Building a 900 HP Porsche 928 Motor For the 928 Motorsports Bonneville Land Speed Attempt The task I had given myself was to see if I could get enough HP out of a Porsche 928 V8 to break one or more world land-speed records. We would build for the BGMS (Blown Gas Modified Sports) class where the record is currently 231.5 mph. Another record we were after was the Porsche marquee record for the 928 of 209.2 MPH. Our math told us that, because we knew our final drive ratio, tire diameters and engine redline; and if our estimates for vehicle frontal area and coefficient of drag were correct, that we would need 750 HP at the tire just to meet the current record. With a 15% drive-train loss, this meant we would require 900 HP at the engine to net the 750 we needed at the tire. (Note the class is Blown Gas Modified Sports cars – there is a “Fuel” class as well and they get to run anything they want in their tanks such as alco- hol, nitro methane, or whatever.) Cars in the Gas class must run the event gas provided – everybody gets the same event gas right there at trackside and then your filler neck is sealed by the officials. Using just straight gas, making 900 HP from this small V8 would be a little more challenging. Also, we didn’t have to make 900 HP once, but repeatedly and for a long time. Unlike a Dyno pull of 6 seconds or so, we would be at wide- open throttle and full load for almost 2 minutes each run – and have to do that several times to get our Bonneville 200 mph license and (hopefully) establish a new world record. The stresses on the engine during these runs are staggering. Over the last decade I had carefully modified and built each engine in my race car and had learned the “do’s and don’ts” peculiar to supercharging the Porsche 928. I had already built a 650 HP motor for my race car and it had per- formed admirably at the Pikes Peak In- ternational Hill Climb where it netted us a podium finish in the Open Division and made us the fastest 2WD car in the class. Good stuff. But for Bonneville, 650 HP wasn’t going to get it done. Every system in the en- gine would need attention if we were to make the HP needed and survive long enough to repeat it. Phone Toll Free: (877)FOR-928M Website: www.928motorsports.com Copyright 2011 928 Motorsports, LLC All Rights Reserved
Transcript
Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt The task I had given myself was to see if I could get enough HP out of a Porsche 928 V8 to break one or more world land-speed records. We would build for the BGMS (Blown Gas Modified Sports) class where the record is currently 231.5 mph. Another record we were after was the Porsche marquee record for the 928 of 209.2 MPH. Our math told us that, because we knew our final drive ratio, tire diameters and engine redline; and if our estimates for vehicle frontal area and coefficient of drag were correct, that we would need 750 HP at the tire just to meet the current record. With a 15% drive-train loss, this meant we would require 900 HP at the engine to net the 750 we needed at the tire. (Note the class is Blown Gas Modified Sports cars – there is a “Fuel” class as well and they get to run anything they want in their tanks such as alco-hol, nitro methane, or whatever.) Cars in the Gas class must run the event gas provided – everybody gets the same event gas right there at trackside and then your filler neck is sealed by the officials. Using just straight gas, making 900 HP from this small V8 would be a little more challenging. Also, we didn’t have to make 900 HP once, but repeatedly and for a long time. Unlike a Dyno pull of 6 seconds or so, we would be at wide-open throttle and full load for almost 2 minutes each run – and have to do that several times to get our Bonneville 200 mph license and (hopefully) establish a new world record. The stresses on the engine during these runs are staggering. Over the last decade I had carefully modified and built each engine in my race car and had learned the “do’s and don’ts” peculiar to supercharging the Porsche 928. I had already built a 650 HP motor for my race car and it had per-formed admirably at the Pikes Peak In-ternational Hill Climb where it netted us a podium finish in the Open Division and made us the fastest 2WD car in the class. Good stuff. But for Bonneville, 650 HP wasn’t going to get it done. Every system in the en-gine would need attention if we were to make the HP needed and survive long enough to repeat it.
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Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt Some of the parts I would need existed, but had to be adapted or modified to the task. Many others didn’t exist at all and would have to be engineered and fabricated from scratch. COMPRESSION RATIO AND DISCPLACEMENT When designing this engine for this event, I had a choice of displacement options and compression ratios. The displacement decision was made easy by looking at the current Bonneville land speed records. The engine size with the lowest MPH record was the lowest hanging fruit on the tree, so we felt the most ripe for a change. This meant I would build for the “B” engine class—engines from 6.11 Liter to a max of 7.19 Liters. By stroking the 928 and boring it out I would build an engine of 6.54L and put it squarely in the “B” engine class at Bonneville. Compression ratio is another matter. When building for boost there are two schools of thought; build with higher compression and run low boost, or build with lower compression and run higher boost. In theory, both engines can produce about the same HP, but I am a member of the group that believes that the lower CR motor will be safer and less difficult to tune. With lower compression, I have a lar-ger cylinder volume to fill with air/fuel mixture, a safer burn, and (arguably) higher outputs. We decided on 8.5:1 compression ra-tio, and about 15 to 18 psi of boost. The custom pistons were made for us by Arias, with molybdenum coated skirts and ceramic crowns.
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Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt Doing the Math After a little engine math we learned that 900 BHP would require the capacity to move 320 CFM into each cylinder and 260 CFM out at ambient pressure (1 BAR); or an average of 2,560 CFM for the complete V8 engine. Then, if we ran about 2 BAR of manifold pressure, we should hit our numbers. I began at the combustion chamber and worked outward from that point on every component and sys-tem from air filter on the intake side to exhaust tips on the other. Every part of every system had to have as much capacity as the next and none less than 2560 CFM. Heads
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Usually, porting a set of heads is up to the skill of the tool operator as each intake and exhaust port is hand-milled to open them up. In many cases, this is the only way it can be done. But no matter how expert the operator, making the intake and exhaust ports match from cylinder-to-cylinder is just about impossible. And with that irregularity, variables from cylinder to cylinder are being built in that will negatively affect the engines smoothness, power, and longevity under high loads.
To correct this and improve on the hand-ported perform-ance head, we developed a CNC milling program on a 5-axis mill for optimizing the Porsche 928 heads. This digital milling process guarantees not only maximum flow, but repeatability from cylinder-to-cylinder.
Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt VALVE SIZES AND SEATS In concert with our CNC porting job, we up-graded from stock 36mm to special 39.5mm intake valves, and also larger 33mm exhaust valves. We opted for lightweight stainless steel as the material for the valves which al-lowed us to have the same valve weight as stock, even though the valves are larger. Tita-nium is also available for the high-rev engines but we didn't think we needed it as we will be staying under 7,000 rpm. Special beryllium-copper valve seats were used to improve the thermal conductivity of the seat and to reduce valve bounce at clos-ing. VALVE SPRINGS At 15 pounds of boost, our 65.2 gram intake valve with a head diameter of 1.899 sq inches will have a virtual weight (physical weight plus air pressure loading) of 28.63 pounds!
This means stronger springs were required to close the intake against the boost pres-sure. Other challenges also include con-trolling valve float from cam lobe toss and seat bounce at 7000 rpm, yet avoid valve spring stack with our high-lift (.442”) cam-shafts. The solution was a custom set of valve springs made from chrome-vanadium wire, shot peened, heat treated and stress re-lieved. Titanium retainers and clips were found and used to hold them in place.
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Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt CAMSHAFTS Of course the large valves and porting alone won’t move the right amount of air without the cams to lift them!
Here we have a certain disadvantage compared to our friends running pushrod motors. Because a pushrod motor can use a 1.4:1, 1.5:1 or even 1.6:1 rocker arm ratio, they can throw their valves open further and faster than a OHC, OHV setup like that in the 928 engine can. Three different sets of cam grinds in varying de-grees of aggressiveness were developed. Tthe last being a special profile with absolute maximum lift that would still fit within the 32v Porsche 928 heads.
Unique to the Bonne-ville application, we need our max HP to come in at maximum revolutions (7,000 RPM) where we will have our greatest aero-dynamic resistance. A combination of spe-cial cams and intake runner lengths would be used to tune the power band to make this hap-pen.
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Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt INTAKE RUNNER DEVELOPMENT 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 old Generation II injectors. The advent of the modern thin-body Generation III 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, opened the radius of the turn, and guar-anteed proper aim of the atom-ized fuel plume at the back of the valves.
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Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt Taper There are two methods of “natural super-charging”, 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 runner taper. The ID dimensions at the base of the runner were set once the head was fully ported. 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.
Here are the finished nylon runners, complete with o-ring seals at the top, injectors and large-bore billet fuel rails mounted.
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Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt 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 transitions and radiuses rapidly.
Changes and adjustments to fitment were made via Rapid Prototyping and fed back into the computer model.
We “hit our marks” on the third manufacturing model, and went right to pressure and thermal testing the runners.
The runners were heated to 200 deg F and tested for 8,640 cycles (0 to 40 psi to 0 = 1 cy-cle) without failure, and with only .002 deflec-tion. They would hold our 20 psi without a prob-lem, and more if we needed it.
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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 in-take 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 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 de-
signing for up to 30 psi of boost, and that’s the reason for the wall thick-ness. Now the plenum sides are added, as well as the inlet tubes at the rear of each plenum.
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PLENUM BALANCE TUBE 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 (1-3-7-2-6-5-4-8), this balance tube will actu-ally feed and equilibrate the forward-most cyl-inders (cyls 1 and 5) with air from the opposite plenum on every cycle.
FINISHED PLENUMS Finally it was time to weld the lids on each plenum, which we farmed out to a certified welder.
They are strong enough to handle 30 psi of boost, they move enough air to sup-port 900+ HP, and still fit under the hood of the 928!
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Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt RAM TUBE and THROTTLE BODY Even though the intake manifold is done at this point, we must keep following the air flow outward and forward all the way to the air filters! A restric-tion 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, sized to provide throttle response as well as max air flow. INTERCOOLER The air travels through the intercooler first before the throttle body. We tried last year’s inter-cooler first (which was designed for a 5.1L motor and less boost) and found at full song we had 18 psi going into the intercooler and only 14 coming out! Way to restrictive. So Bell intercooler was brought in to design and build the intercooler we needed. We gave them the dimensions of the space envelope, the layout, and the CFM and pressures desired, and they did the rest. They always do a great job. The new intercooler is smaller yet moves more air. At the dyno, the same pressure test showed 17 psi going in and 16 psi coming out—only a 1 psi drop! When we are averaging more than 25 HP per pound of boost—finding that 3 psi was like finding 75 HP!
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Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt FORCED INDUCTION Now the supercharger. Again, the math told us how much air we needed and at what pressures. We selected a boost head that would feed this beast from Vortech, their V7 YSI, capable of 1600 CFM at 30 psi. They report it is big enough to feed a 1200 HP motor. The only issue we had was 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.
AIR FILTERS The last step was enough air flow through the filters—which was accomplished by a pair of 3.5” oiled cotton filters feeding a single 4.0” inlet tube.
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Building a 900 HP Porsche 928 Motor For the
928 Motorsports Bonneville Land Speed Attempt Time to go back to the heads! Up till now we have only followed the intake side out making sure that every component can flow the re-quired amount of air to make our target HP. Now the same must be done going the other way - through the exhaust valves to the tail-pipe. We’d already installed large 33mm ex-haust valves and ported the heads to their maximum size.
HEADERS That provided the ID dimension for the Header’s pri-mary tubing, so we would have the smoothest transi-tion possible from the head to the header. Special heavy-duty header flanges were cut, and custom headers made to spec.
X-PIPE AND EXHAUST The headers feed into the exhaust system via an X-pipe to provide side-to-side balancing of the pressure pulses. This had to be custom made to our spec, and we made them in-house. Again, we tried parts from last years setup and fit the old 3” dual exhaust to the en-gine for testing. At the dyno we saw the pres-sure in the intake plenum go up 2 psi at full throttle! Too restrictive. Another hour with the engine math proved it, and told us that we could not push the CFM we needed thru the dual 3’s. Dual 3.5” exhaust would be needed to get near 1000 HP.
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An all-new exhaust was made from 3.5” mandrel bent thin-wall stainless steel and TIG welded in our shop. V-V-band clamps were integrated into the design for the
absolute smooth-est transitions pos-sible.
The finished exhaust has a cross-over with internally fitted directional vanes, and twin stainless steel pan-o-vac couplings. ENGINE OILING Whenever you take what is essentially an engine designed for street use and go racing, oil flow origi-nally designed to adequately lubricate OHC cams and followers from idle to 3500 rpm in street use will quickly oil-flood upper engines now living at 5 to 7000 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 cool-ing the added oil flow would provide.
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Proprietary oil diverters were made and bench-tested, and we came up with two models—one that diverted 10% of the oil from the camshafts to the crankshaft and one that diverted 17%. We went to Road America and other tracks several times for engine break-in and test-ing of our new oiling systems before we left Wisconsin. We also put a window in our cam covers so we could video the oiling of the cams during dyno runs. 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. Rounding It Out The finished engine required special support systems to perform as intended. These were:
Lessening Windage, Crankcase Ventilation, Engine Management, and Cooling System Modifications. Crankcase windage was handled by modify-ing our existing crank scraper and windage system design 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 are needed in the Porsche 928 to redirect the drain oil com-ing out of the heads away from the spinning counterweights as well.
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Outside the engine, twin pan-o-vacs in the ex-haust system were routed through a 12 quart Patterson dry sump oil separator, and then to the engine. The oil extracted from the crank-case cloud is returned to the engine by a Tilton pump. We noticed a restriction in the water bridge of the 928 casting and took it to task. We would be making more heat than ever before with this engine and keeping those heads cool is a must. The restriction was cut out, the passage opened, and a new plate welded in to improve flow thru the heads as shown.
We chose the Electromotive Tec GT system for engine man-agement, as it would provide us the flexibility to control all igni-tion 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 and 116 Bonneville race spec). A barrel of the Bonneville spec 116 octane fuel was 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.
