Have you disconnected your OSAC system?

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cruiser

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Has anyone bypassed their OSAC system in your slant six engine? To do this, I'd assume you just connect the vacuum supply hose directly from the carb vacuum source, to the vacuum advance on the distributor. Do you screw up your engine if you do this? How do you know if your OSAC system (mounted to the side of the air cleaner) is actually working? Earlier slant sixes never used this system. Thinking about disconnecting it in my 1974 six motor. Thoughts, anyone?
 
@slantsixdan might chime in and give some insight. He's really sharp on those systems.
 
It's a form of pollution control. Faster or more timing puts out more pollutants. Bypass it and see if it likes it
 
My 67 273 dart has a manifold vacuum based control in the vacuum advance system. IIRC it is intended to keep vacuum high to the vacuum advance can on deceleration.

It has an adjusting screw and by tightinging it all the way, it does not have any affect.

Do some reasearch and see how it functions, simply removing power from it might make it moot.

"Delays advance for 15 SECONDS" WTF!

Screenshot_20211030-164024.png
 
Has anyone bypassed their OSAC system in your slant six engine?

Yes, but only do it if you want your car to stop running as if its shoelaces are tied together. Don't do it if you like hesitation and mushy acceleration, because you'll be disappointed with the results.

I'd assume you just connect the vacuum supply hose directly from the carb vacuum source, to the vacuum advance on the distributor.

Yep, do not pass go/do not collect $200.

Do you screw up your engine if you do this?

Not even a little bit.

How do you know if your OSAC system (mounted to the side of the air cleaner) is actually working?

It's a purely academic exercise. This system—OSAC stands for Orifice Spark Advance Control—was a cheap and nasty means of squeaking the cars past 1974 emissions standards so they'd be legal to offer for sale. The system delays vacuum to the distributor by a set number of seconds to reduce spark advance during acceleration, eventually letting vacuum through to allow spark advance during cruise. This lessens NOx emissions while severely degrading driveability (meanwhile, the EGR valve is in on both parts of that game, too).
 
Yes, but only do it if you want your car to stop running as if its shoelaces are tied together. Don't do it if you like hesitation and mushy acceleration, because you'll be disappointed with the results.



Yep, do not pass go/do not collect $200.



Not even a little bit.



It's a purely academic exercise. This system—OSAC stands for Orifice Spark Advance Control—was a cheap and nasty means of squeaking the cars past 1974 emissions standards so they'd be legal to offer for sale. The system delays vacuum to the distributor by a set number of seconds to reduce spark advance during acceleration, eventually letting vacuum through to allow spark advance during cruise. This lessens NOx emissions while severely degrading driveability (meanwhile, the EGR valve is in on both parts of that game, too).
Thank you kindly sir! Hope you and yours are doing well and staying sick free!
 
Yes, but only do it if you want your car to stop running as if its shoelaces are tied together. Don't do it if you like hesitation and mushy acceleration, because you'll be disappointed with the results.



Yep, do not pass go/do not collect $200.



Not even a little bit.



It's a purely academic exercise. This system—OSAC stands for Orifice Spark Advance Control—was a cheap and nasty means of squeaking the cars past 1974 emissions standards so they'd be legal to offer for sale. The system delays vacuum to the distributor by a set number of seconds to reduce spark advance during acceleration, eventually letting vacuum through to allow spark advance during cruise. This lessens NOx emissions while severely degrading driveability (meanwhile, the EGR valve is in on both parts of that game, too).
Thanks for weighing in, Dan. I got rid of the EGR system on my engine a long time ago. Sounds like I just need to connect the vacuum line on the distributor directly to the vacuum nipple on the base of the carb (stock Holley 1945), bypassing the OSAC valve on the air cleaner. That way, the distributor's vacuum advance will continue to operate. Sounds like my engine will run better, altho it runs really well right now. I haven't noticed the mushy acceleration that you referred to, BTW. I just wanted to make sure I didn't royally screw up anything with my engine before I try this. Thanks! CRUISER
 
Yup, that's it exactly—just run from carburetor to distributor and pretend the OSAC valve doesn't exist.
 
Yes, but only do it if you want your car to stop running as if its shoelaces are tied together. Don't do it if you like hesitation and mushy acceleration, because you'll be disappointed with the results.

Complete and total bullshit. Dan I know that you think that 47year old emission parts should work like brand new and everything should be OEM. But the fix for this is to run the vacuum line straight from the distributor to the ported vacuum port on the carb and set the timing to 10* BTDC.
 
Complete and total bullshit. Dan I know that you think that 47year old emission parts should work like brand new and everything should be OEM. But the fix for this is to run the vacuum line straight from the distributor to the ported vacuum port on the carb and set the timing to 10* BTDC.

Read it again.
Yes, but only do it if you want your car to stop running as if its shoelaces are tied together.
 
Thanks for weighing in, Dan. I got rid of the EGR system on my engine a long time ago. Sounds like I just need to connect the vacuum line on the distributor directly to the vacuum nipple on the base of the carb (stock Holley 1945), bypassing the OSAC valve on the air cleaner. That way, the distributor's vacuum advance will continue to operate. Sounds like my engine will run better, altho it runs really well right now. I haven't noticed the mushy acceleration that you referred to, BTW. I just wanted to make sure I didn't royally screw up anything with my engine before I try this. Thanks! CRUISER
I’m a bit weary to take of the EGR… What was the result in doing so, Cruiser, and how did you do it?Disclaimer, I’m not singling you out, sir. We just run a very similar system.
 
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