Jet speed formula?

[48hr club]

Can somebody out there tell me what the formula is for horsepower to speed is for a jet boat? Currently I have a 21ft Ultra LX 340hp going 54mph. set back dominator pump

[Jetaholic]

There is none. Horsepower/impeller size governs RPM, and RPM has nothing to do with top speed. Speed is all relevant on the weight and design of the hull, plus how much water you move through the pump at a given RPM.

[BrendellaJet]

more useable power=more speed

[adjones419]

Talk to the guys who sell jetboats on ebay...they have a formula. :rolleyes: :D

[Jetaholic]

Talk to the guys who sell jetboats on ebay...they have a formula. :rolleyes: :D
Don't forget about Craigs List. :D

[BLEWBAYOU1]

Can somebody out there tell me what the formula is for horsepower to speed is for a jet boat? Currently I have a 21ft Ultra LX 340hp going 54mph. set back dominator pump
I would say a 21'er W/340HP @54mph is doing good. My guess if you wanted to see 60+mph you would need about 500hp.IMOA.
Brian
P.S. I must be a post *****,400 post in 6 yrs.LOL

[earlbrown]

The engine and jet only make thrust. The top speed comes from how efficient the hull uses said thrust.

[Jetaholic]

The engine and jet only make thrust. The top speed comes from how efficient the hull uses said thrust.
Exactly. The engine and jet pump have no idea what they're attached to. As was said before, you could tie the boat to a pier and still achieve max RPM...it's just gonna pump water...that's all it does. It's not like a prop that unloads as you gain forward speed...RPM is irrelevant of the actual speed of the boat.

[ck7684]

My friend has a Glastron Carlson CVX20with a stock Ford 460 and it does about 50-55...

[Xlration Marine]

I would say a 21'er W/340HP @54mph is doing good. My guess if you wanted to see 60+mph you would need about 500hp.IMOA.
500 no. Dump the jet and put on a 250xs, 70+. :D :D

[jet4fun]

Brian
P.S. I must be a post *****,400 post in 6 yrs.LOL
indeed you are:)

[GUGS102]

Can somebody out there tell me what the formula is for horsepower to speed is for a jet boat? Currently I have a 21ft Ultra LX 340hp going 54mph. set back dominator pump
Find someone with the same hull that is running where you would like to be and pick their brain. THere are a few guys running 21' ultras here that can give their opinion.
Rule of thumb is 100RPM per 1 MPH, 1 MPH per 20-25 additional HP.
If you are looking at mods, first would be exhaust. It does not matter what you do to the HP if the exhaust can not get it out of the motor. You are making an air pump fired by fuel. The more air you can get in and out the more power it will make.

[smiggley]

I was GPSd at 56mph at 4300rpm with my 21ft Miller, 4 people and 1/2 tanks. Basically stock 454. Added dualplane Edelbrock,Pertronix inside Mallory, Blaster Coil, and Place diverter. Now GPSd at 63mph at 4700rpm in mild chop. I may be adding a Indmar 4" exhaust replacing the smaller Hardin snails. It should pick up a little.http://lh4.google.com/jaycindyjared/R18xjGU4GmI/AAAAAAAAAEk/EbZDMHw8BWA/100_3614.jpg?imgmax=576

[Xlration Marine]

My test boat ran 65 with a stock 330 hp and Dominator pump. This speed was given to me by the good people at hot boat who were doing a shoot in phoenix. Well yea they were shooting my boat and a kapucka, is that how it's spelled??

[Outlaw]

I was GPSd at 56mph at 4300rpm with my 21ft Miller, 4 people and 1/2 tanks. Basically stock 454. Added dualplane Edelbrock,Pertronix inside Mallory, Blaster Coil, and Place diverter. Now GPSd at 63mph at 4700rpm in mild chop. I may be adding a Indmar 4" exhaust replacing the smaller Hardin snails. It should pick up a little.http://lh4.google.com/jaycindyjared/R18xjGU4GmI/AAAAAAAAAEk/EbZDMHw8BWA/100_3614.jpg?imgmax=576
smiggley
Loose that air restrictor on top of the carb and you will see
a little more

[smiggley]

no can do. wont fit under cover. Plus tried it without arrestor and I didnt add squat. Arrestors arent filters, they hardly restrict airflow.

[Outlaw]

There is an article in the HB mag where the tested
different Flame arrestors and log manifolds
and it showed a few hp to gain, but I understand the
no room, although there are some bonnet style remote
filters available,
48 check your pms

[Sleeper CP]

Rule of thumb is 100RPM per 1 MPH, 1 MPH per 20-25 additional HP.
If you are looking at mods, first would be exhaust. It does not matter what you do to the HP if the exhaust can not get it out of the motor. You are making an air pump fired by fuel. The more air you can get in and out the more power it will make.
Does that hold true for a 21' Ultra V bottom a 19' Daytona a 21' Cole V bottom and a 19' Gullwing:confused: And what about weight of the boat.:idea:
I will say that the 250 HP nitrous system added 12 mph. Bumped the boat to 103.
Sleeper CP
Big Inch Ford Lover:D

[396_WAYS_TO_SPIT]

Talk to the guys who sell jetboats on ebay...they have a formula. :rolleyes: :D
Awww hell :D :D :D I knew that was coming.....

[396_WAYS_TO_SPIT]

70+. :D :D
Plus you can mix cake mix,eat weeds,blend drinks,smoke out the no wake zone,cut off arms and legs, and bend props on launch ramps:D :D :D

[Xlration Marine]

Plus you can mix cake mix,eat weeds,blend drinks,smoke out the no wake zone,cut off arms and legs, and bend props on launch ramps:D :D :D
All of the above, but no bent props.
And it's not like you jet boat boys don't cut off an arm and a legg just to fill those pigs up.:jawdrop: :jawdrop: :D :D
And the smoke is skeeter pelant:eek: :eek: