Porting cylinder heads
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==Preamble== | ==Preamble== | ||
| − | The purpose of this article is to acquaint engine builders | + | The purpose of this article is to acquaint engine builders to the possible benefits of cylinder head porting and making more power through the porting process. |
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| + | ==Port volumes vs. HP== | ||
| + | Port volume (or actually cross sectional area) is an important consideration when it comes to how big to make ports. Below is a table by David Vizard showing the relationship between port volumes and HP on a SBC 23 degree head. | ||
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| + | [[File:Vizard port volume vs hp sbc.jpg]] | ||
==Areas to work on== | ==Areas to work on== | ||
| + | Proper porting procedures will result in getting the largest volume of air/fuel mix to the combustion chamber in the shortest amount of time. Porting works hand in hand with valve grinding and seat cutting. | ||
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During the manufacturing and machining processes of a cylinder head, there are areas that are left unfinished. This is due to cost/time restraints imposed on the manufacturers. | During the manufacturing and machining processes of a cylinder head, there are areas that are left unfinished. This is due to cost/time restraints imposed on the manufacturers. | ||
When a port is machined for a seat, often a lip is left below the seat. This lip is sometimes semi-removed using a type of tapered reamer that helps smooth the transition from the seat into the pocket portion of the port. But because this is done quickly and by machine and not carefully and by hand, there is still almost always places where improvements can be made. | When a port is machined for a seat, often a lip is left below the seat. This lip is sometimes semi-removed using a type of tapered reamer that helps smooth the transition from the seat into the pocket portion of the port. But because this is done quickly and by machine and not carefully and by hand, there is still almost always places where improvements can be made. | ||
| − | [[File:EXH PORT.jpg|thumb|400px|left| Arrows indicate lip left after the machining process. This needs to | + | [[File:EXH PORT.jpg|thumb|400px|left| Arrows indicate lip left after the machining process. This needs to be carefully removed so the transition from the seat to the pocket is smooth.]] <br style="clear:both"/> |
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===Gasket matching=== | ===Gasket matching=== | ||
| − | This is a simple process whereby we will match thermostat housing to an intake manifold for better flow of coolant from the engine to the radiator. Begin by cleaning off the surface of both housing and intake mating surfaces. Remove all gasket material and glue with acetone and a gasket scraper. True the surface of slight imperfections by using a mill/bastard file place flat on the gasket surface working the file back and forth. The shiny | + | This is a simple process whereby we will match thermostat housing to an intake manifold for better flow of coolant from the engine to the radiator. Begin by cleaning off the surface of both housing and intake mating surfaces. Remove all gasket material and glue with acetone and a gasket scraper. True the surface of slight imperfections by using a mill/bastard file place flat on the gasket surface working the file back and forth. The shiny spots are the highs and the dull ones are the lows, true these surfaces. When a flat surface is obtained,paint the surface with Dykem dye, lay a new gasket on the surface and insert the bolts in the holes of the intake to center the gasket over the openings. With a scribe, scratch along the gasket edge around the opening. When complete, remove bolts and gasket. This will reveal a scribed line in the purple dye that you will be enlarging up the opening to. |
*If this is an aluminum intake, chuck up a open cut burr that is used for aluminum, and spray it with WD40 or similar lubricant. This will make cleaning the tool easier, reduce friction and heat. | *If this is an aluminum intake, chuck up a open cut burr that is used for aluminum, and spray it with WD40 or similar lubricant. This will make cleaning the tool easier, reduce friction and heat. | ||
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See '''[[Milling cylinder heads]]''' for more info. | See '''[[Milling cylinder heads]]''' for more info. | ||
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| + | ==Reality check== | ||
| + | While porting production heads was the thing to do in years past, nowadays there are relatively cheap, great performing aftermarket heads that will outperform all but the very best (read not ported by a beginner, and ''uber'' expensive) ported production heads. | ||
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| + | Porting is relatively easy to do as far as removing metal goes, BUT knowing '''where''' and '''how much''' to remove makes '''''all the difference''''' between a good performing head and a boat anchor. | ||
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| + | Photos of ported heads can look very impressive. Unfortunately that means nothing for the most part, unless the work was done by a seasoned porter, and there was a lot of track testing done to confirm the results, and/or there was access to a flow bench- along with the knowledge needed to digest the bench's results and turn the data into viable, meaningful, positive changes. So looking at photos can show generalities, but as far as being a useful tool, photos fall far short of giving any really meaningful info. If templates made from flat stock, and ground down valves used as sizing indicators are used to help a porter, this can make a big difference in the outcome. Unfortunately, these templates are hard to come by, as they were the same thing as a CNC program before there were CNC machinery. | ||
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| + | Doing a full-on porting job is very labor intensive and is a dirty, time consuming project- made doubly so when working with cast iron. To bring a set of 305 heads (which are often touted as a cheap, easy head to modify for use on the SBC 350) up to what even a set of stock untouched L31 Vortec heads can do, is hard to do regardless of who you are, let alone someone with no experience. Just doing '''one''' port is a chore. By the time all 16 ports are done along with the cost of the machine shop and parts, most guys will see that buying aftermarket heads or even using a better production casting to start with (like the Vortec) is the better way to go. | ||
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| + | If the decision has been made to use the 305 heads regardless, staying with the "low hanging fruit" like removing/blending the lip that's almost always present where the bowl meets the bottom seat cut (shown in images above), and removing casting flash and irregularities, and careful port matching (NOT gasket matching) can result in an improvement of several percent with only moderate time and effort. Often backcutting the valves gives an improvement for little cost. A true quality valve job can be worth a few percent more and should be considered a 'must-do' on '''any''' production head- and even aftermarket heads need to be checked over carefully. | ||
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| + | As has been said already, the difference in cost between a '''''properly''''' rebuilt, ported and prepped set of production heads and a set of aftermarket heads becomes less the more parts, time and work they consume. But if a production head is going to be used, it makes more sense to start out with the best performing head available rather than using a head because it's cheap (or even free). Remember- the same machine shop time and money will be spent regardless if you're starting with a Vortec head or a 305 head. | ||
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| + | *[http://www.hotrodders.com/forum/305-head-350-sbc-24052-3.html#post1591655 305 heads on a 350 SBC] | ||
==Photos== | ==Photos== | ||
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*[http://www.empirenet.com/pkelley2/DynamicCR.html Dynamic compression calculator] by Kelly | *[http://www.empirenet.com/pkelley2/DynamicCR.html Dynamic compression calculator] by Kelly | ||
*[http://www.kb-silvolite.com/calc.php?action=comp2 Dynamic compression calculator] by KB | *[http://www.kb-silvolite.com/calc.php?action=comp2 Dynamic compression calculator] by KB | ||
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| + | ===Other calculators=== | ||
| + | *[http://users.erols.com/srweiss/calcplv.htm Port Limiting Velocity | ||
| + | or Minimum Port Cross Sectional Velocity] | ||
| + | *[http://users.erols.com/srweiss/calccsa.htm Port CSA] | ||
| + | *[http://users.erols.com/srweiss/calcacsa.htm Average Port CSA] | ||
| + | *[http://users.erols.com/srweiss/calcfps.htm Port FPS / CFM / CSA] | ||
| + | *[http://users.erols.com/srweiss/calcdchg.htm Convert Airflow to a Different Depression] | ||
| + | *[http://users.erols.com/srweiss/calcafhp.htm Estimate Horsepower from Intake Airflow] | ||
| + | *[http://users.erols.com/srweiss/calchpaf.htm Estimate Intake Airflow needed from HP wanted] | ||
| + | *[http://users.erols.com/srweiss/calcve.htm Estimate Volumetric Efficiency] | ||
| + | *[http://www.rbracing-rsr.com/runnertorquecalc.html Inlet Runner and Peak Torque Calculators] | ||
==Related links== | ==Related links== | ||
| − | * | + | *[http://www.centroidcnc.com/cnc_porting_machine.html CNC cylinder head porting and block machines] |
| − | * | + | *[http://www.ruffstuff.com/ Cylinder head porting abrasives] |
| − | * | + | *[http://hubpages.com/hub/Cylinder-Head-Porting-101 Cylinder Head Porting 101] |
| − | * | + | *[http://www.diyporting.com/Shrouding.html Valve shrouding] from diyPorting.com |
| − | * | + | *[http://www.superchevy.com/technical/engines_drivetrain/cams_heads_valvetrain/sucp_0902_chevy_engine_port_variations_measuring/viewall.html How to calculate the optimum intake port volume] |
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