Originally posted by JET-O-VATOR
mainevent i may be way off with this but it is what i found this weekend with my brendella... my rideplate was set downward so i had wat to much boat in the water even with the jet-o-vator up.. i didnt even know any better and squirtin thunder had stopped by and was whatching me make a pass and noticed it so we started playing with it and pulled the boat way out of the water.... before i could not pull more than 4200 rpm and after we did that i could pull 5000 rpm so go fiqure and thats with an a impeller......and i noticed the difference right away, every adjustment we made it kept getting better....so ya i dont know what your boat has but mine has 12-jg-a, back cut shoe (so im told) and a ride plate.
daniel
Hey man thanx for the .02 everything helps me
MAINEVENT
Squirtcha ???,
When he was cruising the boat looked very good. As soon as he opened that thing up it planted the nose, if it were a hydro it would have been fast. It was wet about a foot or two of the bow eye. All the way up about 12 degs. maybe more. Diverter same position portof hydrolic or electric he had no real idea where it was but he tried. same wieght in boat every run. I was able to loosen it up a bit. Not much but some.
Jim
"Soory it is a Dominator A/B impellar"
Only reason I posted that argumentative comment was because cut size w/o mfg means little. Dominator A/B at 4750 rpm = 375 hp, significantly higher than a Berkeley A/B. Depending on where you boat MainEvent, and weather conditions when you spun that 4750, 375 hp lake power could be equivalent to an STP corrected 450 or more (engine builder terms) but not 550 hp...unless you boat Lake Tahoe
Sounds like you have a healthy 454 but I doubt it puts out what your builder claimed.
"Anybody else care to chime in?"
Sure. As long as tact or humor's not requiredjust ideas.
I've also monkey'd with plate angle, wedges and shoes, had the pump setback...none of these changed maximum rpm noticeably. I've also added 260 lbs of weight with no max rpm change. And speed or intake (pump) loading seems to have little affect on my max rpm although if it changed by 100 rpms from launch load to max speed load I wouldn't notice. No QD yet. My experience similar to Dans.
So talking about how ride plate angle can change rpms. Engine only cares about impeller load for max rpm. Impeller load comes from mfg and cut size (constant), and how much cavitation (or ventilation if ingesting air) during operation (variable). A "fully loaded" impeller in my opinion has zero cavitation or ventilation going on within the blades.
Since water's incompressible, density doesn't change as pressure goes up, neither does fluid viscosity. So once the impeller's fully loaded, further increase in intake pressure in my opinion unlikely to affect impeller rpm. In other words, "overcharging the inlet" or "overloading the pump" unlikely to drag down rpm...certainly not to the tune of 800.
Accurately measured race data seems to back this up.
So how can 4200 jump to 5000? A mystery. Assuming your tach readings are accurate, it's possible the impeller's not fully loaded at 5000 rpm's due to cavitation or ventilation. A couple checks may solve this mystery. First, how much lake power does your 455 put out Herc? 5k on a Berk A's pretty healthy assuming the impeller's loaded. Second, you could chart speed vs rpms and see if there's a point where more rpm gives little change in speed...possible cavitation?
ps: Just my thoughts no doubt viewed negatively as controversial or argumentative by some.
jer
Jer,
On Jet-O-Vaders Brendela the rpm change came from tuning not plate. I tuned it I know. The darn thing was set so far retarded I moved the dist. counter clockwise 1 deg. and it died, I had to advance it about 10-12 to get it to run right. But I still think the cam is retarded. And the carb is screwed and it has vac leaks. With that all said no matter on the tune of the engine the nose is Still Planted . Will a back cut shoe creat too much transom lift or tail lift.
Jim
10-12 deg timing change is a large change in HP. my 455 runs 4700 day in and day out except on cool winter evenings it picks up 200 rpm in the cold air here at the river. will someday gps it to see what 4700 with a AA jacuzzi works out to. keep fine tuning your engine and your ride setup and you will probably gain some more. you can also use Jer's Hp info as a tuning tool to make informed changes to your engine to increase Hp that is useable at pump speeds to pick up rpm and boat speed.
I have the same hull. Jack has had experience with it- before I brought my boat to him I went to check his shop out and pick his brain. There was a hondo there with the same bottom as mine, and we came to the conclusion that the Brendella was a copy-given the fact that Irv owned both company's at one time... Jack said the Hondo(green and white-not sure whose it is) had about 600 hp and did over 80. Give him a call and he can explain why you need the back cut shoe. He put a back cut shoe on my intake, butI haven't got it wet yet...
Floored,
This is not my boat it is Jet-O-Vaders, I do understand what you are saying on the timing thats why I posted the facts. But the bottom line of this whole thing isThe gosh darn boat is stuck to the water like glue and no one is adressing my question "Does a back cut shoe give transom lift???". So everyone can through in what ever they want but the bottom line is the Nose is stuffed in the water. What I am looking for is the facts not BS. At this point I could careless what the RPMs are. The boat needs to set right at speed.
Thanks
Jim
Originally posted by LVjetboy
First, how much lake power does your 455 put out Herc?
jer
I think you got somone confused. I am a BBF, I am runnin bout 500HP. Not sure on the RPM yet, I have 2 diffrent numbers 5200 and 5500. Berk "B" imp. I am putting in an new tach today. So next weekend I will get RPM readings.
I think 5200 is right, I think the 5500 was a mistake.
squirtin thunder, sorry I was referring back to Mainevent's original post about engine and rpm's. just a quick ref to the olds engine picking up rpms with the timing change.does jet-o-vader have saddle or nose fuel tank, that affects the settings also?
Woah Jim!
I was kinda hoping someone with more knowledge woulda posted on your question, but I'll take a stab at it.
The backcut shoe is supposed to give the boat more lift in the back. I've run both flat and backcut on mine and to be perfectly honest, it didn't really make a whole hell of a lot of difference.
I'd have to wonder if his hull is straight or not. It almost sounds to me like he's got a hook and it's forcing the bow down, or he's got some hardware dragging. Is he running a shoe now? If he's running a shoe, what is it's relationship with the keelline? Is he running the old angle iron loader? Where are the ramps in relationship with the keelline? Hanging below it, or tucked up in the intake some? If you do a full speed pass, and get out of it..........can you feel hardware (shoe, loader) dragging? Or does it just glide along smoothly?
Each and every boat is a little different. Even the same hull by the same manufacturer can he different. I have a buddy of mine with a Kachina 18 just like mine. He's made the same exact changes that I have and didn't get the same results.
I think in order for anyone to help, you'll have to give more particulars.
I'd think the first thing to do would be to take some hardware measurements, then check to see if the bottom is straight.
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