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04-30-2020, 01:42 PM
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#1 |
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Registered User
Join Date: Oct 2019
Location: Monaca, PA Western PA
Posts: 93
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Confused about ported vs. Manifold vacuum.
Can someone please explain which port I should hook up my vacuum advance on my dizzy to? I am running a blueprint 355 that dynoed at 430hp. With hei. I have read good and bad about using both. I know that we have many experienced machanics on this site. Can someone please explain the correct port to me, please?
__________________
1971 Chevrolet C20, Blueprint 355. Holly Street Avenger 430HP. Turbo 350 1952 Chevrolet Deluxe. Stock. True survivor with 1 paint job 1953 Buick Special. GM 355. Just a good smooth engine. |
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04-30-2020, 01:50 PM
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#2 |
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Registered User
Join Date: Jan 2013
Location: Eastern TN
Posts: 1,919
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Re: Confused about ported vs. Manifold vacuum.
This is one of those try it and see how the motor likes it. Generally manifold vacuum is best. It will give you vacuum advance at idle. You usually do t have an issue with to much advance since it will drop off as the throttle is applied.
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04-30-2020, 03:59 PM
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#3 |
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Who Changed This?
 
Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,088
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Re: Confused about ported vs. Manifold vacuum.
Ported spark was used to reduce emissions back in the day. More advanced timing produces more oxides of nitrogen. Your engine will idle better and potentially idle cooler with manifold vacuum instead of ported vacuum, and will have slightly better off-idle response.
__________________
~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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04-30-2020, 04:14 PM
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#4 | |
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Registered User
Join Date: Dec 2017
Location: Albuquerque NM
Posts: 32
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Re: Confused about ported vs. Manifold vacuum.
Quote:
My mechanic and I started with ported then ended up on manifold vacuum. It runs very smooth across the power band on manifold vacuum. As I recall, it was easier to set a lower idle after we switched to manifold. As others have said, the ported was for early emissions setups. |
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04-30-2020, 04:36 PM
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#5 | |
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Just here to tinker
Join Date: Jun 2008
Location: Holland, MI
Posts: 3,672
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Re: Confused about ported vs. Manifold vacuum.
Quote:
__________________
78 C10 SWB Diesel #1 (wrecked)http://67-72chevytrucks.com/vboard/s...1978+silverado 78 C10 SWB Diesel #2 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=650751 60 GMC Suburban (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=445526 60 GMC 1000 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=298235 67 GMC 1500 (sold) http://67-72chevytrucks.com/vboard/s...d.php?t=803695 86 Suburban(summer unit) http://67-72chevytrucks.com/vboard/s...d.php?t=810697 88 Suburban 4x4(winter unit)https://67-72chevytrucks.com/vboard/...25#post8900725 |
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04-30-2020, 05:24 PM
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#6 |
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Registered User
Join Date: Jul 2015
Location: 2nd left past the stump on a dirt road.
Posts: 2,629
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Re: Confused about ported vs. Manifold vacuum.
Try this for reference material:https://www.crankshaftcoalition.com/...EI_distributor
I use the adjustable vac advance. Gives more room for tuning. |
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04-30-2020, 07:37 PM
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#7 |
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Registered User
Join Date: Oct 2019
Location: Monaca, PA Western PA
Posts: 93
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Re: Confused about ported vs. Manifold vacuum.
Thank you all for the information.
__________________
1971 Chevrolet C20, Blueprint 355. Holly Street Avenger 430HP. Turbo 350 1952 Chevrolet Deluxe. Stock. True survivor with 1 paint job 1953 Buick Special. GM 355. Just a good smooth engine. |
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