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 Vacum Advance Edelbrock Carb
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KeepPace
Sitting Bull

Canada
140 Posts

Posted - 29 Apr 2013 :  10:19:07 PM  Show Profile  Reply with Quote
77 Pontiac 400, Edelbrock Carb, Edelbrock Intake, Stock HEI DIZZY w/t flame thrower.

I am having a lot of trouble figuring out how my vacuum advance is suppose to be hooked up.

So this is what I thought:

I want to set the timing at 10-12 Degrees BTDC with the vacuum plugged and not hooked up to the dizzy.

Vacuum advance Should be hooked up to a source that has no vacuum at Idle ? Im not sure if this is correct because on my carb both have vacuum at idle??

Please help!!


1980 Pace car
76 400

cortcomp
Coyote

USA
5338 Posts

Posted - 29 Apr 2013 :  10:40:06 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I don't know that the edelbrock has a ported vacuum source? I think they're both manifold vacuum. For general dialing in, that's ok for most motors. Do you have a radical motor (i can't keep track of all the current builds on here!) Using ported vacuum vs manifold wasn't an issue for me until i build the choppy low vacuum XE284 build.
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KeepPace
Sitting Bull

Canada
140 Posts

Posted - 30 Apr 2013 :  09:14:37 AM  Show Profile  Reply with Quote
268h cam (not choppy at all)

So where should I hook the vacuum advance up or should I leave it off

Is this correct

Initial timing at idle is 10-12 degrees BTDC?
Timing with vacuum hooked up at idle around 30 degrees BTDC?

1980 Pace car
76 400
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KeepPace
Sitting Bull

Canada
140 Posts

Posted - 30 Apr 2013 :  11:42:34 AM  Show Profile  Reply with Quote
After researching on the trusty GOOGLE this what I found

Initial Timing 10 deg
Total Mechanical 16 deg
Total Vacum 10 deg

= Total timing 0f 36 degrees ( Im not sure what I need for my specfic motor but this should be close ?)

So it looks to me like I am running way to much vacuum advance and I need to restrict the vacuum line? Or would this have to do with wieghts or springs in the Dizzy?




1980 Pace car
76 400

Edited by - KeepPace on 30 Apr 2013 11:44:08 AM
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cortcomp
Coyote

USA
5338 Posts

Posted - 30 Apr 2013 :  12:50:35 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
you can run manifold vacuum with that cam and i'd think you'd be more than OK, and check with bill, cliff, and others on here about the timing amount but it's usually like 10-13 initial and i THINK about 15-18 more mechanical? Vacuum can be a ton more, you need to limit it not use a restirctor. A restricor would, i think, change how fast the vacuum advance came in (delay it for a very short time) but not change the total amount of advance. That is done under the cap, limiting how much the vacuum advance can do. Even on a new, supposedly blue printed HEI from summit, mine was way out of spec.

Same thing going on for someone else here:

http://psp.aquacomp.net/topic.asp?TOPIC_ID=6735
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KeepPace
Sitting Bull

Canada
140 Posts

Posted - 30 Apr 2013 :  1:34:40 PM  Show Profile  Reply with Quote
Do you have idea where I would get an adapter for an edelbrock intake to run intake vacuum and whats the difference

1980 Pace car
76 400
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cortcomp
Coyote

USA
5338 Posts

Posted - 30 Apr 2013 :  1:41:58 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
intake vacuum is vacuum that's always on and you get that from the edelbrock carb or any pipe plug holes in the intake itself. Some carbs (qjets, etc) have a ported vacuum port, where there's little to no vacuum at idle, and as soon as you move the throttle at all, the ports are connected to manifold vacuum. So they're the same as manifold vacuum, only off at idle so there's no vacuum advance at idle. If your carb doesn't have ported vacuum, that's ok, just run off of the normal manifold/intake vacuum ports that come already on the carb.
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KeepPace
Sitting Bull

Canada
140 Posts

Posted - 30 Apr 2013 :  1:57:50 PM  Show Profile  Reply with Quote
Ok, thats what I thought.

Is there any kind of adjudstment on my cardone Dizzy for the vacuum advance.


1980 Pace car
76 400
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Phil
The Great White Buffalo

USA
7222 Posts

Posted - 30 Apr 2013 :  2:05:32 PM  Show Profile  Reply with Quote
quote:
Originally posted by KeepPace

After researching on the trusty GOOGLE this what I found

Initial Timing 10 deg
Total Mechanical 16 deg
Total Vacum 10 deg

= Total timing 0f 36 degrees ( Im not sure what I need for my specfic motor but this should be close ?)

So it looks to me like I am running way to much vacuum advance and I need to restrict the vacuum line? Or would this have to do with wieghts or springs in the Dizzy?




Don't count the vacuum in with the total timing. The total timing should be initial + mechanical advance curve = target total timing.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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KeepPace
Sitting Bull

Canada
140 Posts

Posted - 30 Apr 2013 :  3:06:09 PM  Show Profile  Reply with Quote
Whats the target for total ?

Whats the target for intial?

Whats the target for mechanical advance?

Whats the target for vacuum?

Sorry for all the questions but I just want to get this right.


1980 Pace car
76 400

Edited by - KeepPace on 30 Apr 2013 3:15:03 PM
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Phil
The Great White Buffalo

USA
7222 Posts

Posted - 30 Apr 2013 :  7:24:05 PM  Show Profile  Reply with Quote
You determine the target through the combo as well as what the engine wants. I'd start with something based on an identical or even similar combo that is successful. Then fine tune from there.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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KeepPace
Sitting Bull

Canada
140 Posts

Posted - 01 May 2013 :  11:02:32 AM  Show Profile  Reply with Quote
Its running pretty good now But I have not taken it on the street (still waiting for a tranny dip stick)

After checking last night Im running 12 degrees initail 10 mechanical which I think is pretty good

but around 25-30 vacuum advance alone which even though it seems to run fine I Think that is way too much what are your thoughts on this (again I have not taken on the street)


1980 Pace car
76 400
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Phil
The Great White Buffalo

USA
7222 Posts

Posted - 01 May 2013 :  8:34:46 PM  Show Profile  Reply with Quote
You're still missing the point here. Your mechanical timing curve is too limited. You should be shooting for something in the low to mid 30's to start with and then dial in from there. Think of the vacuum advance as separate to this. Right now you're only running @22 degrees of total mechanical advance (initial + centrifugal advance) which is not enough. Don't try to factor the vacuum advance into the advance curve. You can play with the vacuum advance separately by limiting it if needed or adding an adjustable unit.

How did you come up with only 10 degrees centrifugal advance? That is way low! Do you have front suspension coils in the distributor??

Are you using the stock HEI weights? Hopefully you're not using those crappy (and wrong) aftermarket "kit" weights and center plate!!

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.

Edited by - Phil on 01 May 2013 8:41:59 PM
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Bill Boyle
Horse Feathers (Charter Member)

USA
4797 Posts

Posted - 02 May 2013 :  10:00:29 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Phil is right, mechanical and vac are two separate and distinct operating platforms on distributors.

Always dial in mechanical first. The full mechanical should be in around 3000 rpms.
The full mechanical is the full action of the weights, the end where there is no more advance.

So...if you set your initial (start up) advance at 12 degrees and you full mechanical advances 20 more, the engine is only seeing 32 degrees advance. The 20 will (or should) remain constant. The adjustment for more advance is done with initial. So, if you engine performs best with 34 degrees mechanical advance, you adjustment will be on the initial, that is moving it to 14 degrees.

-------
Vacuum advance comes after this, and is designed to aid the engine in dealing with part throttle operation (when cruising) which is 90% of the time. If you're cruising at let's say 2000 rpm the amount of mechanical advance will be less than full (less than 34 degrees) so, your vacuum comes into play and provides a little extra, increasing it to 34, 35, 36 ... or more degrees. If you were to cruise along at turnpike speeds, where your engine is turning over 3000 rpms, the full mechanical is in play plus some amount of vacuum assist. So, it could be 40.... or 45 degrees...or more. Tailoring vacuum advance can be done with an adjustable unit; before they were readily available, hot rodders limited the vacuum rod travel by brazing in a stop. Both methods are trial and error propositions.

Knowing what the limit of you distributor's mechanical advance is a must know. I hope this is helpful.

Bill

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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KeepPace
Sitting Bull

Canada
140 Posts

Posted - 05 May 2013 :  3:09:03 PM  Show Profile  Reply with Quote
Its very helpful I took it out today for the first time since I put the cam in and it does feel like it is lacking power in the upper RPMs

The dizzy im running is a cardone and nothing is done to it, I have a mr gasket advance curve kit but Im a little afraid to mess with the dizzy cause I dont really know what I m doing !!

1980 Pace car
76 400
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Miles
Sitting Bull

Canada
142 Posts

Posted - 07 Jul 2013 :  2:27:06 PM  Show Profile  Reply with Quote
Of the two vacuum ports on the front of the Edelbrock carb the passenger side is ported and the driver's side is manifold vacuum. I have mine connected to manifold to get the vacuum advance at idle, smooths out the idle on my engine and allows me to turn out the idle speed screw a bit. Seems to perform a little better in stop and start street driving as well. Yours could be different though.
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Total Jackass
Tribal Scout

0 Posts

Posted - 14 Jan 2014 :  04:04:41 AM  Show Profile  Reply with Quote
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I'm a first class jerk and don't you forget it!
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Phil
The Great White Buffalo

USA
7222 Posts

Posted - 14 Jan 2014 :  6:30:58 PM  Show Profile  Reply with Quote
TTT

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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