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Blow Through Carbs - Yes , there are some !!

Discussion in 'The Hokey Ass Message Board' started by Bob the Ferret, Dec 4, 2008.

  1. This is a little bit non-trad but I've been looking into turbo charging after taking Mr. Toad's Wild Ride in a friend of mine's beefed up Buick Grand National . A number of HAMBsters have helped me with the questions I've posed regarding fuel management , so I'm going to give back a little . Because I want to run between 17-20 lbs boost and use intercoolers I had to look at EFI . The friggin' things are expensive , complicated and I couldn't find my ass with both hands and a road map when it comes to EFI . I can usually make a carb run though . I called Barry Grant's Demon Carb . Lo and behold , they make several carbs that are blow through and you don't need to build a box around the carb . WooHoo !!! A number of their upper end carbs come with this option and can take 28 lbs boost. I'm looking at a Mighty Demon 575 cfm for my inliner using twin turbos . The blow through design part numbers end with the code BT , clever no ? One more option for supercharging that don't have them little electrical thingies all over the place .
  2. modelacitizen
    Joined: Jun 24, 2006
    Posts: 877


    I'm interested to see how it works out for ya. I'm one of the younger guys on here that drives modern turbo cars (Evo VIII) but I've also got a model A. I also had an '85 Regal t-type. (fuel injected, non intercooled turbo). I recently sold a '91 Nissan 240sx that had a HUGE sc61 turbo in it. I learned a lot about EFI working on that thing. When I think about how complicated modern engines are, it amazes me how crude the boost control and timing systems were back in the 50's/60's. But they made it work! And I'm sure you will too. Keep us posted.
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 48,703


    The boost control system was usually just a matter of selecting the right pulleys, and timing control was done with weights and springs.

    Surprisingly, these primitive techniques still work.

    And thanks for letting us know about the carbs, neat stuff! Intercooling is a big big help over about 10 psi
  4. bobwop
    Joined: Jan 13, 2008
    Posts: 6,098


    Holley has some BT carbs as well. I am almost certain Quick Fuel makes E85 carbs for BT installation, too.

  5. I had a friend who's band was called "Mr. Toad's Wild Ride"-

    Great name... until Disney contacted them:mad:
  6. brandon
    Joined: Jul 19, 2002
    Posts: 6,334


    go over to and check the forums...alot of tech info over there..... brandon:D
  7. yellow wagon
    Joined: Jun 13, 2007
    Posts: 612

    yellow wagon
    from WI

    the turbo forums have a lot of great info and a lot of cars that are flyin without much invested :)
  8. V4F
    Joined: Aug 8, 2008
    Posts: 4,172

    from middle ca.

    Blow Through Carbs - Yes , there are some !!
    yes we used them on our drag bikes . great carbs . good luck & let us know .. steve
    be careful on the boost . dont out do your fuel system ! we did & have about a dozen 100$++ ash trays !!!!!!!!!!!!!! bikes are cheaper than cars!!!
  9. btmatt
    Joined: Nov 15, 2006
    Posts: 227


    At boost levels listed above, better think about Racegas, E85, or Methanol.
  10. Tman
    Joined: Mar 2, 2001
    Posts: 34,117


    ElP clued me into Methanol injected chemical intercooling................looks like the ticket. I am just learning this stuff tho.
  11. Shaggy
    Joined: Mar 6, 2003
    Posts: 5,208

    from Sultan, WA

    Thats what i've been told too, by a guy that was running a NORMAL holley after a supercharger on a weekend drag racing Torino He said he wasn't running a lot of boost

    57 T-birds ran holleys on their supercharged cars didn't they
  12. Good info !!! I'm probably gonna run lower boost most of the time and make it adjustable from the cockpit to avoid the race gas issue . I thought about mounting a small Moon style tank some where ( I run an electric fuel pump) and keeping that loaded with race fuel , switchable again . from the dash for.. ummm.... passing purposes on the highway . Yeah .. that's it , passing purposes ! You don't want to get caught behind some little old lady in a Lamborgini on a busy freeway . You could use it for racing , but that would be wrong .
  13. Judd
    Joined: Feb 26, 2003
    Posts: 1,894


    I had to run premium gas in a stock HO 302 with paxton at 6 lbs boost. It ran a mechanical pump with boost index line from the blower. Swapped an unblown 351 after it blew the front off the 302, 351 still hasn't outrun the 302 though.

    Attached Files:

  14. tooslow54
    Joined: May 6, 2005
    Posts: 929


    How do I say this nicely...before putting a BG carb on your car call Eddie or Ron at Performance Carb in Ontario Cal or Patrick at Pro Systems. You can google they're name for the #. It takes a lot ( and I mean A LOT) of work to make a blow thru carb work with high boost.
  15. I know some people will be sceptical about these claims, but we used to race with up to 24 lbs boost blowing thru a Holley without a carb box or any intercooler.

    Everywhere we took the car, people crowded around it in the pits, and yelled from the stands every time it made a pass.

    We used a solid (foam) float made for Holley carbs. I think they called it a nitrophyl float. ??
    (hollow floats collapse under pressure)

    I took an aluminum carb spacer, carefully drilled some small air passages in it to line up with some small holes I had drilled into the Holley carb base, to blow CLEAN-AIR boost pressure (no fuel mix) directly to the throttle shaft bushings so I didn't have to put seals on the shafts, and then topped the carb with a Turbo City carb bonnet that was designed for a different use.

    We blew fresh air straight from the turbo into the carb bonnet on top of the bare carb.

    At first we had jetted it way too rich to avoid melting anything on its' upcoming first day out at the track. We read about the warnings, and took them way too seriously.

    We had only a few days before a big meet, and didn't know what to do about a waste gate or a limiting device. No money to work with or enough knowledge learned yet to build one quickly.

    My friend rigged a cheap blowoff valve and stuck it in the turbo boost pipe to the carb. I'll tell you about it later.

    The 9 or 10 to one engine compression needed to be lowered before adding boost pressure. My friend cut his own copper head gaskets. They leaked so badly just a couple days before the races, all we could do was stick in some more head gaskets above and below the copper spacers. With such a TALL combination there was almost no compression left, or any decent quench area with the chambers so big now.

    The race was two days and a long drive away. We weren't even close to being ready.

    As we scrambled to put a car together that we know couldn't be ready on time, we were trying to come up with excuses as to why we couldn't race the car when we showed up at the meet.
    Head gaskets blown? (mostly true), severe carb trouble? (mostly true), new tranny that wasn't working right? (didn't know yet, but it could happen!), but all of them were weak or made us sound like quitters, so we kept going, all the while very afraid we would fall on our faces in front of a large crowd.

    We tow all the way from Missouri to Nashville Music City Raceway and unload the car.

    So here we are at a drag meet with a 35+ year old Studie, a tiny 259 cubic inch Studie stock-block engine, a turbo that wasn't tuned or controlled, a carb running way WAY too rich, a shockingly low 6.9 compression ratio, a fresh PowerGlide that was like starting in second gear, and a rigged-up RADIATOR CAP blowoff valve as a crude turbo control.

    The rear gears were still too tall, set for the low-gear launch of a TH350 trans, much too tall for the mushy second-gear Powerglide launch. No transbrake to load the turbo against for ANY boost at launch time... everything seemed to be all wrong, and we ran out of time to correct any of them.

    The first few runs got everyones attention, and drew a crowd.

    Every time the lights went green, the "other" car would get a jump on the slow starting Studie, usually a few car lengths, then the little Stude would wind up and charge at the other guy.
    Usually between half-track or two-thirds track, with the turbo really blowing and whining, the Stude would fly right past at a really high rate and leave the guy in the other lane wondering what the heck just happened.

    On it's very first time out, the car took Fast Class Trophy.

    We had such fun with the car. It put on such a good show that people would crowd around it to see what in the world that was.

    The turbo would spin up a bit, boost higher, pull harder, wind up some more, boost higher, pull harder, wind up some more, boost higher, pull harder, wind higher, more boost, pull even harder, scream higher, boost more, pull harder, scream higher......

    Near the top end of the track when it was really pulling hard and the over rich carb was dumping too much fuel to the engine, it would often put out a very noticable BLUE HALO glowing under the car (came from the 3-1/2 inch turbo outlet pipe that you couldn't see)
    It was a sight to see.

    So here was a car we put together in a rush at the last minute-
    ONLY 6.9 compression!!! rich carb dumping fuel. gears much too tall.

    NO turbo control except for a 12lb RADIATOR CAP stuck in the side of the boost pipe as a makeshift blowoff valve. (fresh air- no fuel mix)
    Surprisingly, the 12 lb radiator cap actually worked quite well as a boost limiter at "normal" driving on the street, but at the track when it was pulling hard and winding high, the turbo would overwhelm the small "valve" and go past the 23-24 lbs boost mark near the finish line. That was just about the time the fuel pressure suddenly started climbing faster than the boost and an over rich carb got even richer.
    The race was over by then, so it didn't really matter at the time.

    Later on with better carb settings, a better fuel regulator, better head gaskets and a better compression ratio, TH 350 with better ratios and transbrake, we got it running a whole lot faster, but that first outing was the most memorable one of all.

    What a blast we had. I want to do it again.

    A few summers ago, a shop fire (blame a leaky 85 Corvette) took down two buildings, all the race parts, a few collector cars including a nice Studebaker Hawk, and a whole lot of tools, NOS fenders, etc etc.
    No more racing.....

    That car below in my signature line is no more.....

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    Sikeston MO



    Benton Il I-57 Raceway

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    Post.Script. Yes I had nightmares about a 24 PSI blowtorch if something ruptured like an accelerator pump diaphragm or some skinny carb gasket, so we did eventually put the carb in a closed pressure box later for safety reasons.

    Post Post Script- For fun sake, I wanted to use an old pressure-cooker pot as a carb enclosure for the unique effects it would have on the spectators, but my friend Mike insisted on a Granatelli-Paxton cast aluminum carb enclosure for the sake of image.
    Last edited: Dec 6, 2008
  16. tooslow54
    Joined: May 6, 2005
    Posts: 929

    Member story. As they say: "it's better to be lucky than good". :D
  17. 460 willy
    Joined: Nov 2, 2005
    Posts: 249

    460 willy
    from wisconsin

    I had a blow thru carb on a not hamb friendly mustang and had a carb built by a company called CSU carb solutions unlimited. Basically I gave him my setup and he built me a carb ran like a champ right out of the box and made great power. No cheap but well built and never had any issues. Look at the turbo forums there are alot of how too threads for converting suck thru to blow thru. Good luck

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