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PorscheMoparLiterbike
 
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boost retard amount

Hi guys

How much timing does boost retard line take out?

also Both lines go to throttle body..different connection points...how is the distributor pot seeing a different signal (vacuum/boost) for each line?
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Old 04-02-2014, 07:12 PM
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If memory serves me right, without pulling out the books to look at the timing curves (they differ with different years, BTW) I think at full boost it retards something like 8-10 degrees. Some of the better tuners on this forum can check me on that.
From the position of the adjusting nut on your distributor, it would appear you've got quite a bit of static advance dialed in....but then pictures can be misleading. I had to grind the slot on my dizzy so I could rotate it enough in order to get the advance I wanted, which was about 12* at idle if I recall (with both hoses connected).
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Old 04-03-2014, 05:38 AM
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PorscheMoparLiterbike
 
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thanks Mark,

I believe i set it at 28 deg 4000 rpm hoses disconnected when i finiished my engine out DYI in February.

Reason im asking is I drove it for 12k miles prior to my DYI project with the blue line capped. The car had 1 bar boost, stock cams, stock LDZ. No issues.

Now i have sc cams (1.7 mm timed)...still stock LDZ(1 bar).....stock setup for CIS except air injection removed........wondering if i can remove/cap boost retard for a bit more ooomph....
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Old 04-03-2014, 06:24 AM
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mark, mine looks like that too. i have asked others but no real response. i am also curious about others timing at idle because of this.

the retard is only there at idle. it is all out by 1200RPM. well, when yo let off the gas it is back in but once the throttle is cracked again its gone.

yes you can remove it. there is also something else you should be aware of. when boost is applied to both lines, there is no boost retard. i dont know if porsche put some kind of check valve in the throttle body to block boost. i think there is a solenoid that is suppose to block it but all that is removed on my car. i ran without the retard until i put a check valve on the line.
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Old 04-03-2014, 09:15 AM
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I would not run without boost retard, it is there to reduce the chance of detonation. Unless you have a knock sensing system to dial out timing leave it on IMO. Risk is you might be doing another engine out DIY..
Old 04-03-2014, 09:35 AM
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PorscheMoparLiterbike
 
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Thanks guys....should have searched some more before posting...here's Jim from an older thread

""Dual port mid eightees USA 930 distributor

--------------------------------------------------------------------------------

What Mark said about timing during boost is correct.

The factory instructions for setting timing on a mid eightees counter clockwise rotating USA 930 dual pot distributor is remove both vacuum lines (don't bother plugging them because that has no effect on anything) and hold the rpms at 4000 rpm and line up the 26* before top dead center line on the engine pulley with the vertical line on the fan housing using a timing light on #1 spark plug wire.
The instructions are on a sticker on the bottom right side of the engine lid and in the owners manual.

26* BTDC is full centrifical advance with no vacuum advance, vacuum retard, or boost retard from the vacuum pots moving the vacuum advance/retard plate and adding or subtracting timing on top of centrifical advance.
Centrifical advance turns the seperate upper half of the counterclockwise rotating distributor shaft with it's attached star shaped reluctor wheel and the rotor a little bit farther counterclockwise as rpms rise up to 4000 rpms and thats your centrifical advance.
By 4000 rpm the centrifical advance is maxed out so if you can't see the tachometer you can just rev the engine higher within reason while watching the timing mark with a timing light until it stops going any higher - that accomplishes the same thing.

When cruising at steady speed and accelerating before boost pressure starts to happen the red vacuum advance hose coming from a tiny hole through the throttle body just above the butterfly and connected to the advance pot has vacuum in it and pulls the advance/retard plate with the stator windings mouted on it inside the distributor clockwise which is the opposite direction the distributor shaft, star shaped reluctor wheel, and rotor are turning and timing is advanced more than where centrifical advance has it.
Let off the gas and decelerate and vacuum inside the throttle body drops to near nothing and intake manifold vacuum below the throttle butterfly and vacuum inside the blue vacuum retard hose increases and the vacuum retard pot diaphram pushes the advance retard plate counterclockwise which is the same direction the distributor shaft, star shaped reluctor wheel, and rotor are turning and timing is retarded.

Then when boost comes on everything including both the vacuum advance hose and the vacuum retard hoses become pressurized but the way the vacuum pots are designed internally the vacuum retard pot diaphram does nothing and has no effect under boost pressure but the vacuum advance pot diaphram goes into reverse moving the opposite direction it did under throttle body vacuum and becomes a boost retard pot and it pushes the advance/retard plate with the stator windings counterclockwise inside the distributor and thats the same direction the distributor shaft, star shaped reluctor wheel, and rotor are turning so that retards timing under boost.

I did not know that until about a year ago when I pressurized both the vacuum and retard pot at the same time with a mighty vac tool while it was removed from the distributor and watched what happens.
Do that while the motor is running at 4000rpms and you will see the timing drop down to around 18* BTDC with a timing light. That is where timing will be with boost retard working at .8bar boost or above.

I hope that explanatioon helps and I hope I reread it enough times to fix my typo mistakes before posting this.""


Thanks Jim...and you didnt have to type it all over again
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Old 04-03-2014, 10:14 AM
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This is such a wonderful topic and I for one have spent too much time wrapping my head around it, but that writeup does a great job of explaining it all. Many of us run with quite a bit of advance when not on boost in order to gain some performance improvements in the low and mid range, but this understandably necessitates retarding that excess timing once boost starts to build so as not to have too much advance when on full boost. I had my dizzy cranked to the max and used an old-school MSD boost retard module in conjunction with my old-school MSD 6AL ignition. The newer progammable MSD's would be the better way to go. And yes, a knock sensor supposedly will accomplish the same task to remove advance but that particular topic still seems to be debated hotly as to its functionality on air cooled engines. Some swear by it, others don't.

Whatever.....if you're gonna mess with the timing then it's a good idea to understand how the vacuum/boost/mechanical systems affect it.
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Old 04-03-2014, 11:05 AM
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""Whatever.....if you're gonna mess with the timing then it's a good idea to understand how the vacuum/boost/mechanical systems affect it.""

You got it Mark.......i guess i was just lucky running without boost retard before.....im hesitant with the sc cams.....i also have the 6al2 but havnt used it for timing control yet..just ignition source
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Old 04-03-2014, 12:13 PM
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I'm very much on your heels Mr. b5aar, SC cam install in progress (er I guess you could call it progress), and MSD6AL2 being fit this week as well.

Will be looking forward to your timing maps, experiences, etc.

Did you notice any difference w/ the cams? Any notable lump to the idle? I'm hoping for some on top of the off-boost torque 8-)...
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Old 04-03-2014, 12:29 PM
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Definitely more lumpy idle and stronger off boost 1 - 3k rpm. Just nicer drivability at slower speeds it seems....not drastic....but noticeably better.

Im breaking in a newly rebuilt 3LDZ (Yeah I know...long story) so I havnt hammered at high RPM yet.
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Old 04-03-2014, 01:03 PM
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Re reading Jim's post the blue line is vacuum retard not boost retard functioning only with throttle off. Is it then primarily for idle condition retard....I believe I read before something to do with helping catalytic converter work better.
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Old 04-04-2014, 05:18 AM
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Euro distributors have no vac advance and have a more aggressive curve than The dual pot distributors. Full mechanical advance is used on boost which is 26 degrees.
Old 04-04-2014, 08:06 AM
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good reference points Brian. I'm going to plug the blue line. Just like before. 26 degrees is a good goal when I start using the MSD box for timing.
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Old 04-04-2014, 06:17 PM
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Keep what type of fuel you are using in mind. It was my understanding that our 20 degree set point on boost was to compensate for the fuel in NA vs. Europe.
If you run a high octane fuel you should be good. Colder intake temperatures will help also.
Old 04-07-2014, 07:17 AM
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