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I have an HEI (Summit) distributor that needs help. The distributor is connected to a Summit multi-spark/rev limiter box. It seems to be able to muster about 18 degrees of mechanical advance and way too much vacuum advance. It seems to be "all in" by about 3400 rpm. I'd like to see it all in sooner than that and I think I'd like to see more like 20 degrees or more mechanical. I know from the Dyno that 36 deg. total is what the motor likes.

The vacuum advance is another story all together. With my current setup, 16 degrees initial and about 18 degrees mechanical, when I plug in the vacuum can I am at about 54 degrees. No problem at idle or full throttle but it is terrible cruising at about 3000 rpm. It flutters and pops.

I hope y'all can advise me on a few things:
1. Does anyone know of a shop in Dallas that can do a re-curve?
2. Does anyone think I should look for different numbers?
3. Does anyone think I should ditch the HEI and get something else?
 

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I have an HEI (Summit) distributor that needs help. The distributor is connected to a Summit multi-spark/rev limiter box. It seems to be able to muster about 18 degrees of mechanical advance and way too much vacuum advance. It seems to be "all in" by about 3400 rpm. I'd like to see it all in sooner than that and I think I'd like to see more like 20 degrees or more mechanical. I know from the Dyno that 36 deg. total is what the motor likes.

The vacuum advance is another story all together. With my current setup, 16 degrees initial and about 18 degrees mechanical, when I plug in the vacuum can I am at about 54 degrees. No problem at idle or full throttle but it is terrible cruising at about 3000 rpm. It flutters and pops.

I hope y'all can advise me on a few things:
1. Does anyone know of a shop in Dallas that can do a re-curve?
2. Does anyone think I should look for different numbers?
3. Does anyone think I should ditch the HEI and get something else?


You should be able to pop the roll pin out and pull the gear off and pull the shaft out of the distributor body. Looking at the mechanical advance you'll see there's a slot that the limiter pin travels in. Modifying the slot to lengthen the amount of travel or sometimes there is a bushing on that pin you can remove to get more travel and this will give you more mechanical advance. You can use a protractor to guage how much advance there is just remember distributor degrees is half of crankshaft degrees so if you want 20 crankshaft degrees total you'll want to see the mechanical advance move 10 degrees. Change to lighter springs and the advance will come in sooner. You can mix and match the springs till the desired rate is achieved. Put a limiter on the vacume advance or change it to an adjustable. Get your initial and mechanical curve dialed in without the vacume advance connected then start adding a little vacume advance and test drive untill you find out just how much the engine combination wants. It will have fuel injection like response when everything is dialed in.
 

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Discussion Starter #8
Thanks Bob. I'll look at the slot to see about increasing travel. I have an adjustable vacuum advance can but that only sets when the advance comes in. I need to limit how much advance it can supply in total. It dawned on me that I have a Crane adjustable can on another distributor that was right on. Maybe I'll swap that one on to this new distributor.
 

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You can also buy an adjustable one with a lockout, I just installed a new HEI and will need to tune the vacuum advance a well.
 
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