I've made posts about the differences between stopping the advance versus shortening the inside of the slot in other threads.
In this thread lets just stick to helping Dartfreak work through tuning what he has.
Vacuum advance
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In this thread lets just stick to helping Dartfreak work through tuning what he has.
This might help understand how a vac advance works Matt.
What direction do you turn the can to reduce the amount of advance? I just don't recall.
512Stroker
We are all here because we are not all there.
You must be using a tight torque convertor to be able to run 2900rpm @ 60 mph with 3:73 gearing. It has been my experience that when a convertor is tight at cruz'n speed it is also tight during low rpm's. Maybe one reason why it like a higher initial timing.
Is it a stock convertor?
512Stroker
We are all here because we are not all there.
You dont turn the can. You adjust the the amount of vacuum advance with a hex wrench inserted into the connection port. As shown in post#27
I will leave it to halixfax to give the procedure.
That is what I meant, with a 3/32 allen
dartfreak75
Restore it, Dont part it!
Its a boss hog
It is a stock replacement converter its a boss hog street series 2200 it is tight during low rpms when you put it in drive it wants to go. What do you mean by tight at crusing speed? You don't in flashing while crusing do you?
dartfreak75
Restore it, Dont part it!
So if i want it to come all in earlier I would use the lighter springs correct?
512Stroker
We are all here because we are not all there.
All non lockup converters slip at highway speeds.
Higher stall speed off the self converter will slip more. You will hear the term "loose converter" when addressing this condition.
So if you have a 3000 rpm stall speed converter and it slips 10% at cruz'n speed you losing 300 rpm at speed.
My engine will turn 2900 rpm at 60 mph with 3:55 gears because I have a higher stall converter.
On the other side of the coin, I find that hi performance engines that are coupled to a higher stall converter easier to tune at idle because the are slipping and do not place as much parasitic load on the engine.
dartfreak75
Restore it, Dont part it!
Thanks man. I wish I could have afforded a better convertor, but I couldn't so u went with what I could lol. Thanks for the info that helps.
The adjustment does NOT change the amount of advance .
It changes when the advance starts.
So if you have a can that starts advancing @ 6" of vacuum and stops at 18"s for a total of 14* advance . turning the screw 1 turn inside the can will make it start advancing at 7.5" (dont recall exactly) but it will still advance 14* total by 18"s of vacuum.
dartfreak75
Restore it, Dont part it!
Its ok go ahead and explain im actually curious about it also. If you don't mind of course. I already have the fbo kit and plan on using it to limit the total.
dartfreak75
Restore it, Dont part it!
I don't think i did in this post my bad! I did in the other thread. Its a a luniti voodoo 702
Yes, but the lightest springs usually give some advance at idle. The best starting point I've found is one light sprAng and one medium sprAng. Usually that nails it down.
dartfreak75
Restore it, Dont part it!
Does it make any difference to what side the light and medium is on?
I actually answered this in your previous thread. These discussions get too sidetracked and its hard for anyone to stay focused.
And following up on that with Rick the more detailed explainations are here.
Too much timing?
I'll add this -
If you want to stick with the FBO plate, you may have trouble using vacuum advance. Limiting the advance can work, with the right springs in some engines.
If your not married to the FBO limiter and you have the original springs, then it may be easier and better to shorten the slots on the inside.
We won't know until we find out what the advance of your distributor actually looks like.
If you want to read some previous examples and explanations.
1970 Dodge Dart 318 Distirbutor
By shortening the slot on the inside like Rockable did here, then its pretty much a pre-CAP advance. Everything will work as it should without changing springs. Small adjustments on the start can be done by adjusting the spring perches.
I think how and why is pretty well illustrated with Rockable (360 Tune Up) and further discussed with Mullinax."
Advance curves for performance engines using no vacuum advance (Race).
Another timing curve question
P4120701 Small Block Mech Tach drive
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dartfreak75
Restore it, Dont part it!
Yea I read so much stuff on here I forgot alot of the stuff by the time I need to use it and then have to go back and reeread it lol. Thanks again bud I will go back and read all that again.
If you find it helpful. Great. If not, just come back to it for explanations of something specific..
Here's one more. A post where I show some timing curves I tried on my car, and where too much advance caused problems.
Cruise Seems Lean
A good thread where we pretty much stayed focused on the problems with the OP's car.
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You should be able to get it to idle around 700 with that cam .
If you use too light of spring your idle may fluctuate because the advance plates bounce a little at idle and that will be frustrating .
Expect to spend several hours tweeking your dizzy . View it as a game and dont get overwhelmed. You will be really good at reassembling distributors by the time you are done .
If you use too light of spring your idle may fluctuate because the advance plates bounce a little at idle and that will be frustrating .
Expect to spend several hours tweeking your dizzy . View it as a game and dont get overwhelmed. You will be really good at reassembling distributors by the time you are done .
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Your engine has FOUR or FIVE important timing milestones. In order of importance, IMO, they are;
1) Power-Timing
2) Part Throttle Timing
3) Idle-Timing
4) Stall Timing
5) Cruise Timing
All except numbers 4 and 5, ARE DONE/MEASURED WITH THE VACUUM ADVANCE CANISTER DEFEATED
Peak pressure needs to occur at a very specific crank-position, in order to transfer the maximum amount of pressure to the flywheel. Generally, this number is in the range of 25 to 28 degrees AFTER TDC.
If the pressure occurs too early, the engine could detonate, and the power will be down as the engine fights itself.
If the pressure occurs too late, the piston is already racing to the bottom of the stroke, and the potential for performance is lost, and almost worse is that operating this way, a good deal of heat is pumped into the cooling system thru the cylinder walls............ which may lead to overheating, but if not, it will most certainly send a ton of heat into the underhood.
The goal of all these methods of timing control, for us streeters, is to get the peak pressure to occur in the magic 25 to 28 degree window, as often as, and for as long as, is possible..
Except from idle to stall-rpm, because usually, this results in operational difficulties.
Specifically at idle. At idle, it is desirable to reduce the power by delaying the pressure peak, to smooth initial transmission engagement, and to smooth drive-away on the fluid-coupling at Part Throttle. Yes the engine will be snappier with more pressure, (created by earlier timing), but there comes a point where your gas-pedal starts to feel like an on/off switch, and if it happens at an rpm/load setting that you are often in, that becomes very annoying. This is especially annoying with a tight lo-stall TC, and majorly annoying with a manual transmission..
If you defeat the V-can permanently, your engine will be running 100% of the time, on the PowerTiming curve, which is usually adjusted to be as close to the maximum amount of timing your engine can take, at WOT.
If you run your street engine this way, most of the time, the engine will not have nearly enough timing. And so most of the time, the engine will be lazy, and will be sending unburned, or still burning fuel, into the headers. In the headers it will destroy your overlap cycle, which at idle is not a bad thing. But as the Rs increase, you want that Overlap cycle working. The harder you step on the gas, the closer the timing will be to ideal and so, this header-pressure screw-up goes away.
at Part Throttle, with the peak cylinder pressure now seriously reduced by the late PT timing, the engine is very lazy and responds slugishly. With a 3500TC you might never notice it, but at the lower rpms involved on the street, oh-yeah, you will be very disappointed.
At cruising speed, most street engines will want timing of 48 to 56, possibly as much as even 60*. So, by only having 30 to 36, guess what happens to your fuel consumption...... your engine,
"will be sending unburned, or still burning fuel,into the headers"
Consider this;
at about 2800 rpm, your Power-Timing might be 28*. But the Vcan could be bringing in as much a 24 additional degrees, so, then she might be cruising on 52*. But at Part-Throttle, your foot-feeder is simultaneously controlling;
BOTH the fuel/air charge,
AND the timing;
between 28 to 52 degrees,
depending on how far the throttle is open. How cool is that!
That's about as short as I can make it, and it still be meaningful...... lol
1) Power-Timing
2) Part Throttle Timing
3) Idle-Timing
4) Stall Timing
5) Cruise Timing
All except numbers 4 and 5, ARE DONE/MEASURED WITH THE VACUUM ADVANCE CANISTER DEFEATED
Peak pressure needs to occur at a very specific crank-position, in order to transfer the maximum amount of pressure to the flywheel. Generally, this number is in the range of 25 to 28 degrees AFTER TDC.
If the pressure occurs too early, the engine could detonate, and the power will be down as the engine fights itself.
If the pressure occurs too late, the piston is already racing to the bottom of the stroke, and the potential for performance is lost, and almost worse is that operating this way, a good deal of heat is pumped into the cooling system thru the cylinder walls............ which may lead to overheating, but if not, it will most certainly send a ton of heat into the underhood.
The goal of all these methods of timing control, for us streeters, is to get the peak pressure to occur in the magic 25 to 28 degree window, as often as, and for as long as, is possible..
Except from idle to stall-rpm, because usually, this results in operational difficulties.
Specifically at idle. At idle, it is desirable to reduce the power by delaying the pressure peak, to smooth initial transmission engagement, and to smooth drive-away on the fluid-coupling at Part Throttle. Yes the engine will be snappier with more pressure, (created by earlier timing), but there comes a point where your gas-pedal starts to feel like an on/off switch, and if it happens at an rpm/load setting that you are often in, that becomes very annoying. This is especially annoying with a tight lo-stall TC, and majorly annoying with a manual transmission..
If you defeat the V-can permanently, your engine will be running 100% of the time, on the PowerTiming curve, which is usually adjusted to be as close to the maximum amount of timing your engine can take, at WOT.
If you run your street engine this way, most of the time, the engine will not have nearly enough timing. And so most of the time, the engine will be lazy, and will be sending unburned, or still burning fuel, into the headers. In the headers it will destroy your overlap cycle, which at idle is not a bad thing. But as the Rs increase, you want that Overlap cycle working. The harder you step on the gas, the closer the timing will be to ideal and so, this header-pressure screw-up goes away.
at Part Throttle, with the peak cylinder pressure now seriously reduced by the late PT timing, the engine is very lazy and responds slugishly. With a 3500TC you might never notice it, but at the lower rpms involved on the street, oh-yeah, you will be very disappointed.
At cruising speed, most street engines will want timing of 48 to 56, possibly as much as even 60*. So, by only having 30 to 36, guess what happens to your fuel consumption...... your engine,
"will be sending unburned, or still burning fuel,into the headers"
Consider this;
at about 2800 rpm, your Power-Timing might be 28*. But the Vcan could be bringing in as much a 24 additional degrees, so, then she might be cruising on 52*. But at Part-Throttle, your foot-feeder is simultaneously controlling;
BOTH the fuel/air charge,
AND the timing;
between 28 to 52 degrees,
depending on how far the throttle is open. How cool is that!
That's about as short as I can make it, and it still be meaningful...... lol
Great explanation A/J.
I'll disagree with this part, and only this part.
It's important enough to discuss.
It takes a relatively rich mixture to get an engine to idle at a low rpm and not die when engaged with the transmission (through torque converter or a clutch). This is because we are asking the engine to produce close to maximum power at that rpm. Maybe it takes 10 hp for the engine to run at 650 rpm. But it takes maybe 40 hp when the clutch engages and put the car into motion. Run an engine lean and it can only make 20 or 25 hp at 650 rpm. We see this lack of power when an engine is placed into drive (automatic trans) and the rpm and vacuum drops.
With an automatic in drive the engine its not even moving the car, and yet we sometimes see engines slowing down and stalling.
This didn't happen with 'low performance' factory engines. Why? One reason is the high performance engines often have less torque and power at the same idle speeds. Another reason is the hot rodder has set it up to run lean at idle. This only works well if the goal is to run in neutral.
I'll disagree with this part, and only this part.
It's important enough to discuss.
We can always use more power at idle. For sake of this discussion, I think we are all on the same page that we're only concerend with the maximizing power and fuel efficiency. So we will accept that maximum power requires rich mixtures, and this results in lots of CO and HC.
It takes a relatively rich mixture to get an engine to idle at a low rpm and not die when engaged with the transmission (through torque converter or a clutch). This is because we are asking the engine to produce close to maximum power at that rpm. Maybe it takes 10 hp for the engine to run at 650 rpm. But it takes maybe 40 hp when the clutch engages and put the car into motion. Run an engine lean and it can only make 20 or 25 hp at 650 rpm. We see this lack of power when an engine is placed into drive (automatic trans) and the rpm and vacuum drops.
With an automatic in drive the engine its not even moving the car, and yet we sometimes see engines slowing down and stalling.
This didn't happen with 'low performance' factory engines. Why? One reason is the high performance engines often have less torque and power at the same idle speeds. Another reason is the hot rodder has set it up to run lean at idle. This only works well if the goal is to run in neutral.
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AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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@Mattax
What I mean is this;
at Idle, the engine will easily except 20/25/30/ sometimes even more degrees of timing, with the rpm climbing continuously, indicating that more and more power is being produced.
That's fine and all, but you cannot drive your carburated mechanical advance distributor engine, at those numbers.
At idle; you gotta dial the power back, else the engine will pull hard on the convertor, which becomes very annoying at every stoplight.
But more importantly, when you try to run at bigger Idle-Timing numbers, you have to close the throttle to prevent the idle-speed from getting excessive. This, of course, shuts off the transfer slots. And so you have to compensate for the lost fuel at idle, by enrichening the mixture screws. Ok so then you get it idling ok.
But now, when you put it into gear, it stalls.... because the sudden loss of airflow thru the primaries has lost all it's fuel.
Furthermore, if you are just borderline too far closed on the throttle, and you manage to keep it running when putting it into gear, now you have the dreaded tip-in hesitation. This all happens because the root cause is too much Idle-Timing. I'm talking about 20 degrees or more.
I have, for testing purposes, tuned several manual-trans 360s with big-for street cams to idle and drive on 5* of timing, at 550rpm, in 9.44 starter gear with just enough power to pull on hard, flat, smooth, surfaces... like parking lots.. So I know that, at least , is possible. By 12 to 16, the 360 has more than enough power at idle, to deal with traffic, and mine, with a 750DP, will take WOT almost immediately, the tires bursting into flames. lol. An automatic car with even a stock-stall, should have no problem...... unless the cylinder pressure is seriously low.
But who does that?
Oh wait, I know who does that,lol.
What I mean is this;
at Idle, the engine will easily except 20/25/30/ sometimes even more degrees of timing, with the rpm climbing continuously, indicating that more and more power is being produced.
That's fine and all, but you cannot drive your carburated mechanical advance distributor engine, at those numbers.
At idle; you gotta dial the power back, else the engine will pull hard on the convertor, which becomes very annoying at every stoplight.
But more importantly, when you try to run at bigger Idle-Timing numbers, you have to close the throttle to prevent the idle-speed from getting excessive. This, of course, shuts off the transfer slots. And so you have to compensate for the lost fuel at idle, by enrichening the mixture screws. Ok so then you get it idling ok.
But now, when you put it into gear, it stalls.... because the sudden loss of airflow thru the primaries has lost all it's fuel.
Furthermore, if you are just borderline too far closed on the throttle, and you manage to keep it running when putting it into gear, now you have the dreaded tip-in hesitation. This all happens because the root cause is too much Idle-Timing. I'm talking about 20 degrees or more.
I have, for testing purposes, tuned several manual-trans 360s with big-for street cams to idle and drive on 5* of timing, at 550rpm, in 9.44 starter gear with just enough power to pull on hard, flat, smooth, surfaces... like parking lots.. So I know that, at least , is possible. By 12 to 16, the 360 has more than enough power at idle, to deal with traffic, and mine, with a 750DP, will take WOT almost immediately, the tires bursting into flames. lol. An automatic car with even a stock-stall, should have no problem...... unless the cylinder pressure is seriously low.
But who does that?
Oh wait, I know who does that,lol.
Yes. In Neutral!
With no load engines like lean burns. Even with slight to moderate load engines like lean burns.
Power goes up with rpm. So any time we increase rpm we increase power.
The way to compare power is to be at the same rpm, with two different spark leads.
Then load each to the point of stall.
The one that can turn the highest load has the timing that makes more torque and power.
And I'm saying that's not what's happening. It's not that there is too much power. It's not that there is more torque produced by the engine with more spark lead. There's less torque from the engine. Any engine should be able to turn the front pump and converter at idle. When an engine can't do that, its because it doesn't have any power to turn them. A looser converter may slip more at idle rpms, but that would only reinforce what I'm saying is the core problem - not enough power.
The lack of power is even more obvious with a manual transmission if we treated them the same way. I think most of us have driven vehicles where you can put it in first gear without touching the gas pedal and the engine has enough torque to get the truck or car moving. Now if I can do that with some 1950s pickup at 500 rpm, and a hopped up 360 can't do that even at 800 rpm, which one has a more powerful idle?
Its the same thing we see with an automatic transmission when shifted into gear and the rpms drop alot. The reason rpms drop is lack of power.
Yes all the other things you wrote about come into play. But the basic issue was the engine didn't have the power.
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