Marelli and Bosch Distributor Comparison for 2.2L 911T

[id911T]

Back in the mid 2000’s I was just getting my Porsche running. Like many 2.2L 911T owners, I found myself in need of a solution to the Marelli 112BX distributor problem. My distributor was in good shape overall, but the rotor had a menacing crack in it and there were no replacement caps or rotors available unless you found NOS parts which sold for a small fortune. The obvious solution was finding a Bosch 0 231 159 008 distributor, also found on the 2.2L 911T, but everyone else was looking for one too so they were quite scarce. I kept an eye on eBay and found a Bosch 0 231 159 001 (from a 67' 911T/L), which my research on Pelican indicated would work well as the advance curve was said to be close enough. I installed and timed it and that’s what I’ve been running in the car ever since.

Fast forward to now………

I noticed recently that caps, rotors, and rebuild parts are again available from online retailers for the Marelli 112BX and started wondering if there was any reason (beyond originality) to freshen up my original distributor and re-install it. I compared the advance curves (<- note the plural) of the 0 231 159 001 and the 112BX and was surprised at what I found, so I thought I would post it up for anyone else that may have questions about this in the future.

Below is the Marelli 112BX advance curve. The Bosch 231 159 008 is almost identical.




Here are the advance curves for the 0 231 159 001, both early and late versions.






Obviously they look different, but scaling and initial advance can be misleading so I’ve corrected that and super-imposed the images. I’ve put the Bosch 001 image on top of the Marelli 112BX image, it’s a little busy but tells the story.

Early 001, timed to TDC (0deg initial advance):

If set at TDC (like the Marelli is set) static, the early 001 is under-advanced everywhere. Cruise 1100-1500 dist rpm (2200-3000 eng rpm), max torque 2100 dist (4200 eng), and max power 2900 dist (5800 eng) are -4, -6, -10, and -8 deg (crank) relative the Marelli.

Early 001, 6deg (crank) initial advance

If set w/6 deg (crank) of initial advance static, the early 001 is a fair compromise. Cruise 1100-1500 dist rpm (2200-3000 eng rpm), max torque 2100 d (4200 eng), and max power 2900 dist (5800 eng) are +4, +2, -2, and -1 deg (crank) relative to the Marelli.

Early 001, 8deg (crank) initial advance

If set w/8 deg (crank) of initial advance static, the early 001 is over-advanced in the common driving range. If the engine can handle more timing here, than this could boost low end torque and improve cruising fuel economy, otherwise it could be bad for knock. Cruise 1100-1500 dist rpm (2200-3000 eng rpm), max torque 2100 d (4200 eng), and max power 2900 dist (5800 eng) are +6, +4, -2, and 0 deg (crank) relative to the Marelli.

Late 001, timed to TDC (0deg initial advance):

If set at TDC (like the Marelli is set) static, the late 001 is very under-advanced everywhere. Cruise 1100-1500 dist rpm (2200-3000 eng rpm), max torque 2100 d (4200 eng), and max power 2900 dist (5800 eng) are -6, -8, -14, and -14 deg (crank) relative to the Marelli.

Late 001, 8deg (crank) initial advance

If set w/8 deg (crank) of initial advance static, the late 001 is still under advanced at higher engine speeds. Cruise 1100-1500 dist rpm (2200-3000 eng rpm), max torque 2100 d (4200 eng), and max power 2900 dist (5800 eng) are 0, 0, -5, and -6 deg (crank) relative to the Marelli.

Late 001, 14deg (crank) initial advance

If set w/14 deg (crank) of initial advance static, the late 001 is significantly over advanced at lower engine speeds. If the engine can handle more timing here, than this could boost low end torque and improve cruising fuel economy, otherwise it could be bad for knock. Cruise 1100-1500 dist rpm (2200-3000 eng rpm), max torque 2100 d (4200 eng), and max power 2900 dist (5800 eng) are +8, +7, 0, and 0 deg (crank) relative to the Marelli.


So what does all this mean? I think it means that the 0 231 159 001 is a significant compromise on the 2.2T unless the engine can handle more timing down low. If you time the distributor for correct advance at 6000rpm (~35deg), you will being running 6-8deg more advance at cruising speeds. Conversely, if you play it safe then you will lose torque above 3000rpm, especially with the later 001. I think it’s time to dust off the original Marelli………

[doswald]

Stephen, thank you for posting this info.-very interesting comparisons. I had my Marelli rebuilt by Kurt at PartsKlassic and hope to have the rebuild complete and running soon.

dho

[Trackrash]

The problem with the 2,2 T distributors is the fact that they were designed to meet smog requirements and the relatively low compression ratio of the T motor.

In other words the spec is for initial advance to be set at 4 deg after TDC. Which is not what you want, but helps with smog. Idealy you want around 7-10 degrees BTDC.

Then full advance is 35 degs at 6K rpm.

So in reality the stock distributor has more advance than you want.

IMO go into the distributor and bend the stop tabs on the advance weights to limit the advance.