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#1 |
Registered User
Join Date: Jun 2016
Location: Central California
Posts: 13
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I want to run my vacuum advance with manifold vacuum, but my carb (old Edelbrock 1408, discontinued smog compliant carb from what I've heard) only has ported vacuum on the front driver's side, instead of the usual manifold vacuum. I'm wondering if I can tee it in with my power brakes, which runs to the back of the intake manifold to a tee with an unused port. Would this cause any interference with the advance signal or would I be good? Also I'm wondering whether the modulator for the trans should be on manifold as well, as it's also connected to ported.
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1972 C10 Cheyenne w/350 Last edited by mchyphy; 03-31-2017 at 01:21 AM. |
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#2 |
Registered User
Join Date: Nov 2016
Location: lowell ma
Posts: 750
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Re: Vacuum teeing question
Why do you want the advance on non ported vacuum?
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#3 |
Registered User
Join Date: Jun 2016
Location: Central California
Posts: 13
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Re: Vacuum teeing question
From what I've read there's benefits to running manifold vacuum for advancing, like running cooler at idle, slightly better fuel economy at idle, and better off the line throttle response.
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1972 C10 Cheyenne w/350 |
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#4 |
Registered User
Join Date: Dec 2009
Location: El Dorado Ca
Posts: 3,374
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Re: Vacuum teeing question
I have always been told to run ported vacuum
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#5 | |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,628
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Re: Vacuum teeing question
Quote:
Post a pic of your carb and intake behind the carb. I'm sure there's other sources for manifold vac to do everything you need. And there are other vacuum trees available too. |
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#6 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Vacuum teeing question
Only spark should be ported. I'm a big fan of keeping things as GM intended, but some of the reasons for ported spark were emissions based (less advance at idle keeping a hotter EGT netted less NOX or something like that). And in some of those cases they'll run better on manifold.
I'd hook it up like your truck was from the factory unless and until you have a compelling reason not to. Trans should be manifold.
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#7 |
Registered User
![]() Join Date: Sep 2015
Location: Mohnton pa.
Posts: 208
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Re: Vacuum teeing question
Im running a edelbrock carb also. I connected my Hei dist to the tree fitting behind the carb, which is manifold vacume. I have no pinging while driving.
Ive been considering connecting it to the carb to see if there is any performance gains off the line and while im towing. |
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#8 |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,158
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Re: Vacuum teeing question
Ported vacuum is the better way to go. For several reasons. One is that your idle speed won't be affected by your vacuum. Timing at idle is unaffected by vacuum whether in gear and out. Two, coasting with the throttle closed is the time of highest manifold vacuum, by having the vacuum shut off you prevent the engine from running on the idle circuit with a lot of timing advance, possibly causing detonation. (Pull the vacuum advance to full when your idling to see how well the engine runs, assuming that it works properly to start) Not to mention the extra wear on the advance diaphragm from being exposed to the high vacuum level every time you let off the throttle. Virtually every car manufacturer used ported vacuum on carbureted four stroke engines.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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