Using Full manifold vac adv

[Cooter]

I'm tearing down all the small block dist. I have and am finding "T" plates all over the place when it comes to timing slots.

Russ's chart helped me drastically.

[firefighter3931]

Good article on re-curving the pre 2000 MP distributors as well as any OEM factory piece.

http://www.moparmusclemagazine.com/techarticles/engine/mopp_0301_mopar_electronic_ignition_system/

The 2000 and newer MP distributors use a Mallory advance mechanism that employs adjustable stops to limit mechanical advance so no welding is required. 



Ron

[Chippa]

Thx Ron  

Yes thats the article i found to help me step by step was very good!! when i measured up the travel in slot with counterweight dowell in place i had around .141 of travel so pretty close.
There was no audible pinging that i could hear Ron but as stated i think i have ended up with 20* base and 16* mech then i dropped it back to 18 deg base.
Can you have a close look at No.1 plug D/S pic the strap has some black spots on it,does it seem to you like detonation??? maybe i should get some fresh plugs and check
How does it feel??? well from a standing start it will only just turn the 295's...get on the brake a bit and it lights them right up....1st or 2nd gear sitting on say 2000rpm and nail it and its quite responsive so i guess its liking it more once the rpm builds and timing increases..

Will also start looking at some replacement intake manifolds as well that are reasonably priced.....suggestions???
Once again thx to all for your input

Andrew  

[Challenger340]

Ok so i've trawled thru all the threads i can about this subject thats been done many times over, i've looked at all the ported timed vs full manifold vac adv discussions on many different forums.

Some ppl have obviously had some success utilizing full manifold vac to dizzy and it seems the consensus is ported is the way to go...i guess its trial and error for some.

To paint some sort of picture i own a 69 with 440 and 727 trans, 3.23 rear,Edelbrock performer intake,750 holley vac sec and headers that has a fairly healthy size cam i think (around 11" vac at idle and drops to 7-8" in gear) with a MP electronic dizzy.I currently have the vac advance disconnected which has helped with some light throttle pinging that i was incurring.
I have it set at 36 deg total @2600 and have 10-11 deg initial so obviously not really the best in regards to mechanical, i can adv at idle and vac climbs up to about 15" of vac but has over 20 deg when i checked. I know i need to sort the dizzy out and get it re curved or weld up etc but for temporary purposes would it help me at all if i was to hook up to full vac and dial in/limit say an extra 5 or so deg on the vac adv to bump up my initial or am i wasting my time/worth the excercise
All thoughts and advice appreciated .....i'm also going to make myself up a spark plug piston stop and just verify TDC incase i'm out of wack a little on the harmonic balancer..
Cheers Chippa 

I must have missed something ?? please forgive me....but what is it you are trying to do ??

A "Vacuum" advance,(dunno if I even spelled that right it's been so long)....was/is just a Fuel "Economy" Timing Advance ?

Are you trying to find out which way, ported or manifold Vacuum...... gives the best fuel Economy ?

[b5blue]

  Vacuum advance gives the engine the timing it wants at idle. Set up properly, like Don at FBO did for my engine I could feel the difference instantly. Idle was stronger, it dropped less in RPMs when I put the automatic in gear. I netted more torque on the bottom RPMs and my right foot could feel it.
  Top end or transition ping is from too much timing in the dist. mechanical advance. The curve is ether allowing too much total advance or too much advance too soon in the curve.
  It's a dance, more timing in at idle that drops out with increased RPMs (As vacuum drops.) with mechanical advance taking over as the RPMs increase. For a "advanced timing curve" (For a street driven engine.) it's a "U" or cup shape, at idle you have 18 to 22 degrees (Or so depending on your engine's build.) and at the top you have full mechanical 33 to 36 (Or whatever.)  Get it right at both ends and you could still get ping in the middle (Transition.) ripping through the gears if you getting too much timing too soon.
  Now it's my understanding that "ported vacuum" was created to clean up Hydrocarbon emissions in the late sixty's at part throttle. Also for a monster race type setup your never farting around, it's WFO or off for the most part. Experts like firefighter (Ron.) have their engines so dialed in they are probably hitting 500 HP @ idle with chamber quench perfected along with everything else they are light-years away from my stock build 440 so I can't speak for that type of build. I am certain that "if" vacuum advance was of no value it would not have been included on every Mopar dist. made.  Your carb, cam, intake, heads, and torque convertor all effect and set that advance curve through out it's range. Good Luck! 

[Chippa]

Ok so i've trawled thru all the threads i can about this subject thats been done many times over, i've looked at all the ported timed vs full manifold vac adv discussions on many different forums.

Some ppl have obviously had some success utilizing full manifold vac to dizzy and it seems the consensus is ported is the way to go...i guess its trial and error for some.

To paint some sort of picture i own a 69 with 440 and 727 trans, 3.23 rear,Edelbrock performer intake,750 holley vac sec and headers that has a fairly healthy size cam i think (around 11" vac at idle and drops to 7-8" in gear) with a MP electronic dizzy.I currently have the vac advance disconnected which has helped with some light throttle pinging that i was incurring.
I have it set at 36 deg total @2600 and have 10-11 deg initial so obviously not really the best in regards to mechanical, i can adv at idle and vac climbs up to about 15" of vac but has over 20 deg when i checked. I know i need to sort the dizzy out and get it re curved or weld up etc but for temporary purposes would it help me at all if i was to hook up to full vac and dial in/limit say an extra 5 or so deg on the vac adv to bump up my initial or am i wasting my time/worth the excercise
All thoughts and advice appreciated .....i'm also going to make myself up a spark plug piston stop and just verify TDC incase i'm out of wack a little on the harmonic balancer..
Cheers Chippa 

I must have missed something ?? please forgive me....but what is it you are trying to do ??

A "Vacuum" advance,(dunno if I even spelled that right it's been so long)....was/is just a Fuel "Economy" Timing Advance ?

Are you trying to find out which way, ported or manifold Vacuum...... gives the best fuel Economy ?

I must apologize a bit i guess my original intention was to try and increase my initial base timing thru full mani vac but this topic morphed into me just pulling the dizzy instead and increasing my initial via changing/limiting my mech advance and welding up the slots which i'm glad i did...i couldnt care less about fuel economy i'm just wanting to get my timing as good as i can it can be with what i currently have to work with and thats why i just started throwing up everything i was doing in this thread so ppl had a better picture of what i was dealing with...
Hope that explains my crazy mind haha

[b5blue]

  Your not nuts, your braver then I am! Test and tune for a dizzy without a machine to calibrate on is no small task, not to mention WHERE to set things.  I cheated and had FBO do mine, but I needed a new dizzy anyway.

[Chippa]

haha well to be honest it wasnt as painful as i thought it would be   i guess it helps being a tradie (used to tools and machinery) and i have all you great guys giving me lots of guidance   and the fact that i'm old enough and proud enough to say that i come from era where you learnt to fix what you had and not just chuck it in the bin and get a new one...

Plus us Aussies are good at fixing things haha

[Cooter]

And all Big Block Distributors rotate counterclockwise...Not just the ones in down under.

[Paul G]

Your doing well Chippa. Setting up a dizzy will make one dizzy!

I spent last summer fiddling with my dizzy. Finally found it worked best for me using full manifold vacuum, not ported. I am at 18° at idle with vacuum line plugged. Well over 20° at idle with full manifold vacuum connected. 36° total all in at 2100 rpm. I have read that more timing will help the engine run cooler. Hence the switch to manifold vacuum. It seemed to help. I have over heating issues to deal with when we get over 100° for 4 months a year. Manifold vacuum and ported vacuum only have one difference, vacuum at idle. All other aspects are the same. They both produce the same amount of vacuum at cruise, when the throttle plates are partially open, or fully open, only difference between them is when the throttle plates are closed. Emissions are also effected by the two types of vacuum if that matters. Ported vacuum is better for meeting emissions requirements. Not a concern for me. Manifold Vacuum improved the idle quality with the Holley as well. Maybe more timing at idle which means higher rpm allowed the throttle plates to be closed a little more, opening up the idle circuits? Sounds like BS that I don't really understand, but it helped.

When I added the over drive tranny I had to do "the dance" as it was previously called. The overdrive tranny brought my RPM's down to 1500 at cruise, then I had way too much timing for the engine load at cruise. Pinged like a German U boat! Finally after some trial and error a stronger "light" spring cured that by holding back some timing at the beginning of the curve in the RPM band. Using the same heavy spring kept the upper end of the curve the same.

It was lots of fun!

[Cooter]

Manifold Vacuum improved the idle quality with the Holley as well. Maybe more timing at idle which means higher rpm allowed the throttle plates to be closed a little more, opening up the idle circuits? Sounds like BS that I don't really understand, but it helped.

On my 440 with Holley DP, I found that I too was having to open the throttle blades too much to get idle right, causing an over rich idle. I drilled two 1/16th inch holes in throttle blades next to transistion slots. Also opened up rear blades a hair. Solved problem. Mine had too much timing at cruise with full manifold vacuum.