my 5.7 seems too slow....

[ratking20]

recently repowered my searay 220 br. went from a 350 5.7 carb to an efi(gear ratio 1.5)
i had a pretty bad prop(14x19 alum...i think) doing 26mph at wot at 4000rpms
i changed the prop to a stainless 13.88 x 23p and was doing 27mph at wot at 3400rpms

bottom line is i know i should be faster. last year with a tired engine i was in the mid 30's and thought even that was slow. i dont believe a prop is going to get me where i should be although im working on finding the right prop

what else should i consider. i could use bottom paint but there wasnt any growth on the boat when i launched a week ago.
how can i check if all the cylinders are firing? i guess i can start by replacing all the plugs but i thought they were all new. i have all new injectors, manifolds, risers, starter, alternator. compression was good? what else can i do?

 

[achris]

Re: my 5.7 seems too slow....

I would suggest you need a MUCH smaller prop, something around 17" or 19" pitch.... You need to get those revs up in the range 4400-4800...

At 3400 rpm you're probably only making 150-180hp... Hence the low speed.

Couple of things you do need to check.
1. Speed is by GPS.
2. Tacho is NOT the dash tacho (not anywhere near accurate enough).. Use a proper shop/calibrated tacho.

Chris....

 

[ratking20]

Re: my 5.7 seems too slow....

speed is by gps( app on my phone) i used 2 different ones to make sure
tachometer could be off, im not sure how to check

i know the prop needs to be changed, i only used that one as a baseline because my current prop is damaged and i cant tell what size it is. but am i wrong to say that 27 mph is way too slow for my 22 foot bowrider??????

 

[Bt Doctur]

Re: my 5.7 seems too slow....

260 hp in a 25 footer does that ,you should be hitting the 40`s in a 22 footer.

 

[Scott Danforth]

Re: my 5.7 seems too slow....

My searay 190 with a 5.0 was hitting 50mph with a 1.62:1 drive and 15 x 19 stainless Solas prop. My current boat is 26' overall with a 5.7 liter and is just shy of 50. you should be in the 40's without much trouble.

I think you have 2 things wrong. first, the 23 pitch is too much. secondly, are you actually getting full throttle?