Timing a 273

-
my273mopar

my273mopar

Member
Joined
Jul 21, 2014
Messages
10
Reaction score
0
Location
Knoxville tn.
Guys

This is my first MOPAR. I have a 66 Dart with a 273 2bbl. I was checking the timing and on GM cars you disconnect the vac line. But on this car the vacuum line only makes the advance work when the engine is off idle. So my question is should the vacuum source be consent or when the butter flies are opened.

Mike
 
Mike with a 66 Dart.. Welcome. I'm Mike with a 66 Dart. lol The vac advance should be hooked to the ported or off idle vacuum and the hose should be pulled at the distributor and plugged. I use a screw or a golf tee. tmm
 
Yes, disconnect the vacuum hose and plug it to time the engine.


Or leave it hooked up and set the advance to 34°-36° BTDC at 2500 rpm (total timing).
 
krazykuda said:
Yes, disconnect the vacuum hose and plug it to time the engine.


Or leave it hooked up and set the advance to 34°-36° BTDC at 2500 rpm (total timing).
Click to expand...

I'll have to agree. Simplest/best answer.
The OEM base timing spec wont work well with the puppy pee they sell for fuel today.
 
The vacuum is ported, so it is shut off at idle. That can be verifed with a vacuum gauge T'ed into line. Adjusting timing to 34 to 36 with line on, may result in retarted timing for cruise. This may will result in overheating, poor mpg, poor throttle reponse. If you are going to set at 34, do that with line off.

I also belive performance timing is not a adjustment at a single point. It is a 3D table for the full range of RPM and vacuum. That takes a programable ECU.
 
KitCarlson said:
The vacuum is ported, so it is shut off at idle. That can be verifed with a vacuum gauge T'ed into line. Adjusting timing to 34 to 36 with line on, may result in retarted timing for cruise. This may will result in overheating, poor mpg, poor throttle reponse. If you are going to set at 34, do that with line off.

I also belive performance timing is not a adjustment at a single point. It is a 3D table for the full range of RPM and vacuum. That takes a programable ECU.
Click to expand...

I think you got that wrong. All in is 34 at 2500. All in means vacuum and centrifugal advance. Setting that high without the vacuum wouldn't be all in. Then reapplying the vacuum would throw the base timing far too high ( opposite of retarded ).
I'm not one to argue though. This subject has been discussed far too many times in earlier threads anyway. The original question here could be answered through search.
 
RedFish said:
I think you got that wrong. All in is 34 at 2500. All in means vacuum and centrifugal advance. Setting that high without the vacuum wouldn't be all in. Then reapplying the vacuum would throw the base timing far too high ( opposite of retarded ).
I'm not one to argue though. This subject has been discussed far too many times in earlier threads anyway. The original question here could be answered through search.
Click to expand...

The term "all in" doesn't include the vacuum advance just the initial and the mechanical for a total of around 34°. When you plug in the vacuum and rev it to 3000 don't be suprised to see upwards of 50°. tmm
 
I did not think a simple thing like adjusting the timing was so controversial. The spec. I have states 10 deg. before or 5 deg after if it has CAP air cleaner ??? . So now i am really not sure were to set it. So just set the total 34 deg and for get it

Mike
 
That should work for either case, if vacuum is disconnected when setting. Drive and see how that works, starting, at idle, and under heavy acceleration in 3rd without down shift to check for ping. Then try 36, it may be better. Also check that vacuum advance is doing its job, as ToolmanMiie suggest it will add 15 to 20 degrees at high vacuum.

The CAP has special curves in distributor and a vacuum control valve with a green plastic cap, it retards timing at idle, then switches back to more normal off idle.

The factory service manual has specs for all the various engine, carb and transmission variations. With a timing light, vacuum gauge or mightyvac, and tach, it is possible to verfy mechanical and vacuum advance contributions. The specs are loose, but that is often why no two older cars would drive the same.

Setting base timing is just the fixed, minimum setting, mechanical advance adds to that, and so does vacuum advance. Some modify the rates and limits of those to achieve increased performance. That all depends on other engine components, vehicle weight, gearing fuel, fuel mixture and more.
 
my273mopar said:
I did not think a simple thing like adjusting the timing was so controversial. The spec. I have states 10 deg. before or 5 deg after if it has CAP air cleaner ??? . So now i am really not sure were to set it. So just set the total 34 deg and for get it

Mike
Click to expand...

I cant apologize for others quoting me and arguing. I simply agreed with another's post but they don't call that person out. Maybe I should apologize for posting at all.
I personally don't give a flip about fuel millage in this particular car ( there's a ricer for that ). I'd rather my 273 accelerate off the red lights better than a golf cart. Therefore my base timing is about 16 btdc, all in is about 34. Vacuum advance has been disconnected and plugged and it will stay that way.
You could just set yours just like OEM recommends. Good luck with it.
By the way.. The CAP air cleaner does nothing more than capture hot motor oil vapor/mist that would otherwise be vented to atmosphere.
 
my273mopar said:
I did not think a simple thing like adjusting the timing was so controversial. The spec. I have states 10 deg. before or 5 deg after if it has CAP air cleaner ??? . So now i am really not sure were to set it. So just set the total 34 deg and for get it

Mike
Click to expand...

It's not really controversial, it's more like

"what do you have?"

First, as old as all these girls are, can you be certain that you actually have the original unmodified production distributor, and IF you do, does it actually work as it's supposed to? Is it worn? Do the advance mechanisms work?

Second, as old as these girls are, do you still have the all original all production engine AND CAM?

Third, CAP means that "optimum" timing is not what was specified. What was specified is what meets smog.

I would DEFINATELY do what you need to do to mark the balancer or whatever and determine what total MECHANICAL (vacuum unhooked) is along with what initial it takes to "get there."

I would make a quick check "do the advance mechanisms work?" Simple and quick with a tach and a light. You don't need to get that fussy for a quick idea, just see if it advances how much and what RPM you'd expect

Crackedback has written a lot on this. Set your initial with vacuum disconnected, adjust timing for highest vacuum, then see if it pings or the starter kicks back. You can retard it some from this value if need be

Then see what you have for "all in" mechanical and see if the total advance makes sense

Last, plug in the vacuum and check it.

This is a one shot deal PERIODICALLY. Maybe ever couple of years depending on how much you drive. Record your findings, then you know where to time it "next time."
 
Ok

Thanks I now understand what is going on I will take the advice of these last two post.

Once again Thanks

Mike
 
my273mopar said:
Ok

Thanks I now understand what is going on I will take the advice of these last two post.

Once again Thanks

Mike
Click to expand...

I think someone posted this, but this link is a very good read

http://www.forabodiesonly.com/mopar/showthread.php?t=158842

This is a great article

http://www.moparmusclemagazine.com/...mopar_electronic_ignition_system/viewall.html

The thing is.........

as you got into 66 in CA, 68 Federally, and onwards into the 70s, distributor curves and timing specs got more and more "smoggy" and less and less "performance." If anyone has ever replaced your distributor with a parts store "rebuilt," it could likely as not have a "more of a smog" advance in it. Rebuilders are not known for being "correct."

If it has a bit hotter cam, it needs a different setup

And, as I said, the original may not be working optimally, either

Post back if you run into trouble.
 
You must log in or register to reply here.
-

Back
Top