Bill Monk
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So you're saying you go both ways? Just kidding, I couldn't resist!
440 Timing
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I think what happens with this debate comes down to how much vacuum your engine makes. Good vacuum you use the ported. Low vacuum (with the bigger cams) you might find that the manifold will work better because you don't get the reaction from the ported.
I tried both with my 440 build and the ported works the best. It doesn't like manifold at all.
You really have to start with the basics.
1.)Verify you timing on the dampner as being true TDC. (Use a piston stop to verify)
2.)Unhook the vacuum advance and plug the carb port.
3.)Timing light hooked up, check the timing mark at idle on a warmed up engine.
4.)Get a base line at idle while adjusting the distributor. (Say 15* for an example)
5.)Having a tach hooked up where you can read it while under the hood, rev the engine slowly while watching the timing mark. When it stops moving, check what RPM the tach is reading and note where the mark is on the balancer. (Say 34* @ 2000 RPM)
This is the total mechanical advance that your distributor has. (34* - 15* = 19*) 19* is the distributors mechanical advance.
6.)Now hook up your vacuum advance and rev the engine slowly. Watch the timing mark advance until it stops moving. It probably won't stop until it's up around 50*. Take note of the RPM and where the mark stopped.
This is how you find what your timing is doing. If it's getting too much mechanical timing or not enough, the the counterweight stops will need adjustment. If the mechanical timing comes in too soon or too late the advancement springs in the distributor will need changed to get what you need. If the vacuum advance comes in too soon or is off the timing scale, it will need adjusting if its possible with the vacuum advance can that's on the distributor.
The ported is much easier to tune and adjust. When using manifold, you time with the vacuum unhooked so the idle needs to be stepped up to run and adjusted back when you are done. Back and forth. When using ported, just unhook and no adjustments necessary. Set initial, check total, check vacuum, check idle, done.
And if you have a lumpy cam or variance in vacuum at idle it will play hell if your canister is hooked to manifold. My 440 is hooked to ported and runs like a scalded dog. It sucked when I tried it on manifold. I'm running 21/36 degrees without issue.
And if you have a lumpy cam or variance in vacuum at idle it will play hell if your canister is hooked to manifold. My 440 is hooked to ported and runs like a scalded dog. It sucked when I tried it on manifold. I'm running 21/36 degrees without issue.
65Fury440
Well-Known Member
Call 4 Seconds Flat and get one of these ignition limiting plates.
On my old 440 with a 509 cam, it wanted 18-20 initial to run good, but would put it at 40 total and ping.
This plate will allow you to run up your initial to where it runs good, and keeps the total manageable.
On my old 440 with a 509 cam, it wanted 18-20 initial to run good, but would put it at 40 total and ping.
This plate will allow you to run up your initial to where it runs good, and keeps the total manageable.
Dibbons
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Is there a rule of thumb on when ported began (and manifold was left behind) on factory original vehicles? (In my case it's a '72 318)
BSB67
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Taken from the 1406 manual...
The manual for my Mallory dual point says to hook it up to ported.
miller
Well-Known Member
The guys are right, on many points. (Yeah, that's a pun!) Pretty much, no two engines are alike, not built the same. Timing numbers that work for one build, won't for the other, unless they are a lot alike.
Here's a funny, to me anyway. 69 440, built just a little more than HiPo, cam wise.
Brand new (and improved) Mallory dual point, mechanical advance. Going by numbers I remember, from those days, checked the point gaps, set at the 'factory'. .018", just as I remembered. (Didn't bother with dwell, since it usually falls in.)
Slapped that dual point in place, timed it, fired right up. After break-in, up to 600 miles running around, doing great. Hard hitting, no pinging, blah, blah. That was with 24 mechanical advance, 12 initial, besides the gas thing, instant starts.
But, I hate the flaky YH advance weights, so looking at options. Point gaps are 'supposed' to be .020"-.022"! Take it for what it's worth.
Here's a funny, to me anyway. 69 440, built just a little more than HiPo, cam wise.
Brand new (and improved) Mallory dual point, mechanical advance. Going by numbers I remember, from those days, checked the point gaps, set at the 'factory'. .018", just as I remembered. (Didn't bother with dwell, since it usually falls in.)
Slapped that dual point in place, timed it, fired right up. After break-in, up to 600 miles running around, doing great. Hard hitting, no pinging, blah, blah. That was with 24 mechanical advance, 12 initial, besides the gas thing, instant starts.
But, I hate the flaky YH advance weights, so looking at options. Point gaps are 'supposed' to be .020"-.022"! Take it for what it's worth.
BSB67
Well-Known Member
Thanks.
But as written, it suggests that this is simply one of two alternatives when you have a big cam and trying to acquire a lot more initial timing. The other, as mentioned, is to shorten the mechanical advance. And then you can go back to ported. There really isn't anything there that implies that this is better, or for max performance. Big cams simply need more initial timing, no matter how you get it.
For the vacuum advance on a distributor, the term "performance" should be viewed in the context of emissions, fuel economy, and low speed throttle response. Not horsepower or WOT performance.
It is not clear to me where the relationship of ported vacuum timing and emissions got tied together, but is commonly stated as such. The question I have is that relative to full manifold vacuum, or to no vacuum advance at all?
My non-CAP 67 440 with the 4327 AFB has from the factory ported vacuum advance.
Bill Monk
Well-Known Member
From Don Gould at 4secondsflat
Ported or Constant?
Let me try and give you an explanation in layman's terms.... Generally, emissions equipped vehicles use Ported and they are connected to a computer, OBD1 or 2 to retard the timing based on information gather from a multitude of sensors in the vehicle.
Non-Emissions Hot Rods and Street Muscle Cars Pre-emissions use Constant. Many vehicles were built with specs that designated Ported, that was fine in 1975 when we used real gas and we could set the total advance to 25 with 5* initial and have the vac can pull the timing to 34 under load and fuel economy, formulations and costs were not an issue. These cars ran horrible and got terrible fuel economy, more gas ran out the tailpipe than got burned in the combustion chamber.
GM always used Constant Vacuum and built over 300 different set-ups for all there product lines until computers were introduced and everything changed to meet EPA emissions regulations.
So Your Hot Rod gets connected to CONSTANT manifold vacuum and the distributor needs to be set up properly to burn today's fuel formulations. The Vacuum Can needs to be adjusted to pull enough timing in the motor to allow it to burn the today's fuel and limiters installed to set the part throttle cruise timing numbers so they don't pull the timing too high and cause a lean miss at cruise, it's a delicate balancing act to get it all correct.
Your carb has 4 Venturi's, as the air speed or velocity increases with throttle position a venturi creates high pressure in the center to fracture the fuel into small particles and "Opposite and Equal Reaction" is negative wall pressure.
The negative wall pressure is what draws the fuel through the booster and feeds the engine based on throttle position or air velocity. A carburetor is a simple metering device that delivers fuel and mixes it with the air to create clean combustion, the higher the velocity the more negative pressure the more it delivers, it's a pretty simple device.
Ported vacuum: With that thought in mind consider if the distributor hooked to Ported Vac, as air speed increases the ported vac activates and starts to pull more and more timing in the motor as velocity increases. So if you set you total timing to 34* at 3000RPM that's when the ported starts to do it's job and advances the the timing to the total stroke of the vacuum can arm, usually 12-18* (without Limiters) so now have your total of 34* PLUS the stroke of the Canister arm of say 16* net result=50* of total timing under hard acceleration and your motor WILL "Detonate". If you had a OBD1 computer it would pull that timing back to the 34* as all the sensors feed information to it.... and no detonation.
Now to Constant: At idle/part throttle cruise you have high vacuum, the carb is nearly closed causing a restriction which creates the high vacuum level. Under this light load condition and lean AF ratios the motor needs more timing to burn the fuel (Lean Mixtures take Longer to Burn than rich mixtures) so you need more timing at idle and cruise to burn the fuel correctly and completely. When you stomp the throttle you have NO manifold Vacuum so you have NO vacuum timing and at NO time under high load will it ever advance more than the mechanical "All In" numbers. Stop pointing your finger at the carb for rich idle and top end lean conditions.. It's In Your Distributor Tuning! If your Buddy tells you to hook your Hot Rod distributor to Ported Vacuum, find a new friend because that guys advice is going to blow your crankshaft through the oil pan. Same goes for the guy who say's to disconnect it, they obviously have no idea of how it works or what it does or why we use it.
This not hear-say or an opinion its engineering, based on physics formulas, calculated by people who are a lot smarter than me and I know that so I do what they tell me. They come up with the numbers, we set them up accordingly.
Rule of Thumb: If the Motor Makes 8" of vacuum at Idle with 30* of timing in it then it needs a properly calibrated Vacuum Can, we have Mopar and GM vacuum cans that will read 7" of vacuum. most stock or aftermarket Vac cans will only read down to about 15", the odd one (1 out of 100) will read to 12"
We manufacture Mopar vac cans that will read to 7", our Lane Choice Gold Plated VC-1 BB or VC-1 SB
There's all sorts of unqualified guy's on the "Internet" and so called "engine builders" who will try and argue this point with me, I have given up trying to argue with these folks. They have no understanding how a vac can works or what it does, if they did they would realize how ridiculous they sound to us, Jim and I account for over 100 years experience with well over 10,000 happy customers.
Your "Engine builder" may be the best in the world but he's an Engine Builder and very seldom do they know anything about the fine tuning of the vacuum can or distributor mechanical advance system
Ported or Constant?
Let me try and give you an explanation in layman's terms.... Generally, emissions equipped vehicles use Ported and they are connected to a computer, OBD1 or 2 to retard the timing based on information gather from a multitude of sensors in the vehicle.
Non-Emissions Hot Rods and Street Muscle Cars Pre-emissions use Constant. Many vehicles were built with specs that designated Ported, that was fine in 1975 when we used real gas and we could set the total advance to 25 with 5* initial and have the vac can pull the timing to 34 under load and fuel economy, formulations and costs were not an issue. These cars ran horrible and got terrible fuel economy, more gas ran out the tailpipe than got burned in the combustion chamber.
GM always used Constant Vacuum and built over 300 different set-ups for all there product lines until computers were introduced and everything changed to meet EPA emissions regulations.
So Your Hot Rod gets connected to CONSTANT manifold vacuum and the distributor needs to be set up properly to burn today's fuel formulations. The Vacuum Can needs to be adjusted to pull enough timing in the motor to allow it to burn the today's fuel and limiters installed to set the part throttle cruise timing numbers so they don't pull the timing too high and cause a lean miss at cruise, it's a delicate balancing act to get it all correct.
Your carb has 4 Venturi's, as the air speed or velocity increases with throttle position a venturi creates high pressure in the center to fracture the fuel into small particles and "Opposite and Equal Reaction" is negative wall pressure.
The negative wall pressure is what draws the fuel through the booster and feeds the engine based on throttle position or air velocity. A carburetor is a simple metering device that delivers fuel and mixes it with the air to create clean combustion, the higher the velocity the more negative pressure the more it delivers, it's a pretty simple device.
Ported vacuum: With that thought in mind consider if the distributor hooked to Ported Vac, as air speed increases the ported vac activates and starts to pull more and more timing in the motor as velocity increases. So if you set you total timing to 34* at 3000RPM that's when the ported starts to do it's job and advances the the timing to the total stroke of the vacuum can arm, usually 12-18* (without Limiters) so now have your total of 34* PLUS the stroke of the Canister arm of say 16* net result=50* of total timing under hard acceleration and your motor WILL "Detonate". If you had a OBD1 computer it would pull that timing back to the 34* as all the sensors feed information to it.... and no detonation.
Now to Constant: At idle/part throttle cruise you have high vacuum, the carb is nearly closed causing a restriction which creates the high vacuum level. Under this light load condition and lean AF ratios the motor needs more timing to burn the fuel (Lean Mixtures take Longer to Burn than rich mixtures) so you need more timing at idle and cruise to burn the fuel correctly and completely. When you stomp the throttle you have NO manifold Vacuum so you have NO vacuum timing and at NO time under high load will it ever advance more than the mechanical "All In" numbers. Stop pointing your finger at the carb for rich idle and top end lean conditions.. It's In Your Distributor Tuning! If your Buddy tells you to hook your Hot Rod distributor to Ported Vacuum, find a new friend because that guys advice is going to blow your crankshaft through the oil pan. Same goes for the guy who say's to disconnect it, they obviously have no idea of how it works or what it does or why we use it.
This not hear-say or an opinion its engineering, based on physics formulas, calculated by people who are a lot smarter than me and I know that so I do what they tell me. They come up with the numbers, we set them up accordingly.
Rule of Thumb: If the Motor Makes 8" of vacuum at Idle with 30* of timing in it then it needs a properly calibrated Vacuum Can, we have Mopar and GM vacuum cans that will read 7" of vacuum. most stock or aftermarket Vac cans will only read down to about 15", the odd one (1 out of 100) will read to 12"
We manufacture Mopar vac cans that will read to 7", our Lane Choice Gold Plated VC-1 BB or VC-1 SB
There's all sorts of unqualified guy's on the "Internet" and so called "engine builders" who will try and argue this point with me, I have given up trying to argue with these folks. They have no understanding how a vac can works or what it does, if they did they would realize how ridiculous they sound to us, Jim and I account for over 100 years experience with well over 10,000 happy customers.
Your "Engine builder" may be the best in the world but he's an Engine Builder and very seldom do they know anything about the fine tuning of the vacuum can or distributor mechanical advance system
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Bill Monk
Well-Known Member
This is what I was referring to. I can see where my statement on "max performance" was misleading. Sorry, couldn't remember the words used.
Dragon Slayer
Well-Known Member
There are some good articles on this on the web. With Vacuum disconnected you shoot for 32-36 BTDC at 2500 to 3000 RPM. IF you have a later distributor with 30 degrees mechanical adv you may only need 0 to 5 BTDC Initial. If you have an early distributor cam stop with only 15 to 16 degree mechanical advance then you have 12-15 initial advance. When looking at the Service manual this is the difference between non CAP and CAP cars.
As far as vacuum. It adds the additional value on the arm. Another 16- 20 degrees at CRUISE for a total of 50 plus total vacuum.
At Wide open throttle and heavy load (accelerating) engine vacuum goes down and Vacuum not a factor. Think Race car with no vacuum an running on 32-36 total advance. At cruise with high rpm but low load vacuum goes back up and more vacuum advance comes in driving total advance in to the 50s. Needed for better economy and to help burn the less dense fuel mixture under lower loads but high rpm.
Cam certainly changes dynamic from stock, but that is the theory. If you are getting pinging and detonation at cruise you need to lower your total vacuum advance to make it go away, assuming acceleration and wide open throttle is fine. If problems with wide open throttle too, maybe initial dialed back because mechanical is too much or some combo of mech and vacuum.
The alternative which performance guys do is to weld up the slot on the cam stop to reduce mechanical advance to a smaller number like 15deg and dial in more initial.
As far as vacuum. It adds the additional value on the arm. Another 16- 20 degrees at CRUISE for a total of 50 plus total vacuum.
At Wide open throttle and heavy load (accelerating) engine vacuum goes down and Vacuum not a factor. Think Race car with no vacuum an running on 32-36 total advance. At cruise with high rpm but low load vacuum goes back up and more vacuum advance comes in driving total advance in to the 50s. Needed for better economy and to help burn the less dense fuel mixture under lower loads but high rpm.
Cam certainly changes dynamic from stock, but that is the theory. If you are getting pinging and detonation at cruise you need to lower your total vacuum advance to make it go away, assuming acceleration and wide open throttle is fine. If problems with wide open throttle too, maybe initial dialed back because mechanical is too much or some combo of mech and vacuum.
The alternative which performance guys do is to weld up the slot on the cam stop to reduce mechanical advance to a smaller number like 15deg and dial in more initial.
Bill Monk
Well-Known Member
Just posted an article by Don Gould from 4secondsflat on this thread, emission concerns stated well before 1972 but got worse through the 70s
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While everyone is busy having the usual discussion/debate here, we're losing the point of this thread to begin with methinks...
or at the very least, we're confusing the hell out of the guy.
Hey junkpile! You still with us here?
or at the very least, we're confusing the hell out of the guy.
Hey junkpile! You still with us here?
Dragon Slayer
Well-Known Member
It is all relevant. A good read is the 1967 Chrysler Master Training files that are on several websites. Carb section, emission section, and the CAP section. At least that tells you what a stock motor does and how mechanical advance which is RPM based advance, and the Vacuum Canister which is LOAD based advance and retard was designed to work. Some of the posted stuff above is the GM theory and not how the mopar vacuum advance worked especially for the Performance year CAP and Non Cap cars. Lets say 64-71, and using ported vacuum. Which acted like a vacuum on and off switch more than what is described by the other articles. Look at original carter carbs and the vacuum port is RIGHT at the idle blade when closed. When off idle the port is below blade very quickly. Not like it is 1/2" above the blade.
For the original poster at half throttle cruise you have full mechanical advance most likely and full vacuum advance as needed. So your about your 50 total. When you stomp on it from that position and you are detonating it sounds like your vacuum advance is not retarding quick enough and you have too much advance for WOT Full load where you should be around the 34-36 Total number. Or your fuel is bad, not enough octane, or some other aspect of the build is causing the pinging. Including Fuel mixture at the point. If your cruising at low RPM and stomp on it does it still ping?
The theory on why guys use manifold for big cam cars is that they can not get a good idle at the Initial timing needed to be able to start reliably. By adding vacuum advance at idle they can get better idle without sacrificing good starting. But everything needs to be tuned together so that mechanical does not come in too fast while vacuum still on or they will also get detonation at WOT. Or they pick a cannister that limits the max added advance to a smaller number.
But this all varies depending on motor build, how the carb works at the full range of RPM (actual A/F Ratio changes) and how the dizzy is set up.
For the original poster at half throttle cruise you have full mechanical advance most likely and full vacuum advance as needed. So your about your 50 total. When you stomp on it from that position and you are detonating it sounds like your vacuum advance is not retarding quick enough and you have too much advance for WOT Full load where you should be around the 34-36 Total number. Or your fuel is bad, not enough octane, or some other aspect of the build is causing the pinging. Including Fuel mixture at the point. If your cruising at low RPM and stomp on it does it still ping?
The theory on why guys use manifold for big cam cars is that they can not get a good idle at the Initial timing needed to be able to start reliably. By adding vacuum advance at idle they can get better idle without sacrificing good starting. But everything needs to be tuned together so that mechanical does not come in too fast while vacuum still on or they will also get detonation at WOT. Or they pick a cannister that limits the max added advance to a smaller number.
But this all varies depending on motor build, how the carb works at the full range of RPM (actual A/F Ratio changes) and how the dizzy is set up.
Bicylindrico
Well-Known Member
Just wanted to say you will NEVER get a factory spec vacuum canister to work with a lumpy camshaft engine like we all typically run. It will need to be tuned with all of the other parts you installed. Maybe that's why people have so much trouble with vacuum advance. I think it's just easier for most to go with the no vacuum advance "race" distributor as it's all the same at wide open throttle.
Dibbons
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This is what my Pertronix small block distributor #791820 has per email from the manufacturer:
Pertronix vacuum advance
16 degrees total
begins @ 7 inhg
all in @ 14 inhg
Pertronix vacuum advance
16 degrees total
begins @ 7 inhg
all in @ 14 inhg
2quick
Well-Known Member
Or just install a MSD Programmable Box and lock out your distributor. Set your total to what ever you can run and and pull timing from the base on the graph as needed. Way better then any other way of doing it. precise, consistent, and tune-able....
junkpile
Well-Known Member
O.K. guys thanks for all the advise, it has been an overload of information but helpful.
I have my timing set as of this past Saturday at 12 degrees initial, at 2500-2800 rpm I am at 33 with no vacuum hooked up and idel at between 90-1000 rpm. I reconnected the vacuum and I ran the car and got good take off with no bog at WOT and very little ping at all on pump gas. 104 booster took care of that. Ran great but did seem a little slower. Reset the the timing to 14 base (i had marked the disributor because it was set like this initially), did not read the upper this time, pinging at the slightest acceleration under load did just like before. disconnected advance and it was fine with more power. Tried moving timing to 18 but the car hates to idle there very rough weather vacuum is connected or not.
I am sure there is a way to get this motor to perform better but for now I can drive it and if I set the timing to 14 base without vacuum I can play a little harder. Here in Atlanta the heat will determine what happens next but i will have to wait till its spring.
I used to have a very heavy WOT bog, and it made pulling in traffic a nightmare but now it seems to be acting like a normal car. then the timing was at 10 initial, so I am slowly creeping up on the correct set point. I still would like to try the firecore distributor for adjustability. but are there any other tweaks to get a little more out of it without the ping? or would that take a new dizzy or timing curve adjustment to my present set up.
thanks again everyone, you had me in the garage playing, and learning new things and staying away from the honey do lists. Best Weekend in years.
I have my timing set as of this past Saturday at 12 degrees initial, at 2500-2800 rpm I am at 33 with no vacuum hooked up and idel at between 90-1000 rpm. I reconnected the vacuum and I ran the car and got good take off with no bog at WOT and very little ping at all on pump gas. 104 booster took care of that. Ran great but did seem a little slower. Reset the the timing to 14 base (i had marked the disributor because it was set like this initially), did not read the upper this time, pinging at the slightest acceleration under load did just like before. disconnected advance and it was fine with more power. Tried moving timing to 18 but the car hates to idle there very rough weather vacuum is connected or not.
I am sure there is a way to get this motor to perform better but for now I can drive it and if I set the timing to 14 base without vacuum I can play a little harder. Here in Atlanta the heat will determine what happens next but i will have to wait till its spring.
I used to have a very heavy WOT bog, and it made pulling in traffic a nightmare but now it seems to be acting like a normal car. then the timing was at 10 initial, so I am slowly creeping up on the correct set point. I still would like to try the firecore distributor for adjustability. but are there any other tweaks to get a little more out of it without the ping? or would that take a new dizzy or timing curve adjustment to my present set up.
thanks again everyone, you had me in the garage playing, and learning new things and staying away from the honey do lists. Best Weekend in years.
Derwud
Well-Known Member
No, someone that tells you to dial in 50 degrees of total timing does not need to be your friend.. The guy that sits and helps you dial in your car so you can enjoy it, is the guy you wanna call friend..
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