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fredmeister fredmeister is offline
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Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,229
Originally Posted by roxanne68 View Post
Thanks for sticking with this guys, I can tell you from empirical testing that there is no vacuum advance on this unit. The chart below shows what the various vacuums and pressures do the timing while at idle. This was tested with the car running using a vac and pressure pump and measured with my timing light. The attached picture shows which one I am calling port 1 and port 2.

As you can see, there is no vacuum advance, only vacuum retard and boost retard. Both ports function and move very freely at only a couple of psi or couple in of vac. I canít explain why it does not behave as a California unit, but facts are facts. Are there a Porsche part numbers else ware on the unit to further confirm? If it matter, the vacuum canister arm inserts on the left (drivers) hand side of the dizzy when you look down from the rear of the car (hence why vacuum/boost retard the unit as they rotate the plate clockwise.

As the attached pic shows, I current have only port 2 hooked to a boost only source (the intercooler) which is probably not optimum, port 1 is open to atmosphere. I did this to keep my idle cooler not for emissions or power reasons. Therefore, with my timing set to around 26 degrees with no boost at 4000RPM, I get about 18 BTDC with boost based on the above (26-8= 18). I think why I am having the temp issues is that with my distributor boost retard plumbed into the intercooler, and my mechanical boost gauge plumbed into the manifold, my distributor is seeing pressure even though I am not registering boost at the gage, i.e I am getting a couple of psi ahead of the TB even though there is vacuum in the manifold which is enough to pull in the timing from what ever the mechanical is at the cruising RPM -8 degrees of retard. This would explain the temps, no? if I keep port 1 open, and plumb port 2 to a ported vacuum source at the TB, I should get no retard at cruise. I would keep my base timing at 26BTDC, which will net me 18 or so under boost which should be conservative.

There are no emissions equipment on the car.

Great logical testing approach. I just wanted to see what you got for results for 1 important configuration missing from the matrix on ports and timing effect.
Port 1 under vacuum and Port 2 under boost?
Reason I ask is that this is an easy set up to configure with vacuum hoses and there is a history on this board concerning previous posts on this subject and it would be intersting to see what your test results show.
good stuff this discussion.

Thanks Fred
1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 11-03-2011, 07:58 AM
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