Anyone running locked out timing?

[84convertablegt]

Im sure this has been covered a bazillion times but when I searched, i couldnt find an answer. I was wondering what the pros and cons are to running without a vacuum advance and just running a locked out full advance all the time. I know alot of guys do this. What are the pros and cons to doing this. Im having some issues at low rpm's with measly power and then i get a big boost when the advance kicks in. My initial is set around 10-12 I believe last time I set it, i cant remember the total off hand, but its whatever a stock vacuum advance adds. Any help would be appreciated. Also, what is a good starting number for a locked out advance?

 

[84convertablegt]

anyone?

 

[fastback brian]

I run locked out timming. My 289 idles best around 1400-1500 rpms and thats just where most centifugal advances start to work and the engine doesnt make power till 6000 so advance curve really hasent ever helped. Im sure someone would have an special curve that would work for my 289 but the way it is now IT has a rock solid idle, crisp rev off idle and starts very easy thanks to the msd digital retard box. I havent had any other problems, but cant say if what I did would work for you.

 

[rbohm]

if you have a mild street car, dont even consider locking out the advance. you will have drivablility issues, including stumbling, poor fuel economy, hard starting, etc. if like brian you have a high rpm power producer though, then locking out the advance is acceptable.

 

[mfp4073]

I dont know. I ditched my vac advance with my MSD drop in distributor. It harmed me trying to use it (while tuning on a dyno) and have no drivablity problems either. I actually roughed up my idle my messing with my idle mixture and idle speed.

 

[stangonline]

What kind of carb are you running?

 

[84convertablegt]

What kind of carb are you running?

holley s.a. 670

 

[FORCED2DV8]

Several cars that I have built i ran locked out timing, You have to select the proper springs for the distributor to pull timing according to your engine setup.
I have had excellent street manners as well as power, It will not give you the same gas mileage as would running a vacum advance, But when your building a high performance engine, gas mileage isnt really the main concern. I use MSD dizzys usually, use 2 blue spings in the packet, then adjust your base timing for best results, this is just a starting point, but generally works well.

 

[1320stang]

I ran locked down on my race 289, but it was a race only deal. Ran a parts store rebuilt dizzy and a MSD 6AL.

 

[57fairlane]

I unfortunately had locked out timing in the falcon. It had always fallen on its face after 5500 but the dyno proved it. A rib on the underside of the rotor was actually stuck on a crappy weld on the shaft. Took down the spot the shaft and on the rib . . . Instant 15 rwhp through a c4.

So if you know what you are doing, have a more race-oriented motor, I guess you wouldn't have a problem. On my 6300 max RPM street car, I don't think its worth it. Especially when you have it locked out and you don't plan for it.

 

[Tim65GT]

You are talking about only the vacuum advance right?

I think some of the guys are talking about mechanical advance.

I'm not sure what you mean when you say:

... just running a locked out full advance all the time. I know alot of guys do this.

Locking out the vacuum advance is as simple as disconnecting the vacuum line on a non-adjustable type.

My understanding is that Vacuum advance helps you get better gas mileage and doesn't kick in at WOT anyway.

I have an Edelbrock intake and carb, and when I had an Accel distributor, the engine didn't like any vacuum advance and I had to adjust it all out. With the MSD I now have, it runs great with about half of the adjustment.

 

[SoCalCruising]

I run 16* initial and 20* mechanical with locked out vacuum. The motor likes it. When vacuum advance was used initially, I had too much overall advance. Yeah, gas mileage sucks.

 

[84convertablegt]

OK, maybe im ignorant here because im really used to an EFI car where all you have is initial advance and then computer advance. are you saying that on a stock 65 289 distributor that it has both mechanical and vacuum advance? I thought it only had vacuum advance. if it does have both then i am lost.

 

[rbohm]

OK, maybe im ignorant here because im really used to an EFI car where all you have is initial advance and then computer advance. are you saying that on a stock 65 289 distributor that it has both mechanical and vacuum advance? I thought it only had vacuum advance. if it does have both then i am lost.

yes the distributors from the late 50's on through to the mid 80's pretty much all had dual advance, both vacuum and mechanical. there are a few exceptions, like both my falcons were vacuum advance only, and hipo 289's, and boss 302's, and a few others were mechanical advance only.

 

[302 coupe]

yeah, you have mechanical and vacuum advance. Vacuum advance only works at cruise, it uses a full time vacuum source(nipple on intake or somewhere else downwind of the throttle blades) to increase advance. It only works at cruise and part throttle, because those are the only times there is enough vacuum in the intake. There are adjustable vacuum advance canisters that are used to adjust the advance rate. Vacuum advance serves to improve driveability and clean up emissions. When the engine is under load, also known as acceleration, the vacuum in the intake drops so low that the vacuum advance cannot function. In such situations, the advance falls back on the mechanical system, which is cotrolled by weights, springs, and centrifical force. More rpm=more advance(but there are limiting stops built into the base plate), softer springs allow full advance to come in at a lower rpm, and heavier weights will also allow it to advance quicker. Vacuum advance and mechanical advance are dynamic and continually change with engine load and rpm. With true "locked out" timing, the advance system(s) are disabled and the igntion advance is set static. If its set to 36* at 1000 rpm, it will be 36* at 6000 rpm. Locked out timing only serves a purpose on an all out race car. Your starter will not like having to spin over a hot engine while having to fight that kind of ignition lead. Most racers I know that use locked out timing have the starter and ignition system wired seperately. They hit the starter button, let it turn over a few times, then flip on the igntion, this technique will reduce strain on the starter, but again it isn't very practical on a street car.

 

[jerry S]

Most racers I know that use locked out timing have the starter and ignition system wired seperately. They hit the starter button, let it turn over a few times, then flip on the igntion, this technique will reduce strain on the starter, but again it isn't very practical on a street car.

I have a locked out timing on my street car right now but only because the jerk who tuned my car did it *his" way and not according to my instructions. It is hard as hell on my starter and I burn through the gas like it is free. I am rectifying the situation with the installation of an MSD adjustable timing computer (P/N 8981) in the coming week.

 

[likesoldjunk]

A Couple of things...

I think people are too quick to run out and spend a lot of dough
on fancy ignition systems when you don't know the full capability
of what you have, or could have with some junk yard upgrades.

#1 To my knowledge, ALL ford vacum canisters are adjustable.
you just shove an allen wrench (7/32 i think) down the snout.

you need to connect it to the 'ported' vacume outlet on the carburator
that's just below the butterflys. This prevents you from getting
maximum vacum advance at idle.

#2 If your car runs better at idle with higher advance, but it's
too much at speed, you can change out the reluctor arms in the
distributer to give you the delta you need. If you go to the dump
and pull apart a distributer from a big car, a little car, a truck,
etc, you will get a nice assortment. Each Arm has two options.

#3 You can do a pretty good job of bringing in the advance
when you need it just by changing the combination ot heavy
and light springs that come in the distributer.

#4 A duraspark from a 74+ car has lots of advantages, is cheap,
and once you hide the electronics looks original.

I agree you should not go lock out.

You need less advance at idle, or you'll never be able to start it
when it's hot.

Vacume Advance has not downside I'm aware of, and your engine
will run cooler, and you'll get better milage.

 

[ozstang65]

... Vacuum advance only works at cruise, it uses a full time vacuum source(nipple on intake or somewhere else downwind of the throttle blades) to increase advance. It only works at cruise and part throttle, because those are the only times there is enough vacuum in the intake. There are adjustable vacuum advance canisters that are used to adjust the advance rate. Vacuum advance serves to improve driveability and clean up emissions. When the engine is under load, also known as acceleration, the vacuum in the intake drops so low that the vacuum advance cannot function. In such situations, the advance falls back on the mechanical system, which is cotrolled by weights, springs, and centrifical force. ......

I just hope you haven't tuned your car on this assumption - cause it is very wrong!

Vacuum advance is called that for a reason, it uses vacuum to advance the plate inside the distributor that the points or other timing mechanism is attached to.

The vacuum line is placed upstream of the butterflies so that when they are cracked open, the advance mechanism sees the vacuum from the intake manifold and advances the timing. This is needed on a street car mainly when initially taking off or when you mash on the gas at low revs to prevent stalling. When you quickly open the throttle, you very quickly get a lot more air and fuel into the engine, if the spark doesn't move forward to match, then you've got too much fuel and air and not enough time to burn it. Too much advance however and you'll ping your head off!

Due to emissions regs, you'll see some of the later cars with vacuum advance and retard. The retard side gets hooked to manifold vacuum, sometimes both sides go through a temp operated valve so that it only works a certain way when the engine is warm.

A carefully balanced combination of vacuum and centrifugal advance will make an engine more street drivable. Mild street/race can go without vacuum, full race usually work so high in the rev range that even centrifugal isn't needed.

 

[302 coupe]

yeah my bad, I had a brain fart on the vacuum source. With the exception of the early load-matic distributors, the vaccum advance will pull from a part time vaccum source, which references venturi vacuum rather than manifold vacuum. I got in that manifold vacuum schpeil and it screwed up the whole thing. I apologize for the confusion.

Using a more modern distributor (which is normally what we're dealing with), using a part-time vacuum source (draws venturi vacuum from above the throttle), the vacuum advance always wants to advance the timing more and more. More rpm equals more air being pulled though the venturi, so the air must travel faster thru the venturi, which creates a negative venturi pressure, which is also what draws fuel from the carb. Anyway, the vacuum advance during all this is being resisted by spring pressure, from the spring located inside the vacuum advance diaphragm. With an adjustable vaccum advance, the pre-load on the spring is adjustable, which allows you to change the total amount of advance provided by the vacuum system. Normally, by the time the engine gets to about 2500 rpm, the spring is resisting most of the vacuum advance, and the only additional advance must be provided by the mechanical advance system. If you can imagine a graph (rpm on the x-axis and degrees of advance on the y-axis) with two curves(one for vacuum, the other for mechaical) that reach roughly the same point at 2500 rpm, lets say 30*. The vacuum advance curve will rise quickly then plateau off. The mechanical advance curve rises slower but doesn't normally peak until a higher rpm maybe 36* at 2800rpm. If you try to validate all this by doing a quick rev with the trans in neutral, you'll see that its way off, in fact your advance will probably be about 60* or so, lol. Thats because this stuff only works with the engine under load. A trip to the chassis dyno would be the best way to find out whats going on with your timing. Again, sorry for the confusion between the two different types of systems.

 

[fastback brian]

Good info guys...

BEST thing I ever did was install a msd setup. The duraspark would work the same but not as nice.. basiclly the same guts. My msd distibuter can run a stock small ford cap with some minor clearance inside the cap. You gotta have the small cap on a small block for the classic look.