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Thread: carb ?

  1. #1
    I'm thinking of putting on a dual quad setup on my jetboat i've been running two450 holley but i think i need a little more so i had these two 700 holleys laying around but was just wondering if that would be to much on a 454 chev over 30 with closed chamber head and my cam was made to run two 650 if anyone could let me know thanks :idea:

  2. #2
    Honestly yes there more than you need. But I have a few questions first. Compression ratio? Intake? cam? RPM you run? And last, what makes you think you need more??? Mike

  3. #3
    my comp ratio is 10.1 they will be on a weind tunnel ram and with the two 450 i was running it would jump to 5200 and then slowly drop down to 4800 to 5000 that is making me think i need a little bit more so it will keep the same rpm when i ordered my cam i told comp cams it would be on a tunnel ram with two 650 cause thats what i thought they were but turned out thay were 700.

  4. #4
    Senior Member
    Join Date
    Apr 2010
    Apples and oranges to some degree here, but I'll share what I've got. BBF built to approx 500 hp. I was running a single 850 dp on a Weiand Stealth dual plane manifold with a 2" spacer. It was tuned very well and the boat pulled 5200-5300 rpm with an Aggressor AB impeller. I switched to a tunnelram with 660 mechanical secondary carbs and gained NOTHING!
    All I do is suck more gas now.
    The current motor/carb setup is still tuned very well, and the carbs were freshly rebuilt, it runs great, so it's not a setup issue. It just didn't need any more fuel/air than it was already getting with the 850 and a dual plane.
    The tunnelram looks cool, but did nothing for performance.
    I also setup another buddy's boat for him. He was running a BBF with an Edelbrock Performer (dual plane intake), with a Holley 870 cfm vac sec. We swapped to a tunnelram with a pair of 600 vac secs. He gained NOTHING! This boat was near stock so that wasn't really a shocker. Heck he was running a 500 cfm vac sec carb when he first got it, and as all this turned out, he was just as fast with that little 500 cfm as with all the carb/intake changes following that. No kidding. Everything was verified with gps numbers. No guessing.
    Another buddy had a BBF with a different cam and some fresh head work done. He made the same swap as the above guy. He too gained NOTHING!
    Again, all these boats ran well before and after the change, they just didn't gain anything in the performance department.

  5. #5
    Had a 750 double pumper on my 426 bbc ,square port heads...ran about 4800-5000 rpms ..went to tunnel ram and 2 660 center squiters... rpms went to almost 6 grand...both carbs are jetted different front carb has 1 size less then the back carb to make the back carb like a secondary... or at least thats what the tech said...gave him all the specs, cam and everything else on the boat...boat doesnt stall out at all from a dead stop to full throttle

  6. #6
    Senior Member
    Join Date
    Apr 2010
    Man that's the exception! You gained 1000 rpm by just switching to a tunnelram?
    I'd sure like to hear the rest of the specs on that motor, and why it would benefit from so much air/fuel.
    That 1000 rpm translates to approximately a 350-450 hp increase.
    How much speed did ya gain?
    Mine runs 80 mph and 5300 rpm on the motor.
    With a 150 shot of nitrous it only gains 300 rpm and 8 mph.

  7. #7
    I'm equally curious as Squirtcha, and have had the same results on a Nitrous gain. 150 HP and about 450 RPM, some of which I believe was cavitation due to poor loader design (hey, I had the best they had in the late 70's. hahaha).
    Even with my engine upgrades this winter, gaining 70 HP, I lost 150 RPM due to (I believe) the new pro-loader that also went in. Basically neutral.
    You already have 900 CFM on just how much motor? You are going to 1400?!?!?!?
    I've run the numbers on my 454 at 5,000RPM, with perfect 100% VE, she would need 1313CFM of mixture. 70% (much more likely) is 919CFM
    Now, if you are tuned to turn 6K, you would need a shade 1576 CFM IF you were 100% VE, still 1103 at a more likely 70%VE
    If you can spin 6,500 RPM, great, if not, You won't get the TR to function like it is designed, and you'll have such huge carbs on that it may not run well (if at all) below WFO.

  8. #8
    well i just got back from the river its not as bad as i thought it was going to be it idles a little bit higher then before and its running a little bit rich atleast i think at wide open it has a little bit of popping sound to it. it also gained a couple hundred rpm it know runs 5200. so i think by jeting it down it might come around. if any one has or know of anyone with a couple of 600 holleys that would be willing to trade for a couple of 700 holley or want to sell let me know thanks.

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