Power timing

[Houle #382]

This question has probably been asked a million times, when power timing a 440 to 36 degrees at 2500 rpm when all done do you run the car with the vacuum line hooked up or do you block it off at the carb. I test drove the car both ways and there was definitely a difference with the vacuum line plugged

 

[snakeoil24]

Always run vacume

 

[Houle #382]

Always run vacume

That's kinda odd as she ran 100 % better without the vacuum line hooked up

 

[OKDart]

If you do any part throttle driving, use the vacuum advance. Don’t need it for a race car.

 

[Don Frelier]

That's kinda odd as she ran 100 % better without the vacuum line hooked up

Then it's probably too lean.
What carburetor do you have on it?

 

[Houle #382]

Then it's probably too lean.
What carburetor do you have on it?

A modified Edelbrock 650 AVS2

 

[RemCharger]

A modified Edelbrock 650 AVS2

On a 440???

 

[Houle #382]

Then it's probably too lean.
What carburetor do you have on it?

Curiosity got the best of me so I went out and pulled a couple of plugs, light chocolate brown

 

[Don Frelier]

Curiosity got the best of me so I went out and pulled a couple of plugs, light chocolate brown

But have you been running it with vacuum advance?

 

[Houle #382]

On a 440???

Yup and she runs fantastic, my engine builder said too many people over carb their engines, they fell the bigger the better. For the build I have this Edelbrock 650 AVS2 is perfect. Don't forget back in the day these cars from the factory with only had 650 carbs and the carbs today are way ahead of the ones back in the 60's. I spent a good 45 minutes on the phone with a Edelbrock tech and he said the 650 AVS2 is the perfect street carb. He said I could run the 800 AVS2 but I would lose my light to light acceleration and I would only pick up maybe a tenth in the quarter mile over the 650. It was a no brainer best thing I could have done since the car will never see the strip. 3 other guys in my Mopar club have also switched from 750 Holley's to the 650 AVS2 one guy has a 383 RR the other a 71 Challenger 440. Both guys said the same thing why didn't I switch sooner.

 

[snakeoil24]

That's kinda odd as she ran 100 % better without the vacuum line hooked up

Im sure it’s odd if you don’t have it set up right

 

[Houle #382]

Im sure it’s odd if you don’t have it set up right

Ok so which port should I be running off of ? Manifold or timed port which one is the best. One person say manifold another says timed. My initial timing is right around 12 and total is 36

 

[moparedtn]

Just to be clear here, the total timing of 36 degrees you're referring to at around 2500 RPM is set with the
vacuum advance disconnected and the outlet on the carb for it plugged...
Once you've got that "all in" timing dialed in, then you reconnect the vacuum advance if desired - but know
that it is also adjustable, too.

 

[MoparLeo]

"Power timing" is for hi rpm driving. like pedal down, track driving. Advance type doesn't matter since the timing is already all in.
Ported, is for street driving.
You set the initial with the vacuum disconnected and blocked.
Timing curves will depend on what distributor you are running.

 

[RemCharger]

Yup and she runs fantastic, my engine builder said too many people over carb their engines, they fell the bigger the better. For the build I have this Edelbrock 650 AVS2 is perfect. Don't forget back in the day these cars from the factory with only had 650 carbs and the carbs today are way ahead of the ones back in the 60's. I spent a good 45 minutes on the phone with a Edelbrock tech and he said the 650 AVS2 is the perfect street carb. He said I could run the 800 AVS2 but I would lose my light to light acceleration and I would only pick up maybe a tenth in the quarter mile over the 650. It was a no brainer best thing I could have done since the car will never see the strip. 3 other guys in my Mopar club have also switched from 750 Holley's to the 650 AVS2 one guy has a 383 RR the other a 71 Challenger 440. Both guys said the same thing why didn't I switch sooner.

no problem I'd forgot about those 350 horse motors. Had one in my 67 newyorker

 

[Orig69]

I would check the vacuum advance chamber for a vacuum leak.

 

[Geoff 2]

Houle,
A lot of confusion here. But first, congrats on using the AVS & also your sensible thinking about using the smaller carb.

I assume you were 'power' timing by revving the engine & watching the timing mark on the dampener. With Vac Adv connected you will get a false reading because the engine is not under load & vacuum will be high. So you will be getting advance from the VA unit in the reading. VA needs to be disconnected if you are using the method I have described to dial in your WOT timing.
Rarely is Ported Vac Adv [ PVA ] better than Man Vac Adv [ MVA ]. Chrys missed the boat on this.

Here is a simple 5 min test you can do to see if your engine will benefit from MVA.
Engine idling, in gear if auto, slowly advance the dist; keep going until you get the highest idle rpm. Now see what the timing is. If it is, say, 30* then your engine should be using MVA. If, say, current init timing is 12*, then the MVA needs to add 18*. MVA adds timing at idle, PVA does not which why it is useless. Most VA units can add up to about 30*.

 

[Geoff 2]

More info here on MVA, scroll down to post #6

www.hotrodders.com/forum/vacuum-advance-hooked-up-directly-manifold-bad-47495.html

 

[Houle #382]

no problem I'd forgot about those 350 horse motors. Had one in my 67 newyorker

Ha Ha she's not even close to 350, add another 125 and you might be close

 

[dvw]

Here's what ends up happening. No way did the factory engine have 36 degrees total plus additional timing added at high vacuum levels during cruise from the vacuum canister. You have added additional base timing. To get enough base timing now the overall timing may go beyond your desired number. Then you have to reduce mechanical advance in the distributor itself. With that completed everything runs well. Now you dd in advance from an unmodified vacuum advance canister and you have to much total timing. Vacuum advannce is good. Just need to reduce the amount it adds. Some units have an allen adjuster thru the vacuum port to adjust. Others may take some method to limit the amout of travel in the distributor itself.
Doug