1970 Penn yan

[FishingNYS]

Trying to figure out what my top speed for a 23' avenger with a 165 in should be. It won't go over 12 mph. Motors not struggling. Carb has  been cleaned and rebuilt. 

 

The original out drive went bad.  Old case got swapped out for a 3.7litre out drive, which is a 1.84 gear ratio and the 165 is also 1.84. 

 

Brand new prop on it so I assumed the hub wasn't spun out of it.

 

I can do a compression test but I really don't think that's the issue. Maybe she's just slow? But shouldn't I be getting between 25 and 30 mph on a flat day wot? I know she's old but it's been a great boat together out of the sun and troll with

 

I guess I should also mention it is a inline 6

Edited May 8 by FishingNYS

[lost a lure]

What was the speed before you changed the drive?

 

[FishingNYS]

Honestly, I was doing other things whenmy fishing partner at the time tested it out after we stuck bellows in, changed water pump. Problem was he didn't check the out drive oil or something and top end went. I just called the guy who was in the boat when it blew and he said 20 to 25.  If I could get 20 to 25 mph I would be happy.  Might of been a prop seals that went bad. I can't remember exactly why it went. 

Edited May 8 by FishingNYS

[Bozeman Bob]

What size is the new prop vs the old one ? How many RPMs are you getting at WOT ? Are you 100% sure the outdrives are the same ratio ? As in you've spun the prop / prop drive shaft  and counted the rotations to at least get a idea that they are the same ratio ? 

[FishingNYS]

I haven't put it over 3200 rpms. Was told not to run it over that but then I looked in the original owners manual and believe it says 3900- 4300 I believe. I'll measure the prop when I get home.  Going to go out later and see how it operates at the higher rpms.  I can't remember if the original outdrive had cavitation fins or not. The new outdrive has holes drilled for them. I can take the outdrive off and spin the prop or pop the top off and count teeth. I'm going by the sticker on the outside and specs based on mercruiser chart

[Bozeman Bob]

Well , you never opened it up and wonder why you're only getting 12 mph ? Seriously ? You could be right below the speed where the boat gets up on a plane and all you're doing is pushing water . Your tach , should be 1 - 200 RPMs ( with your normal load and gas level ) under the Mfg rated ones , which is usually marked on the valve cover , if you're propped correctly. No , pulling the prop is not going to allow you to count gear teeth.  You have to pull the outdrive , mark both the drive shaft and prop shaft , spin the drive shaft 365 and note how many times the prop shaft turns with one turn of the drive shaft . Doesn't have to be precise , but should give you a ballpark figure of the gear ratio. Report back after you take it out , run it at WOT and trim the outdrive up to just below where it starts to cavitate . You'll feel or hear the RPMs going up at that point . Going to need the RPM numbers from that test ride . 

Yes ,3900 - 4300 rpms is the rating , 4100 + would be the sweet spot , below 3900 means you are lugging the engine , working it to death . Generally they try to have you running a 17 -19 pitch prop , so the drives are all geared for that .

Edited May 9 by Bozeman Bob

[FishingNYS]

We got it up to 24mph sog @3900 rpms. Seemed to run good at 4100. I didn't push it much harder because my kicker motor pull cord broke and didn't wanna be out there with no back up or tools to get the pull start off. We probably never got it fully on plane because my fishing partner told us not to go over 3200...  He probably read the manual and it says first 10 hrs of break in don't go over 3200 but the boat is well over its 10 hr breaking period lol

[Bozeman Bob]

Those in-line 6s are bulletproof.  Hammer it down ,trim it out and take note of the RPMs . That's the only way to know if you're propped correctly. The only thing I would do is swap it out to a electronic ignition , as in no points ,if it hasn't already been done . 

[FishingNYS]

Thanks for the info. If I can figure out how to upload a video of it running I'll post it. It's a good classic. Someone had it inspected in 2017. A little work and she'll clean up nice