives include:
>
>• Use an air-powered die grinder with a maximum speed of 18,000 to
>20,000 rpm and a 1/4" collet. An electric die grinder is OK, but you
>have to be careful to limit the grinder’s speed.
>
>• Wear proper eye protection. Grinding throws off a lot of chips, and
>you don’t want any debris to end up in your eyes. Good lighting is also
>essential so you can see what you’re doing, and gloves are recommended
>to protect your hands.
>
>• To keep grinding stones from clogging when working on aluminum heads,
>lubricate the stones with WD-40.
>
>• To figure out how much metal needs to be removed to match up the
>ports, apply machinists bluing to the gasket template and bolt the
>template to the head and manifold. Then scribe the outline of the port
>opening on both the head and manifold. Remove all metal inside the
>scribed lines.
>
>• When you start grinding, use a rotary round grinding stone for maximum
>metal removal. As you approach the scribe marks you’ve made, blend or
>feather the larger port into the remaining port by progressively
>removing less material as you move farther down into the port. In most
>cases, you want to grind about 1" to 1.5" into the port.
>
>• Once the port has been ground to size, switch to a smaller diameter
>conical rotary stone to profile the small radii at the corners of each
>port.
>
>• To finish the port, use the tapered rolls of abrasive, starting with
>40 grit, then 80 grit.
>
>• The point where the intake port floor curves down to the valve seat is
>known as the "short-side radius." From an air flow standpoint, this area
>is the most critical in any port. Smooth that spot and you can usually
>realize a significant increase in flow through the port. On most
>production heads, the short-side radius will be sharp-edged and rough.
>The goal here is to soften those sharp edges and smooth out the
>roughness.
>
>• Bowl work includes blending the area under the valve seat. The valve
>throat, which is the smallest diameter in the valve pocket just above
>the valve seat, should be about 85% of the valve diameter. If the throat
>is smaller than that, use a combination of the rotary stone and
>cartridge rolls to open it up to the 85% figure.
>
>• Exhaust ports flow best with a polished finish. A smooth finish also
>helps reduce the buildup of carbon deposits. Use a 120-grit or finer
>flap wheel after using the 40-grit and 80-grit abrasives, then polish
>with the medium Cross Buff and finally the fine grade Cross Buff.
>
>• In most cases, you should not attempt to match the exhaust ports in
>the head with the ports in the exhaust manifold or headers. Many stock
>exhaust manifolds, and virtually all tube headers, have larger port
>sizes than the heads. You want that "step" from the port to the larger
>header tube or exhaust manifold because, as pressure pulses flow back
>and forth in the exhaust system, it acts as a "reversion dam" by
>resisting back flow of exhaust gases into the port.
>
>Good shit eh!
>
>
>Shawn Méze
>86' Jetta GLi 8V       84' Scirocco 8V           88' Corvette -SS 30-
>82' Scirocco GTi -FSP 54-     79' "Project FSP Scirocco"
>The Fastest, Quickest, Cleanest and best looking Scirocco(s) in all of
>San Diego!
>http://www.Geocities.com/MotorCity/Speedway/1308/index.htm
>
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