Prop Selection Help - 454 in 21' Baja

[tcgravy]

Hello All -

Need some prop advice. Finished rebuilding a 454 in a 21' Baja Sunsport (shallow vee, open bow, late 80s design). Engine makes about 430hp compared to the original 365hp from a 454 mag. So here's the prop info:

Always had a 25p Turbo prop on it, 14.5" diameter, would run a solid 4800 rpms, good bow lift, no chine walk.
With 25p Turbo on new motor it will rev well over 5000 rpms, and for reliability purposes I would like to keep revs down (dyno also shows peak HP right at 4900 rpms). I would love to top out around 4800-4900.

Would like to go up to at least a 27p. Limited options up to 27 pitch, seems like mirage and turbo are standards, but not sure what else is out there? I also wouldn't mind trying a 4-blade if anyone has a recommendation. I am OK w/ losing 1-2 mph on top end for good holeshot, mid range, and low prop slip.

Please let me know. Thanks.

Tony

 

[Sea Rider]

What's the max wot rpm range for that engine ? Sometimes it's better to slight over rev, could throttle bit less watching tach or add extra weigth to compensate if like running full hammer down. Hole shot will be spot on, good performance through the entite throttle range with slight top end speed decrease.

Happy Boating

 

[tcgravy]

What's the max wot rpm range for that engine ?

The engine makes peak power at 4900 rpms with a nice flat power curve between 4400-5000 rpms. In this rpm range its all between 415-430hp. It was designed this way intentionally because it has cast internals with a 2 bolt block (neither of which like a lot of rpms). Thus I am afraid of over-revving...it seems like I am gonna get excited with that go fast stick sooner or later...

 

[Sea Rider]

Most engines makes peak power around middle to max wot rpm range, is 5000 rpm the most rpm that engine will achieve. Was combo lightly, medium or heavily loaded while running at 4900-5000 rpm ?



Happy Boating

 

[tcgravy]

Most engines makes peak power around middle to max wot rpm range, is 5000 rpm the most rpm that engine will achieve. Was combo lightly, medium or heavily loaded while running at 4900-5000 rpm ?



Happy Boating

It was lightly loaded but I was reaching & exceeding 5000 rpms without even being at WOT.

 

[Sea Rider]

Load affects rpm, less weight more rpm, the opposite if more weight. Need to go for a wot run lightly loaded and check max wot revs to know max wot rpm achieved. If like boating lightly loaded most times can go for a + prop pitch to lower max rpm to factory parameters which isn't known so far.

5 K rpm is the peak power, but for sure not the max wot rpm which is ? Don't worry, won't blow the engine during that wot test.

Happy Boating

 

[tcgravy]

Need to go for a wot run lightly loaded and check max wot revs to know max wot rpm achieved.

5 K rpm is the peak power, but for sure not the max wot rpm which is ?

Did not keep the throttle down long enough on WOT runs to determine what max rpms was. Reason was fear of blowing the engine. When it gets a little warmer here in MI I will give it a full WOT run and report back. Thanks for the help so far.