440 still idles with screws turned in

My head is spinning counter clockwise like the Distributor in this thread

Bee,
It is hard to understand, & mainly because of lack of detailed info about ign operation & the interaction of the four 'suspects': initial, centri, vac adv & WOT timing.

Bee1971 said:

My head is spinning counter clockwise like the Distributor in this thread

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You mean like how a toilet could flush backward?

Geoff 2 said:

although I agree with the sentiment, said the engine needs more compression. 'That cam needs a ton of compression'.

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We don't know CR from OP his engine, but like my engine has a 10.5:1 CR and still makes only 6-7" vacuum, little different cam then OP but duration at .008 is 283/291.
And that low vacuum is no problem, it is the nature of the beast, in this case a healthy engine will show a steady low vacuum signal.
What vacuum should OP have according you? What would you class normal for that cam?
I had spend my time setting up a Vcan, but since it only ends up in engine ping mine is disconnected and the engine is happy.
I tried with the stock Vcan that came with the MSD dizzy and also tried the Accel Vcan you mentioned, all sorts of combinations but wasn't going to happen.
It will only accept a rich idle mixture as you may expect with a cam like that, and a rich mixture burns fast so it cannot run with a lot of advance.
Without the Vcan it idles ok, instant throttle response and burns the tires clean off the rim if i wanted to, maybe it consumes a little more fuel but hey its a 440 and that will never change.
Showing all this information of GM is nice, and it would work similar on a Mopar, STOCK version. The book goes by a stock engine with high vacuum, cams with low duration/low valve overlap and that is not what this is. Now you are facing low dynamic compression and more valve overlap.
It is not a race cam, but it already needs its own setup to run.

The debate of wanting to run low/high vacuum idle advance is up to everyone their own decision, if i could use the Vcan i would have for the purpose of getting a lot of advance at cruising speeds.
The fact is that OP needs to sort his fuel and air out before anything else as he has proven already his carb is not set right. He opened it so far as the engine wants air, even with a lot of advance it still wants that air.
He has to give that air first and the fuel to get a fuel mixture that is on the rich side of the line.
To aid in fine tuning it is handy to increase the initial to something high temporary to allow the engine to idle without having to hold the throttle open, but his engine will be able to idle fine at 850-900 rpm with 18-20* advance.
OP already hasn't shown himself for days anyway, i have given my opinion on what he can do to find a solution for his problem that i have come across before.

Wietse,
My opinion on the low vacuum is as an owner of many Ch engines going back to the 70s. At one time when I was actively drag racing, I was changing/trying new cams every other week. From that experience & with many, many other engines over the years, I think the vac should be at least 10" at idle. Possible reasons for a low number have already been discussed.
The BB Ch is unique [ except for Cadillac ] for having a large rod/stroke ratio. That is great for high rpm, lousy for idle & low rpm. They do not tolerate a lot of cam duration like a BB Chev does. I think it is this thread that I posted the comments by cam grinder Sig Erson about excessive cam duration & loss of low end tq with 440s.
In the 70s, I couldn't get adj VA units here, not even sure if they were available in the US. I was mounting solenoids on the side of the dist that advanced timing once the engine started. No, not ideal, but what a difference it made to idle quality, vacuum & response.
Low vacuum caused by increased cam duration/overlap requires more idle timing. Period. And that is the point: if high vac factory stock cams idle @ 26*, low vac cams need a hell of a lot more. Have gone over this throughout this thread. Will be posting more MVA success stories in a day or two so stay tuned.
The Accel & Crane adj VA units. The ones made for GM dists have a sleeve inside the spring, whereby tightening the AK can lock the thing up & you get no VA! Useless design & the instructions are also useless, written by someone who doesn't understand the issue trying to be solved. I pull the cans apart & remove the sleeve. The best VA units I have found come on Chinese dist that I can get here for $60. No sleeve, worth $60 just for the VA unit. Have not struck the sleeve in Chr VA units.

And no, for the umpteenth time, you do not temporarily increase idle timing. You set it FIRST & PERMANENTLY by the method I described earlier in this thread & then tune the idle cct.

OP now has multiple options given to check and correct his issues, up to him to try and get his car going.
We can debate about Vac adv. till end of times but it's not going to change my mind so for me its effortless to continue this discussion about that subject.

Geof Did you read the section in your pontiac book about AIR distributors. Double action vac can, that is connected to both mva and Port Vac. At idle, the Vac Can retards ignition timing and when throttle blades open it returns to initial setting.

If you read what Chrysler was doing and how they were approaching emissions it was different than GM, but didn't GM have air pumps on cars even performance model Camaros and Corvettes?

I still stand by my comments that much more info is needed. Sure we can assume everything else is right and just think it is carb and ignition tune, but in the last several subjects brought forward where the consensus was advance timing, the real issue was bad ignition coil, warped holley body surface, leaking carb base, and other experience folks could talk about broken valve spring, missing ring, etc....

And as stated a by Wieste, and simple search on MVA or Ported will give you post that last over 50 pages and go on for months. On any forum.

Dragon Slayer said:

I still stand by my comments that much more info is needed

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Yep, still need more details of OP setup to get a more accurate picture of what is going on. (or at least a reply if he got to check/test anything)
A lot of different things are mentioned already, based on the persons knowledge or experienced the same issue which are all valid things to consider.
But to walk in and claim all to be wrong and you are right based on quoting GM books just causes the off-topic crap from the last 3 pages and nobody is any wiser after reading....

Dragon Slayer said:

MVA or Ported

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Oh, don't take it to that extend!!
I have nothing against vacuum advance, it does improve tons of things, I did not manage to use it (yet) on my combo as I still have other things to sort out as a near enough stock type converter that is dragging the vacuum and rpm down when thrown in gear.
Once I get my new 3k stall converter in there, together with a set of Rhoads variable lifters it will be a different engine which will give me a lot more opportunity to use the vac advance.

I think Moparnocar succumbed to tutorial overload sometime last Thursday

He already got rid of the ride, got a Chevy and is new member on the Chevy forum

Wietse LOL and probably true.

Moparnocar said:

Wow, that goes against everything I've read and done on Mopar. I always do 36-38 total. Interesting

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Because most of those "books" are not written for street driving, they are WOT deals or nothing with the Mopar bible and other lit.

Total timing a street driven car is a horrible method/approach. Letting the idle/initial timing fall where it may gets you an engine that smells like a fuel truck dump raw gas out the pipes most of time. Why should the mechanical timing in the distributor dictate how much initial timing an engine has and if that initial is even correct or best for the engine. It's not. Tune the idle FIRST, then get that set up and limit the mechanical as necessary to hit your total number.

If you have it running and warmed up, twist the distributor a little to give the engine more advance, if RPM picks up, it wants the timing.

Think building a house. Total timing is akin to building the roof first and disregarding the foundation/framing etc. Doesn't matter the foundation is on a 45* slope, build the roof. Not going to be the best result. Initial timing is the foundation that the rest of the ignition timing is rooted from. Give the engine the initial timing that it wants and it will run much better off the bottom and through the ranges.

Good luck with it.

DS,
Post #89. Don't know or care if the car had AIR, or EGR, or a host of other emissions crap. Hands up anybody who has improved their engine for more performance by putting a big cam, posted heads, better intake etc & keeps the AIR.....

Cracked,
Great post.
'Give the engine the initial timing it wants...' Correct, go to the top of the class, you get 'it'.

'..if rpm picks up, it wants more timing'. Yup, been there done that more times than I can remember.

Crackedback said:

Because most of those "books" are not written for street driving, they are WOT deals or nothing with the Mopar bible and other lit.

Total timing a street driven car is a horrible method/approach. Letting the idle/initial timing fall where it may gets you an engine that smells like a fuel truck dump raw gas out the pipes most of time. Why should the mechanical timing in the distributor dictate how much initial timing an engine has and if that initial is even correct or best for the engine. It's not. Tune the idle FIRST, then get that set up and limit the mechanical as necessary to hit your total number.

If you have it running and warmed up, twist the distributor a little to give the engine more advance, if RPM picks up, it wants the timing.

Think building a house. Total timing is akin to building the roof first and disregarding the foundation/framing etc. Doesn't matter the foundation is on a 45* slope, build the roof. Not going to be the best result. Initial timing is the foundation that the rest of the ignition timing is rooted from. Give the engine the initial timing that it wants and it will run much better off the bottom and through the ranges.

Good luck with it.

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I'm still here, I won't be around the car for a week or so, I'm definitely gonna try these suggestions, thanks

More MVA info. Actual numbers.
I sold my last Ch in 1994, a 440 powered Dart. I had many Chs prior to that. Have built a lot of Ch engines & transmissions [ & other brands ] & am still doing it including tuning work. Worked on a TQ y'day.
I bought a Pontiac GTO after the Dart, which I still have.
The following stories are about Pontiacs, but apart from the logo on the valve cover, they all work the same; pistons go up/down; valves open/close. But what does vary between them are actual numbers, but not by much. Eg, iron head Pontiac runs best at WOT with around 34-38*. Not unlike a Ch, or Olds etc.
[1] High Perf Pontiac magazine, Dec 06. Written by Ray T. Bohacz, a well respected automotive engineer & author in the US. 'An often overlooked but effective tuning tool is an adjustable VA. These units can be bolted on to a stock Pontiac dist & allow a fine degree of tuning for better throttle response, fuel economy & idle quality.'
[2] HPP magazine Oct 06.
Owner had two F'birds. 1972 model, 455, auto, QJ carb, factory intake, 222/232 @ 050 cam, 8.5:1 CR, starting idle vac 13", 12* init + 15* VA.
1976 model. 455, manual, Torker 2, 950 Holley, 244/252 @ 050 HFT cam, 9.5:1 CR. Starting idle vacuum 8.25". 14* init + 12* MVA.
Both engines had 36* @ WOT.

Results 72 model. '..from ported to MVA, idle speed immediately increased about 200 rpm. After preliminary adjustment, idle quality noticeably improved & vac jumped roughly 1.5". The load generated by placing the trans into gear seemed to affect the engine less, another indication that it was operating more efficiently on the available fuel mixture. A definite improvement on idle, initial take off & light throttle acceleration characterized the overall effect of MVA over PVA. We did not however expect or notice any real difference in part throttle response over PVA. What we did discover though was a smoother transition when re-applying the throttle after coasting at speed..'

Results 76 model. 'The available advance of the aftermarket VA was limited 14* [ see my comment below].....Once installed & connected to man vac, idle speed increased....After resetting the idle speed & readjusting the mixture screws, vacuum increased about 3". The large cam seemed much tamer & idle quality was smooth & stable. Subsequent road tests proved that the engine was largely unaffected by clutch engagement, & acceleration was smooth & effortless. Surging however was still present, although not nearly as severe.....We ultimately limited static timing to 14* & VA to 12*. This limited surging to extreme driving conditions & reduced idle vac 0.5" but there was no detectible loss in idle quality or low speed street manners.'

[a] For this test a Crane VA unit was used. As I alluded to in an earlier thread, these have a sleeve inside which limits the total VA. The 76 could have used a lot more timing but the testers were probably unaware of the stupid sleeve that limits movement.
Increasing the IFR would probably have cured the surging or at least reduced it. This was caused by the large cam duration, NOT MVA. Would have done the same with PVA because at cruise they behave the same.

Why don't we wait for the OP to try a few things, like advance the timing to 30 degrees initial, just for idle, do not drive the car, and see if the throttle blades shut and mixture screws work? I doubt it will but hope I am wrong, maybe Geoff could provide him a vac can part number that will fit his stock mopar dizzy and work with the low vacuum? I would add, measure the vacuum in gear also if it is an automatic, if he can get 10-11" in gear it is a new ballgame, 7-8"old ball game. If his dizzy is a stock mopar performance electronic he may have a ton of centrifical advance and some had reluctor phasing issues.

6bbl,
Good advice but that is EXACTLY what I recommended to the OP back in post #5.
And if anybody else wants to simulate the improvement that MVA would make to their engine, do the 5 min test in post #5. Remember, the bigger the cam, the bigger the benefit will be.