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Old 03-28-2011, 01:43 AM
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Vacuum advance on blower engine

Hi
I am wondering do you need the vacuum advance on a blower engine 350/weiand 144 street driven?
or is it better to have only mechanical advance and ignition box with timing retard?

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Old 03-28-2011, 05:26 AM
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Vacuum advance is mostly for economy. It advances the timing under light load (high vacuum), which gets better gas mileage at cruise. I don't know how much it will affect cruising gas mileage, but the engine will work fine without vacuum advance. Its very common to run race engines without any vacuum advance.

Bruce
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Old 03-28-2011, 06:15 AM
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Not to disagree w/anyone, but I'm of the mind that anytime a vacuum advance can be used, it should be used. Not just as an economy thing, but to aid the engine to run smoother and cooler in some circumstances.

If possible, use electronics to help you w/this. That's a better solution than analog systems not designed for boost- although analog set-ups can surely do the job for less money.

I bookmarked a thread that touches on this subject. It might be of some use to you (as well as doing a search here for more info):
vacuum advance and a blower? There are also threads listed at the bottom of the page that are similar.

Boost referencing the carb as well as taking the vacuum for the advance canister from below the blower is important.
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Old 03-31-2011, 10:09 PM
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After the above thread I continued to test the vacuum advance. I finally got it right about June or so as I got the idle mix leaned out. Gotta like the AFR gage. Gas mileage picked up dramatically and the motor idle speed is even lower. It's about 750-800 in gear and only about 900 hot idle neutral. The 3000 converter seemes to pull much less below 1000 rpm which is what I wanted. The sound of the exhaust is also much quieter. The lugging sound is now gone.

I've done a bunch of hard launches and some 30-90 passing tests. The motor runs perfect with no hesitation and no detonation and it can idle as long as necessary in stalled traffic. Hard to beat this.

The car sat for nearly 3 months without starting it. I cleaned it up and got it ready for an indoor show. It started almost instantly and after a couple minutes it dropped into a nice smooth idle.

The bottom line is try to run the vac adv for street. Racing you can lock it out and pick up the idle speed a little.

I spend a lot of time experimenting and trying things out with this car. It run differently than the blower motors I did years ago mostly because of the poor gas we have to use today. Cam tech and head tech is far superior also.

I've got hand full of stuff I want to try if we ever get rid of this dang snow and salt.
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