Hey Guys, I just wanted to share the nitty gritty and techie details of a recent experiment on my project tbucket with a 90's BMW V8.
First, a little background on the traditional procedure for setting up cam timings on this engine: Bring the engine up to TDC, compression Cyl #1, overlap Cyl #6. Install BMW specific tools known as cam blocks onto machined surfaces on the back of cams. Loosen the cam gear retaining bolts, adjust the cams until the blocks are sitting flush against the surface of the cylinder head. Tighten the cam gear bolts. Now the Intake Centerlines, Exhaust Centerlines and subsequent Lobe Separation Angles are built into the cams and the cam blocks.
In factory trim the intake cams have 246° duration and .382" valve lift. The exhaust cams have 242° duration and .368" valve lift. They are degree'd on a 109° Intake centerline and a 108° Lobe Separation from the factory.
It is possible to order and install aftermarket performance cams, however they are prohibitively expensive for this application. Like, a couple grand $ for a set of performance cams. One would notice the intake cams are slightly bigger then then the exhaust cams. As an experiment I wanted to try this FREE mod by installing and setting up parts from a spare engine, by installing intake cams in the exhaust positions and degree'ing them accordingly. Simulating a single pattern 246°/246° - .368"/.368" cam.
Although the timing blocks would still work for intake sides, the machined faces that the blocks reside on for cam timing would no longer pertain to the exhaust side cam timings.
Theoretically one would simply set up the exhaust cam timings to happen 216° advance of the intake cam timing events for a 108° LSA, or advance the crank 1 full revolution 360° + another 144° to get the 216° (108°LSA) This would work if the valves were parallel to the cylinders. But they are angled. According to BMW tech literature the intake cams are angled 20° and the exhaust valves are angles 19°.
Since all four cams rotate the same direction yet the heads are mirrored, the intake and exhaust valves are angled opposite directions from bank to the other. This means that on Bank 1 there is +20° advance ground into that banks cam and on Bank 2 there is -20° retard ground into that cam in order for the lobes to contact the lifters at the correct angles.
These angles are at cam speed too, so double it at the crank. 20° = 40° and 19° = 38°. To use the intake cams on the exhaust side of Bank 1 I will need to retard the exhaust cam timings 40° and then another 38° from the desired Lobe Separation Angle to align with the exhaust lifter angle. And the opposite is true for Bank 2, the exhaust cam timing would get advanced 78° from desired Lobe Separation Angle.
I was able to verify this 78° split by setting up two intake cams on one bank phased identically with cam blocks. All the lobed pointing the same angle. Then by setting up a dial indicator on the intake and exhaust lifter faces then counting the crank angle ° between lifter moments. I came up with 76°, close enough error % to use the 78° match from tech literature.
How am I get crank degrees from an assembled, running engine installed in the car? By counting the crank trigger teeth on the harmonic damper. This system uses a 60-2 crank trigger, so each leading edge (or trailing edge) is exactly 6° away from the same location on the tooth next to it. The teeth are 2.5° wide and have a 3.5° valley between the teeth.
I took it one step further, removed the harmonic damper from the engine, printed out a 360° wheel, marked my desired locations on the damper and re-installed the damper with my marks where B1 and B2 exhaust timings land and used those marks as my guide for cam timing using the machined flats on the cams & cam timing blocks against the cylinder head. I also advanced my intake cams a couple degrees and moved LSA accordingly.
Reassembled, test fired up:
There is not a dyno near me, nor would I justify the expense for before and after dyno results for such a mild cam change. But I do like to use the Auto-Tune of the standalone fuel injection controller to see if a mod has helped or hindered. If Auto-Tune adds fuel to the VE table at certain cells to maintain the same AFR I know that more airflow is moving through the engine and more power is being made. If Auto_tune takes fuel away, I know airflow was hurt and it's making less power in those cells.
This little change was good, it feels better on the street, more responsive, and Auto-Tune has added fuel in low RPM, mid and high RPM. So I'd say it's a win! Thanks for checking out my project - Mykk
First, a little background on the traditional procedure for setting up cam timings on this engine: Bring the engine up to TDC, compression Cyl #1, overlap Cyl #6. Install BMW specific tools known as cam blocks onto machined surfaces on the back of cams. Loosen the cam gear retaining bolts, adjust the cams until the blocks are sitting flush against the surface of the cylinder head. Tighten the cam gear bolts. Now the Intake Centerlines, Exhaust Centerlines and subsequent Lobe Separation Angles are built into the cams and the cam blocks.
In factory trim the intake cams have 246° duration and .382" valve lift. The exhaust cams have 242° duration and .368" valve lift. They are degree'd on a 109° Intake centerline and a 108° Lobe Separation from the factory.
It is possible to order and install aftermarket performance cams, however they are prohibitively expensive for this application. Like, a couple grand $ for a set of performance cams. One would notice the intake cams are slightly bigger then then the exhaust cams. As an experiment I wanted to try this FREE mod by installing and setting up parts from a spare engine, by installing intake cams in the exhaust positions and degree'ing them accordingly. Simulating a single pattern 246°/246° - .368"/.368" cam.
Although the timing blocks would still work for intake sides, the machined faces that the blocks reside on for cam timing would no longer pertain to the exhaust side cam timings.
Theoretically one would simply set up the exhaust cam timings to happen 216° advance of the intake cam timing events for a 108° LSA, or advance the crank 1 full revolution 360° + another 144° to get the 216° (108°LSA) This would work if the valves were parallel to the cylinders. But they are angled. According to BMW tech literature the intake cams are angled 20° and the exhaust valves are angles 19°.
Since all four cams rotate the same direction yet the heads are mirrored, the intake and exhaust valves are angled opposite directions from bank to the other. This means that on Bank 1 there is +20° advance ground into that banks cam and on Bank 2 there is -20° retard ground into that cam in order for the lobes to contact the lifters at the correct angles.
These angles are at cam speed too, so double it at the crank. 20° = 40° and 19° = 38°. To use the intake cams on the exhaust side of Bank 1 I will need to retard the exhaust cam timings 40° and then another 38° from the desired Lobe Separation Angle to align with the exhaust lifter angle. And the opposite is true for Bank 2, the exhaust cam timing would get advanced 78° from desired Lobe Separation Angle.
I was able to verify this 78° split by setting up two intake cams on one bank phased identically with cam blocks. All the lobed pointing the same angle. Then by setting up a dial indicator on the intake and exhaust lifter faces then counting the crank angle ° between lifter moments. I came up with 76°, close enough error % to use the 78° match from tech literature.
How am I get crank degrees from an assembled, running engine installed in the car? By counting the crank trigger teeth on the harmonic damper. This system uses a 60-2 crank trigger, so each leading edge (or trailing edge) is exactly 6° away from the same location on the tooth next to it. The teeth are 2.5° wide and have a 3.5° valley between the teeth.
I took it one step further, removed the harmonic damper from the engine, printed out a 360° wheel, marked my desired locations on the damper and re-installed the damper with my marks where B1 and B2 exhaust timings land and used those marks as my guide for cam timing using the machined flats on the cams & cam timing blocks against the cylinder head. I also advanced my intake cams a couple degrees and moved LSA accordingly.
Reassembled, test fired up:
There is not a dyno near me, nor would I justify the expense for before and after dyno results for such a mild cam change. But I do like to use the Auto-Tune of the standalone fuel injection controller to see if a mod has helped or hindered. If Auto-Tune adds fuel to the VE table at certain cells to maintain the same AFR I know that more airflow is moving through the engine and more power is being made. If Auto_tune takes fuel away, I know airflow was hurt and it's making less power in those cells.
This little change was good, it feels better on the street, more responsive, and Auto-Tune has added fuel in low RPM, mid and high RPM. So I'd say it's a win! Thanks for checking out my project - Mykk
