Audi's 4.2 V8
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That was actually from Audizine, I mistakenly wrote Audiworld at first because I'm used to nothing but BS on the audizine forums. Technical discussion is usually on audiworld.
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There was a discussion like this on Audizine, where a member posted a very informative post. Remember, the whole process of making RS4's is not terribly effective cost wise, its why the damn thing is so expensive.
------- Start Cut & Paste -------
There is alot of confusion over the fact that Audi makes 3 different 4.2L V8's. There's the port-injected V8 (S4, S5, A8, ...), the FSI V8 in the Q7, and the FSI V8 in the RS4.
The two FSI engines are related, but still different. You see alot of quotations describing the "high-revving version for the RS4". Most of these facts are from the Audi self-study program document floating around, and refer to the differences between the RS4 engine and the Q7 engine.
The S4 engine and the RS4 engine are not related. They only happen to have the same displacement. The RS4 engine is not a "tuned-up" version of the S4 engine. You might say it's a "tuned-up" version of the Q7 engine, but the modifications go way beyond tuning.
A few characteristics of the RS4 engine:
Only one belt, driving the alternator. All other accessories (A/C, water pump, oil pump, hydraulic pump) are chain drive or shaft drive from a special accessory drive gearbox.
Stress-honed cylinders, using a torque-plate.
Tubular headers.
FSI system and heads.
12.5 :1 CR
Dual-mass damper system with unbalance (for high RPM smoothness).
Q7 rods are 36MnVS4, RS4 rods are 34CrNiMo8. Not sure about S4 V8.
Q7/RS4 share pistons (forged), 290 grams.
New cyclonic oil separator system.
4 drive chains with different sprocket sizes RS4 vs Q7.
Quoting ("basic engine" refers to the Q7 engine, not S4):
To match the higher engine power output and RPM, the
following cylinder head components were modified:
Intake ports are charge optimized (based on larger
cross-sections)
Intake valves are chrome-plated hollow stem valves
(for weight reduction)
Valve springs are made of a material with higher
tensile strength and also have higher spring force
To meet the higher fuel requirements, the injectors are
designed for higher flow rates.
Roller rocker arms are more robustly designed, with
peened rollers for higher strength
Camshafts have different timings and larger opening
lengths
Intake valve opening angle 230 crank angle degrees
Exhaust valve opening angle 220 crank angle degrees
The lifters were adapted from the 3.2L V6 engine found
in the TT and A3. They have a larger ball stroke which,
in the course of testing, proved advantageous for the
high-revving engine (with regard to the inflation of the
hydraulic valve clearance compensation element).
The cylinder head has a modified water jacket which
circulates coolant to the area between the intake port
and the injector, thereby reducing the temperatures in
the cylinder head combustion chamber plate.
Due to a modified camshaft drive reduction ratio, the
camshaft adjuster has 25 teeth for the chain drive, as
opposed to 30 teeth in the basic engine.
A reliable supply of oil in all driving situations is critical,
especially in a sports car such as the RS4. The oil supply
system in the high-revving engine was designed for
racing applications in which it is subjected to lateral
acceleration of up to 1.4 g. To ensure this, the sump in
the RS4 has an additional system of flaps.
Design
Four flaps, whose axis of rotation is parallel to the
longitudinal axis of vehicle, are arranged inside a
housing. Each of the flaps opens toward the inside of the
intake end of the oil pump.
Function
When the vehicle is cornering, the oil flows inside the
sump toward the outside of the corner. The two flaps
facing the outside of the corner close and hold the oil in
the sump intake.
At the same time, the two flaps facing the inside of the
corner open to allow additional oil to flow into the intake.
This ensures a sufficient supply of oil to the oil pump.
The 4.2L V8 FSI engine in the RS4 does not use the mapcontrolled
thermostat as found in the Audi Q7 engine.
To achieve more effective cooling, two additional coolers
are used. Coolant flows continuously through one of
the additional coolers. The second additional cooler is
opened via a coolant thermostat.
To avoid excessive heating-up after shutting off the hot
engine, the coolant run-on pump is activated a preset
period of time after the engine is shut off. The pump
run-on time and the need for additional activation
of both radiator fans are determined on the basis of
characteristic maps. Various measured quantities
are included in the calculation (engine temperature,
ambient temperature, engine oil temperature and fuel
consumption).
Q7 has variable-length intake system, RS4 does not.
To enhance the sporty character of the RS4 engine, a fantype
manifold is used in the RS4.
Good separation of the exhaust pulses is ensured by
keeping the individual exhaust pipes apart until they
merge into one. These fan-type manifolds are also
attached by means of a clamping flange system.
The primary and main catalytic converters are metal-type
catalytic converters. Their advantage is that they have a
lower flow resistance than ceramic catalytic converters,
which is good for engine performance.
The front silencer for each of the exhaust pipes is housed
in a common casing. However, the exhaust pipes are kept
separate. The front and rear silencers are absorption-type
silencers. They are notable for their low flow resistance.
Engine management in the new 4.2L V8 FSI is by two
versions of the Bosch MED 9.1.1.
A single control module is used in the Audi Q7 engine.
There are two control modules for the RS4 engine. A
master-slave concept is required here due to the requisite
processing power at engine speeds up to 8250 RPM.
------- Start Cut & Paste -------
There is alot of confusion over the fact that Audi makes 3 different 4.2L V8's. There's the port-injected V8 (S4, S5, A8, ...), the FSI V8 in the Q7, and the FSI V8 in the RS4.
The two FSI engines are related, but still different. You see alot of quotations describing the "high-revving version for the RS4". Most of these facts are from the Audi self-study program document floating around, and refer to the differences between the RS4 engine and the Q7 engine.
The S4 engine and the RS4 engine are not related. They only happen to have the same displacement. The RS4 engine is not a "tuned-up" version of the S4 engine. You might say it's a "tuned-up" version of the Q7 engine, but the modifications go way beyond tuning.
A few characteristics of the RS4 engine:
Only one belt, driving the alternator. All other accessories (A/C, water pump, oil pump, hydraulic pump) are chain drive or shaft drive from a special accessory drive gearbox.
Stress-honed cylinders, using a torque-plate.
Tubular headers.
FSI system and heads.
12.5 :1 CR
Dual-mass damper system with unbalance (for high RPM smoothness).
Q7 rods are 36MnVS4, RS4 rods are 34CrNiMo8. Not sure about S4 V8.
Q7/RS4 share pistons (forged), 290 grams.
New cyclonic oil separator system.
4 drive chains with different sprocket sizes RS4 vs Q7.
Quoting ("basic engine" refers to the Q7 engine, not S4):
To match the higher engine power output and RPM, the
following cylinder head components were modified:
Intake ports are charge optimized (based on larger
cross-sections)
Intake valves are chrome-plated hollow stem valves
(for weight reduction)
Valve springs are made of a material with higher
tensile strength and also have higher spring force
To meet the higher fuel requirements, the injectors are
designed for higher flow rates.
Roller rocker arms are more robustly designed, with
peened rollers for higher strength
Camshafts have different timings and larger opening
lengths
Intake valve opening angle 230 crank angle degrees
Exhaust valve opening angle 220 crank angle degrees
The lifters were adapted from the 3.2L V6 engine found
in the TT and A3. They have a larger ball stroke which,
in the course of testing, proved advantageous for the
high-revving engine (with regard to the inflation of the
hydraulic valve clearance compensation element).
The cylinder head has a modified water jacket which
circulates coolant to the area between the intake port
and the injector, thereby reducing the temperatures in
the cylinder head combustion chamber plate.
Due to a modified camshaft drive reduction ratio, the
camshaft adjuster has 25 teeth for the chain drive, as
opposed to 30 teeth in the basic engine.
A reliable supply of oil in all driving situations is critical,
especially in a sports car such as the RS4. The oil supply
system in the high-revving engine was designed for
racing applications in which it is subjected to lateral
acceleration of up to 1.4 g. To ensure this, the sump in
the RS4 has an additional system of flaps.
Design
Four flaps, whose axis of rotation is parallel to the
longitudinal axis of vehicle, are arranged inside a
housing. Each of the flaps opens toward the inside of the
intake end of the oil pump.
Function
When the vehicle is cornering, the oil flows inside the
sump toward the outside of the corner. The two flaps
facing the outside of the corner close and hold the oil in
the sump intake.
At the same time, the two flaps facing the inside of the
corner open to allow additional oil to flow into the intake.
This ensures a sufficient supply of oil to the oil pump.
The 4.2L V8 FSI engine in the RS4 does not use the mapcontrolled
thermostat as found in the Audi Q7 engine.
To achieve more effective cooling, two additional coolers
are used. Coolant flows continuously through one of
the additional coolers. The second additional cooler is
opened via a coolant thermostat.
To avoid excessive heating-up after shutting off the hot
engine, the coolant run-on pump is activated a preset
period of time after the engine is shut off. The pump
run-on time and the need for additional activation
of both radiator fans are determined on the basis of
characteristic maps. Various measured quantities
are included in the calculation (engine temperature,
ambient temperature, engine oil temperature and fuel
consumption).
Q7 has variable-length intake system, RS4 does not.
To enhance the sporty character of the RS4 engine, a fantype
manifold is used in the RS4.
Good separation of the exhaust pulses is ensured by
keeping the individual exhaust pipes apart until they
merge into one. These fan-type manifolds are also
attached by means of a clamping flange system.
The primary and main catalytic converters are metal-type
catalytic converters. Their advantage is that they have a
lower flow resistance than ceramic catalytic converters,
which is good for engine performance.
The front silencer for each of the exhaust pipes is housed
in a common casing. However, the exhaust pipes are kept
separate. The front and rear silencers are absorption-type
silencers. They are notable for their low flow resistance.
Engine management in the new 4.2L V8 FSI is by two
versions of the Bosch MED 9.1.1.
A single control module is used in the Audi Q7 engine.
There are two control modules for the RS4 engine. A
master-slave concept is required here due to the requisite
processing power at engine speeds up to 8250 RPM.
Thank you for the information
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Joined: Mar 2005
Posts: 651
From: Carlsbad
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FYI, the 2.4L V8s being used in F1 are revving up to 19,000RPM. 
Just because it is revving to 19,000 RPM does not mean that the pistons are traveling at a faster speed. You have to calculate the stroke of the motor and multiply that times the RPM. Obviously a 2.4L motor has much less stroke than a 4.2L motor. Read below:
In order to stay competitive in the ongoing European horsepower wars with the current engine platforms, Audi will have to bring back the almighty turbo. Audi has reached the peak performance potential of their current V-8 and V-10 platforms. The V-10’s in the S8/S6 cars and the V-8’s in the S4/RS4 cars all share the same stroke of 92.8 millimeters. The engine stroke dimension (how far the piston moves up and down) coupled with the RPM dictate the average speed of the piston. The B7 RS4’s engine at 8250 RPM has an average piston speed of 25.52 meters per second. This is faster than ANY current production automobile engine out there and on par with Formula 1 race engines. Current technology does not allow a reliable piston speed faster than this.
Any questions?
Just because it is revving to 19,000 RPM does not mean that the pistons are traveling at a faster speed. You have to calculate the stroke of the motor and multiply that times the RPM. Obviously a 2.4L motor has much less stroke than a 4.2L motor. Read below:
In order to stay competitive in the ongoing European horsepower wars with the current engine platforms, Audi will have to bring back the almighty turbo. Audi has reached the peak performance potential of their current V-8 and V-10 platforms. The V-10’s in the S8/S6 cars and the V-8’s in the S4/RS4 cars all share the same stroke of 92.8 millimeters. The engine stroke dimension (how far the piston moves up and down) coupled with the RPM dictate the average speed of the piston. The B7 RS4’s engine at 8250 RPM has an average piston speed of 25.52 meters per second. This is faster than ANY current production automobile engine out there and on par with Formula 1 race engines. Current technology does not allow a reliable piston speed faster than this.
Any questions?
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Joined: Mar 2008
Posts: 18
From: Cleona, PA
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The S5 uses the 4.2L FSI V8 rated at 354 bhp. This is most likely (for the most part) the same engine that is used in the Q7. Although, according to Audi's website, the CR of the Q7's engine is higher than the S5. It's actually listed as the same as the RS4 engine, so this may be a misprint, but I don't know for sure.
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Joined: Sep 2008
Posts: 120
From: Glendale, CA
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I did some research about this in the past. S5 and RS4 run identical bore and stroke (84.5mm x 92.8mm) so at any given RPM, their piston speed is identical. The S5 runs 11:1 compression ratio versus the RS4's 12.5:1 which can be attributed to head shape or piston dome shape. The compression ratio alone makes up a large chunk of the power difference.
I would be surprised if you couldn't just fit the RS4 pistons onto the S5 and get reasonable gains, but money is better spent exploring forced induction unless you were insistant on keeping all things n/a, which I can understand also.
-Ray
I would be surprised if you couldn't just fit the RS4 pistons onto the S5 and get reasonable gains, but money is better spent exploring forced induction unless you were insistant on keeping all things n/a, which I can understand also.
-Ray
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From: Scottsdale,AZ
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My Manual says that the motor in my S5 has 12.5 compression. I have not seen 11 mentioned anywhere else but in this tread. I'm pretty confident that the S5 and Q7 has the same exact motor (engine management might be tweaked a little but the motor is the same)
Tonny
Tonny
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From: Seattle
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SalesPunk... Where is that from? I'm coming up with a number that's laughable in the stroke department to generate those piston speeds at 19000RPM.
Right about 6mm.
I have a feeling that F1 pistons are moving a bit faster, to travel a slightly longer distance.
Right about 6mm.
I have a feeling that F1 pistons are moving a bit faster, to travel a slightly longer distance.
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Joined: Sep 2008
Posts: 120
From: Glendale, CA
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AutoTrader:
http://carshowroom.autotrader.com.au...48156420080701
MotorTrend:
http://www.motortrend.com/new_cars/0.../s5/index.html
InternetAutoguide:
http://www.internetautoguide.com/200.../s5/index.html
Automobile Mag:
http://www.automobilemag.com/am/2009/audi/s5/index.html
Carfolio:
http://www.carfolio.com/specificatio...ar/?car=155089
Cars.com:
http://www.cars.com/go/crp/research....=&aff=national
For what it's worth, these resources all say that the Q7 and RS4 are both 12.5:1. I'm more likely to believe that the owner's manual has an error, because at least a CR difference explains a great deal of the 70hp difference (along with cams and ECU) from the RS4. If the S5 really has 12.5:1 ratio, then it must just be voodoo.
-Ray
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Posts: 128
From: Scottsdale,AZ
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Well the Q7 engine has the same 354 (says 350 on the Q7)Horse rating 325 ft lbs of torque as the S5 so if it is 11 compression I am sure the Q7 also have 11 compression ratio. Could the manual have a typo yes of course.
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From: Glendale, CA
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It would be nice to just have both cars in the shop at the same time and try to determine how interchangable some of the parts are, like flywheel, cams, or even manifolds, and even the electronic sensor layout. If you could find that out, you'd be that much closer to solving the 70hp puzzle.
-Ray
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Posts: 128
From: Scottsdale,AZ
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Some guy on audiworld a while bback was trying to convert
a S5 to RS4 spec engine with just replacing parts but I think he figured out that it was cheaper to get the MTM supercharger kit (something like $40K) I think if you want a 420 horse motor it would be easier to buy a complete motor from a crashed RS4 (should probably be some out there, if not in the US at least in Europe) I would really want to see what the difference are between the motor. some people say everything is different some say pistons, rods and cams are different.
Tonny
a S5 to RS4 spec engine with just replacing parts but I think he figured out that it was cheaper to get the MTM supercharger kit (something like $40K) I think if you want a 420 horse motor it would be easier to buy a complete motor from a crashed RS4 (should probably be some out there, if not in the US at least in Europe) I would really want to see what the difference are between the motor. some people say everything is different some say pistons, rods and cams are different.
Tonny
