dont know chit about jets some help pls

1949 Views 17 Replies 11 Participants Last post by LakesOnly, Aug 2, 2009

sangerfan76

Discussion Starter · Aug 1, 2009

ok before we get to deep i love my v drive and thats that. but i bought a spectra 20 jet for my family and we love it. i just got it running like a champ thanks to high flow dynamics hooking me up with a awsome set of heads and best service. sooooo i took it out and hammered it. before when it ran like crap it was slow to get out of the hole. now since its running on all 8 holly crap it shits and gits. now seems like the pump is not flowing enough almost like slipping a clutch in a car. i would think it has orig impeller in it on a 12jc pump. where do i get a b impeller to try it and see it it will help . i geuss it comes to how can i make the pump efficient. seems to have been rebuilt before i bought boat and boat was well taken care of.. so i come to the ones who would know

sphss

1 - 18 of 18 Posts

sleekcrafter

· #2 · Aug 1, 2009

Having had a 23 foot sleek craft jet boat, with nearly 700hp, I can tell you that having tried everthing from an A, thru AAA impellers, they all gave the slipping feeling. I sent my AA impeller out to (***)
for a full detail on the front and back side, and re-installed it. Problem gone, wack the throttle and it went.

sangerfan76

Discussion Starter · #3 · Aug 1, 2009

i would think it would feel like it slips but it seems excessive like im useing alot of wasted rpm and power.

Sleeper CP

· #4 · Aug 1, 2009

sangerfan76 said:
i would think it would feel like it slips but it seems excessive like im useing alot of wasted rpm and power.

What rpm range are you talking about

bulb

S CP

Schi-502

· #5 · Aug 1, 2009

Posting numbers...

Like this,

22' Schiada day cruiser
Weight unknown

ZZ502 @ about 460 hp (logs, 850 Holley,4160)
Max rpm, 5200
Max speed, 67 gps

Berk, 12jg, SS "A", Droop and hyd. place diverter

Can't post pictures because I don't know why!!!

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2

Schi-502

· #6 · Aug 1, 2009

Well, I got two outta the files.

Schi-502

· #7 · Aug 1, 2009

recent pictures.

Nope, it aint happenin'.

sangerfan76

Discussion Starter · #8 · Aug 1, 2009

well its running up to about 4600 right now . but i shoots there fast like no load on it. id say were going 50 ish. engine has been rebuilt with good parts. i have a 750 double pump. msd ignition with 6a box. logs on it. i know there is more in it

Malcolm

· #9 · Aug 1, 2009

sangerfan76 said:
i would think it would feel like it slips but it seems excessive like im useing alot of wasted rpm and power.

Sounds like something a V-drive guy would say. Must be working normal.

Malcolm

· #10 · Aug 1, 2009

sangerfan76 said:
well its running up to about 4600 right now . but i shoots there fast like no load on it. id say were going 50 ish. engine has been rebuilt with good parts. i have a 750 double pump. msd ignition with 6a box. logs on it. i know there is more in it

That's a solid boat. It's gonna take a fair bit of power to make it haul the mail.

CK7684

· #11 · Aug 1, 2009

Sounds to me like you need to just go through the pump and make sure everything is tight...
My hull is definately not a "fast" one, but at 4700 rpm I'm at 67 mph...

bp298

· #12 · Aug 1, 2009

23' hallett, junkyard truck 454, berkjg alum A. previously would go to about 4300, slowly get going and some days later get almost up to 47.
now, blueprinted berk, amt A+, blueprinted dps inducer. from stop/idle, will go up to 4050, accelerates like an sob to 40, then aches and groans its way to 50 (still 4050). like the black pearl, except it's blue... still a work in progress, but fun to take my 6k total investment out on the lake and just smile at all the 150-200k boats doing exactly the same things i am.

if your spectra doesn't give you good initial acceleration response off idle, the pump probably needs some attention.

GRoper

· #13 · Aug 1, 2009

rebuild er w and put a loader grate on er if it dosent already have one. sounds like it might be cavitating, a loader grate will help with that.

Shaun

· #14 · Aug 1, 2009

sangerfan76 said:
but i shoots there fast like no load on it.

You do know that jet boats when hitting the throttle instantly go to Max RPM right? The rpms are not going to grab and then slowly climb while boat speed increases.

Sleeper CP

· #15 · Aug 2, 2009

Shaun said:
You do know that jet boats when hitting the throttle instantly go to Max RPM right? The rpms are not going to grab and then slowly climb while boat speed increases.

Something like this; buried the throttle:

900+ hp, it spun to 7,000 and then grabbed at 6,200 Wanted to see how that inducer worked

grn

S CP

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sangerfan76

Discussion Starter · #16 · Aug 2, 2009

its got a loader grate in it. sounds like pump may just need some attn. ill make that the winter project. no complaints just want to make it work its best for wht i have. your right im a v drive guy but i have so much fun with my jet. its out all the time with us

SmokinLowriderSS

· #17 · Aug 2, 2009

Shaun said:
You do know that jet boats when hitting the throttle instantly go to Max RPM right? The rpms are not going to grab and then slowly climb while boat speed increases.

Shaun is quite correct.

For a guy used to a prop boat, engine throttel/rpm behavior is a drastic change in pace.

Consider that what the engine is connected to is a water pump, nothing else.
The RPM of the engine is limited by the back-pressure of ther pump against the engine.
At low to moderate revs, there is no apreciable pressure compared to the engine's torque output to the shaft.

The engine, as long as it is able to output more twisting force (torque) to the shaft than the pump's back-pressure resistance, the engine will accelerate, hence, from ANY RPM, from idle to just below maximum, a full throttle input will wind the engine to full RPM, to the point the pump bowl pressure (which is the resistance against the impeller) overpowers the engine, and RPM stabalizes.

Further, the pump has absolutely no idea, nor interest, in what it is attached to, or whether it is moving or not.

There is only very minor maximum RPM effect on the pump related to foreward motion of the boat, all of it related not to boat motion or speed, but to water suplied to the pump intake.
Sudden pump/engine acceleration can cause cavitation at low speeds, hence Sleeper's noting of spinning 7-grand "before the pump 'caught' ". Once the pump was fully loaded with solid water, it set the maximum rpm of the engine, regardless of fwd speed of 20mph or 120 mph.

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LakesOnly

· #18 · Aug 2, 2009

sangerfan76 said:
ok before we get to deep i love my v drive and thats that. but i bought a spectra 20 jet for my family and we love it. i just got it running like a champ thanks to high flow dynamics hooking me up with a awsome set of heads and best service. sooooo i took it out and hammered it. before when it ran like crap it was slow to get out of the hole. now since its running on all 8 holly crap it shits and gits. now seems like the pump is not flowing enough almost like slipping a clutch in a car. i would think it has orig impeller in it on a 12jc pump. where do i get a b impeller to try it and see it it will help . i geuss it comes to how can i make the pump efficient. seems to have been rebuilt before i bought boat and boat was well taken care of.. so i come to the ones who would knowsphss

sangerfan76,

Wow so you gained 300 rpm with the head swap? Not bad. Yes, jet pumps have a "stall speed"....kinda like driving a car with a 4600 rpm stall speed converter in your case. It should have really good launch, though.

Anyway, I'm writing basically to suggest that you stay with the A impeller, not switching to a smaller one such as a B impeller. Your engine is not cammed or set up for the higher rpms that it would operate at with a B impeller. Stay with the A, maybe cam the engine somewhere down the road to take advantage of the ported heads.

Thanks for the props,

LO

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