How much stress on an engine in a jet boat?

[AntRant]

How much load does a jet put on an engine? For instance... I took my 460 out of a 70's Lincoln Mark III , Now what does the engine think? Would it be equel to puting the car in second gear for start to wide open?

[HammerDown]

Well I dont know what the engine would think...however the stress/load in a boat motor is alot higher than the auto and the marine motor never gets a break unless ya come to an idle...its like driving up hill none stop...or even driving your car with the emergency brake on.
About the red line thing...what ya see on your in dash tach (auto) is conservative...I have no reservations about reving my 468 to 5500, and I'm sure it could take more rpm...but thats just for a few seconds. Now in a auto with a trans...I dont see any issues with droping the clutch at 6000+. And small Blocks seem to take higher rmps longer. It all boils down to the environment the motor is in, Marine/auto and also the condition that perticular motor is in.
If pushed to hard. Anything can and will blow...eventually, just a matter of time.
[ February 20, 2003, 11:17 AM: Message edited by: HammerDown ]

[AntRant]

HD, Havent heard or spoke to you in a while.....Thanks for the info. Going to Owasco Lake in July?

[HammerDown]

AntRant:
HD, Havent heard or spoke to you in a while.....Thanks for the info. Going to Owasco Lake in July? At this time I would say no...but everything with this up and coming summer is a coin toss.

[Blown 472]

The thing to keep in mind as a car is going the load is decreasing, that is why they have trannies to move the mass, jet boats are diff the more rpm the motor builds the greater the load on the motor.

[Mandelon]

How is the load greater? Once the boat is moving, doesn't it take less energy to move it faster than it does to get it going from a standing start? If you were idling and pushed it immediately to say 3500 rpm, it would come on plane and cruise. How is it working harder at a given rpm, its still moving the same amount of water...isn't it.???
Revs come up, and the impeller spins faster. I don't see how the load would change much......It might cavitate at the start.....Splain it to me, Lucy!!!
[ February 20, 2003, 07:11 PM: Message edited by: Mandelon ]

[1tricky1]

I would have to agree with Mandelon. Actually I would suspect the load would be less in your typical 18-20 ft jet application. I believe the motor spins more freely in a jet vs car application. Think about it, when you stab the throttle in a jet, it revs very quick, alot quicker than in a car, unless your on ice or something. But Hammerdown is right in the sense that a jet motor will continue to work harder even at cruising speeds just because a jet needs rpm to work. Regardless, I bet that 460 is much happier in the boat :D

[jim@pj]

The 460 will have to run in a much higher RPM band all day long. High Rpms will eventually wear a motor down if it is not built for it. The ford auto has rear end gearing and a tranny, you don't drive around all day at 4000 RPM. On top of that the auto engine has a cam designed for a different power band. The 460 is a good motor and if you take care of it and don't beat it to death it should be fine. Good luck Jim

[Hal]

A jet pump is the same as a dyno. The more RPM you turn the more power you will need. Its like trying to push a loaded dump truck with your car. :)

[Hal]

How in the hell did I lose a star? I did'nt deserve that. I don't do bad things, I only try to help when I can. :mad: :( :) :D

[Jordy]

1tricky1:
I would have to agree with Mandelon. Actually I would suspect the load would be less in your typical 18-20 ft jet application. I believe the motor spins more freely in a jet vs car application. Think about it, when you stab the throttle in a jet, it revs very quick, alot quicker than in a car, Depending on the pump set up and its' tolerances, it will rev up quicker due to a certain level of cavitation. Revs up great on the trailer out of the water right? Won't pull the same RPM's across the water now will it? No. The faster the motor runs, the faster the impeller is turning trying to move more water through the bowl which doesn't change due to rpm. The more water that is "waiting" to go through the pump as the motor gets up to the top RPM it will pull in the water, the greater the load. If you were running some type of variable nozzle out of your pump, then perhaps the load would remain constant, however, on a standard pump, like Blown said, the higher the RPM, the more load on the motor.

[Jordy]

P.S. I'm sure there are more technical terms that relate to the limitations of the pump and the physics that go along with it, but I'm not that concerned. Think of it as pouring an increasing amount of sand, or even water, through a funnel. Only a certain amount will flow easily through until it starts to back up in the neck of the funnel. That backup is what creates the load on the motor. Capeiche?

[Badboat1]

This is a tricky thing and I think both thoughts are correct,depending on the exact application it will differ a bit,As in impeller size,loader,boat lift,etc.A jet has not a thing hanging under the boat but a bit of loader.Run a 100 and let off see how fast the boat stops.Same thing take a car run a 100. What stops faster boat.Alot more drag in the water so the engine will have to work harder to keep it up and going. Just my thoughts on this.
Badboat1

[Duke]

how about the fact that an engine in a jet doesnt see nearly as much... uhh.. run time as an engine in a car...
a car see's a lot more driving every single day, then a jet boat does, what twice a week, for 8 month's of a year, if that...
so, even if it'll be making more stress in hte boat, it wont be making it as often as if it were in the car... huh?!
just stirring the pot
duke

[Jordy]

Badboat1:
What stops faster boat.Alot more drag in the water so the engine will have to work harder to keep it up and going. Just my thoughts on this. I think if you broke it all down, you'd find out it is far trickier than ever imagined. The drag on the hull and the "stickiness" of the water are definately a factor, granted the initial drag of the hull are overcome to a certain effect based upon the amount of wetted area that the hull is running based upon the speed across the water. All of the inertia of the car remains seemingly constant. Of course the boat will slow much faster when you let off the accelerator but that doesn't play much on the load of the motor as that is an ever changing variable.
As far as Duke's comment, it seems that while the boats don't see as much use, the amount of use they see based upon load and RPM use, most in the 2500-3000+ range would easily quadruple the water time v. time on the road.

[Duke]

jordanpaulk:
[QUOTE]Originally posted by Badboat1:
[qb]As far as Duke's comment, it seems that while the boats don't see as much use, the amount of use they see based upon load and RPM use, most in the 2500-3000+ range would easily quadruple the water time v. time on the road. Do you really think that an engine in a jet works that much harder? just curious, not trying to question your comment.
how about if the engine were in a truck, some towing here and there,
what if you lived on a hill like i do, going up hill and down hill. or going over the grapevine.
Do the engines in jet's, like everyone's on here, run in the same temp. level's as everyday engine's in the world? i'd guess that a jet engine runs cooler then most cars/trucks.. and of course the heat put's more stress on the car/truck right?
just stirring the pot, i kinda got off topic but thats ok..
duke

[MikeF]

When you are driving a car down the road at 75mph, 2000rpm, "part throttle".....you are only letting a small amount of air/fuel into the engine. Cam wants to let alot more in, yet the "part throttle" is only letting X amount of fuel/air in. This is not making much load on the engine.
When you want to go faster in a boat...you open the throttle more, letting more fuel/air in leading to more cylinder filling power to be able to increase the speed of your boat....hence the load get's greater :D .
In a boat depending on how fast you want the impeller/prop to turn (both have different realms that they work in).....it takes HP to turn it. Low in the rev range you have ALOT of torque.
A jet drive will go easily through this "range" rather quickly to where the HP starts to become more than the torque. Unfortunatley, that's where it starts taking ALOT more HP to continue the gain of higher rpm's that everyone is looking for w/ a jet boat (including me wink ).
A prop boat will/can blow or cavitate if you have alot of hull weight with alot of torque (the engine is turning the prop faster than the hull speed). Also, if you have a cam in a prop boat that is too big for the engine (no torque) then you have a sluggish out of the hole boat.
Turbo/superchargers, more CID or Nitrous are good ways for adding more fuel/air to the engine to create MORE POWER wink !
Hope this helps smile_sp .

[Hal]

You can drive around in your car all day at 60 mph in 3rd gear turning 4000 rpm getting 12 miles to the gal and only using maybe 50 HP to do it. You drive around in your jet boat at 4000 rpm and its going to take maybe 200+ HP @ 3 mpg to do it. The speed part comes with the hull design and set up.
You can't compare a jet with a car. Its not the same thing. A jet needs power to make rpms, Thats why most jet boats are big blocks. and yes a jet boat is much harder on an engine than a car would be.

[Mandelon]

As the speed of the boat increases, the amount water is forced into the impeller assembly at a greater rate. Depending on your grate and loader setup.....seems to me that would offset part of the power needed to simply turn the impeller.
I'm no engineer here guys, just trying to understand. Plus, I like to argue!
If the load on the motor increases with speed, then is there a variable percentage of power attributable to the load above what is used for porpulsion??

[HammerDown]

Well, I guess that answers that....

[1tricky1]

jordanpaulk
[/qb]Depending on the pump set up and its' tolerances, it will rev up quicker due to a certain level of cavitation. Revs up great on the trailer out of the water right? Won't pull the same RPM's across the water now will it? No. The faster the motor runs, the faster the impeller is turning trying to move more water through the bowl which doesn't change due to rpm. The more water that is "waiting" to go through the pump as the motor gets up to the top RPM it will pull in the water, the greater the load. If you were running some type of variable nozzle out of your pump, then perhaps the load would remain constant, however, on a standard pump, like Blown said, the higher the RPM, the more load on the motor. [/QB][/QUOTE]
Jordy, Who ever ever mentioned out of water, trailer revving? :rolleyes: I am refering to initial load at full throttle. Of course there are many variables with pump clearances etc, but I'm saying there is more load on that 460 trying to pull that lincoln up to speed from a dead stop than that 460 getting an 18' jet up to speed. Yes, I agree the load will increase across the power band and the faster you go, but initial load has got to be greater in that land yacht :p

[schiada96]

Threr is a lot more load on a boat than a car engine. How much boat fuel do you use in a weekend. If you put that much fuel in your big block truck how far would you get.

[Jordy]

1tricky1:
I'm saying there is more load on that 460 trying to pull that lincoln up to speed from a dead stop than that 460 getting an 18' jet up to speed. You have to remember that there are many gear reduction devices in use to get the land yacht up to speed. The transmission, unless you're starting in overdrive, the differential, unless you're running a 1:1 drive ratio, and event the size of the tires all play into how much load is on that motor in the car. Think about it this way, on flat ground, at idle that lincoln will begin picking up speed, even keep the rpms at 1500-2000 rpms or so, you'll keep picking up speed and run through the gears in the transmission. Try that in a boat and see if you ever get on plane.

[1tricky1]

schiada96:
Threr is a lot more load on a boat than a car engine. How much boat fuel do you use in a weekend. If you put that much fuel in your big block truck how far would you get. You use more fuel in a boat because of more required RPM at cruising speed, not soley because of "load". If that same 460 had no transmission, and had to cruise at 3,000+ all day, believe me, it would use the same amount of fuel as the boat.

[schiada96]

I'm saying the load on the engine at 3000 rpm in a jet boat is not the same as a typical truck at 3000 rpm. The boat will use more fuel. Hence more "stress".

[schiada96]

How many hours is typicaly good for a marine engine before a rebuild 5 to 6 hundred hours?

[Blown 472]

Not only that but you have this mass now moving, to which it takes very little hp to keep it moving, like said before. It also has to do with the fact this is a pump, there was a thread on pump dynamics awhile ago, when a pump reaches a certian rpm it will pump said amount of water, above that it takes more rpm and increases the load on the motor to drive it. I believe the sweet spot is a low rpm for the pump, somewhere in the 3000 rpm range.

[cyclone]

Maybe i can help clarify the boat/vs car effects on a motor. You change your oil in your car every 3,000 miles right? Well a weekend of running my boat hard will break down the oil in my boat, necessitating an oil change. I dont know about you, but when i drive my boat, i'm at no less than 3,500 rpms all the time (B-cut impeller). And if i'm running with my friends who have fast boats, i'm cruising at 4,500rpm just to keep up. So even a cruise from say Laughlin to Needles (about 15-miles) at 4,000+ rpms constantly is alot of work for the motor.

[1tricky1]

I agree with you Jordy and others about a boat motor does see more stress than in a car. But what I keep picturing is that lincoln (land yacht) being givin full throttle from a dead stop or even a roll, the tires hooking up, the front end coming up, the motor torking sideways and that "load" being transferred up to the engine. It just seems to me a (jet boat)boat doesn't see that much "initial load" accelerating up onto plane. :confused:

[Blown 472]

1tricky1:
I agree with you Jordy and others about a boat motor does see more stress than in a car. But what I keep picturing is that lincoln (land yacht) being givin full throttle from a dead stop or even a roll, the tires hooking up, the front end coming up, the motor torking sideways and that "load" being transferred up to the engine. It just seems to me a (jet boat)boat doesn't see that much "initial load" accelerating up onto plane. :confused: But does the lincoln go to full rpm?? or does it build?

[1tricky1]

Blown 472:
1tricky1:
I agree with you Jordy and others about a boat motor does see more stress than in a car. But what I keep picturing is that lincoln (land yacht) being givin full throttle from a dead stop or even a roll, the tires hooking up, the front end coming up, the motor torking sideways and that "load" being transferred up to the engine. It just seems to me a (jet boat)boat doesn't see that much "initial load" accelerating up onto plane. :confused: But does the lincoln go to full rpm?? or does it build? Exactly my point, the lincoln is being givin full throttle, yet it won't rpm because there's to much load on it, and as the weight gets moving down the road the load decreases and rpms come up. The just revs up due to cavitation, hence less "initial load"

[Chris J]

How could I resist getting in on this? Here's my take on some of the differents. First put 30 pound on a childs wagon (with wheels) and tow it around the yard. Now take the same 30lbs and put it on a piece of ply wood and tow it some more. You should notice a difference. Now walk a block or two. Try it again in knee deep water. Water is a much thicker fluid than air. Plus wheels provide less drag than a slide. This is why it take so much more power to go 60mph on water than land.
One more thing the only thing a motor running a pump knows (assuming they do think) is RPM which is directly proportionl to power used. Cars on the other hand are affected by Weight, speed, terrain ect.

[Blown 472]

Ok, load decreases in the car, and increases in the jet.

[1tricky1]

Blown 472:
Ok, load decreases in the car, and increases in the jet. I'm with ya on that one :D Damn, I gotta get my ass to work, talk to ya all later

[Jordy]

1tricky1:
The just revs up due to cavitation, hence less "initial load" Maybe you should see a pump builder and get it looked at then. I don't have that problem.

[1tricky1]

jordanpaulk:
1tricky1:
The just revs up due to cavitation, hence less "initial load" Maybe you should see a pump builder and get it looked at then. I don't have that problem. Maybe we should hook up for a little race to see who's got pump? :D

[Jordy]

1tricky1:
Maybe we should hook up for a little race to see who's got pump? :D Who cares? What does that have to do with anything on this thread? This thread was pretty much beat to death and now the bench racing starts... I'm over it. Oh, and btw, I don't have anything to prove with my pump or my boat. :D :D :D

[1tricky1]

Dude...I don't have anything to prove either, but don't start bashing my pump, and pumping up yours as if it's the most efficient pump built. That comment: (Maybe you should see a pump builder and get it looked at then. I don't have that problem.) was uncalled for - chill! Every pump will have some sort of cavitation/slippage, hence less load than in a car, which was the topic of discussion. argue

[rivercrazy]

Think of it this way. The more you have to put your foot in the throttle consistently, the harder the engine is working.
In a car you romp the throttle to get up to speed and then it takes very little throttle to keep the car moving at a steady speed.
In a boat, to maintain say 40mph in a jet boat you need to keep your foot into the throttle by a significant amount. Throttle position has a lot to do with engine load....

[AntRant]

So what was the Question again? :D

[Blown 472]

AntRant:
So what was the Question again? :D If I had five apples, you had three, she ate six nekked, shit who cares. :D

[Jordy]

1tricky1:
Dude...I don't have anything to prove either, but don't start bashing my pump, and pumping up yours as if it's the most efficient pump built. That comment: (Maybe you should see a pump builder and get it looked at then. I don't have that problem.) was uncalled for - chill! Every pump will have some sort of cavitation/slippage, hence less load than in a car, which was the topic of discussion. argue How the **** did I bash your pump? You implied that when you drop the hammer on a car it won't rev up because of the load, while "The just revs up due to cavitation, hence less 'initial load'" (and those are your words exactly, even the part where you left out "Jet" or "Boat" or what ever you were going to put in after "The" and before "just"). I didn't bash your ****ing pump when I said, "Maybe you should see a pump builder and get it looked at then. I don't have that problem." If you're that much of a ****ing crybaby that a suggestion, not even at you, as we're talking about a hypothetical car v. a hypthetical boat here, that if the pump just cavitates there maybe something wrong with the pump and it needs to be looked at then bud, you have some issues. We need to race... yeah whatever. I don't see anywhere in that two sentence reply where I said my pump was anything great either. You know why? Because it's the internet and nobody ****ing cares. Get over it. Sorry if you feel that threatened from two little lines.
[ February 21, 2003, 01:01 PM: Message edited by: jordanpaulk ]

[Mandelon]

I think Jordy just handed out some lemons!!!! :D :D
[ February 21, 2003, 01:21 PM: Message edited by: Mandelon ]

[RR1/001]

Jordy I think you can take him :)
Go for it <---- http://www.nick.com/all_nick/tv_supersites/spongebob/img/back_talk.gif

[Jordy]

Hey Slowy, what's up with you bud? :D

[Blown 472]

Now, we have the chet/hbjet thing and this??? what is next?? I think we need a group hug. :p

[Blown 472]

Ok, I was trying to take the diplomatic side of it, I think tha king will dole out tha beatings. :D

[Jordy]

RiverDave:
Jordy, I can't believe that you insulted that guys Pump. Shame on you. :D
RD If I was going to insult someone's pump, I am certain I could do much better than that. wink Thanks for the support RD. :D

[1tricky1]

jordanpaulk:
1tricky1:
Dude...I don't have anything to prove either, but don't start bashing my pump, and pumping up yours as if it's the most efficient pump built. That comment: (Maybe you should see a pump builder and get it looked at then. I don't have that problem.) was uncalled for - chill! Every pump will have some sort of cavitation/slippage, hence less load than in a car, which was the topic of discussion. argue How the **** did I bash your pump? You implied that when you drop the hammer on a car it won't rev up because of the load, while "The just revs up due to cavitation, hence less 'initial load'" (and those are your words exactly, even the part where you left out "Jet" or "Boat" or what ever you were going to put in after "The" and before "just"). I didn't bash your ****ing pump when I said, "Maybe you should see a pump builder and get it looked at then. I don't have that problem." If you're that much of a ****ing crybaby that a suggestion, not even at you, as we're talking about a hypothetical car v. a hypthetical boat here, that if the pump just cavitates there maybe something wrong with the pump and it needs to be looked at then bud, you have some issues. We need to race... yeah whatever. I don't see anywhere in that two sentence reply where I said my pump was anything great either. You know why? Because it's the internet and nobody ****ing cares. Get over it. Sorry if you feel that threatened from two little lines. Obviously your not over it yet...you seem to be quite irritated, :p , What, now your back peddling saying you didn't dis my pump? You quoted me and then responded, I need to have "my" pump checked out". Did I cry to that response? no, I called you on your smart ass remark. Yes, this is the internet and a place I enjoy to discuss boating, and I'm not gonna put up with smart asses like you who think they've got it all figured out. You interpreted cavitation as a loose worn out pump and then mouthed off. I was referring to every pump will have some slippage. Alot more than a Lincoln land yacht...stick that in your lemon!

[Mandelon]

stick that in your lemon! Tooooo Funny! :D JP was obviously in a bad mood, despite his gruff looking exterior I heard he's really a pussycat!! :D

[Jordy]

1tricky1:
Did I cry to that response? What other response was there? :confused:
no, I called you on your smart ass remark.
OK genius, now you lost me. As near as I can figure there was only one response, and you didn't cry to it and then you called me on it. Am I the only one missing the point here?
Yes, this is the internet and a place I enjoy to discuss boating, and I'm not gonna put up with smart asses like you who think they've got it all figured out. How was I being a smart ass? I've already said I wasn't talking about your pump. It was a general statement and then your cock size feels threatened and you want to race? How the **** am I the smart ass here? Why don't you look at every other post on this thread and tell me how I'm being a smart ass.
Trust me, if I was going to bag on your pump I would have and you would have known it. You must be pretty ****ing pathetic to pick apart every statement anyone makes and think they are talking about you, maybe some kind of an inferiority complex? But I hate to bust your pathetic little ****ing internet bubble, but for the last time I wasn't talking about your pump. I could care less about your pump. I could care less about your boat. Can I make it any clearer?

[Jordy]

and just so you know, I was on the phone with RiverDave right before he made that post and he's doing it to stir it up more than it has been. Funny how you're the only one who seems to have their little pussy hurt out of this deal.
Enough already.
[ February 21, 2003, 06:18 PM: Message edited by: jordanpaulk ]

[1tricky1]

Geez Jordy, if you wanted to apologize, all you had to do is say I'm sorry.

[Jetty 468]

Sorry but I still laugh when I see the topic here :D How much stress is on one , hold up your hand here if you have own a jet boat and replaced a motor or two !!!!!!

[wfodude]

man this shit gets outta control...As a professional engine builder I can tell you auto motors better go out and run 100,000 miles....You ever see that kinda life in a boat motor? Think of the actual time you're not floatin in the lake bs'ing or drinkin a beverage with friends. you probably are in the throttle and using the motor very few actual miles. YET I see marine engines come in with worn bearings in a few short seasons. Usually not cylinder wall wear but always bearing wear. This wear comes from excessive loading Hmmmmmmmmm just my .02

[Mandelon]

I don't think anyone disputes that there is a significant load on a boat motor. But does the load increase as the speed increases? Its got to be harder for it to get on plane that stay on plane???? Just like getting a car rolling. :confused:

[Hal]

Maybe this will help.
Jet vs Dyno (http://www.berkeleyjet.com/Manuals/dyno.htm)
[ February 21, 2003, 10:41 PM: Message edited by: Hal ]

[Mandelon]

http://www.berkeleyjet.com/Manuals/images/pwr-curve-sm.jpg

[wfodude]

I see where you are coming from. Cars have a couple of advantages.First is a transmission,it makes getting rolling much easier,second is the relatively low rolling resistance of properly inflated tires. A boat has a huge coefficient of drag to fight.We all experience it as we let off the go pedal and get tossed into the dash. Not to mention as someone stated earlier the faster you go you can only stuff so much water thru a 3.25 inch hole. once again just my .02

[LVjetboy]

Hal's comments right on. Takes WAY more power...higher bearing loading and engine wear...to cruise at 60 in a jet than 60 in a car.
As for jet boat engines running cooler...well...check out that oil temperature after a hard run :) Infrequent use is a bad thing too. Moisture and contaminants in the oil left to sit in one spot for long periods can rust and pit parts. More stress for boat engines.
As for the idea that load on a jet boat engine changes with speed because of intake flow or maybe hull drag...well...not significantly. For example, when you floor it, within a second, the engine is at max rpm and max load. And the load on the engine as you come on plane will be the same as the load on the engine when you reach full speed. Unless you let off the throttle of course. Here's a good example of that:
http://users.lvcm.com/lvjetboy/MPDrun.gif
The red line shows engine rpm for a 1/4 mile run. After the pump loads, engine rpm stays the same...not influenced by speed of the jet (black line)
jer

[Mandelon]

Well that's it then. Thanks!

[jim@pj]

Hey before all you folks insult each other any further let me tell you how I see this boat vs. auto thing. I have been doing jet boat appraisals for twenty years and one thing I always tell my client is this. In my opinion, after tearing down many stock jet boat motors, with varing numbers of engine hours, I have come to this conclusion. One hundred engine hours in a jet boat is equal to 50,000 miles on a car engine. So if a jet boat has 300 engine hours, it would be like buying a car with 150,000 miles on the engine. I have not seen a jet boat engine with 400 hrs that was not in need of a rebuild.
Jim www.performancejet.com (http://www.performancejet.com)

[TopCat]

the load on a pump increases the faster you go loading it to the point it becomces inefficent causing so much pressure it slows the impeller so if you could come up with a variable sizing intake you could make your boat really fast ......but to answer the question marine use is more than 5 times more stressful..when was the last time you saw a boat with 100k miles on it
[ February 23, 2003, 10:05 PM: Message edited by: TopCat ]

[wfodude]

jim@pj:
Hey before all you folks insult each other any further let me tell you how I see this boat vs. auto thing. I have been doing jet boat appraisals for twenty years and one thing I always tell my client is this. In my opinion, after tearing down many stock jet boat motors, with varing numbers of engine hours, I have come to this conclusion. One hundred engine hours in a jet boat is equal to 50,000 miles on a car engine. So if a jet boat has 300 engine hours, it would be like buying a car with 150,000 miles on the engine. I have not seen a jet boat engine with 400 hrs that was not in need of a rebuild.
Jim www.performancejet.com (http://www.performancejet.com) Can I get an amen brother
smile_sp

[LVjetboy]

Topcat,
For the run above, about 100-150 rpm loss from hookup to finish, which is approx. 5% increase. Considering full hookup near 50 mph and finish well over 100 mph, I'd say that's not significant compared to overall numbers. Which is why I chose the words for intake flow effect on engine loading vs. speed as "not significant" For your typical lake boat topping out in the mid 60's to low 70's, the term "total wash" maybe even more appropriate.
A variable inlet could recover some, and would be interesting to play with. But likely not worth the added complexity even for a racer, unless jets start running a lot faster?
As for the original question...yes, I think that's been answered quite well by now.
jer
[ February 24, 2003, 03:02 AM: Message edited by: LVjetboy ]

[Hal]

Jer, You got one fine looking boat... :)

[bp]

yeah, but he's gotta learn to keep it in the water, so it'll go faster. :rolleyes:
that data sheet is gonna get worn out from all the cutting and pasting. no one has answered this question yet.. how can a pump NOT be loaded, and have bowl pressure climb at a significant rate?

[LVjetboy]

Thanks Hal.
Ok, I'll venture a guess. Let's see...the bowl pressure was the green thingy right? Well, how about if the impeller is partially loaded during the rev limiter bump with zero intake pressure.
Then as speed increases, that partial load goes to full load as the intake becomes more effective. In this case bowl pressure could still increase along with impeller loading to the point where available engine hp begins to limit rpm instead of the rev limiter. In other words, an impeller spinning at rev limit with 50% cavitation generates less bowl pressure than that same impeller spinning at rev limit with 10% cavitation. The point where the rpm drops to a steady 6750 may mean full loading. At that point there is very little change in loading to the end of the run.
Just a guess,
jer

[jim@pj]

Hey... before you guys insult each other too much over motor stress in a jet boat let me relay what I have found. I have torn down alot of jet boat engines over the years with various running hours on them. What I found was, the average jet boat engine takes a good beating depending on the owner. I have been appraising jet boats for many years and I always tell my clients that 100 hrs on a jet boat engine is at least equal to 50,000 auto miles as a rule of thumb. I very rarley see a stock jet boat engine with 400 hrs that does not need a rebuild. Jim

[jim@pj]

Boy ... I'm losing it... I couldn't find my post so I wrote a new one, only to find out that I was on the wrong page ! I need a beer ,
.. Jim

[LVjetboy]

I was wondering why I got this weird feeling of deja vu.

[LUVNLIFE]

I came here to late. My .02, boat motors have way more stress. The only real victims here are the poor jet pumps. wink :D

[Hal]

I don't think the pump would be the victim. If you take care of your pump, keep out of the sand and rocks it will probably wear out 10 motors before it needs any work. Now if you were talking about jet pump boat owners being a victim, then yes it takes a lot of motor maintenance to keep fast jet boat going. But when some dude with a hot flat bottom prop boat pulls up and wants to race it makes it all worth while. Of course you better win or its back to work again. :) Do we ever grow up? I hope not...
[ March 02, 2003, 08:30 PM: Message edited by: Hal ]

[LVjetboy]

Hmmmm...come to think of it...my poor jet pump, and engine for that matter, only lasted eleven years. Less than a dogs life I suppose. Probably would've lasted longer but I got the urge to upgrade. Then again, I only ran nitrous and aired it out when I felt the need. The need for speed...
So what drive you runnin' Luvin?
jer
[ March 03, 2003, 03:18 AM: Message edited by: LVjetboy ]

[Infomaniac]

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