need advice on modified engine
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 23
Likes: 0
From: Lumberton TX
need advice on modified engine
I have just purchased a 78 L-82 with unkown mileage. The previous owner(s) have replace the factory manifold with headers. They did not do a great job of this as it seems they simply ripped out all of the emission control items that were factory--lots of cut vacuum hoses. My question is am I better off going back to the factory manifold, AIR system, and replacing all of the emission control items they gutted. The headers are in really bad shape and will need to be removed either way. The car runs very rough and has trouble idling--especially when cold.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Welcome to the forum. 
Take a sec to fill out your profile so we can see where you live. If you were in California, then the suggestion would be to put it all back to stock. However, great gains can be had by removing the stock exhaust system and replacing it with better flowing exhaust.
It usually takes a lifetime to figure out what the previous owners do to the cars we buy. We call all previous owners, Bubba, because they never do anything right, and it's a PITA to fix it all.
However, use this opportunity to make some changes that will increase the performance and enhance your enjoyment of the car.
Can you post some pics of the car, the engine, and the problem areas liek cut hoses and such?
Take a sec to fill out your profile so we can see where you live. If you were in California, then the suggestion would be to put it all back to stock. However, great gains can be had by removing the stock exhaust system and replacing it with better flowing exhaust.
It usually takes a lifetime to figure out what the previous owners do to the cars we buy. We call all previous owners, Bubba, because they never do anything right, and it's a PITA to fix it all.
However, use this opportunity to make some changes that will increase the performance and enhance your enjoyment of the car.
Can you post some pics of the car, the engine, and the problem areas liek cut hoses and such?
Racer
Joined: Mar 2007
Posts: 306
Likes: 0
From: New Hampshire
I have headers and side pipes on my 77. I took off the emmissions parts and mine runs great. If your car is running rough, check all vacum hoses for any leaks, then do a good tune-up. I agree that if you live in California or a state that inspects for emmissions, then put it all back to stock.
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 23
Likes: 0
From: Lumberton TX
Thanks for the response. I am not in California or a metro area requiring some high powered emissions control so that is not a real concern. My main concern is will the car run well without the emission control systems in place as factory designed? Another question--how do you get the engine to run well from a cold start without the heat riser system?--this is gone also as the headers do not have this installed. Parts missing are AIR pump, EFE actuator, ERG actuator, and all associated vacuum hosed--catalytic converter is still installed. Carb has plugged vacuum ports all around. Not sure which of these is essential to the car idling properly or cold starting. Also has upgrade high voltage distributor in place of factory system.
Racer
Joined: Mar 2007
Posts: 306
Likes: 0
From: New Hampshire
All I do is pump it two or three times and it starts. Once the car is warm, it starts right away. My old heat riser never worked anyways!! 
I was thinking of going to a manual choke but so far mine seems to work all right. The engine doesn't know if it has emmission controls on it, it's the same block they used before 1974. If the car is tuned properly, I don't think you will have any problems, the car will breath better, your performance will increase and imho, the engine will last longer and cleaner.
I was thinking of going to a manual choke but so far mine seems to work all right. The engine doesn't know if it has emmission controls on it, it's the same block they used before 1974. If the car is tuned properly, I don't think you will have any problems, the car will breath better, your performance will increase and imho, the engine will last longer and cleaner.
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
It should run and idle fine w/o the emissions stuff if set up properly but you need an electric choke for cold weather and to compensate for lack of EFE. Small tube at front of carb and angled down is for choke pull-off. Need vacuum advance too. EGR and AIR doesn't matter. Exhaust sounds bizarre - headers into a single cat? You can run full dual exhaust - probably need to go up 2 jet sizes.
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Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 23
Likes: 0
From: Lumberton TX
It should run and idle fine w/o the emissions stuff if set up properly but you need an electric choke for cold weather and to compensate for lack of EFE. Small tube at front of carb and angled down is for choke pull-off. Need vacuum advance too. EGR and AIR doesn't matter. Exhaust sounds bizarre - headers into a single cat? You can run full dual exhaust - probably need to go up 2 jet sizes.
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 23
Likes: 0
From: Lumberton TX
yes, EGR is not connected and one of the vacuum ports is broken off. How could I tell if this was compensated for? The EFE actuator looks like someone put a hammer to it--broke off clean at the thermostat housing.
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 23
Likes: 0
From: Lumberton TX
Have the GM assembly manual with fairly good pics of what vacuum line goes where--but most of the "where" is missing.
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 23
Likes: 0
From: Lumberton TX
Welcome to the forum.
Take a sec to fill out your profile so we can see where you live. If you were in California, then the suggestion would be to put it all back to stock. However, great gains can be had by removing the stock exhaust system and replacing it with better flowing exhaust.
It usually takes a lifetime to figure out what the previous owners do to the cars we buy. We call all previous owners, Bubba, because they never do anything right, and it's a PITA to fix it all.
However, use this opportunity to make some changes that will increase the performance and enhance your enjoyment of the car.
Can you post some pics of the car, the engine, and the problem areas liek cut hoses and such?
Take a sec to fill out your profile so we can see where you live. If you were in California, then the suggestion would be to put it all back to stock. However, great gains can be had by removing the stock exhaust system and replacing it with better flowing exhaust.
It usually takes a lifetime to figure out what the previous owners do to the cars we buy. We call all previous owners, Bubba, because they never do anything right, and it's a PITA to fix it all.
However, use this opportunity to make some changes that will increase the performance and enhance your enjoyment of the car.
Can you post some pics of the car, the engine, and the problem areas liek cut hoses and such?
Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
it's been a while, so without looking up, it goes something like this. the egr system let exhaust gas into the intake manifold at certain times based on engine load above some minimum water temp. besides the objective of that, it obviously affected the carb mixture. so something in the carb was changed to compensate. at least that was how it was in the earlier models.
i'm not familiar with the specifics of correcting this on a 78 (?) model, but if it were an earlier version, you might start with the jet, metering rod, and air bleed sizes of a non-egr version to get pretty close with the carb metering. a buddy with an earlier version carb had removed the egr with no changes to the carb, and it ran too rich, but it ran.
maybe someone who has done this on a 78(?)-(?) will chime in . . .
i'm not familiar with the specifics of correcting this on a 78 (?) model, but if it were an earlier version, you might start with the jet, metering rod, and air bleed sizes of a non-egr version to get pretty close with the carb metering. a buddy with an earlier version carb had removed the egr with no changes to the carb, and it ran too rich, but it ran.
maybe someone who has done this on a 78(?)-(?) will chime in . . .
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 23
Likes: 0
From: Lumberton TX
It should run and idle fine w/o the emissions stuff if set up properly but you need an electric choke for cold weather and to compensate for lack of EFE. Small tube at front of carb and angled down is for choke pull-off. Need vacuum advance too. EGR and AIR doesn't matter. Exhaust sounds bizarre - headers into a single cat? You can run full dual exhaust - probably need to go up 2 jet sizes.
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 23
Likes: 0
From: Lumberton TX
it's been a while, so without looking up, it goes something like this. the egr system let exhaust gas into the intake manifold at certain times based on engine load above some minimum water temp. besides the objective of that, it obviously affected the carb mixture. so something in the carb was changed to compensate. at least that was how it was in the earlier models.
i'm not familiar with the specifics of correcting this on a 78 (?) model, but if it were an earlier version, you might start with the jet, metering rod, and air bleed sizes of a non-egr version to get pretty close with the carb metering. a buddy with an earlier version carb had removed the egr with no changes to the carb, and it ran too rich, but it ran.
maybe someone who has done this on a 78(?)-(?) will chime in . . .
i'm not familiar with the specifics of correcting this on a 78 (?) model, but if it were an earlier version, you might start with the jet, metering rod, and air bleed sizes of a non-egr version to get pretty close with the carb metering. a buddy with an earlier version carb had removed the egr with no changes to the carb, and it ran too rich, but it ran.
maybe someone who has done this on a 78(?)-(?) will chime in . . .
Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
holley demon different
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Check out upcoming car shows....Corvette shows, if you can find them. Anyone with a stock '78 will be glad to show you the vacuum line routing and what they go to. Otherwise, it's go to several manuals and sort it all out.