Vacuum Advance and why to use it on the street

[Plowman]

I didn't want to post things on a for sale thread, and got some help from my son just to get the ball rolling. I appologize for giving a negative spin on the NOS vac advance.

Surprisingly, there were several on that thread who did not seem to understand the relationship the VA has on an engine with today's pump gas.

There is actually a fellow who writes a decent explnation at this link:
http://www.kitcarmag.com/techarticles/0809kc_tuning_carbureted_kit_car_engine/ignition_timing.html


Quoted from that link "Any original or high-performance aftermarket replacement distributor must have the ignition spark advance curve(s) tuned for your engine and the gasoline you will be using. Most of the high-performance replacement ignition systems, such as an MSD distributor, come with a very conservative ignition advance curve installed in the distributor. A new MSD distributor comes with a selection of advance springs and bushings so you can set the advance curve you want. However, most vacuum-advance-equipped distributors have too much advance for the reformulated gasoline of today."

Locked out distributors and too much VA at idle contribute to overheating (glowing red) pistons rings and premature blow-by. Yes you can drive it, but is not ideal.

Hopefully we get some good posts and comments here, and with some patience I'll try to share my understanding and techniques to get ideal street tunes on todays fuels. We could all learns from a decent thread- myself included.

[Salvatore]

have a stock distributor in my Z/28. Has been curved and VA locked out. Never had pre-ignition, pinging or glowing headers. Run 12 degrees at idle and around 36 at 2,800 rpm's. I run 112 Sunoco mixed with 93 BUT really don't need it. Ran 93 octane for about 10 years with a lead additive but that is not the reason I run the 112 mix now. Kinda run my carb on the rich side if that matters. Its more of a winter setup which IMO is a little safer but that could be old style thinking. Thanks for posting Paul.

[Keith Tedford]

The original factory advance setup in 1969 wasn't even for performance. It was to pass emissions tests. Our 427 came with #68 primary jets and had lean surge at sixty mph. The advance curve was long and slow, not coming in full until about 5K rpm. I forget the exact number any more but I bumped up the initial timing and played with various springs and weights. The difference in performance was impressive. That was when we could get 104 octane gas. With the 91 octane today you can't run nearly as much total advance. I had our L78 running reasonably well but it sure wasn't running original factory specs in the distributor. It will run but not all that well.

[Hemicolt]

There is so much that is being left out here.
Compression ratio and camshaft specs. play a huge part in how much pressure and heat are in a cylinder. Anyone who has looked into camshaft design knows timing events and overlap in a cylinder cycle will determine pressure bleed off.
My engine has thousands and thousands of miles on it. No melted plugs, ever.
Every year I pull the rocker arms to check wear. While doing this I always do a leak down test and have never found any problem in the ring and cylinder package. Engine has no blow by and uses no oil.
This year as well as every year in the past, since the car has been built, I will drive this car in heavy traffic and enjoy not having to pull over due to over heating.
To say that every motor needs a V.A. and can not run a locked out dist., due to todays fuels, shows you may need to play catch up. Contact Patrick James at Pro Systems, if you would like to check my information.

[VintageMusclecar]

My 496 uses a OE distributor with a 22° mechanical advance curve which is all in by <4000 rpm. I run 12°-14° initial and 34°-36° total advance, and with ~11.2-1 compression it runs fine on 93 octane gas. (I also run a 160° thermostat to help ward off detonation)

When I had the distributor curve set, we installed a vacuum advance can which provided very little advance--if memory serves, only around 8°-10° degrees since I knew I would have to keep the total advance limited to be able to run pump fuel.

I have tried hooking up the vacuum advance several times since I got the car running, and every time, simply hooking the hose up literally renders the car un-driveable. Running mechanical advance only, even with a 256°-264° @ .050&quot; cam and 108° LSA, the engine will pull down just fine to &lt;1500 rpm in 4th gear with only an occasional minor hiccup--by 1600 rpm it is totally smooth. Hook up the vacuum advance and it instantly becomes a bucking, snorting Bronco Bull ride from hell. No doubts here, this combination does <span style="text-decoration: underline">not</span> want, or need vacuum advance.

As far as super quick advance curves and/or locked out advance curves;

Years ago I had a 75 Monza with a nice running 400 small block in it....very mild build, never saw the high side of 5500 rpm. It had an HEI distributor with an aftermarket curve kit installed, and I originally had it set up with the medium weight springs which provided a similar curve to what I now run in my Chevelle.

I tried experimenting with the advance springs one day, and simply swapping the medium weight springs for the light springs resulted in a full .4 loss in e.t. At first I thought it was a fluke--there was no tire spin and my butt-dyno was telling me the engine was <span style="font-style: italic">FAR</span> more responsive at lower rpm. I made another run--again, it was .4 off. I stuck the medium weights back in and the .4 immediately came back.

Again, that combination simply did <span style="text-decoration: underline">not</span> like a fast advance curve--despite what my butt-dyno was telling me.

In regards to locking out the curve entirely, one of the more well-known and respected members here tried that recently with less than stellar results. I'll leave it up to them should they wish to divulge the details. I personally have used a locked out distributor one time with successful results, and that was on my old ~800 HP 572 in my last Chevelle. (Of course, the 4K+ converter probably hid whatever low speed driveability issues that may have been present)

I'm <span style="font-weight: bold"><span style="text-decoration: underline">not</span></span> saying there is <span style="text-decoration: underline">never</span> a time or place for either a locked out distributor or an aggressive curve. What I <span style="text-decoration: underline">am</span> saying is that it is entirely dependent on the combination.

My $.02 worth of real world experience. <<GRAEMLIN_URL>>/smile.gif

[Hemicolt]

&quot;I'm not saying there is never a time or place for either a locked out distributor or an aggressive curve. What I am saying is that it is entirely dependent on the combination.

My $.02 worth of real world experience.&quot;


Very well put. A little knowledge can be a dangerous thing. These blanket statements saying that &quot;one rule applies&quot; is the wrong thing to be telling people.

It's like the carb. trick he told me about using on the tunnel ram setup. I can't argue if adding the wire to the metering plate will or will not work when it comes to cutting down the fuel at idle.
We will however try this when we run the engine on the dyno. Before and after results will be recorded and I will report the findings for everyone to see. The reason I will try it both ways is because of what was said above. Every combination will require different things.
I'm still thinking the amount of of vac. at idle is going to determine how much fuel is pulled through the idle circut. I may be wrong in the end, but I'm not going to tell everyone you can or can't before trying it first.

To go in and blindly make the modification without testing it both ways is foolish.

[WILMASBOYL78]

I will certainly bow <<GRAEMLIN_URL>>/worship.gif to the experts and can only offer my &quot;real life&quot; experience. We have a number of L78 Novas which are street driven and one which is occasionally run in the 1/4. They all have factory points distributors...we run vacuum advance on all of them. The engines all have the factory L78 cam, 11 to 1 pistons, big heads, etc..basically stock L78 motors...nothing tricky. For fuel we run a mix of AV Gas or race fuel mixed with 93 pump gas...no issues. Only one of the L78 cars has a &quot;curved&quot; distibutor...our black 1970 TH400. I have never tried running the cars without the vacuum advance...never saw the need to. Most of the factory BB solid lifter motors (68-70) had the #355 unit which had 15* advance..this is the vacuum unit that is in all of our stock distributors.

Again...my info is directly related to driving these cars for many years and knowing how they run. I can't comment on how other people's cars run or perform...only my own. I maintain that &quot;fuel alone&quot; does not determine the results related to vacuum advance or the lack of it...there are many factors that impact performance and tuning.. and each situation is a little different.

wilma <<GRAEMLIN_URL>>/3gears.gif

[Salvatore]

Tom, did you write that on your own or was someone there coaching you?

[PxTx]

There really is a lot to seting upa a VA tune one an old engine with todays gas. Unfortunately, implying hooking it up and saying it doesn't work because isn't the real world things ran poorly isn't a very fair evaluation.

Sam, It seems like you tune is pretty safe. I would not be afraid of running that in the street. What is the reason you choose not to run a VA?

Keith, you are right about the factory tune and configs. They aren not ideal for performance and certainly were not intended for life today. Part of this thred could evolve in to how to tune and old engine for great performance and street manners with todays fuels.

One of the challenges can be that todays unleaded reformulated gasoline is that it is designed for use in a modern computer controlled electronic fuel injected engine with the goal of lowest possible exhaust emissions. The computer that operates with a modern fuel injected engine automatically adjusts the air/fuel mixture and the ignition spark timing in order to obtain the lowest possible exhaust emissions along with the best possible power and drivability.

The leaded gasoline that was sold at your corner gas station until the mid 1970’s was easier to tune for because a tuner could “read” the spark plugs and look at the tailpipe “color” to determine the air/fuel mixture. Today’s reformulated gasoline does not leave any “color” on the spark plug unless the air/mixture is very rich and the tail pipe color is almost meaningless. Most people think their engine is running too rich because the exhaust fumes burn their eyes; this is not true. An engine with a rich air/fuel mixture will have excessive carbon monoxide (CO) in the exhaust; carbon monoxide is an odorless gas that is quite deadly if you breathe too much of it. A engine that has a misfire from things such as: a rich air/fuel mixture, a lean air/fuel mixture or incorrect ignition spark timing will have a lot of unburned hydrocarbons (HC) in the exhaust. Exhaust gas with a high unburned hydrocarbon (HC) content will burn your eyes and make it difficult to breathe

Tracy, I say a lot is being left out, so let's fill in the spaces. If you can, help us oout and get your guy Pat to post here, or maybe try your best to post things he has written in context? Also, since you enjoy the car in heavy traffic, why did you choose to lock your distributor? One last question, what are your leakdown results and what is your threshold of &quot;good&quot; for a street driven motor wiht thousands of miles on it?


Eric, the way you wrote your, it almost sounded like you were talking about hooking the intake to ported vacuum, not manifold vacuum. I hope you don't take this the wrong way- more saying this for the sake of those reading. Ported Vac= emissions cars (with EGR) and Manifold Vac= muscle cars. There are some people who do not follow this but they appear to be trying to use a &quot;custom tune&quot; for help with stock type tire drag racing and probably shouldn't be mixed in here as that could be a great seperate thread.

Tom, I know everyone hates blanket statements, but 15 degrees VA is too much for todays fuels. We've done some great, non-stock tunes wich would pass for stock drivability that work great on todays fuels.

I'm not expert here either, and I've copied and pasted some things above from post my Dad has made and form the Henry Olsen. I have been setting up cars for about 20 years and there are still things I continue to learn from my Dad. Maybe someone else can shed some light on the how and why things are done in their tune for us all to benefit from. Looking forward to the technical discussion.

[Keith Tedford]

When we bought our L78 car in '98, we could still get Ultra 94 and similar. Now, all I seem to find is 91 and the engine would ping. I could back off the timing until the engine stopped pinging but then there wasn't enough timing on the bottom end which can lead to over heating. That's where shortening up the advance curve came into play. You have to figure out where your engine works best on the bottom end. Then figure out where it works best in the upper end rpm for advance. Then tailor the distributor to suit. In my own clumsy dumb ass way I have managed to get close to 200K miles out of the 427 and have run the L78 on unleaded for about 37K miles with zero problems. Running a little rich on the jetting also seems to help with the pinging. If I can have my cars running fine, it can't be all that difficult, yet I'm always reading stories of red hot headers, melted pistons, over heating and engines detonated to death. There are vacuum canisters out there with different amounts of advance. Pick a suitable one. If not get an adjustable unit.

[WILMASBOYL78]

<span style="font-style: italic">&quot;Tom, I know everyone hates blanket statements, but 15 degrees VA is too much for todays fuels.&quot;</span>

Totally agree...but, as I stated, we are running a mix..typically 50% Av gas or 112 with some 93...I also throw in some lead additive..and a little Marvel oil for good measure. I've tried the octane boosters, but I think the mix is the best solution...

Now..to my Italian friend from Santorum Land...

<span style="font-style: italic">&quot;Tom, did you write that on your own or was someone there coaching you?&quot;</span>

Yes...all on my own Sammy...but, when I'm really stuck I check with Cumby..at his age he has to know everything <<GRAEMLIN_URL>>/rolleyes.gif

I'm glad it's Friday...wilma

ps..we got snow last nite

[PxTx]

It can be tough to tell when an engine is pinging. It isn't always audible. Pinging on throttle can be bad enough to be heard but not always. I'm sure many know this, but I figured it is worth mentioning. My point is that you can have a car that is beleive to be in a good state of tune, but pining is occuting. Just because it is being driven and seems to have good power does not mean there is not room for improvment.

I didn't want it to be overlooked that pinging can also occur off throttle when the VA is too much. That is why it is best to limit the VA to 10 degrees on cars with a &quot;Hot&quot; camshaft. I'll qualify a &quot;Hot&quot; camshaft as being over220 degrees @ 0.050. These will like more initial advance and less mecahnical for a total of 32-36 degrees. Running the stock L78 VA with todays fuel can cause pinging off throttle and may not be audible.

Just to clarify Keith, these adjustable VA canisters you are refering to do not adjust the # of degrees, correct?

I would say the majority of the cars we discuss here are best served with a VA with no more than 10 degrees of advance when run on todays fuel. We can discuss the rest of the tune, but that is a key component for optimizing these cars for street duty with as little performance sacrifice as possible.

[VintageMusclecar]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pxtx</div><div class="ubbcode-body">...
Eric, the way you wrote your, it almost sounded like you were talking about hooking the intake to ported vacuum, not manifold vacuum. I hope you don't take this the wrong way- more saying this for the sake of those reading. Ported Vac= emissions cars (with EGR) and Manifold Vac= muscle cars. There are some people who do not follow this but they appear to be trying to use a &quot;custom tune&quot; for help with stock type tire drag racing and probably shouldn't be mixed in here as that could be a great seperate thread....</div></div>

Tried it both ways, ported and manifold, no difference either way...still un-driveable.

I have my own theories why this (and several similar builds I've been involved on) exhibited similar &quot;symptoms&quot;. Maybe I'm right, maybe I'm out to lunch, all I know is I've found methods that consistently work for me. Your mileage may vary (pun somewhat intended <<GRAEMLIN_URL>>/wink.gif ).

Engines with limited low rpm vacuum (read: big cams) seem to be extremely sensitive to the (often drastic) timing changes that can result from the vacuum advance system. Just changing the base timing from 12° to 14° on my current 496 results in ~100 rpm gain in idle speed and requires re-setting the idle trim screws on the carb. If 2° has that pronounced of an effect, imagine what a wildly-swinging timing curve does as the vacuum advance adds and removes timing as the engine begins surging. Mechanical advance isn't affected by vacuum, only rpm, and as such eliminates that variable.

Besides, the car can blow the tires off pretty much at will in the first 3 gears as it sits now...how much more low end does it &quot;need&quot;? lol. <<GRAEMLIN_URL>>/grin.gif

Going slightly off-topic but along the subject of variables on differing combinations, here's a little something to ponder over...

The 3418 Holley on my 496 was pig fat rich across the board in stock configuration on this engine and required significant recalibration. I pulled 3 jet sizes out of it on the dyno and picked up significant power (and it was still rich, I just ran out of dyno time to do further tuning). Once the engine was in the car I found out that it also needed a ton of fuel pulled out of the idle/transition circuits to be happy.

That said, I built another 3418 for a car that belongs to a member here with a stock L78, and aside from dropping the jetting down several sizes, it runs tip top for them.

Again, to reiterate... every combination is different, there is no &quot;right&quot; or &quot;wrong&quot; way to approach the tune under <span style="font-weight: bold"><span style="text-decoration: underline">all</span></span> circumstances. You have to experiment to see what does (and doesn't!) work. <<GRAEMLIN_URL>>/smile.gif

[Tommy]

My last smallblock acted the same as Erics when I attempted to use the VA. Locked out it ran wonderful. For the last several years I have not used any VA on my engines and most of my Dizzy's (dual points) don't even have a Va canister option. The MSD unit I have is the only one with a canister on it and it absolutely did not want to co-operate with me. Totally undrivable. If I knew it was beneficial and might prohibit a melt down and could make it work I would try it but so far it hasn't resulted in any issues not using it. I hammered it up and down the interstates from Alabama to Kentucky and the Smokey Mtns for hours at a time and never worried about a thing. Hook up the va and it won't pull a greasy string....

Tommy <<GRAEMLIN_URL>>/3gears.gif

[PxTx]

Tommy, I hear what you are saying and I've heard it said before. My expereince is that the problem typically isn't a VA problem, but a tune that is less than ideal and done without consideration for the VA benefits. I would not expect your &quot;perfect&quot; tune to run better simpy by &quot;hooking-u&quot; the VA. As you can tell, I really beleive it in as being a crutial component to engine managment and long term engine health.

Just so I can qualify some of these conditions that it doesn't seem to work well on, can anyone validate the following items?

Engine type:

Cam lift and duration @0.050

Number of degrees the VA canister is pulling (should use a dial back timing light to verify, but I undestand if you are only using the stamped # to id the amount of VA)

Vacuum source:- manifold or ported

Initial timing

Mech advance timing

Total advance @ 3000 RPM

There is no argument here that every engine and combo is different. There can still be a common approach to dial in the best street friendly tune with todays pump gas.

The VA tune we are recommending really helps in off throttle conditions. You may be surprised at how similar the different engines with &quot;hot&quot; cams can act in off throttle conditions.

[Hemicolt]

Tracy, I say a lot is being left out, so let's fill in the spaces. If you can, help us oout and get your guy Pat to post here, or maybe try your best to post things he has written in context? Also, since you enjoy the car in heavy traffic, why did you choose to lock your distributor? One last question, what are your leakdown results and what is your threshold of &quot;good&quot; for a street driven motor wiht thousands of miles on it?


Patrick James owns a company called Pro Systems. He builds carbs. and tunes Pro Stock programs as well as other high end race vehicles. Getting him to find time to post on this forum is more than likely not going to happen.
I do not float around the internet looking for things to copy and paste to help support my point of view. I can only give you examples by real experience. That being said everything I posted about what I have done to tune my engine came straight from Patrick James while I was on the phone with him. His phone number is 727-490-5717. He is a super nice guy who has always had the time to help his customers.
Another person that I place faith in is a man named Kirk Jager. If you would like to figure out the mind that this man has, please look at his work with connecting rods. http://www.google.com/patents/US20040107794
I will admit, I copied and pasted this link so you can know who this guy is. He is a much better tuner than he is a machinist, IMO.
Now, the reason I mentioned all that about these two people is because I was having a problem that sounds quite similar to the one some of the other guys have posted on here. The engine would not run properly with mech. advance in place. Some of the problem was fuel lighting in the pipes. This caused temps in the motor to rise and caused overheating, poor drivability, etc. Playing with different timing curves did nothing to help my problem. Based on Patrick telling me to lock out the dist., I went that route. Kirk backed up what he told me, telling me you can't tune these engines like any run of the mill stocker. He told me that there wasn't enough timing at low rpm to burn the air/fuel package. By locking out the dist. and having 32 degrees timing at low rpm, my problems went away. The engine smoothed out and stopped overheating. Retarded timing can cause fuel to light on the exhaust stroke, therefore you will have glowing pipes.
This is why I enjoy my car in heavy traffic. I don't like overheating, pinging. If you think advanced timing is the only thing that can cause those problems, I would suggest building a high h.p., big cubic inch motor and make it live on the street with your tune up theories. A 4.500 bore size with a rod length of almost 7.00 will pull a ton of fuel and air into a cyl. The longer rod causes the piston to dwell at t.d.c for a longer time, giving the piston more time to pull all it can in. This is why your information will not apply to my motor, and my information may not work for you. But on this subject, you will never me ever saying: My way is the only way, and neither should anyone else.


Leakdown has never showed more than .5 to 1 percent and that was only on two cylinders at the valve side. A quick touch on the seats took care of that problem and it's been 100 percent tight every since.
The only reason I did that was because the motor developed an oil leak at the pan and I had to pull the motor to fix it. Pulled the head, fixed the seats and put it on the dyno again while I had it out. EGT's and AFR's were spot on with the dist. locked out at 32 degrees.
If you have anymore questions, I will be more than happy to answer them.

Tracy

[PxTx]

I decided to &quot;float around&quot; and see what I could find about PJ recommending locking out distributors and other timing recommendations. My impressions are that he probably can build a great carb for pure racing applications, but his idea of a street friendly tune just don't make much sense to me.

I've found that he even feels here should be no vacuum advance on old street driven 13 second Buicks, as seen here: http://www.v8buick.com/showthread.php?89820

There was another thread I found where he seemed to continuously beat the locked dizzy drum. The fellow tuning the car felt it was a crutch and stuck with his own approach to find a more street friendly solution. If you care to read- http://www.camaros.net/forums/showthread.php?t=153448

I can appreciate that a performance engine can't be tuned like a stocker, and that is part of the reason I thought this thread has relevance. I know there are better ways to tune performance street engines running pump gas than deleting the VA and locking distributors.

Now Tracy, it kinda seems like there is a bit of an edge to the way you've responded here. Why do you think I haven't built any high h.p., big inch motors and tuned them for he street?

There are several ways to tune and engine for the street. Modern electronics offer plenty of options. What has begun with my Dad's post and my follow-up is that you can achieve great results with modifications to the basic items which were stock on these cars to begin with. I can't see how eliminating the VA and locking the distributor provides a better tune. Help me understand how it does.

Kudos to you on your cylinder leak down results! That is better than many racing engines and something I would never have expected from any street engine. You've got to be doing something right to get those numbers.

[Hemicolt]

This is getting old. As far as helping you understand why I don't run a VA on my Chevelle, all I can do is tell you to go back again and read my last post. I explained it very well. There is no other way I can explain it to you. The facts are the facts. I can't add anything more, because there is nothing to add.
As far as it seeming like there is a bit of an &quot;edge&quot; about the way I've responded, let's look at what you have assumed. You say &quot;why do I think you haven't built any high h.p., big cubic inch motors&quot;?
The reason I said that is because of how you are responding. You keep saying, &quot;help me understand&quot;. If you can't understand it, then I can only think you have never done it.
Let's look at the things you have assumed. I'll use Eric as an example and not only myself. We explained ( in detail ), why your way didn't work. But you have still assumed he and I are wrong.
He is not wrong. I am not wrong. My deal works and works great. I'm making over 700 h.p. with stock LS6 heads and I can drive it. It's dependable, it doesn't melt parts, it doesn't over heat. I get great gas mileage considering what it is. Let it go.
I don't think you are wanting to learn anything. I think you guys are only wanting to prove you are right and everyone else needs to learn from you. Again, you are wrong.
You are trying to poke holes in Patrick James. What did I say? Did I say this / his method would work for everyone? No, I didn't. You point out a guy who said his idea was a crutch. If I wasn't going to try someones advise, I wouldn't ask them. Does his idea work on old 13 second Buicks? I don't know, I have never tried it. But for me to sit back and say he is dead wrong.....I can't. But I won't say he is right either. And I don't think I have said you are 100% wrong as far as a VA not being needed on ANYTHING.
There is nothing wrong here other than you not wanting to accept that someone else may have something that works contrary to what you think is the only way.
I can post a very strong argument that could possibly disprove your dads idea on putting the wire in the metering plate for a T.R. setup. This argument would be based on how an engine draws fuel from a carb.
However, I will not do this because I have not tried his idea, and I will not point to, &quot;I have been doing this for 20 years and I know more than you do&quot;.
It may very well be one of the best tune tricks I have ever seen. If it works, I will be the first one to step up and say, well done. If it doesn't, I will explain why it didn't work for me. I will not say, it doesn't work period.

Also, you say: &quot;My impressions are that he probably can build a great carb for pure racing applications, but his idea of a street friendly tune just don't make much sense to me.&quot;
I have one of his carbs, a 1100 4500 on my engine. Great carb. for my STREET motor. Not pure race.
If youy want to learn how to get perfect engine seal. Look into internal coatings.

[PxTx]

Hey man, Im trying to learn or at least figure out the problems you were having. I can see from your perspective that you got some guy who you don't know all that well challenging your ego. So I kinda get the punchy responses.

From where I stand, I'm trying to see where you (or anybody else) were with the VA and MA tune before you decided to abandon that approach. I've re-read the posts, and despite you saying the facts are there- I still don't have answers to the questions below. Those facts would help me understand. And you know what- I'm fine with it if people didn't verify that data while attempting to make it work.

I'm sorry if you think I'm one of those guys who needs to be right here. Hopefully you've been searching the old posts for lots of your Day 2 info. I've posted in many of those threads over the last 10 years. I think you've got me all wrong today. I believe you are driving your car on the street this way and it clearly bothers you that I feel a locked distributor and no VA is a poor approach for a street car but I'm glad you are enjoying your car on the street.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pxtx</div><div class="ubbcode-body">...

Just so I can qualify some of these conditions that it doesn't seem to work well on, can anyone validate the following items?

Engine type:

Cam lift and duration @0.050

Number of degrees the VA canister is pulling (should use a dial back timing light to verify, but I undestand if you are only using the stamped # to id the amount of VA)

Vacuum source:- manifold or ported

Initial timing

Mech advance timing

Total advance @ 3000 RPM

...</div></div>

[Hemicolt]

Challenged ego? Let's take a look at one of the biggest ego statements I have seen on this forum. It comes from Plowman:

&quot;Do not have time to teach if you don't have the knowledge.&quot;

That was directed at Tom when he disagreed with something Plowman said, that mind you, had nothing to do with the subject where Plowman said it. SuperNovaSS was trying to sell a dist., when he pipes in with one of his random statements that has nothing to do with the subject at hand. That's ego.
Also, ego is you pulling two threads from the internet that disagreed with Patrick James, just so you can try to make an argument that he doesn't know what he is talking about. That's all you have done since the start of all this. Try to make an argument that everyone who has disagreed with you must either be doing something wrong, or they just don't know what they are talking about.
Look at the name of this thread for goodness sake: &quot;Vacuum Advance and why to use it on the street&quot; That's a statement saying,&quot;this is the only way, case closed&quot;.
And again, here you are pointing to your resume of how long you have been doing something. &quot;I've posted in many of those threads over the last 10 years.&quot; If you can't hear yourself, that's ego talking.
I do believe I have asked way more questions on here than anything else. I've asked you, Dave and whomever many questions and valued your opinions. If I have an ego problem, I wouldn't admit to not knowing something.
Now, if you really are wanting to learn something and can't understand what I have told you, prove it. You have yet to address anything specific I have posted on the tech. side of things. Please go back and look at how I explained I had fuel lighting in the pipes. Look at how I explained about bore size, rod length, etc., and tell me exactly what part of that you don't understand. If you can't do that, then drop it and move on. Let it go.

[PxTx]

Just so I understand fuel lighting in the pipes, is that a misfire?

Also how was the timing configured at this time?

[Hemicolt]

Okay. Fuel lighting in the pipes means low or retarded timing. Fuel is pulled in on the intake stroke, compressed on the compression stroke. At this time the plug fires and pushes the piston back down into the cyl., then everything is pushed out of the exhaust valve on the up stroke. I know that you know this, but I'm illustrating. If everything is perfect, the above happens with no side affects.
Now, if timing is retarded the fuel lights late and depending on how much fuel and air are in the cyl., it can still be burning on the exhaust stroke. A 283 Chevy bore and stroke can't pull no where near as much fuel in as a 500 plus inch motor. Take into account .700 to .800 lift cams, etc. and your moving a ton of fuel and air. 10 to 12 degrees of initial isn't enough time to burn it all. Therefore you get fuel burning on the exhaust stroke. This burning fuel enters the exhaust pipes and you get real, glowing pipes. The fuel lighting in the pipes continues to make the engine temps. rise with each rev. of the motor. Pretty soon you get pinging, overheating, etc. You can back off the timing enough in a stoke motor to make the exhaust hotter than hell.
This problem was there with every type of timing advance system. It was burning down at 22 degrees initial. I locked out the dist., rolled the balancer to 32 b.t.d.c and installed the dist. dead on number 1. Every single problem went away.
A friend of mine has a turbo Mustang that ran 9.70's and he drove it on the street. It ran like crap when he first got it together. The pipes would glow so red hot, that you could take screw driver and push a dent into the hot spots. The thing was melting plugs at idle. He tried everything to fix the problem. I asked him to try locking out the dist. and put a bunch of timing in it. If I had not seen this with my own eyes I would not have believed it. 41 degrees of timing, made the thing run right and run cool. They drive the car all the time on the street and have 0 problems.
I hope this helps you to understand what I am saying here. You have to have enough TIME to burn everything that comes into the cyl. Can anyone make 10 to 12 degrees and a VA work on a big motor? I'll never say they can't. I'm just saying that more times than not, people have problems making that deal work.
Here is someting I sent you in the last p.m. that I think everyone can learn from. These are not my words. Enjoy:


I've been on this planet for four decades now. I've picked up on a lot of things and some of the best advice I've ever received, is &quot;sometimes it's better to believe what you see, not what you think&quot;.

Every weekend at racetracks across the country some of the best minds in the business just can't agree on which theory is correct to improve the performance of the vehicle in question. That's just the way it is, performance improvement is a constantly varying science. There are a lot of variables in any equation and if you read or take in information supplied by a source and the source in question is a &quot;been there done that&quot; type of person and you disagree with them....chances are you better keep it to yourself.

I've had customers, racers, engineers and even landscapers send me and offer me up a lot of pretty bizarre ideas and technologies that worked. I was talking to Bret Kepner's cameraman the other day and guess what? He had a good idea he was carrying around in his head. Yes, a cameraman. Not exactly a &quot;been there done that kind of guy&quot; in racing. But, if the late Smokey Yunick were to tell you that the cameraman's idea was correct, then you can bet Smokey tried it and it worked. Back to the quote: &quot;Sometimes it's better to believe what you see, not what you think&quot;.

In my spare time I race alcohol powered go-karts. &quot;It's 90 mph, seat of the pants, let it all hang out stress relief&quot;. I even have a dynamometer in the shop to dyno test my single cylinder wonders. These single cylinder engines, originally designed to spin 2800 rpm now spin in excess of 7500 rpm. But the really great thing I discovered while testing them, is the repeatability of the engine from pull to pull. Yes, you guessed it, what a great engine for testing theories. I've logged more hours dynoing those engines with different fuels and atomization patterns, booster concepts and fuel air calculations than I have racing them. Now I know why the octane ratings RON/MON numbers are derived from a single cylinder engine. I've developed some technologies that made great power on the dyno but were slower on the racetrack and vice versa. Yes, I have a full data acquisition system with track mapping on my kart so I can measure rates of acceleration etc...yes I plug a laptop into my kart after every race. It looks silly but that's racing these days. The bottom line is, if you're standing around the racetrack scratching your head and some old timer or even a local kid that's never touched a car before tells you &quot;I saw that one time and here's what worked for this guy&quot;. Listen to him, because sometimes a voice of experience is more valuable than a voice of theory based assumption.

[PxTx]

Just to clarify, every type of timing advance system you mean just MA and VA, right? How much MA did you have and how much VA did you have? What about the springs and weights on the MA?

I hear your plea to be open mined. I struggle with the fact that you have 1 single static timing on a street engine and I am expected to understand that it is the best set-up for the street because you are driving it. I feel you are leaving a lot on the table as far as the quality of your tune, but the more you explain what configurations you had less success with- the better I'll be able to understand how you got to your static timing tune.

Engies are very dynamic and typically have different timing needs at idle, part throttle, WOT and off throttle deceleration. For those reasons I beleive in a dynamic ignition system is best for street driving.

Look at how many cells there are for timming maps on stand alone EFI systems which are used regularly for big inch, high HP engines driven on the street. From my perspective, static timing seems to be in the minority of conventional ignition tuning configurations.

[Hemicolt]

Started off with the MA MSD I have now. Tried every possible combo of springs and weights. Meaning different initial settings and different advance curves. No matter where we put it, nothing changed. Also tried a VA MSD as a last resort.
Had the same problem as Eric stated. It was undrivable no matter where you set the curve and pinging, glowing pipes, etc. was even worse.
I don't expect you to understand this is the best set-up for street driving. But it is the best set-up for this application.
Again, how am I leaving alot on the table as far as quality of the tune? Please be specific with your answer.
Great gas mileage, great idle quality, 13 inches of vac. at idle which equats into crisp throttle response. I can drive the thing all day long in heavy traffic and it doesn't overheat or load up. I can pull into a stop and let the car set for 5 min. or 1 hour. I put the key in the ignition and bump the switch and it fires every time without dragging or touching the throttle. In 4th gear pulling up a steep incline at speeds below 45 mph or so, no pinging, no power loss. I'm on my second set of plugs in 9 to 10 years.
This is a serious question: Please tell me, how can it get any better?

[PxTx]

It can get better because the way the load and conditions change on the street at various throttle amounts has never been best served wiht fixed ignition.

If you had a coil near plug setup like an LS motor and an electronic ignition map that you could tune- like with something similar to this:

http://www.msdignition.com/Products/Ignitions/Distributorless_Ignitions/Ignitions/6010_-_MSD_6LS_Ignition_Controller_for_LS1-LS6_(24_tooth_crank_trigger)_Engines.aspx

You could then dyno tune the car and really nail down a decent ignition tune.

I'm sorry i can't be more specific because I don't know where you were with the MSD distributor tunes. The certainly can be some challenges on what you are doing. Using box stock MSD distributors aren't really a great start. You probably had to change the MA busing to allow you to have more Intitial advance without being over timed with your total. Sometimes you want the total in by 3k but lightweight springs cause inconsistant timing so you have to stiffen up the springs and make the weights heavier.

Then there is the issue of the VA. What one did you start with? There are adjustable ones, but typically the timing amount isn't adjustable- only the Vacuum diaphram.

One thing to note is that GM supplies their 572 eninges with distributors that include MA. Admitedly, the 720 hp only has MA, but the 620hp even has a VA.

http://www.gmhorsepower.com/images/ZZ572-620.jpg

[Hemicolt]

So now I need to use coil packs and everything that goes with it so I can make it work like a LS motor with a carb.? Lmao.
I believe we are just about done here. How will this look with the chrome reverse wheels for that Day2 look? lol

On the crate motors you listed. The 620 horse has a VA dist. It also has a mild hyd. roller. Yes, those specs are on the mild side for a roller. Looks like they can get away with a VA on that setup. But that's not mine.
The 720 horse has less camshaft than I have and it also has alum. heads. An alum. head does not retain heat like a cast iron head. Again, not like mine. But, on that note. They do not have a VA dist. Hmmm.... wonder why?
I have 32 less cubic inches, no alum. heads but I still make 704 h.p. This is alot more than their 620 h.p. version and almost as much as there 720 h.p. version.
I have more camshaft than the 720 h.p., but have less cyl. head than their 620 h.p. Which goes back to my original statement about cyl. pressure and timing events in the camshaft.
Anyway. We are wasting our time here. You think what I have doesn't work and I know it does. I'm not going to change anything.

[Supergas990]

I don't have dog in this fight, but I understand what Hemicolt is saying. It makes sense and works very well, especially under specific circumstances.

On our 582ci race motor we ran our motor with the advance locked at 36 degrees. This thing was a beast 4.6 bore, 4 3/8 stroke, long rod BBC. Dart 360s and 14.5:1 compression (Motor makes 1,000hp straight up).

At first we had a handful to get it started without the engine kicking back. That was easily solved by adding a retard module for starting only. After getting it to fire, this motor needs the time I can give it to cleanly/completely burn all the fuel getting dumped into it.

Vacuum advance is nice for my 327 street motor, but when you're trying to burn an execessive amount of fuel you need to give the motor time to work.

Blair

[PxTx]

I get what you are Saying Blair. If you were to de-tune the engine for the street and have the varying loads associated with street driving, I beleive the VA is a better for over-all quality of the tune. Fixed timing is not good for all street conditions and not just starting.

[Plowman]

Why did GM make soo many different vacuum advances if they did not work. To save cash?And you know more than GM too.

[VintageMusclecar]

(At the risk of further stirring up a hornets nest...)

Why didn't GM use a functioning vacuum advance on the 1111295 and 1111927 L88 and ZL1 distributors?

[PxTx]

Great question Eric. Fogive me that I don't know what the factory timing specs were on these engines. Did they have any emissions controls? I suspect I know why the VA may not have been utilized, but I am such a Day 2 guy that I honestly don't know how these were in stock form. I'll be the 1st to admit that my tunes aren't always the most &quot;emissions compliant&quot; as the OE's are required.

[Plowman]

Don't have the time to teach?

[PxTx]

I dont' want this going the wrong way here. Let's keep it civil.

[VintageMusclecar]

For comparison's sake only, draw your own conclusions as you see fit.

Stats listed in distributor degrees and distributor rpm:

1111499 distributor:
0°-2.7° @ 500
3.2°-5.2° @ 625
8.5° @ 1000
16° @ 2500

Vacuum advance can # 1116201
0° @ 6&quot; vacuum
7.5&quot; @ 12&quot; vacuum
=============================

1111295 Distributor:
.5°-3.3° @ 700
6.7°-9.5° @ 930
13.5°-15.5° @ 2500
12.7°-15.5° @ 3000

Vacuum advance--locked out
=============================

1111927 Distributor:
.5°-3.3° @ 700
7.5°-9.5° @ 930
14.5° @ 2500 (max)

Vacuum advance--locked out.

I'm done here.

I'm not looking to win any arguments, I'm simply trying to provide useful info.

Take it for whatever it's worth to you.

[Plowman]

Useful info on today GAS with a hot camshafts...Vacuum advanve has to be limited. Useful info.