340 timing

[chargerdon]

As if it isnt complicated enough.   

Here is another article of opinions worth reading:

http://www.hotrodders.com/forum/ported-vs-manifold-vacuum-advance-scenario-151264.html 

PS...  many believe that the ported vacuum port came about to help with emissions...   I.e while high (30 degree) or more timing works well for idle quality, it also tends to make engines produce more NOx fumes at idle...so to meet emissions the mfg went to the ported t vacuum systems to reduce timing at idle to pass emissions and then quickly provide more advance via vacuum when you come off idle to get the throttle response.   Call me unsupported of the environment, but, i don;t give a crap about NOx emissions..   i only drive the Challenger about 500-1000 miles per year anyways.   

[Bullitt-]

So I have been hearin about this Manifold Vacuum thing for some time now N figgured it was just a bunch of know it all's blowin smoke so I went n did some skulking on the WWW.

Turns out this was a conspiracy in the '60s by the Government, Big Oil & a bunch o Tree Huger's to  ruin our lives..     Kinda.... Sorta   

Anyhow I found this article scanned off a real printed magazine, cause I never trust any one source on the interweb, that indeed back in the good ole daze, say pre-'66, that Manifold Vacuum Advance was the way it was done....   

Lotta reading here &  repeats some of what chargerdon had and in addition tells why they moved to Ported Vacuum Advance at the very end of the article.... 

http://www.camaros.org/pdf/timing101.pdf

[73_Cuda_4_Me]

I removed the vacuum advance on my 340, set initial at 18, made and installed limiter plate adding only 16 degrees mechanical total, with mostly stock engine and comp cams xe274/headers/eddy carb... but this is just my setup... up to you and how you want to drive...

As info, though, there is this...

http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html

[chargerdon]

NOW that is a great article...describes why the ported vacuum came into being (poor emissions control)....and supports the PUT is on the Manifold side and why.   Thank you a lot... 

[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?

I tried this today, hooked vacuum advance to manifold vacuum....played with is a bit to add a little timing to the idle...and backed the idle speed off a bit. have about 35 degrees at idle.  In gear idle at 700 rpm.

I found that it helped with the idle quite a bit.  I have always struggled with the stinky idle, regardless of where the AFR meter said the AFR was, could be 14:1 and it would still be stinky...today it did not seem to be stinky at all with this change.  I do not have the AFR meter set up, so not sure where it is.

Driving seemed fine,  did not seem to really affect the performance, car ran fine down the highway and through the city.

The temp out to day was 99 degrees with the heat index, so hot and muggy, car ran at its usual temp, maybe even a little cooler (200 - 220).  Idle siting in traffic it got up to 230...but that was it (and not the first time it has go that hot).

At the end of the day I think it ran "cleaner" than I ever remember.

In the past I have tried the vacuum advance hooked to the ported vacuum, which is the typical set up, and I could never tune out a funny vibration at part throttle.  I have also had it so advanced that it ran horrible lean and very very hot!

I also checked the total timing over 2500 rpm, I am only running around 32 33 degrees, so I think I need to bump that up a little.

But you know, I think you may be on to something here.

Jason

[HP_Cuda]

Sounds like you are on the ragged edge of your timing or you having a cooling system problem running 200-220. Mine sticks at 185 pretty much all the time no matter how I drive it.

AFR should lead you to the most optimal carb setup as far as tuning goes.

[Cudajason]

Sounds like you are on the ragged edge of your timing or you having a cooling system problem running 200-220. Mine sticks at 185 pretty much all the time no matter how I drive it.

AFR should lead you to the most optimal carb setup as far as tuning goes.

Yeah that or I have no idea what I am doing on the timing!!!     Possible!!!

wow 185, I am never that cool. 

I often wonder if my block is gunked up and plugging the rad...rad is a record original, 2 years old.  That really made no difference when I changed it out.

Just to be clear I spent a lot of time over the last few years tuning the carb with the AFR...mad a tone of difference.  I currently have not bog of idle and it runs pretty good everywhere. Not that I don't want a bit more power, but pretty happy with the carb.  Might change when I put the AFR meter back on with the new exhaust...but well see.

Either way, I might try a few more things on the timing side for now.

Jason

[Cudajason]

On 340's I actually prefer to lock the timing @35 BTC.     Just a bump of the key and it fires right up and throttle response is instant. Every time I try different springs and advance curves I always end up going back to locking the timing advance. When I would run the lighter spring for quick advance I would have issues getting them to return all the way and causing it to idle high until I shut it off and fire it back up. Now I run mini starters so I'm not sure if factory starter will have issues or not cranking over the motor with that much timing. But I think it would do fine. Something to think about.

As previously stated don't run the vacuum advance. That will always cause problems.

@Shane Kelley ....you sir are a genius...I tried locking out the timing at 35 degrees on my 360, and good lord my car has never run better.

I tried it at 37...and had a little rattle at light throttle...thinking it was detonation.

Car fires right up, hot or cold.  At part throttle from idle it feels like the tires are slipping...its instant no hesitation. A little more and the tires will bark!!  I had the carb tuned pretty good and did not have a bog, but man it just jumps now.

At full throttle from idle its still a little flat, but that could be the 3.22, old cam, and stock stall converter, or a little more carb tuning (need my AFR meter back!!!

Of course I tried a brake stand...because I had too...and holly hell...it just lit up the tires like they were nothing...very smoky!!  

My only compliant is that the idle is a little smelly again.  I do not have the vacuum advance hooked up, so I may try that to add a few more degrees at idle and clean that up.

I will admit I had my doubts on this set up, but man does it work!!!

Jason

[Shane Kelley]

@Cudajason what carb you running? Glad the locked timing helped you!

[Cudajason]

@Cudajason what carb you running? Glad the locked timing helped you!

I am running a 750 Holey with Vacuum secondary.

Jason

[Shane Kelley]

@Cudajason what carb you running? Glad the locked timing helped you!

I am running a 750 Holey with Vacuum secondary.

Jason

I figured you were running some sort of Holley variant. Here's what happens with those. You raise the timing at idle and that increases your idle speed. So you turn the idle screw on the carb to back down the idle speed. This totally jacks up the idle circuit. The primary throttle blades need to partially cover the slot in the base plate. (see pic) You need to remove carb and set the blades in position. Use the secondaries to achieve the desired idle speed.