2005 Chaparral Signature 290 - Repowered

[csa1130]

Hello All,

New to the forum here. I just repowered a 2005 Chaparral Signature 290 with brand new drop in 350 MPI's. The old engines were 5.0 MPI's. The drives are Alpha One Gen II drives. Just curious about propping the new engines. I'm just about to the 10 hour mark on breaking in the engines and curious about propping them. Been out a few times been varying RPM and have not been past 3/4 of WOT, about 3800 RPM at most. Speed as per GPS at 3/4 throttle has been about 27 MPH and around 21-22 MPH around 3100 RPM. Previously with the old engines I recall being around 26-28 MPH at around 3300-3400 RPM and probably closer to 33-34 MPH around 4000 RPM. Start to fall off plane around 3000 RPM and in the past could stay on plane around 3000 RPM. Currently have 4 blade props not sure of the size or pitch. Just curious what a starting point would be with the new engines. I know the torque and HP are greater on the new engines. About 80 HP more combined on the 2 new engines. Any help would be appreciated.

Also, It's a cruiser not looking to break any speed records...LOL. Just looking for a nice combination of cruising speed and getting up on plane and staying on plane.

 

[alldodge]

Things don't add up
Your using the prop but getting less MPH at same RPM, maybe your not remembering correctly?

 

[Pmt133]

We either need to know drive ratio and prop pitch or you need to verify your tach. I agree somwthing either isn't adding up or you are remembering incorrectly.

With no other changes other than increased power, rpm for rpm the 350 and the 305 should be identical.

 

[csa1130]

Okay, appreciate the feed back. It is definitely possible I am mis-remembering my RPM and speed from last season. Next time I get out I will double check where I am at again RPM and Speed wise. The drives are the original drives that came with the boat. Alpha one Gen 2 drives. I believe they are 1.62:1 ratio. I believe the new full package 350 MPIs with new drives and all are 1.47:1 ratio. At least from what I see online. I only did new engines not drives.

 

[alldodge]

I believe they are 1.62:1 ratio. I believe the new full package 350 MPIs with new drives and all are 1.47:1 ratio

This will change things, going to higher gear ratio you should be going faster with same prop at same RPM