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Thread: Roost or Boost

  1. #1
    I have a Youngblood TX-19 that I am working on. Spent a lot of time on it last winter. We flipped it and straightened the bottom, It wasn't to bad to start with but.. you know.. it had some scratches and was easier to gelcoat upsidedown anyway(thanks Instigator). While it was apart I sent the pump to Jack at MPD (Smart,very helpful, nice guy)for a better shoe setup. The Snoot and Place Diverter came from Dwane at HTM (also very helpful) along with a 4* wedge. Last year 69.6 gps this year 72.8. I tried to keep everything else close to the baseline so I could measure the difference. Same fuel load, very close air temp ect. When I was going for top speed this year I kept raising the nozel to find the fastest setting. The best for top speed was one notch from all the way up. Do I need to put the droop back on to air this boat out and keep a better thrust angle? It looks like I'm wasting alot of energy shooting roost.

  2. #2

  3. #3
    How big is the engine and what rpm are you turning?

  4. #4
    It is a 454. 4900 rpm bronze Agressor A.

  5. #5
    Looks to be about right for that rpm and that impeller. It seems to be holding the rpm down......might cut it to a B or B/C if you cam can continue turning rpm higher.
    Might put on a droop to free it up a bit (boat will ride better, but don't expect huge gains in speed). Fairly sure you don't have enough hp to use that snoot.

  6. #6
    How much HP will it take to use this setup effectively? I'd rather add the power instead of cutting the impeller. My plan was to add a 540 after I got the baseline on the changes made. I did get 81.3 gps with a 100 nos hit but I was to busy driving to remember to look at the tach.

  7. #7
    Put the 540 in and you'll be fine (roller cam?!). Todd goes around 94 w/ his 540 and Randy used to do around 95 w/ the 496 he has......but I do not know his #'s since he place the engine in his new CP19.
    I'd still cut the impeller though to at least a B....(more like have Jack do it! )

  8. #8
    I'm No Expert shaun's Avatar
    Join Date
    Feb 2009
    San Clemente, California
    I'm not really a big fan of the scoops but the more boats i see with that squashed and fat looking scoop the more i like them. Nice looking boat!

  9. #9
    From the info you've posted so far dragboat, I get the following:
    454 making 444HP @4900 RPM (impeller power usage curve)
    81.3 mph, was making 547HP (+100 N2O), should have spun 5244RPM
    Agressor A is a big impeller, equivilant to a Berk AA in my understanding.
    A cut to an "A" (if the engine still has headroom in the power curve and hasn't topped out yet) nets 300 more RPM on the same 444HP, 79.4MPH, no laughing gas.
    Give us a dyno sheet or alternatively, post or pm me every build detail you have and I'll build a DD engine run to see what the engine has left in it.
    I think the biggest question is "how wet is the hull still riding?" Is the lift needed? A set of side pix or video at WFO on smooth water would help the decision-making process.
    Keep in mind, some tuning changes will net relatively big gains, some small ones. It just depends on how big or small of a issue you improve with the tuning adjustments.

  10. #10
    Duane HTP
    If you are running in the first notch down from the top for best speed, you need about 2 degrees more wedge between the bowl and the Snoot. This will cause the water to bend the amount that you need at a larger diameter which saves a lot of drag. Then your boat should run it's fastest with the diverter straight out or 1 notch up. Try It and post the results.

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