20' chaparral 5.8 40mph@3500 ?

[a70eliminator]

Hi I'm new to this forum and this is my first post so be easy on me.
I'm the new owner of a 1990 chaparral with the Ford 5.8
First time out the other day and WOT was only 3500 RPM although my speedo was reading 41MPH which felt about right, do you think my tach is off? I hooked up a known good tach at home on the muffs and it seemed to match RPM's but that was only up to 1500 or so I didn't want to rev up any more on the muffs. Any how it seemed pretty close, I guess what I'm wondering is if my in-dash tach is correct and I tune the engine and get the 4400 WOT spec then it seems like this boat would do 50MPH easy if it does 40 at 3500, does this all sound about right for a 20' chaparral sport cruiser whatever? thanks.
Oh. by the way prop is a 14-1/4x19.

 

[Haut Medoc]

Re: 20' chaparral 5.8 40mph@3500 ?

Welcome to iboats.....
Verify your tach.....
You might be able to get close to 50, but something is up if you only get 3500 with that prop, time for some diagnosin'......
I'd trust a GPS before I would trust a speedo.....​

 

[Don S]

Re: 20' chaparral 5.8 40mph@3500 ?

Did you try adjusting the trim on the drive?
I assume your boat is OMC powered?

 

[a70eliminator]

Re: 20' chaparral 5.8 40mph@3500 ?

Adjust the trim? why no sir, I just put it all the way down and left it at that. Please rehurse me on the teqnique of trimming, I have 0 experience on trim, I wasn't sure if operating while underway was the right thing to do, What if I pulled it up too far would it burn up the impeller?

 

[Don S]

Re: 20' chaparral 5.8 40mph@3500 ?

Go for a ride and play with it.
Once on plane, trim it up to max speed and rpm. When the speed starts dropping and the rpm starts going up, you are trimmed up TOO much, trim it back down.
If the bow starts bouncing up and down on smooth water, that is called porposing (sp), again, just trim it down.

Just play with it at different speeds and times, you will figure it out how it works best for your boat.