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TTYTWSTR19
06-21-2001, 08:18 AM
I HAVE A 19' CONDOR TUNNEL. AFTER SEIZING MY BBC 496 THIS WEEKEND, I AM PREPARING TO BUILD A BLOWN BBC ZZ502. I AM CURIOUS WHAT OTHERS OUT THERE ARE SPINING FOR RPMS ON THIER BLOWN BBC. MY MOTOR BUILDER WANTS TO KEEP THE RPMS DOWN AROUND 5000-5200, AND INCREASE THE IMPELLER SIZE FROM A 'A' TO A 'AAA'IN MY DOMINATOR 12S PUMP. THE NEW 502 WILL HAVE AT LEAST 1000HP. WHAT KIND OF PERFORMANCE CAN BE EXPECTED FROM THIS SET UP AND HOW MUCH IS TOO MUCH PUNISHMENT FOR RPMS ON THE BBC?
THANKS GUYS,
JK

Jetmugg
06-21-2001, 08:55 AM
It's going to depend mostly on what you want to do with the boat. If you know where the power peak will be for the engine, then set the impeller size so that the engine will hit it's peak. This will give you the highest speed possible, but may be trading some engine life. I suspect that your power peak may be something above 5200 rpm. If you set up an "AAA" impeller, you may not reach the full power potential of the engine.
A guy named Mike W is currently dialing in a blown 509 Chevy in a 21 foot Liberator tunnell. He hangs out at the RealJetBoats message board and website. Mike will be glad to share his information with you.
SteveM.

jet496
06-21-2001, 11:19 AM
I'm not even close to a jet boat expert but I'll throw in what I know. I had the new 496 HO with a B impeller. It hit the revlimiter out of the hole which was a pain in the butt. We changed to a AA impeller & now it runs approx. 61 mph @ 4800 rpm. Could probably gain more speed with an A impeller, but I'm satisfied with the speed right now since my wife & kids are in the boat with me most of the time(Great family boat plus the low rpm's should keep me from over-taxing the motor life). I,m considering going for some speed & building up to 700+ hp or so in another hull (would talk to John West about just getting that). I was told by someone who races jet boats that he actually runs a C impeller & travels 130 plus mph. I figured he had a special cut well above a AAA impeller. Nope, just a little ole' C, one that if ran in my 425 hp boat would hit the roof on rpm's. Interesting, huh.

froggystyle
06-21-2001, 03:53 PM
Here comes my proverbial two cents. I have a blown 468 in a 19' Eliminator Daytona with a 12JG and a AA impeller. At 108mph, it ran 6600 RPM's. I get a great holeshot, and more accelleration than I care to keep my foot in. I am running at or around 900 hp. A AAA would probably slow me down a lot, as my peak power should be at 6500-6600. The combo works. If you are running significantly more power, try bumping your impeller up from that. If you have a setback jet, the change is pre-school, so you can do either.

TTYTWSTR19
06-22-2001, 04:43 AM
THANKS FOR THE INPUT. FROGGYSTYLE, HAVE YOU HAD TO DO ANY MAJOR UP KEEP ON YOUR BLOWN BBC? WHAT KIND OF CRAZY MODS DO YOU HAVE IN THAT PUP TO SPIN 6600 RPMS? WHAT PUMP MODS, IF ANY, DO YOU HAVE? WHO DOES YOUR PUMP WORK? I'D LIKE TO SEE THE SAME KIND OF #'S THAT YOUR DAYTONA IS RUNNING. TRIPLE DIGITS ARE COOL!! THIS IS MY FIRST SQUIRT BOAT, SO I DON'T HAVE MANY RESOURCES OR CONNECTIONS, SO ALL YOUR HELP IS APPRECIATED.
THANKS,
JK

froggystyle
06-22-2001, 07:47 AM
Without boring everyone else, and looking like I am trying to sell the boat to you, check out the classifieds for all the specs on the boat. Long story short, it is a AA, droop, 15 degree plate, diverter, rideplate, and plenty of power. I think the fuel system is a good place to build reliability into your boat, as nothing gets killed faster than a leaned-out blower motor. Overkill this aspect, and run a scoche rich and longevity should follow.

MellowYelloW
06-25-2001, 09:08 PM
froggy...i am also new to jet boats. and since joining this elite group of fellow jet boaters i have learned a great amount. but i still have lots of questions. like what does having the pump set back do for performance? and the wedge ...how does that help...these may sound like stupid questions...but i am sure you all were wondering the same thing at some time.
thanks
brian