Timing and heat ported as opposed to full and effect temps - Chevelle Tech
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post #1 of 21 (permalink) Old May 15th, 19, 1:45 PM Thread Starter
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Timing and heat ported as opposed to full and effect temps

I have another post that we were discussing heating and cooling, but was curious on the effect of running Ported vs Full vacum at idle and too much advance. Do these effect more heat at idle? I have read conflicting information - more timing creates more HP so more heat, but running full vacum adv at idle creates better burn to keep things cooler.

I am running a 383, new motor, all machine work and prep done properly, running 34 degrees total timing, the cam is 465/488 lift and duration of 279/289 with a 112 LS. Running full vacum to the distributer. Compression is at about 9.1. No pinging, no hard starting and pulls great when driving.

Just would like some thoughts or experiences of anyone who has tried running both, full vacum and ported and what the effect was on your temps at idle.

Not looking for advice on cooling suggestions, have that covered on the other post and I am trying a few things there, just looking for information on timing and heat effect at idle speeds.

Thks

Rich

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post #2 of 21 (permalink) Old May 15th, 19, 7:19 PM
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Re: Timing and heat ported as opposed to full and effect temps

Try it and find out. Experimentation is a great way to learn.

First Guess: No big difference if the cooling system is adequate. Bigger difference if the cooling system can't keep up, or if there's additional reasons the engine might run warm--lean air-fuel mix, air conditioning problems, etc.
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post #3 of 21 (permalink) Old May 15th, 19, 7:40 PM
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I did it a couple years ago after reading about the difference between ported and full vacuum. I switched it from ported to full and noticed zero change in temperature
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post #4 of 21 (permalink) Old May 16th, 19, 1:48 AM
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Re: Timing and heat ported as opposed to full and effect temps

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Originally Posted by JF74chevelle View Post
I did it a couple years ago after reading about the difference between ported and full vacuum. I switched it from ported to full and noticed zero change in temperature
I have also tested zero difference on my car If I run ported or non ported even had less initial with old hei distributorvand didnt saw a change.

I think Schurkeys guess is right.

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post #5 of 21 (permalink) Old May 16th, 19, 8:21 AM Thread Starter
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Re: Timing and heat ported as opposed to full and effect temps

Thks guys, Thankful for your feed back, quite honestly I don't want to run it on ported vacum, it runs so much better on full. I'll try it just for the heck of it, but will continue the path of different shroud, fan spacing etc.

Thks

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post #6 of 21 (permalink) Old May 16th, 19, 1:19 PM
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Re: Timing and heat ported as opposed to full and effect temps

There is more to it than that. First you need to make sure there is adequate vacuum advance at cruise, then move it over to full manifold and adjust carb a/f mixtures accordingly.. It does make a difference because leaner fuel mixtures require more advanced timing to run efficiently. It will drop temps and smooth the idle of a more radical cam.
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post #7 of 21 (permalink) Old May 17th, 19, 6:05 AM
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Re: Timing and heat ported as opposed to full and effect temps

This ^
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post #8 of 21 (permalink) Old May 17th, 19, 1:54 PM
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Re: Timing and heat ported as opposed to full and effect temps

If your initial and total is close to correct ported or non ported vacuum has very little to Do with operation temp.
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post #9 of 21 (permalink) Old May 17th, 19, 1:59 PM
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Re: Timing and heat ported as opposed to full and effect temps

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Originally Posted by Gtogeoff View Post
This ^
If you have a Leyland or a cam for a girl
For Us that use a more manly cam theres not enough vacuum in gear for manifold vacuum. Not even with your beloved Crane can. If you need help with your Chevelles cooling system just let us know if its your Leyland your talking about go to another forum. Any pics of your Chevelle yet or is your Camera still broken?
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post #10 of 21 (permalink) Old May 17th, 19, 3:04 PM Thread Starter
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Re: Timing and heat ported as opposed to full and effect temps

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Originally Posted by Chevelle 1969 View Post
If your initial and total is close to correct ported or non ported vacuum has very little to Do with operation temp.
Thanks - How do you determine "correct" with the cam I mentioned and a stroker. My total is at 34, and no pinging and no hard starting, and runs nicely. I assume if anyone of those are an issue then I would have to back it down. I certanly can't set it at a stock application as there are no settings for it.

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post #11 of 21 (permalink) Old May 17th, 19, 3:23 PM
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Re: Timing and heat ported as opposed to full and effect temps

Rich, if it runs fine on manifold-leave it. I have never really noticed any variations of temps at idle between ported,manifold or no vacuum advance when the curve is right and it sounds like you are all set. Can't over think this stuff, its farm simple
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post #12 of 21 (permalink) Old May 17th, 19, 8:47 PM
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Re: Timing and heat ported as opposed to full and effect temps

LESS advance usually runs warmer has always been my experience with these. It isnt as stinky either, marginally. With a lumpy cam there were overriding concerns so full went back on. Believe it was an emissions thing.
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post #13 of 21 (permalink) Old May 18th, 19, 2:52 PM
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Re: Timing and heat ported as opposed to full and effect temps

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LESS advance usually runs warmer has always been my experience with these.
That has been my experience. Back in the day when I lived in CT and my wife's bone stock 1977 Chevy V8 needed its annual sniff (which it almost always failed with "stock settings) I turned the distrib. to decrease the advance. Presto it passed. Every time. The trick was to get it sniffed and get outta "dodge" before it overheated. This was not a performance car with all the endless curve modifications and carb tuning and and and that we do with cars that are discussed here. It was just a DD that for whatever reason drove great with the stock timing and whatnot settings but always flunked the test.

Turn back distrib. get a Passed sticker for the window....turn distrib. back to normal advance setting and .......happy motoring until next year. Sometimes after testing I drove down the street from the test station pulled over within sight of the test station and bumped the timing right there on the side of the road. I had an index mark painted on the distrib. and the manifold. All ya needed was a distrib wrench to back off the clamp and retighten it after "tuning".
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post #14 of 21 (permalink) Old May 18th, 19, 4:26 PM
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Re: Timing and heat ported as opposed to full and effect temps

34* total is a little light, did you try 18 initial, 36-38 total to see if things change? I did not see where your initial was stated.

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post #15 of 21 (permalink) Old May 19th, 19, 5:06 AM
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Re: Timing and heat ported as opposed to full and effect temps

In the 70s after ported vac adv had been in use for a few years & emissions got tighter- & engines ran hotter- manufacturers incorporated a temp switch into the cooling so that once temps reached a critical temp, ported VA was switched to manifold VA to cool the engine. I doubt the manufacturers would have gone to this expense if this didn't work....

This is the description in my Motors Manual 1973-78 models, for GM cars. Others are similar. " ...the thermo vacuum switch is added to the system on some engines. The switch senses engine coolant temp & if temp reaches 220*, the switch valve moves to allow manifold vacuum to reach the dist & advance the timing to & allow the engine to run cooler."

The Crane adj vac adv unit will work down to as low as 5~6" of vacuum which will cover most peoples needs.
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