Vacuum distributor ?

[72442conv]

Vacuum advance, where we are concerned with these cars is mostly for driveability. The engine will not make any more power with or without the vacuum advance connected. At full throttle you have no vacuum so the vacuum advance does nothing. From a performance standpoint vacuum advance is useless.
Now for the driveability issue. A well set up distributor with a full mechanical advance will work perfectly and will have excellent driveability. The first thing is to set up you mechanical advance. You normally want a lot of initial advance with about 34-38 degrees total advance as soon as the engine will take it without detonation. I normally set up my distributors at 16 degrees initial advance with an additional 20 degrees (for a total of 36 degree) all in by 2500 RPM if the engine will take it that soon. High compression engines may detonate with that fast of an advance so you may need to have the advance come in later for a high compression engines.
You can add the vacuum advance and it will definitely make a nicer idle and will have better part throttle response as you will be putting in additional timing. Fuel economy will also be better. But I have found that on high compression engines you will need an adjustable vacuum advance canister to avoid detonation.
You basically want to set up your mechanical advance for full power. Then hook up you vacuum advance and see if the engine will take it without detonation. If it detonates get an adjustable canister and start taking timing off it until you get rid of the detonation. This will give you the best performance, drivability and fuel economy, but can take quite a while to achieve.
I have no time to deal with it anymore so I just set my mechanical advance and forget about the vacuum advance. Car will make the same power with or without the vacuum advance so screw it
BTW the lower compression motors will take better to vacuum advance than higher compression engines.

 

[AZCOWBO]

It should. Usually a lumpy cam will hurt things like power brake boosters, but it doesn't take much for vacuum advance. Just make sure you put the line to the ported outlet on your primary carb, not the secondary.

Don

Allright, a dumb question. On a closed chamber Weiand Ram with twin 525s Road Demon Jr's,which is considered the primary carb? Also, can you connect the transmission vacumn line to the same carb, which I have the PCV line connected to the back of the rear carb.

 

[Lee_in_KC]

Ron, you will only have a "primary" carb if you have progressive linkage. The primary carb is the one that opens first. If you have straight linkage, both carbs are opening together, so no primary or secondary carbs. And yes, you can hook up the vacuum advance to the same carb as the PVC, but use different taps. I would recommend using the unported tap for your vacuum advance.

 

[72442conv]

Allright, a dumb question. On a closed chamber Weiand Ram with twin 525s Road Demon Jr's,which is considered the primary carb? Also, can you connect the transmission vacuum line to the same carb, which I have the PCV line connected to the back of the rear carb.

Normally, if you have a progressive linkage and inline carbs, the carb in the rear will be the primary one. That way the fuel coming into the manifold will come in close to the center for better fuel distribution. If the first one was the primary the front cylinders would get more fuel than the rear ones.

 

[Screaming Metal]

Well....Lee is right. Whichever one you setup to run your lowspeed off of is your primary carb. Its best to do the progressive throttle setup unless your a drag racer racing a Altered....then your gonna 'tune' it to not run at anything below 2500 rpm....that means your gonna be idling at about a grand...strictly race/ hot street stuff there.





Usually on a 2x4 setup on the street, the rear carb is usually the primary carb, with the progressive linkage going to the front carb. There are variations on this....some tunnelrams are setup for the carbs to sit sideways and all.

The main headache on a tunnelram is the size of your carbs, too much fuel, and your tuning....Whichever way you go and however you decide your gonna tune it...wether you build your progressive linkage yourself or you buy a linkage kit...don't buy the kits that have a round rod sliding thru a bushing...only get the kits that have the likage with a flat linkage with a slot in it for moving the stop. Look at the photos before you buy and ask these questions.

The round rods sometimes hang closed and offer alot of resistance to open, OR---and I don't say this lightly,...OR...they'll hang wide ass open, which is a whole bunch of no-fun! THE SLOT IS ALWAYS BETTER! Me, myself....I build mine from a cable going to the rear and a bell-crank with a slotted arm and a adjustable stop that actuates the front card..

On your secondary carb...have your low speed screws and your idle screw all the way off....and set them up so they both hit full throttle at the same time and release to idle smoothly. You want to idle off your primary carb. Be sure to run return springs on both carbs also...

I set mine up with a spring on each carb and and a spring returning the linkage also. Its not how much spring you got on there...its where you got them hooked up to........ubsafe!

 

[Wild Mango]

Well....Lee is right. Whichever one you setup to run your lowspeed off of is your primary carb. Its best to do the progressive throttle setup unless your a drag racer racing a Altered....then your gonna 'tune' it to not run at anything below 2500 rpm....that means your gonna be idling at about a grand...strictly race/ hot street stuff there.





Usually on a 2x4 setup on the street, the rear carb is usually the primary carb, with the progressive linkage going to the front carb. There are variations on this....some tunnelrams are setup for the carbs to sit sideways and all.

The main headache on a tunnelram is the size of your carbs, too much fuel, and your tuning....Whichever way you go and however you decide your gonna tune it...wether you build your progressive linkage yourself or you buy a linkage kit...don't buy the kits that have a round rod sliding thru a bushing...only get the kits that have the likage with a flat linkage with a slot in it for moving the stop. Look at the photos before you buy and ask these questions.

The round rods sometimes hang closed and offer alot of resistance to open, OR---and I don't say this lightly,...OR...they'll hang wide ass open, which is a whole bunch of no-fun! THE SLOT IS ALWAYS BETTER! Me, myself....I build mine from a cable going to the rear and a bell-crank with a slotted arm and a adjustable stop that actuates the front card..

On your secondary carb...have your low speed screws and your idle screw all the way off....and set them up so they both hit full throttle at the same time and release to idle smoothly. You want to idle off your primary carb. Be sure to run return springs on both carbs also...

I set mine up with a spring on each carb and and a spring returning the linkage also. Its not how much spring you got on there...its where you got them hooked up to........ubsafe!

Well, yes, back to the vacuum advance. The other thing having vacuum advance does apart from get you another 10% mileage in cruise is it keeps the engine from fouling up with the "heavy" ends of the fuel. The "heavy" ends are the tarry deposits that are very hard to burn and otherwise carbon up those pristine combustion chambers. By getting the fire started good and early there is a more complete burn before the exhaust valve cracks open. This also keeps the head temps up, further helping the process.

Listen to Screamin's words. Nothing worse than having a runaway on the street. Think about what you would do if your ride did it - can you reach the ignition switch with the thing accelerating at full noise? Have a practise so if it happens you won't be trying it for the first time. Can your brakes overpower the engine?? Try it and see, could well be a surprise there too. U B Safe, few enough brothers as it is....

 

[AZCOWBO]

Ron, you will only have a "primary" carb if you have progressive linkage. The primary carb is the one that opens first. If you have straight linkage, both carbs are opening together, so no primary or secondary carbs. And yes, you can hook up the vacuum advance to the same carb as the PVC, but use different taps. I would recommend using the unported tap for your vacuum advance.

I have the straight linkage, no progression. Since I have a closed chamber intake, can I actually adjust the front carb down to nearly zero flow and not have detonation issues with four of the cylinders? I was told with a close chamber intake, that progressive linkage couldn't be used.

 

[Screaming Metal]

I have the straight linkage, no progression. Since I have a closed chamber intake, can I actually adjust the front carb down to nearly zero flow and not have detonation issues with four of the cylinders? I was told with a close chamber intake, that progressive linkage couldn't be used.

Now, if your talking 2 seperated 4 bbl carbs without a common plenum below the carbs, then having your tall runners going directly to the carbs...yes...a progressive wouldn't work. Its a totally different animal to tune and make idle decent, along with the power characteristics.
Lee, Mango and I were referring to the common open plenum type tunnelram thats been used since the late 60's and 70's that you can pick up fairly cheap at the flea markets, swap meets and used part houses....

Lee and Mango got you covered on the vaccuum advance. Always remember this....all engines are different...what might run super sweet on one will be like a sour grape on the other...even if they're setup identical, using the same parts...a certain amount of experimentation is usually in order....to achieve the maximum performance.