1985 CM23 update

[Chachie]

outdrive.jpg

download/file.php?mode=view&id=10320

prop clearance.jpg

It's a 5.7 . Prop says 15 x 17p on it I believe it is an aluminum. an you guys identify the out drive series also? 1985 mid engine

[cmattj]

Yes she rides beautiful. Could probably use a higher pitch prop though. I'm running a 17 pitch, would like to try out a 23 pitch.

Looks terrific!! I’m glad she’s stretching her legs.

That plastic bolt on tail is to push her over on plane quickly. Remove it and you’ll pick up some speed. ( but the nose will stay higher on take off with the drive tucked fully in)

And as the gang is telling you the Prop you have is good. You need to be touching 4200 ish to even consider going up. She actually is not freeing up now so don’t strain her.


A 19 may give you a better cruise speed but you’ll go backwards as soon as you Wide open as she can’t pull through it. And you’d loose mph and tire her out quickly lugging it.

[thunder550]

That looks like a Gen 1 Alpha drive. From what I'm reading, a 5.7 should be 4400-4800 RPM. The 17p prop seems ok from what I know, I'm wondering if there is something else preventing you from hitting higher RPM.

[Big Block Power]

Yea t555555000000 is correct. Alpha drive. On the port side of the drive it may say on the sticker what gear ratio it is. But it may be gone also. That is a aluminum prop. You will gain hole shot and every other performance opportunity switching to a stainless steel prop. The whaletail that's on there says it has a issue getting on plane properly. With the correct prop you can get away without using that. You may want to try some 4 or 5 blade props. But finding the correct one will take some work. A 17 x 15 is to large of a diameter in my opinion. Find a 17 or a 19 energia prop maybe. It's a great 3 blade prop. Or a 19 high five prop or a 17 or 19 vensura/offshore prop 4 blade.
You may have to buy and sell a few too.lol you find the correct set up. But you really need more rpm at Wot. Don't worry what your buddy is cruising at. He prob has a diff engine, drive ratio and prop.

[thunder550]

Yes to everything BBP said ^^

Places like www.bblades.com and www.propgods.com will help you select a prop and will let you demo props for a fee.

[nolaboater99]

Ok....hold on everybody. I just got back from a week's vacation and need to chime in. I have had this same model for 14 years....sorta.

Jason, your boat has an Alpha 1 Gen 1 drive with a 1.50:1 gear ratio. Your motor should be turning 4200-4600 RPMs at wide open throttle (WOT). First, take that damn fin off the outdrive. The CM23s never needed it to get on plane nor will the boat ever porpoise. Remove it and throw it in the trash. Now, without that drag, run the boat again at WOT and see what RPMs you get. With a clean bottom (the boat, not yours), a well-tuned motor and a medium load you're looking for 4200-4600 RPMs.

You have a 15" x 17" aluminum prop; this is the right diameter prop for our boats. Every 2" change in pitch will change the WOT RPMs by about 200. Lets assume you remove that plastic piece of shit from the drive and you hit 4200 RPMs. If you want the RPMs higher you will want to go DOWN in pitch to a 15" x 15" and that would bring RPMs to about 4400. If you went to 19" pitch you would bring the RPMs down to 4000 which would be lugging your engine. You don't want to do that.

If you do change props you should go to a stainless one. The blades on an aluminum prop will flex at speed causing a loss of "bite". The SST props have a much sturdier blade and hub, with little to no flex, and will give you more consistent performance. A 4-blade prop will give you a better hole-shot but the additional blade surface area will create additional drag and lower your top speed.

How do I know all of this? Because I went through it all years ago with this same model boat. I am trying out a new prop right now on my boat. It is a SOLAS 14 3/4" x 17" SST but remember, my motor has about 100 horses more than yours and I want to turn close to 5000 RPMs. The guys who are currently working on my engine recommended this prop and the initial test, before the motor stuck a valve and bent a pushrod, are very favorable. These guys are hydroplane and performance boat experts. Let me ask them Monday or Tuesday what they recommend for your boat.

Try it this weekend without the fin and let me know what you find out.
Shawn