Intake Runner Development For The 32v Porsche 928

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comIntake Runner Development for the 32v Porsche 928Featuring the928 Motorsports High-Flow IntakeThis application is an intake manifoldflange for the 32-valve Porsche 928engine.Our design goal was to make an intake runner that would:1) out-perform the stock intake runners, and2) be of a modular design useful formultiple head and plenum configurations (single plenum, dualplenums, and individual throttlebodies), and3) be robust enough to also handleboth boosted and naturally aspirated applications.Doing the MathBefore the design of a complete intake manifold system can be begin, there are some measurements and calculations that should be done to make sure it performs as intended. The engine specs, plus the intake runner length and diameter effect the volume and velocity of theair charge, and locate the power band within the desired RPM range.Careful engineering also allows the pressure waves known as the “Helmholtz effect” toincrease flow at the back of the intake valve just as it opens, thereby increasing volumetricefficiency by as much as 10%. To take advantage of this, proper intake bells must be used tocreate the pressure wave reversal to send the pulse back to the valve from where it came.As this article is about the development of the intake runners only, and our customers maywant to finish their system with individual throttle bodies (ITB’s) or single or dual plenum manifolds; the discussion and calculations for finished total runner length and plenum size havebeen omitted.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comIntake Runner Development for the 32v Porsche 928Featuring the928 Motorsports High-Flow IntakeInjector placementOwing to the size and type of injectors available toPorsche when the original manifold was designed,a fairly large intrusion into the intake runner existsto make room for the Type 2 injectors. The adventof the modern Type 3 injector allows us to reducethis intrusion into the runner, and permits more airto travel though.In addition, we canted the runner away fromthe injector slightly, which had several benefits.It further reduced the intrusion ofthe injector into the runner wall,it smoothed the transition fromthe runner into the head andopened the radius of the turn,and guaranteed proper aim ofthe fuel plume at the back of thevalves.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comIntake Runner Development for the 32v Porsche 928Featuring the928 Motorsports High-Flow IntakeTaperThere are two methods of “natural supercharging”, that is, increasing the velocityof the air at the back of the intake valve.The first is the Helmholtz Effect, usingproper inlet bells to reverse the pressurewave in combination with intake runnerlength to time the pulse so it arrives atthe back of the valve just as the valveopens; and the second is valve taper.A tapered intake runner increases air velocity at the back of the valve, and is aninexpensive way to gain HP from yourintake system.Taper and intake runner length are often overlooked in ITB setups, where the ITB’s aremounted directly to the heads or very close thereto. In our design, the ITB’s can be mountedatop our runners, and benefit from the midrange torque that the runner length provides andthe velocity increase from the tapered runner. All systems, boosted or NA, whether usingsingle or dual plenums or ITBs benefit from the increase in velocity that a good tapered runner provides.The dimensions at the base of the runnerwere set after the head was fully ported using a special 5-axis CNC process that 928Motorsports developed. These heads flowmore CFM than Brodix heads for NASCARmotors within our RPM range.Working up from the finished ported head,we established the diameter and taperdesired in the intake runner, the length ofthe runner, the injector angle and fitment,and the mounting surface for the plenum.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comIntake Runner Development for the 32v Porsche 928Featuring the928 Motorsports High-Flow IntakeDesign DrawingsComputer-Aided Design of thispart was a must. It afforded usthe opportunity to model manydifferent iterations, and makechanges to flutes and radiusesrapidly.Ryan Silva operated the SolidWorks software, and codesigned the finished part withCarl Fausett from 928 Motorsports LLC.Changes and adjustments to fitment weremade via Rapid Prototyping and fed back intothe computer model.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comIntake Runner Development for the 32v Porsche 928Featuring the928 Motorsports High-Flow IntakeMaterial Choice and Material SpecsGlass-reinforced Nylon (Nylon 12 GF) and later, Micro-Carbon Fiber* were selected for their strengthto weight ratios and relatively low cost of production when compared to an aluminum or similar casting. Their insulative properties to help keep the plenums and injectors cool was also a plus.Chart courtesy Solid Concepts, Inc.WeightIn Nylon GF (as tested) a pair of our intake runners weigh exactly 4lbs. Optionally, we canalso manufacture them in Nylon MCF (Micro-Carbon Fiber) where the runners would now be3.096 lbs. In comparison, if made in aluminum, the same part would weigh 8.0 pounds.REFERENCE DATACast Aluminum (2000 series) weighs 0.0997lb/in 3Aluminum billet (6061) weighs 0.0975 lb/in 3Nylon GF is0.050 lb/in 3Nylon MCF is 0.0387 lb/in3*Micro-Carbon Fiber uses very short strands of carbon fiber, instead of traditional carbon-fiber mat. It lends itselfto radiuses better than fiber mat, and has omni-directional strength and stability.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comPressure and Thermal TestingOur choice of materials needed to be tested for burst strength on boosted engines and thermal stability on hot race engines.Our data shows the cylinder head of the 928 engineto be at about 185 deg F surface temp at full load, sowe applied 200 degrees to the glass-filled nylon intake runner and 20 pounds of pressure to test it.The question we needed to answer is how much ofthe nylons burst strength we would lose at 200 degF. Using a timing solenoid and pneumatic switchmechanism, the pressure in the runner would go to20 psi and holdfor 9 seconds,then release tozero for one second, then repeat. This cycle repeated 6times per minute, allowing us very high cycling numbersfar in excess of what the engine would see in a givenrace.After we had logged 4,680 cycles (9 seconds on, 1 second off) on the manifold at 200 degrees at 10 psi withoutany failure, we raised the pressure to 20 psi while stillholding the GF nylon the at 200 degrees. We ran another 8,640 cycles like that also without any failure. We measured elongation of the part to beless than .002 per cycle, well within limits and far away from the materials rated tensilestrength.Next, we raised the manifold pressure from 20 psi to 40psi, and the RTV silicone gasket sealant blew out.To continue high-pressure testing of the runner, wemoved the runner to an actual cylinder head of the engine, using the stock intake manifold gasket and noRTV. Now we could run at 40 psi and did so for 8,640cycles without any measureable changes or failure.These tests proved to us our intake runner could withstand both the under-hood temperatures and the pressures it would need to survive in our application.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comColorizationWe didn't think many customers would warm to the natural-nylon look, and its tendency tohold greasy fingerprints and dirt.Early experimentation with dyes showed us how to color the casting in a manner that waspleasing to the customer, and we have already developed a flat black, red, and an“aluminum gray” colorization to the GF nylon.Another benefit of our colorization process is thatthe dyes penetrate the nylon to a depth ofabout .003”, making all butthe deepest scratchesinvisible, and far more durable than paint.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comFlow Bench TestingThe finished intake runners were flow-bench tested as were the original Porsche 32v intakemanifold runners.We checked all the runners in the OEM intake manifold and found cylinder #7 to be the mosttypical, and based our measurements there.Measurements were conducted in such a wayas to isolate the runner design only, and remove the plenums from consideration.The stock intake runners flowed 244.75 CFM.The 928MS intake runners flowed 356.89CFM.All tests were performed on the same day on the same machine, and at 28.5 Hg.As a point of reference, 360 CFM per cylinder will support 800 HP in 400 ci V8engine, not withstanding fuel selectionand aspiration.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comAdaptabilityThe finished product lends itself nicely to Individual Throttle Bodies, Single Plenum and DualPlenum manifolds, boosted or naturally aspirated.Where single-plenum manifolds are concerned, the strength of the material in tension needsto be checked as the heads move away from each other because of thermal expansion of thealuminum block.Our tests show that the Porsche 928 engine expansion from cold to hot engine, measuredacross the heads, is .034” - .005” This is well below the material strength of Nylon GF andNylon MCF, showing that single-plenum manifolds would be no problem with these runners.Fuel Rail Mounts Built InIn keeping with our concept of modular design, the fuel rail mounts were designed-in to theintake runners in such a way that easy access to the mounting bolts is still maintained. Thispermits removal of the intake as a unit with injectors and fuel rails still attached, as shown.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comFinal Assembly:These pictures show one possible conclusion to the intake manifold design using our hi-flowrunners.The application for this engine is a hightorque road racing motor, and taking a shotat the Land Speed record for Porsche 928’s.This Intake Runner was the last step to a total improvement of air flow throughout the32v 928 engine.First, the new intake runners are mounted tothe heads Then the plenum floor is put in place. We canprovide a CNC-cut plenum floor for these intake runners upon request. It makes fabricatingyour own plenum easy!The bells that make up the top of the intakerunners were set at the proper height off theplenum floor.Copyright 2010 928 Motorsports, LLC All Rights Reserved

Phone Toll Free: (877)FOR-928MWebsite: www.928motorsports.comWe experimented with mock-ups of both round-roofplenums and flat-roof plenums.For this application, the flat-roof was preferred as itplaced our plenum volume closest to the ideal sizewe had calculated. .The sides, floor and roof of our plenum is made from0.25” 6061 aluminum. That’s thicker than mostwould use, but we are designing for up to 30 psi ofboost, and that’s the reason for the wall thickness.Now the plenum sides are added, as well as the inlettubes at the rear of each plenum.A “balance tube” is often only 3/4” in diameter,just enough to balance out plenum pressures.This one is a full 3.0” in diameter, and doesmore than that.Owing to the unique firing order of the 928, thisbalance tube will actually feed and equilibratethe forward-most cylinders (cyls 1 and 5) withair from the opposite plenum on every cycle.Copyright 2010 928 Motorsports, LLC All Rights Reserved