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Technical Opinions about a BBC distributor

Discussion in 'The Hokey Ass Message Board' started by 56don, Apr 28, 2019.

  1. I have a 396 Chevy engine I am installing in my 65 Vette.
    The engine is rebuilt, mostly a stock 325 HP engine. Edelbrock intake and carb, oval port head engine.
    The distributor I was going to use is a 1962 Corvette dual point mechanical only advance. I have to run a Corvette distributor in order to utilize the cable driven tachometer.
    The engine was assembled several years ago and I can't find the cam card so I am not sure what the specs are. I remember its a Comp Cam hydraulic and not very radical.
    Question: This is my first BBC engine and I wonder if a distributor with no vacuum advance would be good with this engine for street use. The only other mechanical only distributor I had dealings with before was a 427 Ford and it was fine with no vacuum advance.
     
  2. Two things jump out in your question. "Mostly stock" and "street use". If street includes highway use then stay with vacuum advance.
     
  3. Yep, if fuel economy is unimportant, run the no vacuum distributor. Expect mileage in single digits...
     
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  4. Truck64
    Joined: Oct 18, 2015
    Posts: 3,154

    Truck64
    Member
    from Ioway

    There's no good reason not to utilize vacuum advance on a street driven engine.
     
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  5. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,959

    porknbeaner
    Member

    Everyone will give you different advice most of it is that you cannot run a street motor without a vacuum advance.

    I tossed a full mechanical Vette distributer in an L-79 motor that I had in a '57 wagon in about 75 and have never looked back. I still normally run no vac advance on the street.
     
  6. Street driving a car like this will be a lot more enjoyable with a vacuum advance distributor. It will idle cleaner, have better light throttle response and if it's an auto trans you won't have to slip it into neutral at a stop light.

    You can make the mechanical advance only distributor work "better" but it's a lot more horsing around to get the total distributor advance and the rate of advance where you want them. Doing it really right would require a distributor machine and the knowledge of how to use it. And the time and the patience to balance out the initial timing, total timing, the amount of advance built into the distributor and the rate of advance.

    The advantage to using vacuum advance is that it senses the changing engine load conditions which are present in a street driven vehicle. The mechanical advance responds only to changes in engine RPM. In that respect it's a lot like an older mechanical fuel injection set-up that was designed to idle (somewhat) and provide maximum engine output at wide open throttle. Everything in between is a compromise at best. Not exactly the same conditions a street driven engine experiences.
     
  7. But I suspect that's because you've got the knowledge and just enough patience to take what you've got and make it work the way you need it to. :rolleyes: More power to ya! :cool:
     
  8. Thanks for the opinions so far.
     
  9. Truck64
    Joined: Oct 18, 2015
    Posts: 3,154

    Truck64
    Member
    from Ioway

    It isn't required, but there's no benefit to running without it.
     
  10. jaw22w
    Joined: Mar 2, 2013
    Posts: 732

    jaw22w
    Member
    from Indiana

    Yep. It will work, but would get better mileage and run cooler with vacuum advance. If you can't get a dist. with vac and tach drive, then run it without.
     
  11. jaw22w
    Joined: Mar 2, 2013
    Posts: 732

    jaw22w
    Member
    from Indiana

    I totally agree with everything you said except for needing a distributor machine to set up the advance rates and amounts. Your engine IS a distributor machine. All my distributors have the mechanical and vacuum advance adjustably limited (my own little mods) to achieve the correct setups. I agree that it would be a lot easier in a machine, but lacking that, you do what you have to do. I only bring this up to let people know that they can do it themselves in their own shop.
     
  12. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 5,114

    Bandit Billy
    ALLIANCE MEMBER

    The 396 in my 69 Camaro runs with no vacuum advance, pertronix added 10 years ago, runs hard and gets ok mileage considering. One doesn't drive a 65 BBC corvette for fuel mileage. o_O
     
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  13. squirrel
    Joined: Sep 23, 2004
    Posts: 42,677

    squirrel
    Member

    you'll be fine with the distributor you have, assuming you set up the advance curve in a reasonable way. Vacuum advance will give a slight mileage improvement and possibly help it run a bit cooler (probably not enough to notice)

    Folks seem to be ignoring the fact that you have the distributor already, and that is worth something, if it means you don't have to buy another distributor.

    But if you do decide it's ok to buy another distributor, get one for a mid 60s to early 70s Vette, most of them have vacuum advance, and single points, and tach drive, and will work fine.
     
  14. If you decide to swap distributors, you can go with a cheaper more common part if you convert to electric tach. A quick search on Google will tell you who offers the conversion. Probably most Corvette suppliers offer this.
     
  15. Ha , thats for sure. The mileage part doesn't really bother me, its the drive ability I was questioning. Like I earlier stated, I use to run a mechanical advance distributor in a FE Ford and it was good, but I was young and never could keep my foot off the go pedal. I am older now and just cruise around blocking traffic...:rolleyes:
     
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  16. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,959

    porknbeaner
    Member

    Or with it. LOL

    There is actually an advantage to running sans the vac canister. More swing on your distributer. :D:D :D
     
  17. Truckdoctor Andy
    Joined: Jan 13, 2017
    Posts: 697

    Truckdoctor Andy
    Member

    Little known fact: some of the 366 truck engines were built with out vacuum advance. When I worked on school buses, I had some 1982-1984 buses built like that. They had HEI distributors with plastic “block offs” in place of the canisters. Those buses didn’t run any better or worse than the newer buses with it. I say go for it.


    Sent from my iPhone using The H.A.M.B. mobile app
     
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  18. squirrel
    Joined: Sep 23, 2004
    Posts: 42,677

    squirrel
    Member

    those buses had the throttle wide open most of the time they were moving..no need for vacuum advance
     
    Johnny Gee and Fordors like this.
  19. ^^^^^ Boats as well.
     
  20. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,959

    porknbeaner
    Member

    My neighbor has two dump trucks with 366s. They are a tall deck motor, I am no expert on the BBC motors (factory) in my world that would fall into Jim's ( @squirrel ) realm but I don't imagine that the distributer from a '65 Corvette would work. They also have a hex oil pump drive like a Ford instead of a blade that is more common on a GM product.

    One truck had a vac advance HEI when he got it but the advance pod was rusted completely off. The other had a pints distributer that was about as big around as a quarter with what appeared to be some sort of a governor on it that was a not hooked up. I had a Buick vac advance pod (new in the box) that bolted one so we used it and the other truck got a new HEI. Greatly improved the low speed , manners of both.

    The take off in my mind is that the points distributer was pretty much shot anyway (needed bushings) and the HEI was not a full mechanical to start with.

    Someone mentioned that you need a distributer machine to set the advance properly. I don't own a Distributer machine and am not a "ignition" man by trade. But I have never had any trouble getting one set up. You can tell if it needs a little more or a little less lead and when. Even the guy in the distributer shop has to know at least a little bit about tuning to set one up.
     
  21. I have been using a fully mechanical, dual point distributor in my 375 HP 327 since 1968 with zero troubles, easy street manners, and can "tune" it for long trips to get 18 mpg....with 3.70 gears. Anyone who says these distributors are not street friendly needs to stick with a Honda......not a hot rod.
     
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  22. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,959

    porknbeaner
    Member

    I laugh at the mileage thing. My 400+ horse 355 gets upwards of 20 MPG with a full mechanical Mallory and has since 1997. I guess if I had a vacuum advance I would be getting 25 or 30.

    Mileage and manners come from tuning. Well and a good combination of parts I guess.
     
  23. squirrel
    Joined: Sep 23, 2004
    Posts: 42,677

    squirrel
    Member

    kinda makes me wonder how you guys figure gas mileage!
     
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  24. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,959

    porknbeaner
    Member

    Mine has actually been measured and by more then myself. We were getting 22 in the pusher on the highway the @raven measured it on a trip we made. Full tank, check mileage and fill it back up. Divide the miles by the fuel and BaBam fuel mileage.

    I would be offended if it were just me figuring the mileage because I can cypher real good. But I am not because someone else did the cypherin', :D :D :D

    On a side note and just for clarity to the masses Jim does not offend me, uh ever. I respect Jim. Some of you other guys now that is a different story. ;)
     
  25. distributorguy
    Joined: Feb 15, 2013
    Posts: 28

    distributorguy
    Member
    from MN

    A standard Vette distributor with tach drive is readily available used on Fleabay. I recurve them all the time for good throttle response, so you don't need dual points or a numbers matching core. Recurved with the right vac unit would be the way to go so you can keep your tach functional.
     
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  26. Are you questioning ability to calculate, or honesty????? Either one is an insult. Several trips over 550 miles each, accurate odometer, simple math......my 3rd grade grand son could do this.
     
  27. I was the first to say go vacuum. But I have little to go by. Only the few fact's OP posted. What all is the 396 made up of? Trans? Gears? Driving habit's? With that out of the way. My 56 "Honda" has a cast iron distributor with a locked out breaker plate where vacuum canister use to be that's phased to distributor cap. The curve takes care of the rest.
     
  28. deathrowdave
    Joined: May 27, 2014
    Posts: 1,581

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    Squirrel is the winner of the chicken dinner ! IMO . The Vette distributer is set up for high performance street usage drivability . The vacuum advance was for fuel economy and to help with fuel economy . A close advance curve to the vacuum advance , in a non vacuum advance , you will end up near the same in the end . WOW that’s a lot to think about . Just run it and set it up to a total advance around 37* and enjoy it . Myself personally I don’t drive anything hard enough to warrant a dual point anymore . My old Harley had dual points , but if you spun it fast enough to float it , you would be needing a trip to the hospital , because the hot oil tossed from the hole in the crankcase would have burnt you to a crisp !
     
  29. greg32
    Joined: Jun 21, 2007
    Posts: 1,899

    greg32
    Member
    from lemont,IL

    Your 325hp 396 has 10.25 compression, and iron heads. It won't run with vacuum advance without pinging on 93 octane. So, you don't need it anyway. Put a timing tape on the dampner and play with the mechanical advance curve. You'll want it to start advancing fairly quickly off idle, all in around 2400 rpm, but every motor is different.
     
    Montana1 likes this.

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