PORPOISING (NEED HELP)

[PLACECRAFT20]

I HAVE A 20' PLACECRAFT DAYCRUISER WITH A 330HP HARDIN MARINE BBC AND A 100HP NITROUS SHOT. THE BOAT HAS A BERKLEY 12JG WITH A (A) IMPELLER, SHOE AND RIDEPLATE, LOADERGRATE, AND A PLACEDIVERTER. THE BOAT RUNS 6O ON THE GPS AND 65 ON THE BOTTLE. THE PROBLEM IS AT ABOUT 50 TO 55 IT BEGINS TO PORPOISE AND CONTINUES TO GET WORSE AS SPEED INCREASES UNTILL IT JUMPS OUT OF THE WATER. I AM LOOSING SPEED AND MY WIFE IS READY TO BAIL.I HAVE AJUSTED THE RIDE PLATE UP AND DOWN AND CAN CHANGE THE RIDE HEIGHTH BUT NOT THE CAVITATION ANY SUGGESTIONS? THANKS MITCH

[78Eliminator]

hey

[22 placecraft]

add trim tabs to the boat.
try bennet 9x12 tab.
with these tabs you can set boat
on its tail and improve performace while
elimating porpoise.
placecraft boats #626-442-9793

[Mohavekid]

See Froggystyle's discusion/explanation on porpoising on the "boat rides like ass" thread. It explains the dynamics involved.
Good luck.

[Eric455]

you know i find it realy hard to beleive that a 20 foot day cruiser with a hardin 330hp bbc does low to mid 60's. i dont find that very funny and i think that is bullshit. not to be a dick head butt. i have a 18 foot southwind t-deck with a 470 hp 454 bbc. with a jg pump/a impeller. and i hardly do mid 60's on gps. now yes i now that you have a shot of nos that gives you 100 more hp but it still doesnt make sence. and yes my pump has been worked. heres a pic of the boat. http://free.***boat.net/gallery/Reader_Rides/Jet_Boats/BOAT_4.JPG http://free.***boat.net/gallery/Reader_Rides/Jet_Boats/BOAT_1.JPG\
and a buddy of mine does 67.4 on dps with a 550 hp 454bbc and his is a 2000 ultra 18' jet.
eric can anyone tell me how he does mid 60's with a 20 330hp bbc. please i really want to know.
eric

[Omega21]

Eric-
Cool boat... but I'm confused. How is it that your Omega pulls 72 mph @5200 rpm with a stock 455 Olds? Also, how is it that your t-deck with that pretty Chevy won't outrun your Omega? Especially being 3 feet shorter with 80 more hp?
http://free.***boat.net/ubb/ultimatebb.php?ubb=get_topic;f=11;t=000348#000012
Not tryin to piss you off, but I just don't get it. Your thread before gave me great hope for my fiberglass slug...but now it doesn't seem to make sense??
Just curious.
Todd

[LVjetboy]

Now I'm sorry I missed that whole thread...
I think I have a good idea what jets will and won't do with speed and hp.
jer

[Eric455]

that is because i checks speed with a speedo on the omega and it was messed up it was giving me wrong info, now is your that much of a smart ass go ahead and read the whole post and you'll find out what happened.gps is the way to these days and so i went out and bought my self a gps.the omega with the olds ran 48.3 mpg top speed @ 5200 rpms on gps. and yes the speedo was stil telling me that i was doing 70's. and yes i did admit that i was wrong telling people that my olds did 72. so please next time read the whole post. thank you
eric

[PLACECRAFT20]

GUY'S I AM GREATFULL FOR THE REPLY'S. I REALLY DONT KNOW IF I HAVE A STOCK 330HP HARDIN MOTOR OR NOT. I HAVE ONLY ADDED ROLLER ROCKERS & MSD IGNITION. THE HEAD CASTING NUMBERS SHOW TO BE A PEANUT PORT HEAD SO I DONT THINK THIS WAS A 405HP MOTOR. I AM REALLY NOT SURE IT IS A HARDIN MARINE ENGINE. I DO HAVE THE ORIGINAL RECIEPTS FROM THE OWNER. THE BOAT WAS RIGGED & SOLD BUY EARL MCCOY OF E.J. ENTERPRISES IN DALLAS TEXAS. THE BOAT WAS VERY WELL TAKEN CARE OF AND STILL LOOKS BRAND NEW. I AM THE SECOND OWNER. THE RECIEPTS SHOW 330HP BUT THEY DONT SAY HARDIN MARINE. THE BOAT DOES RUN 58 TO 60 DEPENDING ON THE PORPOISING ON A CHEAP $100.00 GPS AT ABOUT 5000RPM.THE NOS ADS ABOUT 600 RPM. THIS IS NOT WHAT I WOULD CALL A NORMAL DAY CRUISER. IT JUST LOOKS LIKE A 20' PERFORMANCE BOAT TO ME. I WILL SEND PICTURES IF SOMEONE WILL TELL ME HOW.
[ September 19, 2002, 08:20 AM: Message edited by: PLACECRAFT20 ]

[Omega21]

Wasn't tryin to be a smart ass Eric, and I did read the whole post...just saw what you said and things weren't adding up. Sorry..
"and i checked it sith a gps this time, i checked it 4 times, yea the water was glass, but still. i did hit 72 and that was at 5200 rpms i hit 67@ 4600 rpms"
"and if you think i'm lieing let it be so. but anyday anytime. the gps is correct. and these are the #'s i get."
Todd

[FoMoCo]

On that Southwind I would check your pump, or your grate to see if somethings not matched. My 18 Kachina with a 429 BBF apx 500hp runs 82mph with a mpd prepped pump! My buddies Southwind with a very mild 454 and a place diverter runs 72 mph. these where all verfied with a gps...What Intake grate are you runnin, and are you runnin a Diverter?
www.fomocomotorsports.20m.com (http://www.fomocomotorsports.20m.com)