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#1 |
Registered User
Join Date: Dec 1999
Location: New York
Posts: 288
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which vacuum port?
Wondering which port on my Edelbrock 1406 to use for distributor vacuum line. I've been using the passenger side, but today I switched to the driver's side, and the engine picked up considerable rpm's. Not sure if that means it's better, but got me to wondering which side I'm supposed to be hooked up to. Does it make any difference?
Thanks, Chris
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RLTW 70C10 72K10 72K10 Cheyenne 72C10 Cheyenne Super |
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#2 |
Progress = 0%
Join Date: Nov 2001
Location: Kansas City, MO
Posts: 2,108
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Driver's side is correct. Do you have the owner's manual for the carb? If so, I belive it explains the differences of the two ports.
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Jason - '67 GMC swb | '57 Bel-Air 4dr hardtop | '56 210 4dr Wagon | 2000 GMC Sierra |
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#3 |
Registered User
Join Date: Dec 1999
Location: New York
Posts: 288
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Slammed, I checked out your website. What a beautiful truck!! Man, you have done some really great work there. Let us all know when you finish it!
I somehow lost the owner's manual for the carb, which is a real pain. Why driver's side? Does your manual say why? Thanks, Chris
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RLTW 70C10 72K10 72K10 Cheyenne 72C10 Cheyenne Super |
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#4 |
Registered User
Join Date: Jan 2001
Location: Killingworth, CT. USA
Posts: 3,378
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I have found using the ported vaccum on the pass side works best for a daily driver looking for fuel economy. No need for full vaccum advance at an idle on a stocker.
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1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist. |
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#5 |
Fabricate till you "puke"
Join Date: Jun 2002
Location: Ill
Posts: 9,403
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For the most part, hot cams & fat carbs like full manifold on the vac advance.... to set them up usually requires a little recurving & an adjustable adv can. The chevs ran full manifold vac to about the mid 60's, till the carburation was leaned out going into the 70's . Most of the factory vac cans put out way too much vac timing, & were too conservative on the intial/mechanical advance for performance usage. even my old plow truck (stock 355, with a crane 266) is running full manifold on the vac advance. I would say try it both ways.......run it how it works best
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69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears.... |
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#6 |
Used to have a truck
Join Date: May 2002
Location: port orchard WA
Posts: 1,552
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OK heres the deal. When you hook up your distributor to manifold vacuum ( ported ) you give it full idle vacuum which boosts your timing at idle. That allows you to set it at 10 degrees static or so for easy starting with a stock starter. Once it is started you develop vacuum and your timing jumps up to 25-35 degrees or so . That gives you a smooth idle with anything over a stock cam. It also gives you excellent throttle response off idle. When you gas it your vacuum level drops since your throttle plates are opening up and with it the amount of vacuum advance you are gaining. So your vacuum advance goes down while your mechanical advance begins to take hold . That allows you to avoid detonation under full throttle while still giving you higher than normal advance under cruise conditions. I run a very mild cam and high compression for a street motor. With 92 octane I can run almost 45 degrees of total timing under cruise conditions. That drops to 32 or so under WOT so I avoid detonation .
For a motor you want to run good. Use 12 or so degrees timing with the distributor disconnected . Hook the vacuum line to the distributor up to manifold ( vacuum at idle ) vacuum. If your goal is to maintain low NO2 levels at idle then by all means hook it up to venturi ( timed ) vacuum. Thats all it is good for.
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No truck :-( |
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#7 |
Registered User
Join Date: Dec 1999
Location: New York
Posts: 288
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I've gotten an education here - thanks much for the replies and information. I'm going to give the full manifold vacuum a chance.
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RLTW 70C10 72K10 72K10 Cheyenne 72C10 Cheyenne Super |
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#8 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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While agreeing with the aformentioned explination, (and learning from it myself) but I still say that once an engine has been modified, you need to test and play with it looking at things such as idle quality, MPG, and performance.
I know mine likes having the vac disconnected all together. |
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#9 |
http://public.fotki.com/street
Join Date: Nov 2002
Location: Winnipeg, Canada
Posts: 169
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ported side is best for a a mild engine
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#10 |
Registered User
Join Date: Dec 1999
Location: New York
Posts: 288
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switched to the full manifold vacuum side today and got a big improvement in performance. I was having some bogging under load at low rpms; this cleared it up nice. I will have to agree with the advice - test out both sides or neither to see what works best. Thanks all for the help.
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RLTW 70C10 72K10 72K10 Cheyenne 72C10 Cheyenne Super |
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#11 |
Used to have a truck
Join Date: May 2002
Location: port orchard WA
Posts: 1,552
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One more thing I forgot. If you have a big cam , using ported vacuum will allow you to run a lot of advance at idle. That will let you close your throttle plates more than you normally to maintain idle which has the added benefit of letting you actually tune your idle mixture with the idle mixture screws. That way you get a smoother transition from idle to primary feed circuit so you dont get that nasty bog action and you spend less time monkeying with the crutch AKA the accelerator pump.
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No truck :-( |
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#12 |
Recovering 67-72 Addict
![]() Join Date: Oct 2000
Location: North Bend, WA
Posts: 1,788
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My understanding is that the two types of vacuum available are full manifold vacuum and ported vacuum. I think that MIKEP is talking about full manifold vacuum but calling it ported vacuum?? Anyway, the benefit of ported vacuum was used when EGR systems were used in the 70's and into the 80's. I have had great success in using the full manifold vacuum. I pulled the info in the following post from the Camaros.net site. There was a serious ignition guru over there.
http://64.246.42.114/vboard/showthre...threadid=31344
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68 Short Fleet 4x4; 427; BTO Level 3 700R4; NP205; Dana 60 front and rear; 4" lift with 35's; Disc brakes; AGR variable ratio steering; factory bucket seats; factory tach and tilt. "Friends call me cruzer cuz I like fast cars and fast women" |
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#13 |
Used to have a truck
Join Date: May 2002
Location: port orchard WA
Posts: 1,552
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Ported = manifold
timed = venturi
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No truck :-( |
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#14 |
Fabricate till you "puke"
Join Date: Jun 2002
Location: Ill
Posts: 9,403
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Those terms can be confusing at times, due to the way they are listed, or used...... To look at a Holley diagram, the nipple on the metering block is refered to as "timed spark"(above the throttle plates). The nipple in the base of the carb is refered to as manifold vacumn(below the throttle plates). now go look at the edelbrock site on the exploded veiw of their type carb......#51 is listed as "fulltime vacumn port", & #50 is listed as "ported vacumn port"! I have always refered to timed spark as ported......as there is a small port drilled above the throttle plates to eliminate the vacumn signal @ idle.......AL
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69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears.... |
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