Greetings, Audi Fans!
This is the tech article we promised to do on the engine and related hardware in our Land Speed Record holding, 1993 Audi S4 sedan race vehicle. This article will detail all of the modifications and the majority of specifications of the engine, turbo system, intake and exhaust systems and inter-cooler system, as well as engine management and ignition etc. In particular, I will discuss the details involved with making the horsepower required to push an S4 sedan to over 250 MPH, while running at max boost and rpm over a five mile course and, surviving to make a successful back- up run the following day.
So let’s get started. The engine in the race car is the very same Audi 5 cylinder that came in the car from the factory – Audi engine code AAN. Every part has been modified, massaged or upgraded. It does retain the factory block and head castings as well as the factory forged steel crankshaft. The bore is 82 mm, stroke is 86.4 or approximately 2.3 liters displacement and it produces in excess of 1000 horsepower.
Cylinder Block Preparation:
View of cylinder finish (customer engine)
After several hours of hot tanking and cleaning, the interior of the block is heavily de-burred and all the sharp machining edges around the main bearing webs are rounded and sanded to aid oil return and strengthen the block. The head bolt and main bearing cap bolt holes are prepped with a bottoming tap for the ARP studs that replace the factory fasteners in these areas. The main bearing caps are shot-peened and all their cast surfaces are polished smooth.
The block is then decked to provide a perfectly square, flat surface for the head gasket to seat on.
The main bearing saddles are line-honed to make them perfectly straight and to add bearing clearance. The combination of line honing and aggressive polishing of the crank is used to produce a main bearing clearance of .003 and factory main bearing inserts are used, as is the factory four piece thrust bearing assembly. * A modification of critical importance is grooving the lower main bearing shells to match the upper ones which facilitates 360 degree feed pressure to the rod bearings on the non cross drilled crank.
The cylinder bores and their finishing is of extreme importance in terms of power production and durability. The cylinders are bored and honed to fit 82 mm pistons. The bore is not made any larger than this so as to leave adequate material behind to resist cylinder wall flexing under extreme pressure and mechanical load, and, to keep the sealing surface between cylinders wide enough to reliably hold the gasket.
The cylinders are honed to produce .005 piston to wall clearance using a steel deck plate that mimics the distortion of the cylinder caused by the torque and load on the head studs. The honing process is critical to perfect ring seal and is a method called “plateau honing” in which progressively finer stones are used to produce a nearly glass smooth bore finish. I use a 500 grit, diamond hone for the last part of the process and set the hone to produce a 25 degree cross hatch which is critical to the cylinder wall retaining just the right amount of oil during operation.
Crankshaft:
Pauter Rods / FRP Prepped Crank & Main Caps
The factory AAN crank is checked for straightness and dimensional consistency. Note* Most of these cranks are just about perfect from the factory in the important aspects of journal concentricity and flatness - if they have never been damaged or modified.
The crank exterior surfaces are de-burred to remove forging flash and all sharp edges left from machining are sanded blunt with a die grinder, again, to remove stress risers and strengthen the part.
Finally, the leading edge of the main journal oil holes and the trailing edge of the rod oiling holes are elongated with a die grinder to improve oiling and the crank journals are micro polished.
Stock AAN Main Cap – Before and After Polishing
Pistons, Rings and Coatings:
FRP Wiseco Piston – Gas Ported - Total Seal Gapless Second Ring (after running at Bonneville)
The pistons are an FRP design, produced by Wiseco Piston from 2618 alloy. They are a strutted, slipper skirt design, with flat tops, deep valve reliefs and a lightweight tool steel wrist pin (62 grams). The compression height is such that the piston has a positive deck height of .030 and a final compression ratio of 10 to 1. There are radial gas ports in the top ring’s upper land.
Piston rings are a highly critical part of this engine’s performance equation.
The top ring is a gas nitrided steel design with a barrel face and is 1.2 mm thick. The end gap is held at a tight .018 and works with the gas ports to provide very high sealing integrity. * The relatively tight gap in the top ring is possible because the engine is never run hard until the engine is fully warmed allowing the iron block cylinders to expand to their hot dimensions.
The second ring is a Total Seal “Gapless” design that uses a machined base ring with an interlocking rail to provide a gapless seal that backs up the top ring and aids the oil ring in keeping oil out of the combustion process. It is 1.5 mm thick. It is hard to overstate the effectiveness of the Total Seal Gapless rings. The engine has virtually zero blow-by and this design has been proven to increase the negative pressure signal to the intake system thereby making cylinder filling more efficient.
The oil ring assembly is a standard tension type and 2.8 mm in thickness.
The piston’s crowns are coated with PolyDyn thermal barrier coating. This ceramic coating is a key to the durability of the engine and is also used to coat the total combustion chamber surface, including valve faces and the interior of the exhaust ports, as well as the turbo exhaust housing and exhaust manifold.
*Note regarding break in: The piston and ring assembly is installed dry, without any oil or other lubrication. The rod and main bearings are, of course, coated with engine assembly lube. The oiling system is primed and pre heated (tank heater) and the engine, starting for the first time, is immediately placed under a light load and is not allowed to idle. The rings are now seated and will show a 100 percent ring seal on the leak down tester. The break in oil is left in the engine until dyno work is complete.
Connecting Rods / Rod Bearings:
ACL Rod Bearing – Pauter Rod – Perfect Bearing and Crank Journal (after running at Bonneville)
These are highly critical components in an engine producing over 225 HP per cylinder and running at full boost, at 9000 to 9500 rpm for an extended period. The rods in this engine are manufactured by Pauter Machine. They are of extremely high quality. They are machined from E4340 vacuum melt chrome moly forgings and are made in the United States.
They have a special low windage beam design, are 144mm long and have the structural integrity to maintain concentricity of the bearing housing (big end) under extreme load and rpm.
The rod bearings are ACL Race Series with a molly disulfide coating. These bearings have extra clearance, the clearance profile is more elliptical and they have a slightly higher crush loading in the rod cap. Final rod bearing clearance is .003
Engine Balancing:
The rotating assembly is precision balanced within a one gram tolerance. The crank is fitted with bob weights representing 100 percent of the rotating weight and 52 percent of the reciprocating weight. The piston, rings, pin and small end of the rod constitute reciprocating weight and the large end of the rod and bearing assembly comprise the rotating weight. The counter weights are drilled to balance the crank.
*Using 52 percent of reciprocating weight as opposed to 50 percent is called overbalancing and is done to make the engine run smoother between 7,500 and 10,000 RPM. Your street five cylinder should be balanced at 50 percent.
Click here for a full tech article on 5-cylinder engine balancing
Oiling System:
Peterson Fluid Systems Dry Sump Oil Pump
Custom FRP Dry Sump Oil Pan
Interior of Oil Pan
The oiling system utilizes a custom FRP designed and built dry sump oil pan, and a Peterson Fluid Systems three stage pump driven by a mandrel on the crank balancer and an HTD belt. There is a custom closure plate that carries the crank seal and fits in the space normally occupied by the oil pump.
The pump is a unique four lobe design (Peterson Fluid Systems R4) and is mounted to the block on the driver’s side. This pump system is highly efficient and produces 10 inches of vacuum at 8000 engine rpm.
The oil tank is 2.5 gallon Peterson tank, mounted in the rear seat area and is plumbed with Dash 16 lines by Brown and Miller Racing Solutions.
The oil is Amsoil Dominator 15W50 racing oil and is used after the motor is broken in. This heavy weight oil works in conjunction with the engine’s wide bearing clearances to protect the bearings under extreme loads and temperature.
Crankshaft Damper:
Custom FRP Ati Super Damper – Integral Cam Belt Drive
This component’s importance cannot be overstated. The crankshaft’s torsional deflection at this power level is extremely hard to control and will, in fact, destroy the factory damper and it’s mounting, as well as breaking the stock cam belt drive hub.
I worked directly with the staff of ATi Performance Products to design a custom racing damper with an integral cam belt drive cog machined into the mounting hub. The damper is rated to 1000 HP and 10,000 rpm and is very similar to units used on all Sprint Cup V8 engines. The damper’s mounting hub is sized for a .001 interference fit with the crank nose and presses on over the full length of the crank nose, solid against the front main bearing journal. It is keyed with a 3/16ths hardened woodruff key and is retained by the factory crank bolt. The drive hub has an integral seal race that integrates with a big block Chevy crank seal in the front closure plate.
In the process of engineering this solution, the cam drive belt was increased in width from 19 mm to 25 mm to add a margin of safety in driving high lift cams and high rate valve springs.
Crankshaft Dampers - How They Work
Cylinder Head and Cams:
Polydyn thermal barrier coating on combustion chambers
In terms of power production, no areas are as critical as the ability of the cylinder head to exchange air and the adequacy and correctness of the valve opening and closing events, as dictated by cam timing. This part of the Audi’s performance has evolved over countless hours of flow testing, development of port shapes and size, valve seat angles, valve shapes and selection of camshafts.
*While all of this work was performed in house at FRP, I owe a debt of gratitude to Mr. Paul Burke. Paul is a brilliant engine man and offered his council in the areas of cam timing and cylinder sealing specific to high boost- small displacement, extreme output and high rpm operation.(Paul can be reached at info@ BMW Power Parts.com and, info@performancepartsracing.com)
In developing the cylinder head, a great effort was made to maximize the average flow of each port as opposed to just trying to maximize flow at full lift. Large gains were made in later stages of development in maximizing low lift and mid lift flow.
Intake flow @ .500 lift is 274 CFM while exhaust flow is 201 CFM also @ .500 lift. For comparison, the stock head flows 198 CFM and 137 CFM respectively.
Finished Combustion Chamber Ports – Valve Seats – Before TBC Coating
Cylinder Head specs are:
34mm stainless steel intake valves, 29.5 mm Inconel exhaust valves, FRP porting on intake, exhaust and the combustion chamber, which is opened to bore size and fully relieved for flow enhancement and shaped to encourage mixture homogeneity and high turbulence.
Valve seat angles are proprietary but I can say that the intake seats are cut with 4 angles while the exhaust seats have 3 angles and a radius. The valve seat design aids flow and mixture homogeneity.
Piston top to quench pad clearance is .042 which is critical to combustion chamber efficiency.
The valves are manufactured by Supertech and I have found them to be of superior design and consistency of dimension. The chrome silicon high rate valve springs and titanium retainers are Supertech shelf items and are of extremely high quality. The valve springs are installed with 95 pounds of seat pressure.
Valve seals are BMW 7mm low profile units.
As mentioned earlier, the combustion chambers, valve faces and exhaust ports are coated with PolyDyn ceramic thermal barrier coating.
Cams and Cam Installation:
Cams & Lifters (after running at Bonneville)
DLC-coated Lifters
This is the main area where I will be intentionally vague and not fully forthcoming as these specs are proprietary.
The cams are from Cat Camshafts, are solid lifter naturally aspirated grinds, with the intake and exhaust cams selected from different cam sets.
Intake and exhaust lift is in the area of 12mm, duration @ .050 lift is proprietary, but the cams are installed with a 110 degree intake centerline and a 113.5 degree exhaust centerline.
The lightweight lifter buckets are from Supertech and are DLC (Diamond Like Carbon) coated to reduce friction and prevent scuffing of the highly loaded exhaust cam lobes. DLC is available from Supertech.
Cylinder Head Installation:
This is another extremely critical area.
The head gasket is a standard Victor Reinz multi layer steel gasket. O rings are not used. The gasket is machined to a size just larger than the finished bore size so the compressed edges of the gasket do not protrude into the bore masking the valves and hindering transfer between the combustion chamber and the cylinder bore.
The head bolt seating surfaces around the studs are machined for flatness and hardened washers with an extra large O.D. are used with high grade alloy (non shelf stock) ARP studs to retain the head.
The cylinder head studs are torqued to 87 ft. pounds and are re-torqued after five to seven dyno pulls at which point the studs need approximately 180 degrees rotation to be back at 87 ft. pounds.
I re-checked the head studs after our qualifying run of 250.009 mph while in impound, and they were all perfect requiring no further tightening.
Intake and Exhaust Manifolds:
Custom FRP Intake Manifold
FRP Turbo Manifold
The intake manifold is an FRP custom design that utilizes runners with a 5 degree taper and a plenum volume of 5.5 liters displacement. It is fitted with an 80mm Chevy LS1 throttle body.
The turbo manifold is the same FRP unit that we sell to the public. It is a rotational firing ,T4 flange with a 44mm waste gate, a merge collector and primary tubes with an inside diameter of 40mm. It is constructed entirely from thick wall 304 stainless steel and is coated inside and out with PolyDyn thermal barrier coating.
Turbo System:
Garrett Turbine Housing, Four Inch Down Pipe, Plenum Baffle
Garrett GTX 4202R Compressor, FRP Turbo Manifold
The turbo is a Garrett GTX 4202R with a machined billet impeller wheel, two and one half inch I.D. compressor discharge and a 1.15 A/R turbine housing. The turbine housing is ported and polished internally to reduce restriction. Back pressure in the manifold collector stays below 1.5 times boost pressure.* Keeping this ratio as low as possible is critical in engines designed for top speed events. The turbine housing is coated inside and out with the same TBC.
*Note: This engine runs with what seems to be relatively moderate boost pressure of 33 psi. This is somewhat deceiving because the volumetric efficiency of the engine is very high and boost pressure only exists relative to resistance; i.e. the engine moves air efficiently enough that the turbo charger is actually working much harder to produce 33 pounds of boost than it would on less efficient engine.
The waste gate is a standard Tial 44 mm unit and the blow off valve is a 50 mm unit also from Tial.
Intercooler:
Top of Air to Water Inter-Cooler
This is another area of great magnitude with regard to power production. The inter-cooler is a custom “air to water” design that utilizes a pair of Bell Intercooler cores, stacked one on top of the other. The cooler is fed with ice water from a 30 gallon tank located in the front passenger seat area. Circulation of the ice water is via a 23 gallon per minute pump.
The tank is filled with 10 gallons of water and sixty pounds of fresh ice, just before each run. At the end of the run, all of the ice is melted leaving only moderately cool water.
Intake air temps at the throttle body stay below 80 degrees F. at full boost. *The ability to control intake air temperature to this degree is a huge factor in tuning the engine for maximum power, and, in the car’s overall performance.
Fuel System:
The fuel system is comprised of a trunk mounted fuel cell with parallel feed dual Bosch 044 Motorsport fuel pumps feeding a Dash 10 transfer line with Dash 8 return. An Aeromotive rising rate pressure regulator is set to 58 PSI base fuel pressure and it regulates pressure in an 034 Motorsport fuel rail. Injector info is proprietary- but the flow rate is 160 lbs. of fuel per hour.
The fuel we run at Bonneville is a “sanctioned event fuel” and is a high latent heat, 118 octane, leaded race fuel which is chemically optimized for forced induction engines.
Ignition and Engine Management:
Ignition is provided by five 034 Motorsport high output ignition coils with FRP / Taylor Cable, 8mm spark plug wires.
Engine management for ignition, timing, and fuel and boost mapping is provided by a 034 Motorsport Stage IIC electronic control unit, which has been perfectly reliable during the four years of the car’s development.
The total electrical system is powered by a single 16V AGM battery. There is no alternator. We observed increased efficiency of all electrical components with the change to 16 volts.
Engine Tuning and Mapping:
This is another area of extreme importance and, I believe, one best left to people with great expertise in this particular discipline. I have been extremely fortunate to have the support and services of Brendan Rudack, of Apikol, who has handled the tuning of our engines since the inception of the project four years ago. Brendan is a fine engineer and has deep and broad experience in tuning Audi / VW engines.
The engine is tuned to a flat 12.5 to 1 air fuel ratio and max timing advance is 22 degrees. The initial A/F ratio was targeted at 11.5 to 1. The mixture was gradually leaned out. Power was still increasing at 12.5 to 1 where we stopped in order to leave some margin for safety’s sake.
Conclusion:
I hope you have found this article interesting and enlightening. We are taking this year off from competing at Bonneville in order to concentrate on customer engines. We will however be returning in 2014 in hopes of significantly raising the record we now hold, if, funding permits.
I need to take this opportunity to thank all of our sponsors, many of which were mentioned in this article. All of them produce outstanding products and their support has been crucial to our success.
And, of course, thank you to Audi and the Volkswagen Audi Group for producing the cars that are such an inspiration to all of us.
Jeff Gerner @ Four Ring Performance Engineering
Engine tear-down photos:
The following are tear-down photos taken after running at Bonneville
(well, it was until he totaled the car last month :( )