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DIY - Porting and Polishing

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  • DIY - Porting and Polishing

    Head Porting for the Do-It-Yourselfer

    Taken from the technical staff of
    Standard Abrasives Motor Sports Division at sa-motorsports

    Here's an interesting head porting fact: In many cases, the greatest performance gain per dollar spent comes upon application of basic porting procedures to a production cylinder head.

    These basics can be done by any do-it-yourselfer, even those with no porting experience, using the Deluxe Porting Kit and the Gasket Removal Kit (part nos. 260001 and 260005) from the Standard Abrasives Motorsports Division, along with a die grinder and some common hand tools.

    There is a significant difference between basic head porting for a street-high-performance or weekend racer application and the very complex cylinder head work you see in a Pro Stock drag race motor or a NASCAR Winston Cup race engine. Doing full-on race heads requires the services of an experienced cylinder head professional, so Pro Stock, Winston Cup and similar heads are best left to experts. Basic head porting, however, is easy that even beginning hot rodders can do it well.
    Basic cylinder head porting will improve the performance of any production cylinder head by removing flaws that come through mass production. Basic porting does not attempt to correct any design or engineering deficiencies. Once your porting project turns to that, you're beyond the scope of basic porting techniques.

    Why is basic port work important to your engine's performance? It reduces the restriction in the engine's intake and exhaust tracts. Reduce that restriction and you let more air into the cylinders. If you have more air, you can add more fuel. The result is increased horsepower.

    Most of the work in a basic porting project is focused on reducing those restrictions which are caused by: 1) "steps" that may obstruct intake air flow as it transitions from the intake manifold to a smaller intake port entry in the head; 2) casting bumps, ridges or other marks, such as those you may find on port floors or roofs; 3) sharp edges, such as those you will find around the valve guide bosses at the top of the valve pockets; and 4) the point where the intake port floor curves down to the valve seat.

    Basic porting, while somewhat time consuming, is not hard work. It takes about 10-12 hours to do a set of average V8 heads. Some week nights and a weekend invested in your heads and your basic porting project will be complete.


    At this point I have left out some information which may be seen as helpfull by others concerning the materials used, techniques, cast or Al heads, and matters of safety. If you would ilke the information it can be found at the link provided above as well as pictures to better demenstrate the methods used.


    Step 1: Removing Old Gaskets and Marking the Intake Ports

    Even though the heads have been cleaned, the gasket and deck surfaces should be conditioned to remove all traces of old gaskets, paint, gasket sealer, corrosion and dirt. The use of a putty knife or scrapper for this purpose is not acceptable because neither will clean those surfaces completely. If your heads are aluminum, a putty knife or scraper may even damage those surfaces.

    The Standard Abrasives' 3-inch Gasket Removal Kit is the proper way to condition the gasket surfaces without damaging them. It contains surface conditioning discs for use on cast iron and aluminum along with a holder pad that attaches to your die grinder.

    Disconnect the grinder, install the Standard Abrasives' surface conditioning disc holder into the chuck and tighten the nut. The conditioning discs use Standard Abrasives' unique Soc-AttTM locking system, so installation is as simple as a twist of your wrist. Reconnect the grinder, put on your eye protection and gloves, then start removing the gaskets the easy, Standard Abrasives way. Once the gasket surfaces are down to bare metal, disconnect the grinder and remove the conditioning disc set-up.

    In most cases, your port work will start with enlarging the "port entry" area to the size of the openings in the intake manifold gaskets. Later, you will reshape the ports in the intake manifold to this same size.

    To ensure the head port entry and the intake manifold port end up the same size, you scribe an outline of the intake gasket openings on the head and the manifold. Machinist's bluing is used for this. Apply it to the intake gasket surface around the intake ports and allow it to dry. Place the new intake gasket in its normal position and hold it with manifold bolts. Scribe the inside perimeter of each intake port onto the gasket surface of the head, then remove the gasket.

    Pay close attention to the position of the gasket on the head. If it is upside down or backwards, your scribe marks will be in the wrong locations. That will cause a serious problem with your port work.
    Last edited by fpgt'91; November 3, 2006, 10:29 AM. Reason: Automerged Doublepost
    Ford Probe GT'91:

    K&N, UDP, Fidanza Flywheel, Race Concepts cross drilled/slotted F&R rotors, Goodridge SS lines, AutoMeter Gauges, Lo-Tek A-pillar pod, H4 conversion, 35F%20%R tinted, Andys Auto Sport Intimidator 2 Body Kit

  • #2
    Step 2: Preparing the Intake Port Entry

    Install the large, conical, rotary grinding stone (part no. 263901) from the Porting Kit into the grinder's chuck. Tighten the chuck then reconnect the air hose or electric cord. Remember to put your eye protection back on if you remove it during the change.

    Now you are ready to do your first porting work. You will enlarge the port openings in the intake gasket surface by removing material inside of the scribe marks you made. Then, you'll blend or "feather" the now larger port opening into the remaining port by removing progressively less material as you move down into the intake port. In most cases, you want to grind from the port entry to about 1-1.5 inches into the port.

    From your initial practice on the junk head, you know that the stone removes large amounts of material rather quickly so pay attention to control of the grinder. It is better to go over the work with several light-to-moderate passes rather than doing one heavy pass, remove too much and possibly render the head useless.

    Certain heads, such as Chevy small-block V8 units, have pushrod holes in close proximity to the port wall, just downstream of the port entry. Enlarge the port entry too much and you will grind into a pushrod hole. This may destroy the head or at least cause a very expensive repair. Adequate work on the practice head will help you avoid that.

    To see how far you can enlarge the port, go back to the junk head and grind one of its port entries until you cut into the pushrod hole. After that, you will know how much you can grind in that area without damaging the head.

    Once you have removed the majority of material with the large stone, you may need to switch to the small diameter, conical rotary stone (part no. 263061) to profile the small radii at the corners of each port.

    The most important thing to remember about rotary stones is they remove large amounts of material. They are not for final surface finishing. There may be basic port projects that do not require removal of large quantities of material. An example might be a production head on a high-performance engine. Those heads may already have fairly large ports and you will find the material to be removed inside the scribe marks is minimal. In that case, the rotary stones may be unnecessary.

    Disconnect the grinder, remove the stone and install the short cartridge roll mandrel (part no. 269111). Cartridge rolls come in a variety of sizes and shapes. The Kit includes straight rolls in two grits and three diameters, half-taper rolls in two grits and two diameters and full-taper rolls in two grits. Different grits are necessary to get the proper finish. Cartridge roll work starts with 40-grit then switches to 80-grit. It is not practical to go from a virgin surface or one that has been worked on with the rotary stone to proper finish with only the 80-grit. It takes too much time and you'd need more 80-grit rolls than there are in the Kit.

    Large-diameter, straight cartridge rolls are for finishing relatively flat surfaces like port walls, floors and roofs. The small straight rolls are for finishing long, radiused areas, such as the corners of intake ports, or areas of convex curves such as the corners of the valve guide bosses or the short side radii. The half-taper and full-taper cartridge rolls are better used on surfaces with concave curves, such as the "bowl" areas at the top of the valve pocket or combustion chamber corners. Additionally, half- and full- taper rolls are better to use when the tool approaches the work from a steep angle, such as working on the valve guide boss through the valve hole.

    With the mandrel in place and tightened, place one of the large, straight 40-grit cartridge rolls (part no. 263161) on the end of it. Note the little orange spot on one end of the roll. Point the spotted end towards the grinder, then screw the roll onto the mandrel. Reconnect the air or power supply.

    Begin finishing the flat areas in that first 1-1.5 inches past the port entry. Only work deeper in the port if there are excessive bumps or casting flaws. Remember to feather the smooth area into the surrounding virgin metal at the end of that 1-1.5-inches down the port entry.

    Once you have worked the port entry with 40-grit, switch to the large, straight 80-grit cartridge roll (part no. 263163). The 80-grit gives you the smooth, but not polished, surface that is correct for intake ports. Once you finish the 80-grit step, stop, remove your gloves and feel the surface. When your tactile "QC checker" senses the right finish on all the port walls, you're done.

    Step 3: Short Side Radius and Bowl Work

    The point where the intake port floor curves down to the valve seat is known as the "short-side radius." From an airflow standpoint, this area is the most critical in any port. Smooth that spot and there usually is a significant increase in flow through the port.

    With most production heads, the short-side radius will be sharp-edged and rough. The goal is to soften those sharp edges and smooth the roughness. Depending on the location of the radius and how you are approaching it, you may keep the short mandrel in the grinder or you may need to switch to the long mandrel (part no. 269149). Start with the small diameter, 40-grit straight cartridge rolls (part no. 263021) and, depending on the location of the radius and the tool angles necessary to approach it, you may also need to use small, 40-grit, half-tapered (part no. 263351); large, 40-grit half-tapered (part no. 263751) or 40-grit, full-tapered (part no. 263301) cartridge rolls. Again, you start with 40-grit and switch to 80-grit.

    Short side radius work is the first time you will bring abrasives near the valve seat and that is the one place you want to avoid hitting with any abrasive or rotating part of the grinder. Even though you will have a valve job done to your heads once the port work is finished, it doesn't take much of a hit on the valve seat to render it unusable even after a valve job.

    The next step is to do the roofs of the valve pockets and the valve guide boss. Called "bowl work", this will require a mix of the different small-diameter, tapered and straight cartridge rolls. Remember to start with 40-grit and finish with 80.

    The valve throat is the smallest diameter in the valve pocket just above the valve seat. A general rule is that the valve throat should be about 85% of the valve diameter. If you measure the throat to be smaller than that, using a combination of the rotary stone and cartridge rolls, open that diameter up to the 85% figure. If you attempt to open up the valve throat, first practice the technique on your junk head.
    Last edited by fpgt'91; November 3, 2006, 10:38 AM. Reason: Automerged Doublepost
    Ford Probe GT'91:

    K&N, UDP, Fidanza Flywheel, Race Concepts cross drilled/slotted F&R rotors, Goodridge SS lines, AutoMeter Gauges, Lo-Tek A-pillar pod, H4 conversion, 35F%20%R tinted, Andys Auto Sport Intimidator 2 Body Kit


    • #3
      Step 4: The Exhaust Port

      Goals for the exhaust port are similar to those we achieved with the intakes: To reduce restriction to gas flow, but your methods are going to be a bit different.

      Exhaust gases carry combustion by-products, of which carbon is a component. Over time, carbon deposits build up on the exhaust port walls and that can impede exhaust flow. To make the port walls more resistant to carbon build-up, in the final step you will give the exhaust port as smooth a texture as possible, a "near-mirror" finish, if you will.

      The initial exhaust port work is very much like what you did to the intakes. The major part of the finishing and polishing will often be done with small-diameter, straight and tapered cartridge rolls. Do the port exits, bowls and valve guide work just like you did on the intakes.

      Once you are done with the cartridge rolls, remove their mandrel and install the Standard Abrasives Combination Mandrel (part no. 269201) and screw the 120-grit flap wheel (part no. 262618) onto it. The flap wheel is used to take the finish one step past what you put on the intakes. Use the flap wheel on every part of the exhaust port you can reach.

      Once your flap wheel work is done, remove it and install one of the small, hex-socketed set screws into the Combination Mandrel. Tighten it, then screw one of the maroon-colored, 3-ply, 1 1/2- inch, medium-grade, Cross BuffsTM (part no. 265054) onto the set screw. Standard Abrasives Cross- BuffsTM are the most unique product in the Deluxe Porting Kit. They were designed exclusively for automotive use. Of all abrasives in the Porting Kit, Cross Buffs TM are most sensitive to grinder speed and should be run at 10,000 rpm for best results. Also, Cross Buffs TM need to be used with a light lubricant, such as WD-40.

      Begin working the exhaust port with the medium Cross Buff TM. Once you have hit as much of the port as you can with the medium, make a final pass with the red, 3-ply, 1 1/2-in. very-fine-grade, Cross BuffTM (part no. 265056). When you are done, the exhaust port walls will have that near-mirror finish that will resist carbon deposits.

      In most cases, you never port match the exhausts. Many stock exhaust manifolds and virtually all tube headers will have larger port sizes than do 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. If you end up with the rare situation where the stock exhaust manifold has ports smaller than those in the head, you will need to port match. Use the same technique used to match the intakes.

      Step 5: Polishing the Chambers

      You want to put the near-mirror finish on the combustion chamber walls for two reasons: 1) As a deterrent to carbon build-up; and 2) to eliminate any sharp edges that can cause pre-ignition. The first thing to do is clean up the stems of your junk valves (Cross Buff TM or one of the surface conditioning discs will work well) then install the valves into the chamber you will be working on. They will protect those all-important valve seats as you polish the surrounding chamber surfaces.

      Spray the head deck with machinist's bluing, then install one of the head gaskets you will use to assemble the engine. Scribe the outline of each chamber hole in the gasket on the deck.

      Most important to remember during chamber work is that you want to remove as little material as possible. Every bit of metal you polish away increases chamber displacement a tiny bit and reduces your compression ratio a corresponding amount. For that reason, you must not use the rotary stone for chamber polishing unless you need to unshroud the exhaust valves.

      Nevertheless, you cannot polish the chambers with just Cross Buffs TM. You must use the cartridge rolls first. Next, smooth the sharp edges where the chamber meets the deck, but do not grind past the line scribed around the chamber. You may need the larger cartridge rolls for the chamber's flat surfaces.

      Exhaust valve "shrouding" occurs when, at high valve lifts, exhaust flow is impeded by the closeness of the chamber walls to the edge of the open exhaust valve. Shrouding is common with pre-1971 Chevrolet small- and big-block V8 and early 289/302 Ford Windsor heads. At .300-.400 valve lift, there should be 3/16-in. or more between the edge of the valve and the adjacent chamber walls. If you do lack 3/16-in. clearance and there is material between the edge of the chamber wall and the gasket opening scribed on the head; remove material along the chamber wall such that exhaust valve shrouding is reduced. Only remove material inside the scribe line and only enough to achieve the clearance.

      Once your chamber work with cartridge rolls is complete, go over all surfaces with the 120-grit flap wheel. Finally, do the chamber with, first, the medium Cross BuffTM and then, the very-fine Cross Buff TM.

      As a final-touch that will enhance engine cooling, take a small-diameter, 40-grit, straight cartridge roll or the small rotary stone and remove any casting flash that is in the coolant openings in the head decks. You will be surprised at how much of that you find.
      Last edited by fpgt'91; November 3, 2006, 10:45 AM. Reason: Automerged Doublepost
      Ford Probe GT'91:

      K&N, UDP, Fidanza Flywheel, Race Concepts cross drilled/slotted F&R rotors, Goodridge SS lines, AutoMeter Gauges, Lo-Tek A-pillar pod, H4 conversion, 35F%20%R tinted, Andys Auto Sport Intimidator 2 Body Kit


      • #4
        Step 6: Port Matching the Intake Manifold

        If necessary, clean the gasket surface of the intake manifold with the surface conditioning discs in the Standard Abrasives Gasket Removal Kit and apply the machinist's blue.

        Get out the intake gaskets you used to scribe the intake side of the heads and install them onto the intake manifold. Verify that the correct sides face the manifold. Scribe an outline of the inside of the intake port openings on the manifold.

        Port-match the intake manifold using the cartridge rolls. If there is a lot of material inside the scribe marks to remove, use the rotary stones. If you are doing your basic port project on an engine with an aluminum manifold, remember to use a more gentle touch than you would if you were working cast iron.

        So...does it work?
        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.

        Final Remarks
        Your basic porting project will go more smoothly if you organize your work. Dividing the job into sections will enhance your consistency and shorten time on the job by reducing the amount of tool changes.

        Start on the intake port entries first. Hit them all with the rotary stone, then do the cartridge roll work. Next, do the intake bowl work. The third section of the job gets all the exhaust ports and bowls. Finish the heads by doing the chambers. Close out the whole job with the intake manifold port matching. Hold-off on having a valve job done on the heads until all abrasive operations are complete. A multi-angle valve job is best on heads destined for any high-performance application because it offers additional improvement in low-valve-lift air flow.

        And as a final bit there is always more information available through them, via the link and downloadable PDF files as well, but the main reason I posted this was because I know how many people hate links, and I thought I'd make it that much easier for all to see and become a little more educated on the subject.
        Ford Probe GT'91:

        K&N, UDP, Fidanza Flywheel, Race Concepts cross drilled/slotted F&R rotors, Goodridge SS lines, AutoMeter Gauges, Lo-Tek A-pillar pod, H4 conversion, 35F%20%R tinted, Andys Auto Sport Intimidator 2 Body Kit


        • #5
          WOW> And to think I was just gonna ask a question about how to P&P myself... Excellent write-up


          • #6
            I really want to bring this thread from the depths, for one it was hell to find and it was a great write up (just missing pics!) for all of us, would an admin sticky this please!
            Posed by jicks = I'm either hungry or horny, so If you see me without a boner, make me a sandwhich.


            • #7
              Sticky this preety please.


              • #8
                like it

                very nice write up thanks much for posting this


                • #9
                  This shall be stickied once I get on a computer (posting from iPhone with no mod powers).
                  Pr0n - my Anti-Drug.
                  1G FAQ - A MUST READ for 1G's! ~ 1990 PGL = WRECKED! & Sold! ~ 2004 Nissan 350Z Touring
                  "Let me hear you make decisions without your television."

                  Enjoy PT? Support it.


                  • #10
                    this is really useful info, imma gonna dig in once i get my junk head to practive a bit before i start to rebuild my engine.
                    Dutch owner of a 1st gen probe GT 1992.
                    its a W.I.P restoration project.


                    • #11
                      Anomaly did you sticky yet


                      • #12
                        Pr0n - my Anti-Drug.
                        1G FAQ - A MUST READ for 1G's! ~ 1990 PGL = WRECKED! & Sold! ~ 2004 Nissan 350Z Touring
                        "Let me hear you make decisions without your television."

                        Enjoy PT? Support it.


                        • #13
                          sticky sticky sticky stick jerry jerry jerry jerry...

                          wut pron time