SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: el mojado on August 27, 2012, 06:16:08 PM
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my boat hit 58 mph at Silverwood lake. conditions were a little choppy. 454 MarkV Air Gap edelbrock manifold, HEI ignition, Holley 750 Vac Sec carb, exhaust logs, berkeley split bowl jet ( unknown impeller size), place manual diverter. in better conditions i believe i should hit 60 mph. i was running at 4900 RPM. what are your opinions about my results? am I right on? is this as good as i'll get? I'm happy with the results unless i should be running better. its a 18.5 Eliminator Bubbledeck. thanks for your opinions
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should be faster
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Really.... by how much? What am i missing? :banghead:
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Really.... by how much? What am i missing? :banghead:
so many things come into play, would really need to see a pic of it at speed, do you have a diverter? i would think that the hull is riding really wet.
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Yes i have a diverter. I dont remember er at which position i was in when i was testing it. Which way for speed? I think i was roosting (up) a little due to the chop.
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Can you explain what it means for the boat to be "riding wet"... oh yeah, i also have a ride plate.
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Riding "wet" is similar to what a heavy boat would do... even at speed you're not able to get most of the boat out of the water.
The 454 should be either a Mark IV a Gen V or a Gen VI.
Depending on what heads are on it and if there are any upgrades to the compression, cam, valves... you might be around your top speed for what your working with.
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Whats the elevation at silverwood? That could slow you up too.
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Its a GEN V. As for any internal engine work; I'm not sure. I assume none. The previous owner dodnt mention any. It only had a Edelbrock parformer intake on it. If i had any engine work done it wouldnt look the way it did when i got it.
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Mine's faster at Elsinore than Silverwood. Silverwood has to be over 2500'
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Will a carb spacer do anything positivefor me?
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Not really on the carb spacer. Your running where you should be with your basically stock set up. 60mph is good. 4900 rpm's is also close to where you should be. Numbers will always move around a little depending on conditions, but not by more than 2 or 3 mph. Diverter position is 3 or 4 notches up from bottom. Look behind you, the jet stream should be just above the water level. Make GPS runs with your diverter in different positions to see which one your boat likes best.
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Thanks for all opinions....when it comes time for a jet rebuild, what impeller size should i be looking to make sure is in there? I am not racing the boat. I just want a fun all-around boat. I do use ot for pulling my brave buddies on the tube
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My Nordic bubble in NA form. Bbc roller cam Brodix heads with mild
compression ran 73mph gpsd with a B impeller. That eliminator should be faster than that.
pump sounds like it needs some work. Make sure throttle linkage is opening the carb. all the way.
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carburetor is opening 100%...
Nordic: what do you think should be a doable top MPH?
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Nordic's engine is much stronger than yours. I disagree that yours should run any faster. You have a stock motor with logs as well. Don't think about impeller size until you take yours apart and find out what's in it. Then do your research to find out what you really want out of your boat.
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got my boat to go 100 mph today and she handled it well...........just north of Wells Nevada passing 2 semis >:D
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my opinion (witch dont mean shit) is this, rpm is rpm i dont care about h/p it takes a certain amount of h/p to turn an impeller a certain rpm... i think you said you are turning 4900 rpm. so that being said, all we have left is weight, wetted surface and pump efficiency. you pick wich one or all is keeping the boat from getting the mph....
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My boat runs your same speed GPS'd and close to 5k rpm when its maxed out with two people and loaded with ez up, fuel, two coolers amps subs yada yada.. No frills 454 with a Q-jet, droop ride plate and diverter on a fresh dominator pump. Your boat being an 18'6" and mine being just over 21' open bow and loaded, your boat should walk away from mine and be in the low 60s. I havent GPS'd mine at Silverwood though, I will be there Friday so I will have a GPS number for comparison.
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Setup has a lot more to do with making a boat fast than HP does. First time I ran my white boat, it did 68. This was a sub-300lb hull with a fresh 550ish HP 496 BBC. A little over a year later, I had
it running consistantly in the mid low '90s, and got it into triple digits once in just the right water. I just dialed in the pump, shoe, ride plate, nozzle, and trim plates...and it found me 30+ mph. Keep screwing with it...I bet there's at least another 10mph in it without major changes.
My little shitbox outboard runs about 60mph with the motor trimmed down....it'll run in the low 80's with about 4 degrees of trim in it, because the 4 degrees gets all but about 10" of boat
out of the water. Not a lot of change with a big result, just as an example.
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Thanks for all opinions. They all make sense to me. I wish i could test it out at the river more often where the water is so much smoother. But I'm stuck with Silverwood. Oh well. Sounds like I've got to find the sweet spot with the diverter. I'll keep u guys posted on any more results. i might go out again mid September.... i understand that if i want to go fast i need ore HP. I just want to go asfast as i can qoth my set up. If all i can get is 60mph, thats cool. But if i can find a few more for free, well thats even better!