Vacuum Advance with MSD?

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MrBelvedere2

MrBelvedere2

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Here is a question I have that I hope you guys can shed some light for me. On my 1967 Barracuda notchback I just bought, it has MSD igintion, 6AL box, pro-billet distributor, blaster2 coil, just not MSD wires. I have been reading alot about how Vacuum advance is important on the street, and it is mainly a street car. It has a nice built 360/904/3.23 sure grip combo. I noticed that the MSD billet distributor does not have any vacuum advance. I am not familiar with MSD that well, Do i still need vacuum advance or do you not need it with MSD, is it mechanical advance then? thank you for any information.
 
Pete's right. As long as you have it set up correctly it'll run good. It would just mainly get better fuel mileage with vacuum advance.
 
I ran across this article the other day researching this topic. I also noticed that by applying about 10 degree initial to keep the mechanical at a lower 22 degree total without the vacuum advance canister and then adjusting the vacuum advance canister to bring the total to 28 degree's plugged into constant vacuum worked well for a nice idle in park as well as in drive. I achieved this with a 560/580 cam.http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html
 
WOW Great link CudaFish I was wondering what the net difference between ported and manifold vac the Edlebrock DVD was telling me to use the ported side when I should be using the manifold outlet for my setup which explains the really low idle at stop while in gear problem I was having thanks
 
Your welcome! I too have used the ported side many times, it works well in some applications, it does make the adjustments different.
 
Using manifold vacuum verse ported vacuum to add timing at idle is a bandaid. The problem with having the vacuum advance activated at idle is off idle tip in preformance is compromised, some times to the point of causing a significant bog. The story in the link is flawed by the fact that he states ported vacuum was an emissions thing that's not true, ported timing has been used for as long as vacuum advance has been around. The early 70's emissions changes put temperature or transmission controlled switchs into the vacuum line to limit advance. I even recall seeing some Fords with advances that could move the timing in either direction form the base setting.

The proper way to set up your timing is to adjust the initial timing to achieve max manifold vacuum, then adjust the mechanical advance to what the heads want. Once those are set you add the vacuum advance and adjust for part throttle perfromance.
 
Ok, so how do i know what advance curve it is since it is mechanical advance? I have been told that with the comp cam 268 duration, 454 lift that i won't get the vacuum i need to make it function properly, and that the mechanical advance is better. I am going to put a timing light on it tommorrow and at least see where the timing is set. thanks for the tips so far.
 
vacuum advance is SOLELY FOR GAS MILAGE and you don't need it.

You can run a max initial with fast curve [fast as it'll take] and still get kinda close to any milage the vac canister would give you.

Sometimes the compression is nice and high for the cam and you find yourself not being able to really run much more than 38'ish degrees, so it's not like were talking much more than 5 or so degrees.

I used to run one and had it not ping and cruise nice at 46 OR 48* total w/vacuum advance, thing was if I stood on it while cruising, it clacked [detonated]...
by the time I took some timing out of the canister it was not much left to matter and I also thought why I built it in the 1st place and fk it.
still got 15mpg with a hot 340 solid cam motor, not bad.
jmo
 
If you run the dizzy locked out...is there a maximum amount of initial you can run or just as much as possible before you get starter lag?
 
MrBelvedere2 said:
Ok, so how do i know what advance curve it is since it is mechanical advance? I have been told that with the comp cam 268 duration, 454 lift that i won't get the vacuum i need to make it function properly, and that the mechanical advance is better. I am going to put a timing light on it tommorrow and at least see where the timing is set. thanks for the tips so far.
Click to expand...

Do you have a dial back type timing light? If so you can check the amount of mechanical advance it has and at what rpm it comes in. Unhook the vacuum advance so it doesn't skew your readings.

I can't imagine that little cam won't pull enough vacuum to pull the vacuum advance. A buddy of mine has a cam that's 20 degrees bigger than that in a 340 and it pulls the vacuum advance. You have to remember vacuum goes up as rpm's increase so for example vacuum at idle @ 700 rpm may only be 10 inches but as soon as you bring it up to 1000 rpm the vacuum will be possibly 2-4 inches more which is plenty to pull a vacuum advance to it's limit. You have even more vacuum at higher rpm until you get to the point of the throttle being open quite a way.
 
74Burntorange said:
If you run the dizzy locked out...is there a maximum amount of initial you can run or just as much as possible before you get starter lag?
Click to expand...

locked out does nothing but spark at the amount of degrees it was set at.

So if you lock out a distributor on a motor with the proper cam/compression ....Yes you are at the mercy of starter kick back..Unless you have/install a retard module. Retard mod would allow the timing to automatically retard the timing to a set amount that allows start up with out kickback. After start up it's still locked at what ever it was before and will not change.
 
I learned that I can put a toogle switch on the pos. side of the coil to turn it off and crank the car and then flip the switch to turn it back on. Its like using a retard switch but allowing the starter to start going before I give it spark.
 
Remember, just cause it'll cruise at 40+* of timing doesn't mean you wanna set a lock'd out distributor there, it won't like it and will get real flat on you power wise if it don't detonate/ping whatever... let alone now the carb has to 'try' and compensate for the 'no no' tuning wise.
 
yes...I need to mess with the carb more...maybe mess with transfer slots
 
no they should be fine now with 35* initial and only 1/2 a turn on the screws.

not to hyjack but what convertor do you have? that'll play a big part, along with 'cylinder pressure'.

tiny carb might help it idle too.


bandaids
 
I run the MSD distr on both the 340 and 360 cars without vacuum advance. The MSD fires twice each time a spark is required until the RPM is 3000 + RPM then it changes to single fire. Thats why a dial back timing light will not provide accurate information. The MSD has a centrifugal advance incorporated which makes some adjustments. With a single fire dist I would highly recommend a vacuum advance for the reasons stated.
 
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