Print

Email

Designing and Building a World-Record Beating Porsche V8

Page 2 of 2


Plenum Development
After the finished intake runners were mounted to the heads the plenum floor was put in place. The inlet bells that make up the top of the intake runners were set at the proper height off the plenum floor, and at the proper distance from the back of the valve. Even though the top of the runner would be completely encased within a pressurized plenum, the bells are still necessary to benefit from the Helmholtz effect.

We did the math on both a large single-plane plenum and smaller twin plenums with a balance tube between them, and opted for the twin plenums as the finished volume was closer to the ideal volume for us.

The sides, floor and roof of our plenums were made from 0.25˝ 6061 aluminum. That’s thicker than most would use, but we were designing for up to 30 psi of boost, and that’s the reason for the extra stiffness. Then the plenum sides were 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. Because of the firing order of the 928 (1-3-7-2-6-5-4-8), this balance tube will actually feed and equalize the forward-most cylinders (cylinders 1 and 5) with air from the opposite plenum on every cycle.

The finished plenums were strong enough to handle 30 psi of boost, and move enough air to support 900+ hp, and still fit under the hood of the 928. Even though the intake manifold is done at this point, we kept following the airflow outward and forward all the way to the air filters! A restriction at any point will negate all the other work and choke off the engine.

We opted for a single pressurized 4.0˝ ram tube to supply the two plenums with a dead- head design to keep the pressure up and equalized in the two plenum chambers.

The ram tube is fed by a large 4.0˝ throttle body, which is sized to provide best throttle response as well as maximum airflow.

Bell intercooler was brought in to design and build us a new aftercooler. We gave them the dimensions of the space envelope, the layout and the cfm and pressures, and they did the rest. They always do a great job. The new intercooler was smaller and yet moved more air with less pressure drop than the last one we had been using. A pressure test on the dyno showed 17 psi going in and 16 psi coming out – only a 1 psi pressure drop. Our old aftercooler was giving us a 4 psi drop, and when you’re averaging more than 25 hp per pound of boost – finding 3 psi more in the system is like finding 75 hp.

For the supercharger, we selected a boost head that would feed this beast from Vortech. Their V7 YSI is capable of 1,600 cfm at 30 psi, which they said was big enough to feed 1,200 hp. The only issue we had was that neither our 8-rib or 10-rib belt drives could pull the V7 YSI without belt slip or breakage. So a new cogged crank pulley and tensioner system had to be made to handle the load.

Engine Oiling
Whenever you take what is essentially an engine designed for street use and go racing, oil flow originally designed to adequately lubricate OHC cams and followers from idle to 2,500 rpm in street use will quickly oil-flood upper engines now living at 5,000 to 7,000 rpm constantly.  I felt if we didn’t modify and control the oil distribution in the motor we could pump all the oil up into the heads and starve the sump before the land speed run had finished. This is because the high-speed thrashing of the lobes and cam chain will entrain air into the oil, causing it to cling and resist flow back to the sump. Liquid oil enters the heads a lot faster under pressure than foamy air-oil mix can drain back via gravity alone.

In addition, any oil we could divert from the heads would increase flow to the main and rod bearings – and boy they could sure use it. Not only would the added flow increase their load bearing capacity, but we would also get benefits from the increased cooling the added oil flow would provide.

We went to Road America and other tracks several times this year for engine break-in and testing of our new oiling systems before we left Wisconsin. Our primary focus was the oil restrictors I had placed in the heads. We’d bench-tested these restrictors in the shop and had quantified two versions, one that diverted 10% more oil to the crank from the cams and one that diverted 17%.  

Because of the high boost levels and high-lift camshafts we were running, our valve springs were already 50% stronger than stock just to control the valves correctly. So we went with the 10% oil diverters in this application. But I worried that because of the hi-lift lobes and high-strength springs we were using the friction and wear between lobe and  follower would be so great – and if I missed my numbers, I’d save the crank bearings only to ruin the cam lobes.

All spring and summer we tested, then we would pull an oil sample and a camshaft cover, ship the oil sample off to be analyzed and visually inspect the lobes. Each of the tests and inspections came back positive – all indications were that I hadn’t diverted too much oil to the crank and we still had enough oil up top to do the job.   

 

---

928 Nylon Intake Runner Design and Development

The Manufacture-On-Demand (MOD) process lends itself well to 928 Motorsports’ nylon intake runner that was designed in-house by Ryan Silva and Carl Fausett using Solid Works. The dimensions at the base of the runner were set by the finished dimensions after the head was fully ported using a special 5-axis CNC process that 928  Motorsports developed. These heads flow more cfm than some NASCAR heads within our rpm range.  

Working up from the flange, Fausett and Silva established the diameter and taper they desired in the intake runner, the length of the runner,  the injector angle and fitment, and the mounting surface for the plenum. The Rapid Prototyping process from Solid Concepts was used to make several models representing each iteration so final fitment could be inexpensively tested on the heads directly, and changes quickly made.

When Fausett and his team were satisfied with fitment and contours, the final design needed to be tested to confirm it was pressure and thermally stable. The race car these will be fitted to will experience up to 20 psi of boost pressure, and they wanted at least a 20% safety margin above that. Rather than test all 8 intake manifold runners at once, they had Solid Concepts make a single intake runner for their destructive testing.

The data shows the cylinder head of the 928 engine to be at about 185 degrees F surface temp at full load, so they applied 200 degrees to the filled nylon intake runner and 20 pounds of pressure to test it. The question that needed answered was how much of the nylon’s burst strength would be lost at 200 degrees F.

Using a timing solenoid and pneumatic switch mechanism, they set the pressure in the runner to rise to 20 psi and hold for 9 seconds, then release zero for one second, then repeat cycle repeated 6 X per minute, allowing very high cycling numbers far in excess of what the engine would see in any given race.

After Fausett had logged 4,680 cycles (9 seconds on, 1 second off) on the manifold at 200 deg F at 10 psi without any failure, he raised the pressure to 20 psi and continued holding the GF nylon at 200 F. He ran another 8,640 cycles like that also without any failure. Fausett measured elongation of the part to be less than .002˝ per cycle, well within his limits and far away from the materials rated elongation at break rating.
Next, they 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, they moved the runner to an actual cylinder head of the engine, using the stock intake manifold gasket and no RTV.  Now Fausett could run at 40 psi and did so for 8,640 cycles without any measureable changes or failure.

These tests proved to Fausett and his team that their intake runner could withstand both the underhood temperatures and the pressures it would need to survive in their run for a world speed record.  

---

 

Rounding It Out
The finished engine required special support systems to perform as intended. These were:  crankcase ventilation, engine management and cooling system modifications.

Crankcase windage was handled by modifying our existing crank scraper and windage system to fit the longer throws of the stroker crank. Directional screening is used below the baffles so that once the oil drops down, it stays down, and out of the rotating assembly. Special deflectors were needed to redirect the drain oil coming out of the heads away from the spinning counterweights as well.

Outside the engine, twin pan-o-vacs in the exhaust system were routed through a 12 quart Patterson dry sump oil separator, and then to the engine. The oil extracted from the crankcase cloud was returned to the engine by a Tilton pump.

We noticed a restriction in the water bridge/thermostat housing of the 928 and took it to task. We would be making more heat than ever before with this engine and keeping those heads cool was a must. The restriction was cut out, the passage opened, and a new plate welded in to improve coolant flow through the heads.

We chose the Electromotive Tec GT system for engine management, as it would provide us the flexibility to control all ignition and fuel events and react to boost pressures dynamically. It would also allow us to carry different engine maps for each fuel we would be running (110 at Road America and the 116 octane Bonneville race spec).

We had a barrel of the Bonneville spec fuel shipped in so we could set the tune with the exact same fuel in the motor that we would have to run at the Salt Flats.
 
Final Results
Horsepower: 760 at the tire, 900 at the engine; Torque: 701 at the tire, 825 at the engine. Click on the link below to see a video of Carl's record breaking run.

Carl Fausett's Porsche 928 Record Run

Carl Fausett is a member of the Society of Automotive Engineers (SAE) in Horicon, WI and CEO of 928 Motorsports, LLC. His products and racing team have been featured at Pikes Peak, Road America, the Bonneville Salt Flats, and other top venues. Carl is available through his website www.928motorsports.com.