for you guys on manifold vaccum on advance dizzy

[juit 34]

went to the shop and my mechanic plug the carb to ported and 10 D initial

 

the car hears and runs ok but its running a lil hotter

 

I want to change it back to full back but before I go to my past set up I want to know how you done this and your set ups

 

what are your settings?

 

are you plugged on the air intake or carburetor plate

 

whats your:

 

initial timing?

 

end?

 

I have pertronix 2, 302, holley 4160, edelbrock intake 2121, 1 inch 4 hole spacer

Edited October 18, 2014 by juit

[barnett468 418]

we need answers to all these questions to best help you otherwise we will be guessing.

 

typical timing on a mild build with 10:1 or less static compression is around 10-12 at idle and 32-34 total at around 2600-2800 rpm.

 

what is your compression?

 

what is your timing is at idle?

 

what was it before he changed it?

 

 

plug the dist vacuum for now.

 

what yis our timing at idle with it unplugged?

 

what is the total timing?

 

what rpm does it reach total timing?

 

what heads do you have?

 

exactly what are your cam specs?

 

what is your rear gear ratio?

 

how far is it bored over?

 

what is your outdoor air temp?

 

how wide is your rad?

 

how many rows deep 2. 3 or 4?

 

how thick is the core?

 

is it aluminum or brass?

 

what is your thermostat rating?

 

have you looked in your rad to see if any tubes look plugged?

 

how big is your carb?

 

what are the jet sizes?

 

does it run hot at idle or on the freeway or both?

.

Edited October 18, 2014 by barnett468

[DocWok 30]

Looks like juit was only after some simple help from fellow members.

 

Not an interrogation.

 

Is your 'knowledge' really that comprehensive that whether the radiator is aluminium or brass would help form a correct response?

[Brian Conway 264]

A lil hotter is not going to hurt anything. You can back out a degree or two by turning the dizzy counter clock wise. When turning CC start with 1/4' intervals. Mark your block so you will know where you stated. I'am guessing that you don't have a timing light ? Brian

Edited October 18, 2014 by Brian Conway

[juit 34]

Looks like juit was only after some simple help from fellow members.

 

Not an interrogation.

 

Is your 'knowledge' really that comprehensive that whether the radiator is aluminium or brass would help form a correct response?

 

I think the rad Q if because on the heating prob, but the car was not over heating when I had my adv plugged to the manifold

 

yes simple help and curious of your setting since manifold vac is a hot topic for some people

 

what are you runing thats all

 

 

my car is stockish

 

 

A lil hotter is not going to hurt anything. You can back out a degree or two by turning the dizzy counter clock wise. When turning CC start with 1/4' intervals. Mark your block so you will know where you stated. I'am guessing that you don't have a timing light ? Brian

 

yes I have a light it was set at 10 idle

 

but I dont know if he moved the advance

Edited October 18, 2014 by juit

[DocWok 30]

Hi juit,

 

Generally speaking having full manifold vacuum (either from a carburettor connection point or direct to manifold) is the preferred option.

 

As for timing, the more advance your motor can tolerate without 'pinging' under load the better it will run both from a performance perspective and also how hot it will operate.

 

Some engine combinations can handle more total advance than others, so there is no set figure for all engines. I wouldn't worry too much about what your timing setting is at idle, it's the maximum total timing that's the important thing.

 

Sounds like your engine timing is 'retarded' compared to what you previously had.

 

You could take your car for a drive and advance your timing a bit at a time until it just starts to 'ping' under load (this may take several attempts and adjustments).

When you just start to hear a pinging noise under load then stop and retard the timing a bit until the pinging noise no longer happens under load.

 

Hope this is of some assistance to you.

 

This should be the best that you can hope for with your current set up.

[barnett468 418]

connecting to manifold vac is the last option and is used mainly on engines with huge cams. none of the mfg's did that on distributors that had both mechanical and vacuum advance. your engine will run improperly if you have either too little OR too much timing.

 

your car should have sufficient timing if you use the specs i suggested.

 

its possible your timing is incorrect due to a slipped outer damper ring or excessively stretched timing chain. you need to check these things or set the idle timing by ear, rpm and a vacuum gauge.

Edited October 18, 2014 by barnett468

[1969_Mach1 333]

I agree with barnett468. Connecting to manifold is the last option. Connecting the vacuum advance to ported vacuum like your mechanic did is correct for your situation. The base timing of 10 to 12 degrees BTDC at idle is a good starting point, and will probably be correct, as barnett468 also mentioned. Be certain there is no vacuum at the vacuum advance on the distributor when setting or checking the base timing at idle. If a hot running engine is an issue after these are correct, you need to look at other items, dirty partially plugged radiator, correct fan setup, etc.

Edited October 18, 2014 by 1969_Mach1

[juit 34]

it was runing fine before the swap

[1969_Mach1 333]

I still think you mechanic connected the vacuum advance correctly by attaching it to ported vacuum.

[DocWok 30]

Ported vacuum connection will have your pick up point above the carburettor throttle butterflies, this was mainly designed for pollution control to raise combustion chamber temperatures at idle thereby lowering emissions.

 

You will get more benefit on a street performance motor from having your vacuum advance connected to a direct vacuum source (below the throttle butterflies) either on the carb of the manifold.

[juit 34]

what I read is the manifold vac gives you better MPG, performance, and cooler engine

 

I was getting the 3

 

thats why Im interested in your settings

[SWPruett 83]

One GM guys writes an article that tells everybody to connect to manifold vacuum and everybody believes it's the best thing since pants with pockets. Leave the vacuum reference line at the ported vacuum port, check total advance AND verify the curve and make absolutely sure you know that the idle and part throttle A/F is correct before assuming anything.

[DocWok 30]

Well juit, lots of opinions from both sides of the fence.

Guess it's up to you to try both ways and see which one gives you the best idle quality, the best part throttle driveability and the best fuel economy without the engine running hotter than it did before.

Good luck.

[juit 34]

Im reading this article wich its kinda cool, but is on a duraspark dizzy http://www.carbdford.com/viewtopic.php?t=5543

[barnett468 418]

hello juit. . first of all with all due respect i think you are asking the wrong question because telling you what timing i run on my 500 hp engine with a blower on it wont help solve your particular overheating problem. . this is why i gave you a general spec that i have run on maybe 1000 cars. . also unlike possibly some others here i am also aware of your carb issue which i tried to help you with which unfortunately you still seem to have some problem with, and timing and jetting are somewhat inter related.

 

one of the reasons i asked so many questions is because not everyone thinks of looking at all the things i mentioned, and even though you said it did not run hot before the change to a different vacuum source, you could still have a partially plugged radiator or an excessively stretched timing chain or slipped damper ring etc.. . if your chain or damper ring are incorrect your timing numbers will be abnormal and therefore difficult to properly set.

 

manifold vac mainly affects idle it will not improve mileage much if at all because as soon as your throttle is opened more than around 1/8 of the way ported and manifold vac are exactly the same. . . also you cannot or should not run the timing retard section of a duraspark box unless it is determined that it will be beneficial in your particular case.

.

Edited October 20, 2014 by barnett468

[barnett468 418]

also, as someone asked, yes, i can definitely tell some things by knowing if a rad is aluminum or not, especially if it is made overseas. . the bottom line as i and some others have mentioned,, is that in your case, if you have overheating or performance problems using ported vacuum and typical timing settings, you have other, bigger problems that are causing these things. . also once your engine is runninng, it will idle and run the same irregardless of whether it is connected to ported or manifold vac because 10 degrees of idle timing is still 10 degrees no matter how you go about getting it. also it is optimal too run almost as much timing as an engine can tolerate under normal driving conditions irregardless of how this is achieved.

Edited October 20, 2014 by barnett468

[juit 34]

hello juit. . first of all with all due respect i think you are asking the wrong question because telling you what timing i run on my 500 hp engine with a blower on it wont help solve your particular overheating problem. . this is why i gave you a general spec that i have run on maybe 1000 cars. . also unlike possibly some others here i am also aware of your carb issue which i tried to help you with which you still sem to have some problem with and timing abnd jetting are somewhat inter related. . one of the reasons i asked so many questions is because not everyone thinks of looking at alll the things i mentioned and even though you said it did not run hot before the change you could stilll have a partially plugged rad or an excessively stretched timing chain or slipped damnper ring . if your chain or damper ring are inncorrect than your timing numbers will be abnormal and therefore difficult to properly set. . manifold vac mainly affects idle it will not improve mileage much if at all because as soon as yoour throttle is openeed more than arounf 1/8 of the way ported and manifod vac are exactly the same. . . also you cannot or should not run the timing retard section of a duraspark box unless it is determined that it will be beneficial in your particullar case . . i bhas ret

 

 

thanks man I hear ya,

 

no my balancer is not slipped and timing chain is like 6 months old

 

the rad is stock , Im not over heating the engine is running a lil hotter sorry if I didnt explain my self

 

Im asking if you are doing this and curious of your specs

 

tomorrow Ill do a road trip again and see any changes

Edited October 19, 2014 by juit

[barnett468 418]

no prob your welcome . everyone simply wants the best outcome for you . . i have tried ported vac on many engines but rarely used it so hopefully this explains my comments more . . i am connected to ported vacuum and run 12 at idle and 34 all in at 2600 on one of my moderate hp 302 engines.

 

also, in your case, if you run between 8 to 12 and it runs warmer than it has before, you have a problem that is unrelated to timing . . engines that are bored .030 or more will typically run warm in warm weather with a stock 2 row rad . if an engine is .060 it definitely needs a big rad . . if you do not have a fan shroud it can run overly warm etc.

Edited October 20, 2014 by barnett468

[j69302 11]

What else did your mechanic do? Switching from manifold vac to ported isn't enough of a difference to be causing this - in fact, you should end up with less advance (at idle) than you would with ported, and should run cooler.

 

 

How is timing being set? To properly set it, the vacuum advance line need to be plugged so it is disabled while setting timing. 10* with the advance plugged, will read about 14-16 when the advance is hooked back up. In reference to :

also once your engine is runninng it will idle and run the same irregardless of whether it is connected to ported or manifold vac because 10 degrees of idle timing is still 10 degrees no matter how you go about getting it.

 

The quoted part is correct, if timing was set with the vacuum advance hooked up. If it was NOT set with the advance hooked up, you WILL get different timing at idle between the two vacuum sources.

 

 

 

Is your timing set the same as before? (besides the vacuum source)

Did he changed the timing? (besides the vacuum source)

Something made him switch it from manifold to vacuum. What were you having him do in the first place?

 

Is your distributors mechanical and vacuum advance curves PROPERLY adjusted? I bet not. New units don't even come with proper advance curves, and unless you had your distributor advance curved adjusted, than yours is probably incorrect.

 

How much hotter is "running hotter". Is it over heating? if not, and it runs ok, I'd leave it. it will run better this way.

 

Your vac advanced should ALWAYS be hooked to PORTED. Don't get me started on this manifold vs ported myth.

 

Vac advance feature was designed to work at part throttle conditions, and be almost no affect at idle or full throttle, which is why ported source is used, because its limited at idle and full throttle, but strong at part throttle. The exact opposite of manifold vacuum, strong at idle, low at part throttle, and nothing at full power.

 

However, Going from ported vacuum to manifold vacuum, without changing anything else, would advance your timing at idle quite a bit, because the vacuum advance would be MAXED OUT when in this configuration, and might be advanced too much right now for idle, which could make it run warmer.

 

Is it possible you originally had it on ported, and then he switched it to manifold vacuum, resulting in more advance at idle as explained above?

 

What carb do you have, and where is the vacuum advance line plugged into it? A picture would help.

Edited October 19, 2014 by j69302

[juit 34]

When i had it on manifold:

Autolite 2100

Stock manifold

2 inch spacer

Smaller alternator

 

What i have now

Holley 4160

1 inch spacer

Eddy 2121 gasket matched ports

Bigger alternator

 

The alternator made the idle a lil smoother so i had to lower the idle screw like 200 rpms

[barnett468 418]

hello;

 

thanks for the info and none of those things would necessitate the use of manifold vac and nine would cause it to run hot at idle. a lean carb could cause it to run a bit hotter at cruise speed but these things really aren't the cause of your prob.

[DocWok 30]

Hi juit,

 

Here's a link to an informative article from a knowledgeable person that may also be of interest to you.

http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm

[SWPruett 83]

Hi juit,

 

Here's a link to an informative article from a knowledgeable person that may also be of interest to you.

http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm

 

Tada! There it is again!:no:

[juit 34]

what do you think of this video?