Vacuum Advance and why to use it on the street

[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 "sometimes it's better to believe what you see, not what you think".

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 "been there done that" 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 "been there done that kind of guy" 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: "Sometimes it's better to believe what you see, not what you think".

In my spare time I race alcohol powered go-karts. "It's 90 mph, seat of the pants, let it all hang out stress relief". 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 "I saw that one time and here's what worked for this guy". 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.

[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?