Vacuum Advance and why to use it on the street

[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 [img]<<GRAEMLIN_URL>>/rolleyes.gif[/img]

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 [img]<<GRAEMLIN_URL>>/wink.gif[/img] ).

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. [img]<<GRAEMLIN_URL>>/grin.gif[/img]

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. [img]<<GRAEMLIN_URL>>/smile.gif[/img]

[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 [img]<<GRAEMLIN_URL>>/[/img]

[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.