Ever put your finger over the end of a garden hose to make it spray harder?

The nozzle inserts do the same thing, sort of. Typically a jet boats top speed is determined by the speed or velocity the water jet leaves the rear of the boat providing the forward thrust.

If memory serves a 100MPH boat has to have the water leave the nozzle at nearly 170MPH!

Lets say the water leaving the rear nozzle was coming out at 60MPH, the boat would probably go about 30MPH (very light boat) now lets say the same boat with a nozzle inset 20% smaller has a nozzle velocity of 72MPH the boat could potentially pick up 2-3 MPH (these are bogus numbers but you get the idea), the limiting factors are; boat size/weight, thrust angle, pump pressure and available HP, one thing to keep in mind also, the smaller the nozzle, the less surface area is available for forward thrust, so kind of a compromise.

Hope this helps

I guess you would need to define "normal", as soon as you add power, Place Diverters, Droops, loader grates and so on I guess its not really normal any more, if the boat is light enough and set up right, it will make a difference, Had one in a daycruiser and it did pick up a little top end (3-4mph) but was a Pig out of the hole, same nozzle in the small block (355) Southwind 19' with a snoot, ride plate, shoe, loader and so on was worth closer to 5MPH and actually came out of the hole a little better.

I guess it would depend on;

1. what the boat is used for.
2. how heavy the boat is.
3. what kind of power is available (you have to be able to gain pump pressure)
4. if you have the money to spend, even if it does not work.

Maybe try borrowing one for a weekend to see if it makes a difference? When we were racing we borrowed everything.

Thanks for the info.  I guess I'll just leave well enough alone and see what I have.  Got a GPS now so I'll have to check the next time out.

Im curiouse now, i have a 3 3/16 in mine. Can't wait to try it out

2sav

im interested too...cant seem to get my pig of a boat over 40, maybe a loose jet too, any info please.

Too much rum on board

2sav

hey greg=i have a set of these =if you want to try them you are welcome too =doug