Can I eliminate the vacume advance on a duraspark distributor from in an 85 GT mustang simply by not hooking up the vacume line to the diaphram. After all when setting the timing this vacume line is removed and pluged. Is there really a need to run it. I have an old Ford motorsport duraspark type distributor also that is basically the same thing as the stock unit and it does not have any of the vacume advance componets. Its completely mechanical. Just wondering if I can run the stock unit as a mechanical.
Duraspark distributor ????
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that other distributor probably has no steel cam gear on it so be sure to swap the gear from the 85 to that one if you use it on a roller engine. don't unhook the advance, you will never get it timed right. either it will be to advanced and be very hard to crank or to retarded and backfire a lot.
rd
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You can simply remove the vacuum line and plug it at the source.
Then you will have only mechanical advance.
The reason people say this will be a part throttle driveability problem is because the vacuum is used at low rpm for advance and the stock mechanical springs do not provide full advance until 3000 to 4000 rpm.
You cure this by installing lighter springs.
You can set the max mechanical advance by using the desired slot on the advance plate.
This will cure the part throttle problem and give you full advance by 2000 or so rpm.
A loose converter and or big rear gears helps.
My 82 has had this for a year and had run its best with 6 deg base timing and 32 deg total, using the 13 L slot in the advance plate. I do have a 3k converter and 4.10 gears, so 800 to 2800 rpm is not important.
Then you will have only mechanical advance.
The reason people say this will be a part throttle driveability problem is because the vacuum is used at low rpm for advance and the stock mechanical springs do not provide full advance until 3000 to 4000 rpm.
You cure this by installing lighter springs.
You can set the max mechanical advance by using the desired slot on the advance plate.
This will cure the part throttle problem and give you full advance by 2000 or so rpm.
A loose converter and or big rear gears helps.
My 82 has had this for a year and had run its best with 6 deg base timing and 32 deg total, using the 13 L slot in the advance plate. I do have a 3k converter and 4.10 gears, so 800 to 2800 rpm is not important.
Found this searching the net. Good information here. Thanks for the tips. I'll check out the ligthter springs and advance plates.
Duraspark re-curve information
Duraspark re-curve information
It's also worth considering that with dissimilar springs, that you can recurve your distributor at different rates. Further, if you have the attachment tab bent on one of the spring attachments so that the initial "take-up" on one of the springs is retarded slightly from idle, you can have a multi-step, fully mechanical advance that is pretty similarly curved to a vacuum advance. The only place you're likely to suffer is in that "idle, to off-idle" range. This area is where you will experience (as discussed earlier) the potential for starting / cranking problems and also likely have the biggest affect on your fuel burn rates. If economy and / or emissions are not a huge deal to you (they probably aren't), then you may want to do away with your vacuum advance. I've kept mine hooked up, but only because I have a CraneCams Street / Strip adjustable distributor that allows me to electronically map my advance curve without having to monkey with springs, tabs, and keys. I love it! Good luck with yours.
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