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OSAC Valve. Yes or No?
https://slantsix.org/forum/viewtopic.php?t=21160		 Page 1 of 1
Author:  bwhitejr [ Wed Dec 20, 2006 3:33 am ]
Post subject:  OSAC Valve. Yes or No?
I am experiencing pinging between gears (high vacuum situation), but not under cruise conditions (9-10" vacuum). Should I put the OSAC valve back in the vacuum advance circuit? It seems that is what it is designed for.

bwhitejr
Author:  Jeb [ Wed Dec 20, 2006 6:23 am ]
Post subject: 
Have you tried adjusting the vacuum advance pod with an allen wrench. I have done forgot what size. Do a search and it will turn up a ton of stuff.
Author:  SlantSixDan [ Wed Dec 20, 2006 9:20 am ]
Post subject: 
The OSAC valve delays vacuum to the distributor by between 7 and 17 seconds each and every time vacuum is applied to it. It cannot help your engine run better — it always makes it run worse. If you're getting pinging, adjust the vacuum advance and/or recurve the distributor and/or reset the base timing so as to eliminate it (or run higher-test gasoline...!)

Not sure what you mean by pinging "between gears". Light-throttle acceleration...?
Author:  bwhitejr [ Wed Dec 20, 2006 4:28 pm ]
Post subject:  OSAC Valve. Yes or No?
I have an A-833 OD, so when I say between gears I mean, when I shift and run the RPM's up. The pinging shows up when accelerating in 3rd gear, not in 1st gear or 2nd gear. I have been watching the vacuum gauge and I get 17-20" of vacuum while I am accelerating in 3rd gear.

BTW, every vacuum pod I have checked works like this (which is exactly opposite from what the Mopar Six Cylinder Book says):
On my 3874876 vacuum pod R11
all the way CW the arm starts moving @5 3/4", stops @ 8 1/2"
5 turns CCW from all the way in starts moving @6 3/4", stops @ 9 3/4"
8 turns CCW from all the way in starts moving @7 1/4", stops @ 10 1/2"
10 turns CCW from all the way in starts moving @ 7 3/4", stops @ 10 3/4"

So why does it say to turn it CW to reduce vacuum advance? It would seem like you need to go CCW to reduce the vacuum advance.

Someone walk me through this. :?:

bwhitejr
Author:  argentina-slantsixer [ Wed Dec 20, 2006 4:56 pm ]
Post subject: 
you can't reduce the advance significantly using the spring regulation. You just adjust the kicking in and out spots. Your 11 pod seems a little too much for a manual car IMHO... what are you running for rear end ratio? Does the 5 turns CCW have solved this issue? if not, you might wanna use another d with less built in advance (or wrap a iece of stiff wire on the arm, between the square travel stop and the end, to reduce travel of the arm, if you don't have a different pod)
Author:  SlantSixDan [ Wed Dec 20, 2006 5:23 pm ]
Post subject: 
↑ ↑ ↑ Yeah, what Juan said. ↑↑↑
Author:  bwhitejr [ Thu Dec 21, 2006 3:49 am ]
Post subject:  OSAC Valve. Yes or No?
I have a 9R governor plate and a 11R vacuum pod. I am running 12.5* BTDC initial. I have a 3.55 rearend with an A-833OD with 0.71 4th gear. I have 9.69:1.0 CR, a Holley 390, Offy manifold, Clifford split headers into 2 1/2" Flowmaster Series 50 SUV muffler and a nameplate 4800# vehicle. I have taken the original heavy distributor spring out and replaced it with a Mopar recurve spring.

The truck runs better without the vacuum advance (seems peppier) although the gas mileage suffers. The timing tab I have on the front of the timing chain cover is of the fixed type and is probably off for starters. (I would be curious if any has actually measured how much they are off by.)

I guess it is unimportant about the actual numbers as long as the results are right.

bwhitejr
Author:  dakight [ Thu Dec 21, 2006 4:13 am ]
Post subject: 
Before you can know accurately what your timing really is you need to know where true TDC is. Use a piston stop and degree wheel to accurately locate TDC then remark your harmonic balancer accordingly. 12.5* initial seems a bit much to me, but if your timing marks are not correct it's impossible to know what you really have.
Author:  DusterIdiot [ Thu Dec 21, 2006 6:15 am ]
Post subject:  Tolerance...
Quote:
12.5* initial seems a bit much to me
It depends on how tolerant his build is, I run 14 initial at 9.2:1 compression in a 3500 lb car and it has good pickup at the low end...in his case he has to get the timing marked correctly so we can see how much, when and where, then get the springs to match his acceleration habits, and also get a vaccuum pod that is "in" during highway cruise, and "out" when he is at 3/4+ throttle...
with 9.7:1 compression he may want to dial in a distributor that is closer to 8BTDC initial, 22 degrees of advance (11R governor), and the 10X vaccuum pod (or slightly less for safety...but not a 6.5X)

THe other thing that is killing him is the 3.55's....4800 lb brick should be 3.91's or 4.11's with the OD...


-D.Idiot
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