Thread: Msd 6al 6462
View Single Post
356-930 356-930 is offline
Acceleration Junkie
 
Join Date: Aug 2007
Location: Laguna Beach, CA
Posts: 263
Garage
Quote:
Originally Posted by dsiegel360 View Post
356-930,
Thanks for shedding light on this.

How does this MSD recognize boost?

According to the porsche manuals, my 88 is supposed to be set at 25-27 degrees at 4000rpm's (with advance and retard lines pulled off and plugged). After set and lines put back on, warm idle is at TDC.

With the MSD I can run several degrees ATDC?

I don't really understand "3 deg per psi, 20 deg max." Does this mean that... if at idle- TDC gives me 26 degrees at 4000rpm (lines off and plugged), that with MSD I can get an idle of 1- 3 degrees ATDC so that the MSD can retard 1-3 degrees on boost?

If so, is this safely curved for the span between idle and boost?

I know little about distributors and timing. Thanks for the education.

Doug
Quote:
Originally Posted by dsiegel360 View Post
356-930,
Thanks for shedding light on this.

How does this MSD recognize boost?

According to the porsche manuals, my 88 is supposed to be set at 25-27 degrees at 4000rpm's (with advance and retard lines pulled off and plugged). After set and lines put back on, warm idle is at TDC.

With the MSD I can run several degrees ATDC?

I don't really understand "3 deg per psi, 20 deg max." Does this mean that... if at idle- TDC gives me 26 degrees at 4000rpm (lines off and plugged), that with MSD I can get an idle of 1- 3 degrees ATDC so that the MSD can retard 1-3 degrees on boost?

If so, is this safely curved for the span between idle and boost?

I know little about distributors and timing. Thanks for the education.

Doug
The MSD 6AL 6462 has a timing control unit with a built in boost sensor (which you will have to plumb into your intake manifold or tee in wherever your stock boost sensor is located). The amount of retard is user controlled with two potentiometers, one on the timing module and one you can locate on/under dash - wherever you wish. The potentiometer on the timing unit is adjusted to tell the module at what pressure to begin to remove timing, the remotely located pot is used to tell the timing unit how many degrees/psi to remove.
As example, if you set the timing unit to begin retard at 6 psi and the remote to remove 2 deg per psi and you run 1-bar boost, you will have remove 14 degrees of timing at full boost.
An extreme example: Initial timing at 4000 rpm is set to 48 degrees. Set the MSD to commence boost retard at 1-psi with pull out rate of 3 deg per psi. By the time boost reaches 8-psi, timing will be 28 deg advance and remain there to full boost (20 deg max timing retard). If your distributor has a mechanical boost retard, timing would of course be further retarded with boost.
You note Porsche recommended timing at 4000, no vac/boost component should be 25-27 deg adv. You should find out how much boost retard your distributor provides. This will tell you what Porsche wants for max timing under boost, an important baseline benchmark. If not available, put the distributor on a testing machine, pressurize the boost port, see what you get.
I admittedly know little about what constitutes "safe timing" but I seriously doubt one needs to be concerned about timing below boost or "just into" boost. The higher the boost, the higher the effective compression, combustion pressure and temperature and negative consequence to the engine.
Old 04-15-2008, 04:54 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)