hey everyone, could use some help finishing my first swap. i found the vac diagrams but nearly everything with emissions was not hooked up when I bought my 86z 4bbl w/700r4. vin H.

650 edelbrock carb has one port in the back that was used (vacuum) which i have my brake booster(?) hooked into and of the 3 vac ports in the front of the carb, the 2 small ones on the outsides were capped off. What goes in the middle on the big vac port?

and is there supposed to be a vac hose for the tranny? I either didnt unhook it when i swapped the 305 for the 350 or I am losing my mind? there is a black box thing(canister) kinda flat on one end and rounded on the other that has a line going in and coming out just dangling, its about a 1/4" hose

saved a 1000 dollars doing the swap myself but all these little things are killing me.
Any help is appreciated and TGO is awesome!!! Hopefully someday I will be able to contribute not just ask questions

 

700R4's don't use a vacuum modulator.

 

thanks for the quick reply, one more quick one for you if you dont mind, Brake booster to back of carb, black canister to vacuum on intake and is that all i basically need to get her running? shes been sitting a month now with a brand new (rebuilt) engine and its killing me!

 

Assuming you're running a vacuum advance HEI you'll want to hook up the advance module to ported vacuum (above the throttle blades of the carb). Technically, anything else can be left disconnected, but you'll want the brakes hooked up if you want to drive it.

 

the front large port is for your pcv. if you are using a breather instead of pcv then you can just cap that off. do not use a vaccum port above the throttle plate for your vaccum advance. you will never be able to get a good torque curve. the changes in vaccum is what gives you your torque curve with the vaccum advance. the vaccum advance is used to change your timing as you accelerate. the more you accelerate the more vaccum you produce when the throttle plate is opened. so when you accelerate, the timing will increase in degrees. that is why it is called a vaccum advance. and yes a 700r4 is electronic controled. there is a port on top of the trans but it is not used for vaccum. it is for the trans to breath. If you live in a rainy enviroment you might want to put a hose on it and direct it to somewhere dryer like up by the engine.

 

Yeah, like when you put your foot on the gas and open the throttle blades.

 

That's not even close to correct. The vacuum advance is used to add extra timing under low load/high manifold vacuum conditions, like when the throttle is mostly closed. The thin mixture in the chambers needs extra time to burn under these conditions. As you open the throttle, manifold vacuum decreases, and the amount of vacuum advance decreases as well.

The advance will increase as engine speed increases because of centrifugal advance, controlled by the weights and springs, not by vacuum.

And a 700R4 is not electronically controlled, it's a conventional hydraulic transmission. The only electrical control is for the torque converter clutch.

 

My bad, I got lost in the details while multi-tasking and gave bad info. As mentioned, mechanical advance deals with engine speed, and the vacuum advance deals with engine load. Vacuum advance works by decreasing engine timing under higher load levels to prevent detonation.
It still doesn't change the fact that ported vacuum is where the vacuum advance is normally connected. But in theory there can be advantages to having it connected to manifold vacuum.

 

Thanks for clearing up the confusion with the vac for tranny. Glad I dont have one, just more stuff to hook up wrong, lol.
This is getting kind of off topic now but Drew mentioned a vac hose for the HEI, thats the distributor right? I dont think I have one on there either. It has a couple of wiring harness' I have a pic from the old engine. BTW, whats all this talk I hear about timing

 

If you dumped the computer controlled carb, you need to dump the computer controlled distributor too. You'll need a vacuum advance distributor.

 

Yeah unless you want the stock computer controlled carb, you can't use that distributor, you need one with a vac advance. Go to the parts store and tell them you need a distributor for a 1981 camaro. Should have what you need but check it to make sure. It will have a little silver can on the side.

 

That's kinda right. What happens is when the engine is at part throttle cruise, engine vacuum increases since the butterflys are mostly closed. This increase in vacuum pulls on a diaphram inside the vacuum can on the distributor and advances the timing. The vac advance only adds extra timing to the total timing (initial timing + centrifugal advance). The second you start going up a hill and give it more gas or open the butterflies, the manifold vacuum drops and so less vacuum is being pulled on the vac advance diaphram and some of the advance is taken out, but only from the extra timing put in by the vac advance. The total timing will still stay the same, the vac advance doesn't ever mess with that, it only adds to it.

As far as connecting the vacuum to a ported vs manifold source, that's a whole nother can of worms. My personal opinion is to try both and see what the motor likes. You're looking for the best quality idle. Technically if you have your distributor adjusted correctly you won't need a full manifold advance at idle. Say if you are running a little cam that pulls 15in of vac at idle in park and 13 in gear, and you're only running 10 degrees of initial advance, you could benefit from the manifold source and get a better idle.

Now say you have a healthy cam that gives you 13 in park and 6 in gear and your vac advance doesn't come in until the engine gets 10in, this could cause problems. In park the rpms would be high since it's getting more advance but then when you drop it in gear the advance goes away and idle rpm drops. This could give you something like 1000rpm in park in 500 in drive which would jerk the car pretty hard when you shift from park to drive, let alone produce a good idle in park and a lousy idle in gear.

In this case the best thing to do IMO is to connect it to ported vacuum and then advance the initial timing to a point where you get a good idle in park and in gear, and only a 100-200 rpm drop. You might be at 20 or 25 degrees at this point and when the centrifugal comes in it would give you a lot more than the engine wants so you have to dissassemble the distrbutor and fill in the advance slots or get a spring/weight combo that only gives you the amount of centrifugal advance you need. Then again you will have to drive the car and see if it can tolerate that high of an initial timing in the first place.

Sorry to get all technical but I felt like explaining why the blanket statment "don't connect it to ported because you will never get a good torque curve" is wrong. Sometimes running ported is better, sometimes running full manifold is better. Just depends on your particular engine and how you set up your distributor.

 

IIRC, back in the day vacuum advance was always connected to manifold vacuum. Ported vacuum came into vogue later on to reduce idle NOx emissions.

There are still reasons why one or the other might work best for a particular combination, so it's best to try them both and see which one works for you.

 

keep in mind also some EST/ESC distributors did have vacuum canisters

for example on the 1982 k-10 pickups with 305 4bbl E4ME and the early EST system.

in which we own one of.

it is 7 wire HEI and has vacuum advance

1103465 distributor stamping

in which i have sitting right here in front of me as i type this,

look it up for yourself


im tired of ppl saying the computerized HEI all did not have vac advance.

when there were actually some made.

also some of the early '80s 305 caprices were vacuum advance with EST 7 wire HEI

same..

ive owned one of those also.

 

Yea some electronic hei's did have a vac can too. Just look for a distributor with only a 3 wire plug comming out of it and you will be okay.

 

I am not sure which distributor to buy to get the most bang for my buck.
a Jegs,
Mallory
accel
MSD

any suggestions
should I go top dollar or will it affect my performance if I dont, I do have the 8.5mm wires from jegs, I liked the color, lol, and they were only 35 bucks

 

For a mild engine you don't need anything especially elaborate. More expensive aftermarket distributors do tend to be easier to set the advance curves on.

 

I have more questions about distributors but this thread is way off course, I'll go somewhere else. Thanks for the help everyone, I do not have a vac line for my tranny on the carb'd 86z stock 700r4.