Intake Runner Development for the 32v Porsche 928 Featuring the 928 Motorsports High-Flow Intake This application is an intake manifold flange for the 32-valve Porsche 928 engine. Our design goal was to make an intake runner that would: 1) out-perform the stock intake runners, and 2) be of a modular design useful for multiple head and plenum configurations (single plenum, dual plenums, and individual throttle bodies), and 3) be robust enough to also handle both boosted and naturally aspirated applications. Doing the Math Before 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 the air charge, and locate the power band within the desired RPM range. Careful engineering also allows the pressure waves known as the Helmholtz effect to increase flow at the back of the intake valve just as it opens, thereby increasing volumetric efficiency by as much as 10%. To take advantage of this, proper intake bells must be used to create 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 may want 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 have been omitted.
Intake Runner Development for the 32v Porsche 928 Featuring the 928 Motorsports High-Flow Intake Injector placement Owing to the size and type of injectors available to Porsche when the original manifold was designed, a fairly large intrusion into the intake runner exists to make room for the Type 2 injectors. The advent of the modern Type 3 injector allows us to reduce this intrusion into the runner, and permits more air to travel though. In addition, we canted the runner away from the injector slightly, which had several benefits. It further reduced the intrusion of the injector into the runner wall, it smoothed the transition from the runner into the head and opened the radius of the turn, and guaranteed proper aim of the fuel plume at the back of the valves.
Intake Runner Development for the 32v Porsche 928 Featuring the 928 Motorsports High-Flow Intake Taper There are two methods of natural supercharging, that is, increasing the velocity of the air at the back of the intake valve. The first is the Helmholtz Effect, using proper inlet bells to reverse the pressure wave in combination with intake runner length to time the pulse so it arrives at the back of the valve just as the valve opens; and the second is valve taper. A tapered intake runner increases air velocity at the back of the valve, and is an inexpensive way to gain HP from your intake system. Taper and intake runner length are often overlooked in ITB setups, where the ITB s are mounted directly to the heads or very close thereto. In our design, the ITB s can be mounted atop our runners, and benefit from the midrange torque that the runner length provides and the velocity increase from the tapered runner. All systems, boosted or NA, whether using single or dual plenums or ITBs benefit from the increase in velocity that a good tapered runner provides. The dimensions at the base of the runner were set after the head was fully ported using a special 5-axis CNC process that 928 Motorsports developed. These heads flow more CFM than Brodix heads for NASCAR motors within our RPM range. Working up from the finished ported head, we established the diameter and taper desired in the intake runner, the length of the runner, the injector angle and fitment, and the mounting surface for the plenum.
Intake Runner Development for the 32v Porsche 928 Featuring the 928 Motorsports High-Flow Intake Design Drawings Computer-Aided Design of this part was a must. It afforded us the opportunity to model many different iterations, and make changes to flutes and radiuses rapidly. Ryan Silva operated the Solid Works software, and codesigned the finished part with Carl Fausett from 928 Motorsports LLC. Changes and adjustments to fitment were made via Rapid Prototyping and fed back into the computer model.
Intake Runner Development for the 32v Porsche 928 Featuring the 928 Motorsports High-Flow Intake Material Choice and Material Specs Glass-reinforced Nylon (Nylon 12 GF) and later, Micro-Carbon Fiber* were selected for their strength to 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. Weight In Nylon GF (as tested) a pair of our intake runners weigh exactly 4lbs. Optionally, we can also manufacture them in Nylon MCF (Micro-Carbon Fiber) where the runners would now be 3.096 lbs. In comparison, if made in aluminum, the same part would weigh 8.0 pounds. REFERENCE DATA Cast Aluminum (2000 series) weighs 0.0997lb/in^3 Aluminum billet (6061) weighs 0.0975 lb/in^3 Nylon GF is 0.050 lb/in^3 Nylon MCF is 0.0387 lb/in3 *Micro-Carbon Fiber uses very short strands of carbon fiber, instead of traditional carbon-fiber mat. It lends itself to radiuses better than fiber mat, and has omni-directional strength and stability.
Pressure and Thermal Testing Our 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 engine to be at about 185 deg F surface temp at full load, so we 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 of the nylons burst strength we would lose at 200 deg F. Using a timing solenoid and pneumatic switch mechanism, the pressure in the runner would go to 20 psi and hold for 9 seconds, then release to zero for one second, then repeat. This cycle repeated 6 times per minute, allowing us very high cycling numbers far in excess of what the engine would see in a given race. After we had logged 4,680 cycles (9 seconds on, 1 second off) on the manifold at 200 degrees at 10 psi without any failure, we raised the pressure to 20 psi while still holding 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 be less than.002 per cycle, well within limits and far away from the materials rated tensile strength. Next, we raised the manifold pressure from 20 psi to 40 psi, and the RTV silicone gasket sealant blew out. To continue high-pressure testing of the runner, we moved the runner to an actual cylinder head of the engine, using the stock intake manifold gasket and no RTV. Now we could run at 40 psi and did so for 8,640 cycles 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.
Colorization We didn't think many customers would warm to the natural-nylon look, and its tendency to hold greasy fingerprints and dirt. Early experimentation with dyes showed us how to color the casting in a manner that was pleasing 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 that the dyes penetrate the nylon to a depth of about.003, making all but the deepest scratches invisible, and far more durable than paint.
Flow Bench Testing The finished intake runners were flow-bench tested as were the original Porsche 32v intake manifold runners. We checked all the runners in the OEM intake manifold and found cylinder #7 to be the most typical, and based our measurements there. Measurements were conducted in such a way as 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 356.89 CFM. 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 V8 engine, not withstanding fuel selection and aspiration.
Adaptability The finished product lends itself nicely to Individual Throttle Bodies, Single Plenum and Dual Plenum manifolds, boosted or naturally aspirated. Where single-plenum manifolds are concerned, the strength of the material in tension needs to be checked as the heads move away from each other because of thermal expansion of the aluminum block. Our tests show that the Porsche 928 engine expansion from cold to hot engine, measured across the heads, is.034 +-.005 This is well below the material strength of Nylon GF and Nylon MCF, showing that single-plenum manifolds would be no problem with these runners. Fuel Rail Mounts Built In In keeping with our concept of modular design, the fuel rail mounts were designed-in to the intake runners in such a way that easy access to the mounting bolts is still maintained. This permits removal of the intake as a unit with injectors and fuel rails still attached, as shown.
Final Assembly: These pictures show one possible conclusion to the intake manifold design using our hi-flow runners. The application for this engine is a hightorque road racing motor, and taking a shot at the Land Speed record for Porsche 928 s. This Intake Runner was the last step to a total improvement of air flow throughout the 32v 928 engine. First, the new intake runners are mounted to the heads Then the plenum floor is put in place. We can provide a CNC-cut plenum floor for these intake runners upon request. It makes fabricating your own plenum easy! The bells that make up the top of the intake runners were set at the proper height off the plenum floor...
We experimented with mock-ups of both round-roof plenums and flat-roof plenums. For this application, the flat-roof was preferred as it placed our plenum volume closest to the ideal size we had calculated.. The sides, floor and roof of our plenum is made from 0.25 6061 aluminum. That s thicker than most would use, but we are designing for up to 30 psi of boost, and that s the reason for the wall thickness. Now the plenum sides are added, as well as the inlet tubes 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 does more than that... Owing to the unique firing order of the 928, this balance tube will actually feed and equilibrate the forward-most cylinders (cyls 1 and 5) with air from the opposite plenum on every cycle.
The finished plenums are placed atop the intake runners, and are waiting for the intake tubing and throttle body to be attached. They will handle 30 psi of boost, move enough air to support 800+ HP, and still fit under the hood of the 928!
Rounding It Out Of course a big intake manifold alone doesn't make HP. You need the rest of the engine to match! We have done the research to develop maximum-flow from the 928 32v heads, and have them flowing as much as 324 CFM at.450 of intake valve lift. This was a 56.6% improvement over stock, and on par with Brodix racing heads used in NASCAR. A complete description with flow charts about our CNC head porting program is available at our website here: http://www.928motorsports.com/services/32_valve_heads.php With the big valves to match: http://www.928motorsports.com/parts/32v_valves.php In addition, the high performance camshafts needed to produce these lift and flow numbers have also been developed and tested. More information about our highperformance Camshafts is available at our website here: http://www.928motorsports.com/parts/camshafts.php And you need the right exhaust headers; designed to properly port-match these monster heads, and we have them too. More information about these headers is available at our website here: http://www.928motorsports.com/parts/big_port_header.php Finally, you may want a modern stand-alone Engine Management System to dial it all in and control those big injectors you will use to feed the beast. We have that for you too, here: http://www.928motorsports.com/parts/tec_gt_engine_management.php