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1984 Chevy K1500 Vacuum requirements
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carrerad
New User
Jan 26, 2008, 9:24 AM
Post #1 of 4
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1984 Chevy K1500 Vacuum requirements
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I have a 1984 K1500 that I am converting from a Automatic Trans to Manual and putting a modified, carbuerated 350 with no emissions, I am going to run a vacuum secondary Holley carb and am going to hav e all accessories usable a/c etc. What vacuum lines are needed, my guesws is I can get rid of 90% of this squirrels nest for this can anyone help?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 26, 2008, 12:39 PM
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Re: 1984 Chevy K1500 Vacuum requirements
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Plain manifold vacuum needed to brake booster all by itself. Carb should say what spuds provide what type of vacuum for whatever is needed for distributor (unknown) and for EGR if equipped,
T
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carrerad
New User
Jan 26, 2008, 2:19 PM
Post #3 of 4
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Re: 1984 Chevy K1500 Vacuum requirements
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Thanks for the quick reply. That helps a lot. All of the emissions stuff is a real pain to figure out. I have one more issue, The truck has a vacuum canister which besides all of the emissions stuff has a line to the Carb, fuel pump and Fuel tank I believe. Does this have to be there, what is its purpose for these three connections?
FYI I found a great list of vacuum diagrams on Autozone's website, I know there was another fellow with a 86' 305 GMC with vacuum issues.
Thanks Again for the help!
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 26, 2008, 5:26 PM
Post #4 of 4
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Re: 1984 Chevy K1500 Vacuum requirements
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Ok: This vehicle by model year is exactly the cut-off year where you would not be allowed to use it on public roads in Massachusetts. Any emission control that was ever used in the original automobile/truck can't be altered much going back to 1963 which was the last model year with no mandated emission controls at all. 1964 started with just a pcv valve.
You have a vacuum reservoir for the heat and A/C vents which are vacuum actuated and that must stay. Same with the power brakes.
The other canister is evaporative emmision control which is designed to catch raw hydocarbons (gas vapors) in a charcoal canister when the vapors on top of fuel in tank or even the vapors in the float bowl of carb can't be vented directly to atmophere. Upon starting the engine the canister and other controls send the vapors to be burned in the engine. That system doesn't hurt HP at all but does create more vacuum hoses that connect to the maze sensing coolant temp and the temp inside the air cleaner as to allow what to happen when. All of that could go if the gas tank could vent thru a vented gas cap and carb just vent the tad there underhood.
The carb vent: Think of it like a common toilet! If you sealed up the back of the toilet tank the water couldn't drop out or when it tried to refill would fight against an air lock - got the idea?
Ok: so you need those to operate. Many of the other hoses are sensing engine temp and air temp in the original air cleaner housing and allowed engine to warm up faster and get the choke off asap while keeping a cold engine running as well as possible. They would also delay the use of the EGR until warm. These things make a lot of hoses and lower emissions but aren't working againt you for power at all. EGR is a great way to control knock at part throttle. Working well it doesn't hurt HP at all and allows lower octane fuel to be used. The camshaft has been using exhaust gas to cool the combustion temperature for smoother idle and also prevents knock. The HP ones defeat what is called "exhaust valve overlap" and make the engine run lousy at idle and slower speeds and basically you cover up all the flaws with VERY high octane fuel which you really can't find easily.
The original snorkeling of warm air for intake air really helps. If you operate this engine in very cold weather you'd hate it with all that defeated. Cold (I mean something like below 70F perhaps) slows down the atomization of the fuel/air mixture but if allowed to get too hot would cause knock.
Lot's of stuff goes into the engineering of an engine.
With this all modified YOU have to figure out what the distributor needs and when. Even the HEI ign wasn't vacuum advanced the same way in every make and model. If you want to fiddle with ign go back to 1973 for a dist and get "uniset" points with an adjustable vacuum advance or some aftermarket stuff is available.
Study up on the priciples and a lot of this will make sense
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