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6-71 help

Discussion in 'The Hokey Ass Message Board' started by bigalow1, Dec 12, 2010.

  1. bigalow1
    Joined: Feb 17, 2008
    Posts: 105

    bigalow1
    Member
    from 496 C.I.

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    Location: chicago
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    help

    </TD><TD class=alt1 id=td_post_5966907 style="BORDER-RIGHT: #e5e5e5 1px solid"><!-- icon and title -->[​IMG] Need help w 6-71 ??
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    <!-- message -->Hello,
    I am new to this forum. My name is Bill , I have an 8.5 to 1 440 Dodge, and I have a 6-71 Blower on my back
    I have searched this forum and have read some very comprehensive threads on roots superchargers. I hope I can get some advice on my potential application? I want to run a 6-71 Blower at minimul boost 4-5psi on the street I have a good runnind 440 now and don,t want to melt it down from stupid mistakes
    Here Goes:
    440- 50 miles on rebiuld(actually 500 CID stroker)
    Forged crank single key
    Fliud vibration Dampener
    HD rods
    Forged flat top pistons
    8 to 1 comp with a gasket change
    3 inch exhaust
    241 dur @.050 528 mech cam
    MSD 6Al ignition
    I bought a supercharger book
    Can I Successfully use a 6-71 at 4-5psi on this combo
    how much trouble will i have to get it runningcie: carbs
    I will buy a new set-up from DYER if I am confident that everything will not melt down from bone head mistakes/
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  2. squirrel
    Joined: Sep 23, 2004
    Posts: 50,966

    squirrel
    Member

    I don't see any potential problems. Might swap the damper for a steel hub, I think the stock mopar pulley bolts are only 5/16"? blower pulley bolts are 3/8, and you can get away without running a damper because the blower belt does the job of damping (20 years and 80k+ miles on my blown 454 with a steel hub demonstrate it)

    I have the "cheap" 4777 holleys on mine, modified slightly, although the experts will try to sell you on $2k worth of special boost reference blower carbs.

    Keep the carbs a bit rich, and the timing a bit retarded, and it should last forever.
     
  3. From what I've read, that duration on the cam might be a bit much for the combination you are talking about. If you are shopping with Dryer they will give much better advice than I can.
     
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 50,966

    squirrel
    Member

    I don't see a real problem with the cam, as long as you set up the drivetrain to work with it. The cam determines the RPM range of the engine, and it's pretty much the same with or without the blower. If anything, the blower will "tame" the cam during street use, letting you get by with quite a bit less gear/stall than you'd need without the blower.
     

  5. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Whats the lda on the cam in question?
     
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 50,966

    squirrel
    Member

    biggest thing is to make sure the fuel system can supply enough fuel to the carbs....leaning out under load is bad.
     
  7. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

  8. bigalow1
    Joined: Feb 17, 2008
    Posts: 105

    bigalow1
    Member
    from 496 C.I.

    Oh thank you gentleman I have come to the right forum.
    I keep reading that the a single keyed crank will shear the key??? If i run only 4-5psi of boost will this still be a problem.??
    I am thinking of underdriving the 6-71 by 10 percent?/ Been looking at the BDS charts

    The power valve set-up has me scared.??/(Plus there are so many carb options??) Could you elaborate more on your carb set-up Squirrel
    Where can I find a good book on set-up and tuning??

    Squirrel-I can run my 6-71 with out the Dampener and just the Blower pulley???
    The motor is balanced(rotating assembly)
    Took me 3 yrs to put the car together so I am not looking to do burn outs every chance I get. Run a blower and take it kinda easy
    I was about to give up on the Blower. I could not find any help

    I have to sell the wifes car when she isn't lookin to buy the Dyer unit so I have to be sure I know what I am doing.!!!! (kidding)
     
  9. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,475

    landseaandair
    Member
    from phoenix

    Double keying the crank would be a good idea. With low boost, and a good ARP bolt (tight), you might? be OK. With the amount of money you have invested already, I'd probably do it right though. I'm also a big believer in referenced power valves, you run much cleaner at cruise and idle and have guaranteed full enrichment under boost.

    I've used some basic gold 750 vac. secondary blower carbs from this guy in the past.

    http://motors.shop.ebay.com/lstahle/m.html

    Good budget carbs and they worked perfect out of the box.
     
  10. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,475

    landseaandair
    Member
    from phoenix

    Also, as falcongeorge was probably getting at, you will do best with a cam that has a wide lobe separation. When an engine is force fed, a lot of overlap will cause you to be less efficient by blowing extra unburned air and fuel out the exhaust.
     
  11. Cirelli
    Joined: Apr 5, 2009
    Posts: 169

    Cirelli
    Member
    1. H.A.M.B. Chapel

    Yes! With 8 to 1 compression & a 10% underdrive you can use it as a daily driver, take long 2 or 3 thousand mile roadtrips & still have fun at your local dragstrip. Blowers are dependable, engines start easily, and the gas mileage isn't too bad if you keep your foot out of it.
     
  12. filthy frank
    Joined: Jan 25, 2008
    Posts: 541

    filthy frank
    Member

    bigalo, ive heard of a lot of guys saying, yeah, im just going to cruise it !yeah right, if i was you, id put on a crank hub, and have it double keyed and internaly ballanced, does your manifold have a spring loaded pop off valve ?just to be on the safe side !
     
  13. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,475

    landseaandair
    Member
    from phoenix

    I don't think it needs to be internally balanced, they do have counterweighted hubs. I agree with you on the "yeah right" part though, the temptation is always going to be there for more boost. It's only a pulley change away from 10 lbs.
     
  14. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Yup.
     
  15. trey2618
    Joined: Mar 15, 2009
    Posts: 23

    trey2618
    Member
    from Cisco

    I too agree with Filthy Frank and Landseaandair, I said the same thing and an older hot rodder around here told me "You build something that looks fast someone will challange you, Even the Fonz couldn't just be cool and get the girls , There were times he was forced to fight" I thought a lot about what he told me and decided better to overbuild than rebuild.
     
  16. bigalow1
    Joined: Feb 17, 2008
    Posts: 105

    bigalow1
    Member
    from 496 C.I.

    I need to pull my crank out to double key it right???of course
    What happens if the single key breaks-bad news????
    My cam has 110 degree's of seperation???
    My rotating assembly is ballanced and now I am running a fliud dampener.
    [B]I don't understand the balancer aspect????[/B]With all your help I am getting my confidence Back
    The Fonze analogy was funny. LOL Your right ,sometimes I slick my hair back!
     
    Last edited: Dec 12, 2010
  17. Capt Crash
    Joined: Jan 21, 2008
    Posts: 108

    Capt Crash
    Member
    from Colorado

    Keep the fluid dampner. It will work fine. If you had a stock elastomer type dampner, then you would want to replace it. You do not really need a dampner at all, but you do need a blower hub at the least. Since you already have the fluid dampner keep it. I ran a stock 350 chevy for a couple of years at 6 lbs of boost with a single keyway. It worked fine until one day the dampner cracked. I would pull out the crank and have a machine shop or a shop that deals with electric motors cut 2 keyways in it. That should work just fine and it will give you some peace of mind.
    Brian
     
  18. AG F/C
    Joined: Oct 20, 2009
    Posts: 364

    AG F/C
    Member

    I would 86 the damper. You want the blower pulley as close to the end of the crank as possible to reduce nose fatigue and possible breakage. The blower hub will accomplish that.

    Don't screw around with compromises even at 5# the stocker woodruff key won't put up with much crap. If it shears and the hub spins you will have a boat anchor for a crank. You'll know it when it spins though..

    On gas you want the 110* lsa to reduce cylinder heat. Yes blow down will reduce efficience a bit but if you ever want to up your OD for more boost you will have less chance for the typical heat related issues. Even running 5# on 8-1 your effective compression ratio is higher than 10.5-1. Pump gas will be at it ragged edge at that point. Methanol, run wider for heat 114-116* but not gas.. If you are absolutly sure you won't bump it up later you'll be fine in the wider LSA cams.

    Is this a stripped blower?
     
  19. squirrel
    Joined: Sep 23, 2004
    Posts: 50,966

    squirrel
    Member

    I run about 7 psi on 7.5 compression and use 87 octane almost all the time, lots and lots of miles on it, no problems, same pistons in my for the past 20 years.

    I also didn't double key my crank, but the snout on a BBC is a lot bigger than a 350 and the hub is a nice tight fit on the crank. A big block mopar has a big snout, but usually not a very tight fit on the damper, iirc. It's a crapshoot, if you think you're gonna get boost happy then you'd be better off pulling the crank and getting it machined for the other key. You'd probably need to get a hub then to use the extra key though.

    If someone has experience with mild blown big block mopar cam selection, great...but from my experience a few degrees difference one way or the other isn't gonna make nearly as much difference in real life as it does in theory. Except maybe on a mopar, they're not as forgiving as chevys as far as cam choice....

    As far as jetting and power valves, I just have mine set up a bit lean on the primary side of the primary carb (it's progressive, which I hear is a blower no-no but it works fine for me) and a couple numbers richer on the rest.

    I'm sure I could go a tenth quicker and get half a mpg more if someone who knew what they were doing gave my car "the tune". Oh well.
     
  20. bigalow1
    Joined: Feb 17, 2008
    Posts: 105

    bigalow1
    Member
    from 496 C.I.

    I have a great running BB now but I just can,t leave it alone!!/?
    I will have the blowe by the end of the month-Santa is going to leave a big box under the tree.
    i hope I can find you guy's come january when i install it and have to pick carbs??
    IS there a supercharger set-up book or tech article??/
    What about the backfire issue and blowing the blower off?
    I looked at a book at Barnes and Nobles but is pretty general and lots of pretty pic's
    My first season I will be tinkering with the blower and i know i will take it easy-Experiecing the Learning curve
     
  21. photoman
    Joined: Feb 6, 2004
    Posts: 406

    photoman
    Member
    from Texas

    Buy your stuff from a reputable company and call them with your questions. They will be able to help you and you paid for the service. Might as well use it.

    Gary Dyer has been around for decades and has ~much~ experience running blowers on street cars. He's local to you also. The only "bonehead" mistake you might make is running the motor hot or with too much ignition lead. Keep those in control and you'll be fine.
     
  22. bigalow1
    Joined: Feb 17, 2008
    Posts: 105

    bigalow1
    Member
    from 496 C.I.

    Thanks, Gary seemed friendly on the phone and his shop is 7 miles from my house

    I considered buying a used 6-71 on E bay for about 3/4 the price.
    Buying a pretty new one from Dyer and recieve some help will probally far out way saving $750.00 If I new what I was doing maybe a used unit but i don't.

    I really aprieciate all the response to my thread!!!!:)
     
  23. Screamin' Metal
    Joined: Feb 1, 2009
    Posts: 506

    Screamin' Metal
    Member
    from Oklahoma

    What he said X 2!!!!:cool: Definitely ditch the dampener and go for a steel drive hub. Be careful with belt tension if running the 3" belt. This puts alot of strain on the crank snout. I've known people to snap the end of their crank off. A gear-belt doesn't have to be tight, thats what the cogs on the belt are for....believe me, it won't slip if its just a little loose....

    Be sure and run a intake that has a pop-off. If yours don't, a machine shop can make one into your intake, no problem. Stay away from burst-plates....only run the spring loaded pop-offs.

    Shoot for about 7-8 psi on your drive, you'll pick up a few more horses and torque. Gas milage is directly proportional to how heavy your foot is. Tire wear, the same. Run a boost gauge....you can tune with it and troubleshoot both.

    Pinging and detonation is a enemy of a blown motor. Make sure you have it timed accordingly. The 6AL system is built for that, also, don't spin your motor above 5000 or 5500. With 8 psi of boost 500 rpm ain't gonna make more power, but it could be the straw that broke the camels back with your rods IF you spin it too high.

    Ran a 6-71 and a 8-71 on a BB Poncho for almost 20 years on the street....
     
    Last edited: Dec 13, 2010
  24. bigalow1
    Joined: Feb 17, 2008
    Posts: 105

    bigalow1
    Member
    from 496 C.I.

    I rread if the belt doesnt slip and the engine backfires really bad things will happen???
    A cog belt or V belt?
     
  25. bigalow1
    Joined: Feb 17, 2008
    Posts: 105

    bigalow1
    Member
    from 496 C.I.

    Food for consideration???
    My leather jacket usually is not to far away/?
    My 500 Ci runs pretty strong now and i can play Fonzie all i want=FUN
    Hate to be with out a car to drive this summer if my blower set-up went south!?
    Maybe i should have some patience and start putting together a blower short block??? I won't have it running as soon as i would like because of the total cost.
    Patience could be a virtue in this case?
    I have a another 440 in an old dart that needs some lovin?///
    The thought of another summer hot rodding around in my wifes turbo beetle with the flowers scares me
     
    Last edited: Dec 13, 2010
  26. Screamin' Metal
    Joined: Feb 1, 2009
    Posts: 506

    Screamin' Metal
    Member
    from Oklahoma

    If your gonna run a blower, run a blower. V belts are cool....if theres a malfunction and the blower locks up, it'll save ya....your belts will slip. BUT, its hard finding a matched belt set thats exactly the same size. Get one to tension, the other is slightly loose. The only way around this is a spring loaded idler for each belt.
    A cogbelt/ gilmer belt/ Gates power drive belt....they're the same thing, just a different name. A flatbelt with cogs on it so the cogs meet the milled teeth on the pulleys....there is no slip. If things lock up and your running a gilmer, its gonna break!

    Just build a good quality, mild BB Mopar....and you'll be stompin' around with about 550-600 horses, can drive it everyday just like I did and Squirrel does....and you can drive it on cross-country if you want. Just do it right and you won't have any issues.

    Now, there is 1 piece of advice I can give you. You don't need the blower carbs....you can do that yourself if you do your homework. But ALWAYS run a screen type lower blower gasket and/or screened intake gaskets. You'll be suprised what one of those alum. lungs can suck in. Theres only a few thounsandths of a inch....(0.003-0.007) between the rotors....as you can see....you can suck in a leaf and guess what....your blower can lock up. Something soft and small, turning at pretty good rpm....the blower will swallow it and mash it up, flies and small bugs, no problems, but the potential for messing up is good. Run good air cleaners and make sure all the openings on your carb is sealed....like the linkage hole for the top choke plate. Plug that off! I've never run a choke on blown motors in over 30 years.....
    Pump your throttle while spinning....she'll light off, if not, you got a problem!

    Just build yourself a good quality motor and you'll have no problem. Check with The Blower Shop, Dyers, BDS....they'll help ya out....:cool::D
     
    Last edited: Dec 13, 2010
  27. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,475

    landseaandair
    Member
    from phoenix

    Shops like BDS and Dyers have good tech info online and I can't say it's not possible, but unless you're using nitrous, I've never heard of a street gas engine popping a blower.
     
  28. squirrel
    Joined: Sep 23, 2004
    Posts: 50,966

    squirrel
    Member

    I run a choke on mine...well, half a choke. I cut off part of the choke plate, and adjusted the fast idle screw up a ways. Makes it easier to drive on cold mornings. Pull the choke knob out, pump twice, foot off the throttle, it fires up and stays running by itself.

    Great advice about the screen above the blower, I've always run one, never had any problems with the blower locking or anything.

    If you plan to put a lot of miles on it, get the pulleys hard anodized. Raw aluminum pulleys seem to wear out pretty fast, maybe it's because of all the dust in the air here? I only get about 20k miles out of them.
     
  29. bigalow1
    Joined: Feb 17, 2008
    Posts: 105

    bigalow1
    Member
    from 496 C.I.

    Is that the chevy in the pic that you drive that much?? Thats really cool !!!
     
  30. What SQUIRREL and SCREAMINMETAL said. The engine in the car in my Avatar is a bone Stock DeSoto Hemi, 7.5:1 CR, single key crank, 6-71 GMC Blower, underdriven, 5lbs boost, 3" Gilmer drive, 2 unreferenced Carter 4761 carbs, Stock damper, and runs fine on 87 Octane. The engine is a Bear and I drive it everywhere...not problem #1. You DON'T need to go overboard ($$$), you just need to do your home work. BTW, it turns 11.8/119 in the 1/4, as pictured, on Street tires and through the exhaust...
     

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