Quote:
Originally Posted by seattle smitty
Thanks much, Steve; this is going to be a great thread!! I hope that somewhere in the course of developing it you will speak specifically to those of us who are trying to improve the fuel efficiency and useful power of our daily-drivers and work vehicles.
Also, could you advise us on the consequences of EGR systems for ignition advance curves. I disabled the EGR on a Mopar 318 years ago and was rewarded with an engine that would ping when climbing even small grades. I temporarily "fixed" the problem to some extent by disconnecting the vacuum advance. Then I studied EGR and learned that the factory recurves (advances) the distributor for best efficiency with EGR. My recourse, then, was to get distributor weights and springs from an older engine to put on my EGR-less '73 engine.
Nowdays I'm more likely to recondition all the emissions systems and leave them in place. But I'm rebuilding a car now ('87 Dodge Colt Vista wagon by Mitsubishi with the G63B engine) which has a notoriously troublesome EGR system, so I'm getting rid of it. The problem is that there was never a pre-smog G63B, so I have to figure out how to recurve my distributor. There surely are others here facing a similar situation. Steve, can you give us any guidance for coming up with a non-EGR curve?
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Although you might initially think that the cooler combution chamber temperatures caused by an EGR system would allow you to run more timing, this is not so. The reason being, that the recirculated exhaust gas does not burn very well.
As you noted in your post, you temporarily “fixed” your problem by disconnecting your vacuum advance. Of course, you probably saw a drop in mpg.
Anyway, a nice smooth advance curve is dependent upon:
1) Proper weights and springs providing proper mechanical advance.
2) A vacuum advance that is coordinated to work in conjunction with the mechanical advance.