vacuum advance

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furydan

furydan

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I am running a 318 bored 40 over with kb pistons, comp 286 cam, 302 heads with an edlebrock carb and intake. I also have electronic ignition. My question is: Should I run the vacuum advance off of the timed port on the carb or the full manifold port off the carb. I have a choice. Right now I am running off of the timed port.
Dan
 
I would keep it on the timed port. That's where it's supposed to be.
 
furydan said:
I am running a 318 bored 40 over with kb pistons, comp 286 cam, 302 heads with an edlebrock carb and intake. I also have electronic ignition. My question is: Should I run the vacuum advance off of the timed port on the carb or the full manifold port off the carb. I have a choice. Right now I am running off of the timed port.
Dan
Click to expand...

if you want full manifold vac. then you need to set your dist. up for it. i'm running full manifold vac. in my car. initial timing is at 14* but at idle with the vac advance its at 30*. the car idles smoother, is peppier at lowwer/cruise speeds and light throttle and it seems to be running about 5* cooler.

i have 20* mechanical advance ( all in at about 3100 rpm) ad 16* of vac advance.

good thread about it here: look at greg_moreira posts... http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=6813633&an=0&page=0#Post6813633
 
abodyjoe said:
if you want full manifold vac. then you need to set your dist. up for it. i'm running full manifold vac. in my car. initial timing is at 14* but at idle with the vac advance its at 30*. the car idles smoother, is peppier at lowwer/cruise speeds and light throttle and it seems to be running about 5* cooler.

i have 20* mechanical advance ( all in at about 3100 rpm) ad 16* of vac advance.

good thread about it here: look at greg_moreira posts... http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=6813633&an=0&page=0#Post6813633
Click to expand...

Just set mine up with vac off manifold , everything is working great , no more pinging , runs well at all speeds , much better off the line and around town
 
I run 34 degrees of timing all of the time, got a start retard so it cranks over. I tried 10 degrees of vacuum but after a few days I could feel how the motor didn't run as smooth, so now I run no extra advance, just 34 all the time. Has loose 3.91's and a 3,000 stall, no lugging and no pinging.
 
dodge freak said:
I run 34 degrees of timing all of the time, got a start retard so it cranks over. I tried 10 degrees of vacuum but after a few days I could feel how the motor didn't run as smooth, so now I run no extra advance, just 34 all the time. Has loose 3.91's and a 3,000 stall, no lugging and no pinging.
Click to expand...

So your saying that when you set your timing, you set it @ 34 degrees btdc and just leave it like that?
 
Yes, its an MSD E Curve dist and i have the switches set for lockout. The nice thing is the start retard which backs off the timing 20 degrees while cranking, once the engine speed hits 500 rpm or more then the retard is off and engine has 34 degrees all of the time, no matter the rpm. Works great, now if it had a stock converter and 2.73 gears, I'm sure the motor would ping at low-lugging rpm's
 
I know it came stock with a manifold vacuum source, But I wasn't sure with the edelbrock set up about which port to use. I think I will try the manifold port tonight.
Set the timing to 14 btdc with vac disconnected. Then hook up vac.It will probably increase the rpms a bunch when I hook the vac up. I guess I should then adj carb to get the rpms back down...That's where I get confused because then doesn't the timing change with rpms? How do you get the right timing and the right rpms at the same time?
Maybe I should take a class in auto 101 how to set timing.
 
Are you sure it was originally manifold vacuum supplied. Most were venturi vacuum supplied.
When it comes to vacuum advance, The more I read the more confused I get.
Can manifold vacuum source be better than just disconnected ? Does manifold vacuum even drop enough to cause the advance servo to respond ?
Can I assume what works best for performance also reduces mpg ? I would forfiet a little mpg for better throttle responce and overall performance from a totally stock 2 brl. engine.
 
RedFish said:
Are you sure it was originally manifold vacuum supplied. Most were venturi vacuum supplied.
When it comes to vacuum advance, The more I read the more confused I get.
Can manifold vacuum source be better than just disconnected ? Does manifold vacuum even drop enough to cause the advance servo to respond ?
Can I assume what works best for performance also reduces mpg ? I would forfiet a little mpg for better throttle responce and overall performance from a totally stock 2 brl. engine.
Click to expand...


vac. advance should help mpg either way its hooked up. either way it drops out when your on the floor boards with the throttle and you revert to mechanical advance. the vac advance will help mpg at cruising speeds and low speed driving. you need less throttle to get the car moving with more advance. with manifold vac used you'll have all that advance even at idle. all that advance will cause the idle to rise. so you turn the idle down to where ya like it. that = less gas being used. then when pulling away from a stop the more timing makes it possible to use less throttle to get the car going.

going ported vac, will do the same thing just not at idle and pulling away from a stop. cruising though it will allow you to use less throttle to pick up speed.
 
Thanks Joe. I was just looking at how easy it would be to T it in with the primary choke pull source which is manifold vacuum.
 
worth a try. just have to make sure the dist. is set up right for it. if not you may end up with way too much timing at idle.
 
RedFish said:
Are you sure it was originally manifold vacuum supplied. Most were venturi vacuum supplied.
When it comes to vacuum advance, The more I read the more confused I get.
Can manifold vacuum source be better than just disconnected ? Does manifold vacuum even drop enough to cause the advance servo to respond ?
Can I assume what works best for performance also reduces mpg ? I would forfiet a little mpg for better throttle responce and overall performance from a totally stock 2 brl. engine.
Click to expand...

All I know about the original vacuum source is from our formula s 273. It has the stock carb and manifold on it.There is only 1 vac fitting on the carb and it has a lot of suction when the engine is at idle.
It is only running a single point dist, my dual point dies when I apply any advance from the vac adv. I have to leave the vac advance disconnected if I want to run the dual point on the s car.
 
Forgive me if I'm wrong. I haven't seen them all.
That carb should have a port on the lower back for the primary choke pull and one higher up on the right side for the spark advance.
No wait ... Formula S is a 4 brl. so ports would be a little different.
 
So I set the initial timing @ 14 btdc and the total with the vac adv on the manifold side looks to be about 30 or so btdc. Cars seems to run a lot better, but when it is hot, hard to turn over. Maybe one of those hi torque mini starters would be my next move.
 
furydan said:
So I set the initial timing @ 14 btdc and the total with the vac adv on the manifold side looks to be about 30 or so btdc. Cars seems to run a lot better, but when it is hot, hard to turn over. Maybe one of those hi torque mini starters would be my next move.
Click to expand...
Get a timing retarder for during starts. Not sure of the Details but Dodge Freak uses one. I'm sure He'll chime in and give more info. Good luck, Sounds like you got it 99% fixed.
 
I got a mini starter also. With 14 initial timing there should not be a problem, there is no vacuum until the motor runs. My start retard is built in to the E Curve dist

The old cheap trick years ago was a on/off switch by the drivers seat to turn the ignition off/on. You would crank the engine with the ignition off and once it was cranking over flip the ignition on. Was great for a weak battery or starter or lock out timing
 
dodge freak said:
I got a mini starter also. With 14 initial timing there should not be a problem, there is no vacuum until the motor runs. My start retard is built in to the E Curve dist

The old cheap trick years ago was a on/off switch by the drivers seat to turn the ignition off/on. You would crank the engine with the ignition off and once it was cranking over flip the ignition on. Was great for a weak battery or starter or lock out timing
Click to expand...

I am working on getting a mini starter for it. The current starter is a many years old rebuilt that was in the car when I bought it. I figure it is just losing it's power, especially running a higher compression that stock with the new motor.

This is all in an attempt to keep the car from missing during coast conditions. Acceleration is good, but maintaining constant speed, the car misses a lot. Doesn't really low you down, it is just an irritating pop-pa-pop out of the exhaust.
Also looking into getting a brand new distributor. The current distributor looks relatively new and clean, but I don't know if it is causing the trouble.
I am running an electronic ignition. The control box is just a year old and the wiring was new then too, just the dist was used.
 
furydan said:
So I set the initial timing @ 14 btdc and the total with the vac adv on the manifold side looks to be about 30 or so btdc. Cars seems to run a lot better, but when it is hot, hard to turn over. Maybe one of those hi torque mini starters would be my next move.
Click to expand...

Have you tried about 18 btdc initial timing and no vacuum advance at all?
I have reservations about overly advanced timing causing a misfire during start. I dont know what effects that will have on the timing chain and/or other mechanical parts.
 
Timing chain should not be a problem but I heard the rod bearings do not like overly advance timing/ 34 at idle is just fine, its when its 45 or so it can be a problem, more so with tall rear gears and the engine lugs
 
furydan said:
This is all in an attempt to keep the car from missing during coast conditions. Acceleration is good, but maintaining constant speed, the car misses a lot. Doesn't really low you down, it is just an irritating pop-pa-pop out of the exhaust.
Also looking into getting a brand new distributor. The current distributor looks relatively new and clean, but I don't know if it is causing the trouble.
I am running an electronic ignition. The control box is just a year old and the wiring was new then too, just the dist was used.
Click to expand...



If you have surging at part throttle, you can adjust the diaphram in the vacuum advance with an allen wrench in the hose nipple by turning clockwise (I think).

It's probably set at midway and I think there's approximatley 12- 14 total turns available.

I'm not sure about the popping when coasting, that may be a lean carb or an exhaust leak sucking in fresh air.
 
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