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Old 09-05-2014, 06:32 PM
 
Location: Eastern Washington
17,106 posts, read 56,712,890 times
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I still have a 71 Impala, originally it had "transmission controlled spark" where it got no vacuum advance except in 3rd (high) gear. I went through it and de-smogged it, put on an adjustable vacuum advance unit, and can get up to about 17 MPG as opposed to Trapper's friend getting only 8 back in the day. This is with small-block 400 ci and Turbo 350 trans, 2.73 gears.
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Old 09-05-2014, 06:53 PM
 
Location: A safe distance from San Francisco
12,350 posts, read 9,627,178 times
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Quote:
Originally Posted by M3 Mitch View Post
I still have a 71 Impala, originally it had "transmission controlled spark" where it got no vacuum advance except in 3rd (high) gear. I went through it and de-smogged it, put on an adjustable vacuum advance unit, and can get up to about 17 MPG as opposed to Trapper's friend getting only 8 back in the day. This is with small-block 400 ci and Turbo 350 trans, 2.73 gears.
My '71 Bonneville had that and it was a nightmare. It developed an intermittentcy where that vacuum valve would open and close rapidly at highway speed and felt like the engine had a bad irregular miss.

I finally got fed up with it and bypassed that valve altogether with a hose routed directly to the distributor and adjusted the distributor timing accordingly.
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Old 09-16-2014, 03:16 AM
 
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