VANOS refresher course

[Wldeyefoto]

While building the "Dragon" motor for my Z8, optimizing the VANOS system to take advantage of the upgrades has been of particular interest to me, and I thought some of you might enjoy a little refresher course on this remarkable system.

VANOS stands for VAriable NOckenwellen Steuerung (variable cam control) and is BMW's nomenclature for a system to adjust valve timing to optimize an engine's performance under varying conditions.

There is a VANOS system to control intake valve timing and another VANOS system to control exhaust valve timing. When both are used on an engine, the system is called DOUBLE VANOS. The Z8's engine incorporates DOUBLE VANOS.

The following explanation is over-simplified but hopefully adequate for discussion purposes. The purpose of the intake system on an engine is to combine air with fuel and deliver the mixture to the cylinders where it can be compressed, ignited by a spark to create power, then sent to the exhaust system for elimination. In order for the air/fuel mixture to enter and leave the cylinders, it must pass through openings in the cylinder heads. These openings have valves in them to control whether they are open or closed. Whether the valves are open or closed is determined by the camshafts which have lobes on
them to force the valves into the open position, while springs force the valves to close.

The important thing to understand is that on most engines (without VANOS) the rotation of the camshafts, thus the timing of the openings and closings, is fixed in relationship to the rotation of the crankshaft and therefore the positions of the pistons in the cylinders. The trouble with a fixed relationship is that as the engine runs at different speeds, the optimum timing of the delivery of the air/fuel mixture and its subsequent release into the exhaust system varies. This means that a fixed valve timing system can only deliver optimum conditions for combustion at one specific rpm; every other rpm will be a compromise.

Enter DOUBLE VANOS! By developing a way to vary the relationship of the camshafts' rotation to the crankshaft's rotation, BMW can optimise the timing of the delivery of the fuel/air mixture and its release into the exhaust system. This is accomplished by a moveable camshaft drive gear with a helical timing gear. As the camshaft drive gear moves in or out, the helical cut of the timing gear forces the camshaft gear to rotate forward or backward slightly. This changes the timing of the camshafts' rotation relative to the fixed rotation of the crankshaft, thus allowing the valve timing to be advanced or retarded. The onboard engine computer is put in charge of deciding what that timing should be to optimise engine performance and it uses hydraulics to move the shaft in or out. The Z8's DOUBLE VANOS system can adjust the intake valve timing by 54 degrees while the exhaust timing can be adjusted by 39 degrees. The adjustments take less than 250 milliseconds.

The benefits of having DOUBLE VANOS on the Z8 include high torque at low and medium speeds, reduced emissions, better fuel consumption and smoother idling. When combined with the Z8 engine's individually controlled throttle butterflys, engine performance can be controlled to an unprecedented degree, resulting in what many consider to be the finest production engine BMW has ever built.




Grease Monkey

[Gobosh]

Thank you for taking the time to explain VANOS.....BMW engineering really is amazing

[Z8Bob]

It will be interesting to see how well the V10 S85 motor holds up and the new V8 version for the new M3.

Personally the torgue from the bigger displacement motors is a nice kick in the pants.

[bach24]

than the S62 and I suspect that the V8 in the upcoming M3 won't either. The V10 produces torque all the way up to 7,900 rpm, but virtually the same max figure as the s62. My seat of the pants experience was that torque felt the same. I also felt that the Z8 was faster than the e60 M5. Maybe it's the air in my hair syndrome, but...

[Z8Bob]

Given the displacement of the V10, it should not be a suprise. My Z8 with the Quaife LSD with even more torque is quicker to 60 than the E60 M5, in triple digits the E60 just pulls away.

The Air in My Hair Factor is the BIG argument for an M6 Cabriolet acquisition.

[Michael]

Making any midifications to the helical gears (timing) or cam profiles?

Besides using higher viscosity oil, will you be installing the factory upgrade which prevents hydraulic leak down during rest?

Do you know if the factory upgrade is just a check valve?

[Wldeyefoto]

A few things to keep in mind:

Best Z8 0-60 time I've seen was 4.2 seconds running an open differential and RE-040 runflats (275 rears). E-60 M5 was clocked at 4.1 seconds by Road and Track magazine using the European-only F1 style launch control mode where the car's computer manages wheelspin and running a LSD plus Continental SportContact 2 tires (285 rears).

0-100 for Z8 was 10.2 seconds. M5 was 9.5 seconds.

1/4 mile time for Z8 was 12.6 seconds at 112 mph. M5 was 12.4 seconds at 116 mph.

Final drive ratio on Z8 is 3.38. M5 is 3.62.

The M5's final drive ratio is equal to a 7% increase in torque when compared to the Z8 at all rpms.

Rear tire diameters are very close.

Z8 has 6-speeds. M5 has 7 speeds.

Ratios: Z8 / M5

1st 4.23 (6% advantage) / 3.99

2nd 2.53 / 2.65 (5% advantage)

3rd 1.67 / 1.81 (8% advantage)

4th 1.23 / 1.39 (13% advantage)

5th 1.00 / 1.16 (16% advantage)

6th 0.83 / 1.00 (20% advantage)

7th NA / 0.83

Z8 engine displacement is 4941 cc.

M5 engine displacement is 4999 cc.

Z8 horsepower is 394 @ 6600 rpm with 368 lb/ft of torque at 3800 rpm.

M5 horsepower is 500 @ 7750 rpm with 383 lb/ft of torque at 6100 rpm.

Z8 engine redline is 7000 rpm. M5 is 8250 rpm.

Z8 curb weight (according to BMW) is 3494 lbs. (*actual curb weight of Z8 is 3685 lbs.) M5 is 4035 lbs. according to BMW.

Z8 weight to horsepower ratio = 8.87 (lbs/hp) (*9.35) M5 = 8.07

Z8 weight to torque ratio = 9.49 (lbs/lb-ft) (*10.01) M5 = 10.51

If we factor in the 7% torque advantage the M5 has due to its final drive ratio the M5's lbs/lb-ft ratio becomes 9.84.





Grease Monkey

[Wldeyefoto]

As far as I know, the updated VANOS system utilizes a check valve to prevent oil leak-down at rest which causes the dreaded VANOS "tick" upon start-up. I have found that running 10W-60 helps to minimize this problem.

The cams have a custom profile developed by Dinan and we will be using solid lifters as opposed to the stock engine's hydraulic lifters. VANOS timing is controlled by the engine CPU and will be adjusted on the engine dyno to optimize power output. We will be running very light weight racing pistons and rods designed to handle the increased rpm limit (8000).Grease Monkey

[z8.bob]

and my GM spec Quaif has a 3.64 LSD ;-) Sort of evens out the party and gives the nod to the ancient Z8

[Wldeyefoto]

You are absolutely correct! Updated with 3.64 gears, LSD, non run-flat tires and carrying substantially less weight, your Z8 is more than competitive with the current state-of-the-art from BMW. Not quite ready for the museum, I'd say! Grease Monkey