Egr deletion
#1
05-06-2009, 10:35 PM
Egr deletion
I am getting rid of the EGR system on the '79 400 that I've been building.
I will be keeping the existing 2 bbl as I am on a budget and will be selling this truck when I get it done. Is there anything that needs to be done to the carb to compensate for the missing EGR air?
Jason
I will be keeping the existing 2 bbl as I am on a budget and will be selling this truck when I get it done. Is there anything that needs to be done to the carb to compensate for the missing EGR air?
Jason
#2
05-07-2009, 07:27 AM
Laughing Gas
#3
05-09-2009, 05:26 PM
Hi RCrawler:
I would agree with the other reply you got that you won't need to re-jet the carburetor for an EGR disconnect, unless you want to enrichen the main mixture by a size or two because the factory supplied jets were running the engine too lean. Depends on what your carb. was supplied with. The better way to do this however, is to run economy sized main jets (not too lean), and then replace the orifices with larger diameter ones in the fuel enrichment system. Then you get the extra fuel flow for power and cylinder cooling when you need it, not at steady state cruise when you don't, wasting fuel.
For the ignition distributor however, when I disconnected my EGR, the distributor vacuum advance balance spring setting needed to be changed drastically, because of severe part throttle pinging. The curve is set up at the factory to try to regain the losses in efficiency because of the great amount of exhaust gas (basically Nitrogen) being introduced into the combustion chamber at part throttle to lower peak chamber temps that cause NOX formation.
When you disconnect the EGR, you'll need to reduce the amount advance for a given amount of vacuum applied to the vacuum diaphragm. When I started, the diaphragm started to advance the points at only about 8" of vacuum. After I "unwound" (CCW)the allen head screw (3mm?) inside the vacuum nipple of the vacuum advance unit about 16 turns, the advance began at about 15" of vacuum, and the part throttle knocking was gone. I had a lot of carbon build-up on my pistons, so I had to back off the adjustment a lot. But basically, you're reducing the amount of part throttle advance, until you get rid of the pinging.
To adjust the distributor, on a hot day, using the octane fuel you intend to run normally, I would start with disconnecting the advance, and advancing the distributor basic timing until it starts pinging at full throttle/ RPM (up to about 36 degrees maximum advance - I'm not sure if it's OK to go beyond this even if you can), then back off a little. Then play with the vacuum advance until you're just below the limit for knocking a part throttle operation. This should give you timing for maximum power at WOT and maximum part throttle fuel economy for the octane fuel you're running. If you plan on towing sustained heavy loads, I might back off these timing limits a little more for an extra margin of safety. You don't want to be knocking pulling a trailer up a long hill on a highway.
There's a lot more to the science behind NOX formation, combustion chamber temps, and the few thousandths of an inch thick thermal barrier of air in a combustion chamber that protects the surfaces from direct contact with the high heat of combustion, and how detonation scrubs that layer away causing melted parts, but in a nutshell, ... one of my relatives
, don't detonate!
I got great improvements on my stock engine, even more after I changed the cam, gears, and did some head work. I think you'll be pleased with the improvements you'll get from the EGR removal.
I would agree with the other reply you got that you won't need to re-jet the carburetor for an EGR disconnect, unless you want to enrichen the main mixture by a size or two because the factory supplied jets were running the engine too lean. Depends on what your carb. was supplied with. The better way to do this however, is to run economy sized main jets (not too lean), and then replace the orifices with larger diameter ones in the fuel enrichment system. Then you get the extra fuel flow for power and cylinder cooling when you need it, not at steady state cruise when you don't, wasting fuel.
For the ignition distributor however, when I disconnected my EGR, the distributor vacuum advance balance spring setting needed to be changed drastically, because of severe part throttle pinging. The curve is set up at the factory to try to regain the losses in efficiency because of the great amount of exhaust gas (basically Nitrogen) being introduced into the combustion chamber at part throttle to lower peak chamber temps that cause NOX formation.
When you disconnect the EGR, you'll need to reduce the amount advance for a given amount of vacuum applied to the vacuum diaphragm. When I started, the diaphragm started to advance the points at only about 8" of vacuum. After I "unwound" (CCW)the allen head screw (3mm?) inside the vacuum nipple of the vacuum advance unit about 16 turns, the advance began at about 15" of vacuum, and the part throttle knocking was gone. I had a lot of carbon build-up on my pistons, so I had to back off the adjustment a lot. But basically, you're reducing the amount of part throttle advance, until you get rid of the pinging.
To adjust the distributor, on a hot day, using the octane fuel you intend to run normally, I would start with disconnecting the advance, and advancing the distributor basic timing until it starts pinging at full throttle/ RPM (up to about 36 degrees maximum advance - I'm not sure if it's OK to go beyond this even if you can), then back off a little. Then play with the vacuum advance until you're just below the limit for knocking a part throttle operation. This should give you timing for maximum power at WOT and maximum part throttle fuel economy for the octane fuel you're running. If you plan on towing sustained heavy loads, I might back off these timing limits a little more for an extra margin of safety. You don't want to be knocking pulling a trailer up a long hill on a highway.
There's a lot more to the science behind NOX formation, combustion chamber temps, and the few thousandths of an inch thick thermal barrier of air in a combustion chamber that protects the surfaces from direct contact with the high heat of combustion, and how detonation scrubs that layer away causing melted parts, but in a nutshell, ... one of my relatives
, don't detonate!I got great improvements on my stock engine, even more after I changed the cam, gears, and did some head work. I think you'll be pleased with the improvements you'll get from the EGR removal.
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