340 timing

[culp71]

WOW!!
so I'm glad I posted these questions, as I would have never thought that locking out all advance in the timing would do the trick. so I eliminated the vacuum advance to distributor, reset timing closer to 30 (@3000)...what a difference. definitely headed in the right direction now. I am planning to take the distributor apart this eve and see what it has for adjustment and or curve that I can change or lock. (it is a Proform brand distributor from Jegs was sold as a "official mopar" performance distributor)
looks like it should work just fine.
thanks to all.

[Cudakiller70]

This topic is very timely, I was just about to start a topic on initial timing.  I've been trying to figure out my timing all week.  Got the new tank and fuel line in, mounted the rebuilt carb and got it to fire and idle.  I didn't have a helper to hold brake in gear so set the idle mixture adjustment screws on the carb to get 19 inches of vacuum and set the idle to 850 rpm while in park.  Vacuum advance is disconnected.  Went to check the timing with my new light and the timing mark was not visible.  I was planning on setting it to 8-10 degrees advanced.  Some investigation revealed that the distributor was installed 180 degrees out.  Found approximate TDC on #1 compression, and installed distributor so the rotor points at left front of the intake and rewired the cap.  While doing that I found the mark on the damper and highlighted it with a silver Sharpie.  I also added a line about 1.5" advanced and another ~2.2" advanced, just slapped them on because I was guessing the TDC mark was hiding under the water pump.  Got it started and adjust the distributor by ear for best idle.  I now see the extra marks I make with the light and it has an advance function that tells me my best idle is at ~34 degrees.  Go down to 25-ish and it idles like crap and dies.  Still doesn't idle all that great yet.  I have not driven  the car yet.  This is freaking me out.  I am suspecting the timing chain skipped, cam was installed wrong, or the damper has failed.  I'm in the process of making a piston stop to verify TDC on #1 is correct on the damper.  It is a 71 340 in a 73 Cuda with 727 auto trans.  I really have no info on the motor.  Cam sounds fairly stock or is a mild aftermarket.  Chrysler electronic ignition and distributor, Holley 650 DP, LD4B intake, and headers with crushed tubes that probably don't help anything.

I was not aware you could set the timing to 35 and lock it out.  How do I tell if that was done?
What's this about dialing out the advance with an allen wrench? 

I haven't touched one of these motors in 30 years and the learning curve has been steep.  I was going to start tearing the front of the engine apart after verifying TDC to check the timing chain so I'd appreciate some guidance on other potential causes.  I've been trying to read up all week but haven't found a case similar to mine yet.

Did you get this resolved?

[chargerdon]

Quote:  "so I eliminated the vacuum advance to distributor, reset timing closer to 30 (@3000)...what a difference"

Wow...  If i did that on my 74 360 with Mopar Purple 508 cam, Id never get it to turn over, once its warmed up !!   So, unless you have installed a kill switch to the coil, I cant see how you can get away with that.

On my 360 I set the timing as follows:
1) plugged off the vaccum advance and then set the static timing to around 15 degrees to start, then used vacuum and rpm gauge to set the timing to the point that if ran the best with the best vacuum...   Then test drove the car to make sure i wasnt getting pinging and then after shutoff, and it sits for about a minute, try to start the car...and make sure it wasn't "kicking back" and preventing starting.   Re-adjust up and down, to find the MOST timing it could take and still start ok and not ping on the road.  Then read the timing, and it ended up being at about 20 BTDC.

2) Adjusted the vacuum advance to add another 10 degrees at idle to give total at idle of 30.   

3) Knowing that the idle static timing was at 20, i put in the mopar distributor an advance limit plate set to allow another 16 degrees of mechanical advance to give a max of 36.     (recognize, that Vacuum advance is NOT added to the mechanical advance, but merely adds advance before the mechanical can reach its max)

The difference between 30 static and no vacuum advance, and 20 plus 10 vacuum is simple.   At 20 static and engine not running, i can turn it over to get it to start, then vacuum is added and ive got the 30 at idle.   30 static and it wont turn over !!   

Oh well...   and yes, idle is a problem, as the Mopar 508 cam (292 advertised duration) with only 110 just doesn't make that much vacuum at idle to get the car running smooth enough that it has smooth acceleration from stoplight...   I only get about 4 bars at idle...  Because of this i am seriously considering swapping cams to a lunati voodo with less duration and overlap...   

[Rumple]

Wow, I didn't know using vacuum advance could add 15 degrees!

No wonder folks get into trouble when using it. 

The vacuum canister on the MP distributor I got with my electronic ignition kit adds 17*.  I farted around with the allen wrench for awhile but could never get it right. Finally just disconnected it. After reading this thread I think I may revisit it.  Good info! 

[Shane Kelley]

Quote:  "so I eliminated the vacuum advance to distributor, reset timing closer to 30 (@3000)...what a difference"

Wow...  If i did that on my 74 360 with Mopar Purple 508 cam, Id never get it to turn over, once its warmed up !!   So, unless you have installed a kill switch to the coil, I cant see how you can get away with that.

On my 360 I set the timing as follows:
1) plugged off the vaccum advance and then set the static timing to around 15 degrees to start, then used vacuum and rpm gauge to set the timing to the point that if ran the best with the best vacuum...   Then test drove the car to make sure i wasnt getting pinging and then after shutoff, and it sits for about a minute, try to start the car...and make sure it wasn't "kicking back" and preventing starting.   Re-adjust up and down, to find the MOST timing it could take and still start ok and not ping on the road.  Then read the timing, and it ended up being at about 20 BTDC.

2) Adjusted the vacuum advance to add another 10 degrees at idle to give total at idle of 30.   

3) Knowing that the idle static timing was at 20, i put in the mopar distributor an advance limit plate set to allow another 16 degrees of mechanical advance to give a max of 36.     (recognize, that Vacuum advance is NOT added to the mechanical advance, but merely adds advance before the mechanical can reach its max)

The difference between 30 static and no vacuum advance, and 20 plus 10 vacuum is simple.   At 20 static and engine not running, i can turn it over to get it to start, then vacuum is added and ive got the 30 at idle.   30 static and it wont turn over !!   

Oh well...   and yes, idle is a problem, as the Mopar 508 cam (292 advertised duration) with only 110 just doesn't make that much vacuum at idle to get the car running smooth enough that it has smooth acceleration from stoplight...   I only get about 4 bars at idle...  Because of this i am seriously considering swapping cams to a lunati voodo with less duration and overlap...

What starter are you using? I'm running a stock Mopar mini starter on a 11.1 340 with a 507 lift and 312 duration and my timing is locked @ 35 degrees. I only get a slight amount of push back when it's hot. But very minimal. My lobe separation is 107 and the center line is 102. So that does bleed some compression off and could possibly be a reason I don't have issues.   

[chargerdon]

Again, i'm not the only one on this site experiencing  the "kickback problem' to start the engine when its warmed up.   I'm not talking about compression heat making engine physically harder to turn over,  i'm talking about that a good starter doesn't turn the engine fast enough to overcome ignition before top dead center from trying to run the engine backwards.   

There are other articles in here about that problem anytime the static timing is set to more than 22-24 degrees BTDC.   Some people talk about the Expensive versions of MSD ignition systems having a setting to "retard the timing automatically" when cranking until the engine fires then increasing the timing to what you set, others talked about a simple solution is to put a switch in the coil line, open the line then begin cranking, and then close the switch to get the engine to fire...   I don't like the latter,..and i'm not going to spend hundreds on an MSD ignition...   Not when the simple solution is to keep the static at about 20 (or less) and then let the vacuum advance bring the timing up to the about 30 degrees once engine starts.     PS...for this to work well, keep the vacuum line on the "constant vacuum, not the ported vacuum side of the carb".   Also, i got this tuning info from the tech support from the people making: https://www.ebay.com/itm/Mopar-Distributor-Mechanical-Advance-Timing-Limiter/323099910935?hash=item4b3a416317:g:6yAAAOSwQJhUdOgX

[Cudajason]

Again, i'm not the only one on this site experiencing  the "kickback problem' to start the engine when its warmed up.   I'm not talking about compression heat making engine physically harder to turn over,  i'm talking about that a good starter doesn't turn the engine fast enough to overcome ignition before top dead center from trying to run the engine backwards.   

There are other articles in here about that problem anytime the static timing is set to more than 22-24 degrees BTDC.   Some people talk about the Expensive versions of MSD ignition systems having a setting to "retard the timing automatically" when cranking until the engine fires then increasing the timing to what you set, others talked about a simple solution is to put a switch in the coil line, open the line then begin cranking, and then close the switch to get the engine to fire...   I don't like the latter,..and i'm not going to spend hundreds on an MSD ignition...   Not when the simple solution is to keep the static at about 20 (or less) and then let the vacuum advance bring the timing up to the about 30 degrees once engine starts.     PS...for this to work well, keep the vacuum line on the "constant vacuum, not the ported vacuum side of the carb".   Also, i got this tuning info from the tech support from the people making: https://www.ebay.com/itm/Mopar-Distributor-Mechanical-Advance-Timing-Limiter/323099910935?hash=item4b3a416317:g:6yAAAOSwQJhUdOgX

So you are pulling the vacuum for the vacuum advance from manifold vacuum? 

[Chryco Psycho]

Using manifold vacuum to the vacuum advance is bass ackwards , the timing is fully advanced at idle with the highest vacuum & runs away / retards as the throttle is opened .... why would anyone do this ??

[Shane Kelley]

Using manifold vacuum to the vacuum advance is bass ackwards , the timing is fully advanced at idle with the highest vacuum & runs away / retards as the throttle is opened .... why would anyone do this ??

That's how a GM vacuum advance system works. Complete opposite of a Mopar. 

[Cudajason]

Using manifold vacuum to the vacuum advance is bass ackwards , the timing is fully advanced at idle with the highest vacuum & runs away / retards as the throttle is opened .... why would anyone do this ??

Agreed...it is certainly not how it is designed to work.

Jason

[chargerdon]

Guys...I am NO EXPERT..so i could certainly be wrong, heck sure wouldn't be the first time.   

However, i adopted my technique because of two things...   One is the recommendation from the tech support guy from where i bought the mechanical advance limiter plate that i put in my distributor to limit the total advance to 20-22 static plus 14 mechanical for total of between 34 and 36.   I found it hard to believe as well, as he told me the instructions sheet from Edlebrock telling us to put the vacuum hose on the timed vacuum side is incorrect and goes back to the early days of pollution controls.   He said that the need for greater timing diminishes under load.   I always thought the opposite.  Of course the need for higher advance increases as engine speed increases hence the mechanical advance.   He pointed me to this article:

http://www.hotrod.com/articles/set-ignition-curves-create-optimal-performance/ 

In this article there is a paragraph that states that at "low load" i.e. idling and light cruising, the need is for higher advance because the air/fuel mixture being partial is not as tightly packed, and thus needs an earlier ignite to burn well.   And at higher loads (greater or even WOT) the air fuel mixture is more tightly packed and needs less timing because it will ignite faster.   This makes some sense if you think about it...  set the static timing too high and car will still idle well and not ping, until you open the throttle..then it will ping because the higher load charge has a faster burn front and now the timing is igniting the air/fuel mixture too soon.   

there is a paragraph that states:  "Even with 9.5 or 10.0:1 compression, the application of a big camshaft means the cylinder pressure at low speeds will be greatly reduced compared to a milder cam. This engine would respond to more vacuum advance at cruise speeds at part throttle to improve its driveability and throttle response. Our experience shows that connecting the vacuum advance to a manifold vacuum source will add timing and help the engine idle better in gear with an automatic transmission.

So...on a big cam you need lots of static timing to get it to idle well and under low loads...i.e. idle and cruising...   But at this high a static you would have kick back unless you use a gear driven starter to overcome it, or an expensive Ignition system like MSD that has settings to retard the ignition at very low (starting rpm).   

Now regarding which port to attach the vacuum advance hose, recognize that Chrysler started using the timed port to help meet the new at the time pollution controls.   The difference between the two, is that at closed throttle...i.e idle there is near zero vacuum on the timed port, so the vacuum advance is non-functional at idle...   at light/part throttle the ported vacuum opens up and gives vacuum so advance during light throttle.   The Manifold port gives maximum vacuum..ie.advance at idle or closed throttle and not at WOT.   SO at heavy to WOT they both respond the same..ie the advance goes away,  but at closed throttle (idle) the manifold port gives max vacuum and thus allows you to set the static at a lower setting so as to not get kick-back stopping starting...and still goes away under heavy throttle. 

Now, again, i'm not a mechanic, and i don't take my car to the track where trial and error would show me the error in my ways, but, i do know that plugging the hose into the manifold port on my 74 with 360 built to 9.5 compression, Mopar Purple performance 508 cam (292 advertised duration), edelbrock 1405 carb, edelbrock RPM Air Gap intake manifold, and Patriot full headers with 2500 stall converter, idles at 800 rpm in drive, the BEST at about 20 BTDC static plus 10 vacuum for combined 30 at idle and still without kickback for starting because until started there is zero vacuum and hence your starting at 20 BTDC and idling at 30...   .   Im just a car enthusiast, so i welcome any and all discussion on this topic.  Maybe he and this article is all wet ...but... 

[Cudajason]

That is an interesting read...I love to tinker with my car, I may have to give this a try.

Jason

[Chryco Psycho]

I agree to a point , more timing will make the engine run better
Adding more initial timing & a shorter curve helps for sure .
What makes no sense to me is manifold vacuum  is max at idle adding extra timing ,  which can also be done with more initial timing , so as you open the throttle vacuum drops retarding the timing while mechanical advance adds more timing so now the timing is not moving as vacuum is retarding at the same time mechanical is advancing

[Bullitt-]

I can just see Neil now........   

[Chryco Psycho]

 
IIRC the some of GMs had a the vacuum advance backwards & worked as a vacuum retard where the advance plate inside the dist in the same direction as the rotor so manifold vacuum would retard the timing which would work correctly