Prop choice challenge

[drivehard]

Here is my situation:

1995 Bayliner Capri 2050LS with a 1.62 Alpha I gen 2 I/O
Home built small block chevy 355 cu. in. with 4 bbl. marine Edelbrock carb and Edelbrock intake...est. about 275 hp.

I am currently running a 21 pitch Mercury Vengeance prop. I obviously have a great hole shot...but no top end. Right now I top out about 52 mph at just shy of 5000 rpm, but I am only at about 3/4 to 7/8 throttle. Obvioulsy I need to step up in pitch.

Previous engine was the stock 305 with 2 bbl. Mercarb with 190 hp. That engine would push this outdrive/prop combo to 4600 rpm at ~50 mph.

Do I go to a 23 pitch higher performance prop (thinking stilletto) or do I go to a 25 pitch Vengeance? Any other suggestions? I am looking for an overall performance package.

Thanks!

 

[Crownie2]

Re: Prop choice challenge

The Turbo I is a better performance prop. I used one with very good resultson my 20' Crownline...

I also am partial to the Merc Enertia.

Bob

 

[walleyehed]

Re: Prop choice challenge

The Turbo1 has a very high concentration of bow-lift compared to what you are running now.
The prop differences are very wide.....I would ask if top-end is "really" what you may be looking for and the only way to know what you can get out of that engine is run it to the stops with the prop you have now.
We run a 228 at 6000 for extended periods and have no problems...all we need from you is just a short time at WOT to determine where you actually are.
Does the boat require quite a bit of positive trim for the best ride/speed, or just a bit of positive trim?

 

[John_S]

Re: Prop choice challenge

With a '95 Merc, I suspect it is Thunderbolt V, which has a rev limiter near 5K rpms. Is there a way to defeat it to get max wot rpms? I haven't seen any way to defeat that, but it would be nice if there was.

 

[walleyehed]

Re: Prop choice challenge

Darn limiters are pieces of crap as far as I'm concerned...The next best choice is to obtain a loaner in good condition, in a 25 pitch and let's let'er roll and see what it'll do.....I "think" it will top out with a 23 in the Vengeance. Anyway, try a known 25 and we'll go from there.

 

[drivehard]

Re: Prop choice challenge

The Turbo1 has a very high concentration of bow-lift compared to what you are running now.
The prop differences are very wide.....I would ask if top-end is "really" what you may be looking for and the only way to know what you can get out of that engine is run it to the stops with the prop you have now.
We run a 228 at 6000 for extended periods and have no problems...all we need from you is just a short time at WOT to determine where you actually are.
Does the boat require quite a bit of positive trim for the best ride/speed, or just a bit of positive trim?

When I am at cruising speed, I can't put much trim at all, or it will porpoise pretty badly. I think I read somewhere that the vengeance prop may be a contributor to that. When I pick up the pace (over 4000 rpm), I can trim it out pretty far...not much change in ride quality, but it does get more efficient. I don't have to go too far though (no where near the top or anything).

This engine isn't going to do much over 5000 rpm no matter what prop I have on it. I'm runnning 305 heads, so flow is going to drop off pretty hard after 5000. I built it to run between 4400 and 4600 top speed...

What will the increased bow lift do for me? The Bayliner 2030 is a pretty light boat for its length, with a shallower hull design (from what little I know).

I would for sure like a lower engine cruising speed, and I know the higher pitch prop will do that for me. Thanks for the help guys...keep it coming.

 

[drivehard]

Re: Prop choice challenge

Just wondering if there is any more advice out there. Looking to buy my new prop this spring. Thanks!

 

[steelespike]

Re: Prop choice challenge

I would just add that the best cruising speed could be just on plane to 500 to 1500 higher.Have to experiment to get the best.

 

[wca_tim]

Re: Prop choice challenge

Go to the local shops that do a lot of business and borrow props... I wound up being able to try 8 or 9 late last summer when setting things up. I just paid for one, they let me take three or four at a time and then we settled up based on the one(s) I wanted to keep at the end. That was from one shop. The other just wanted my phone number and loaned me whatever I wanted to try from their used ones. I was surprised when they were both so helpful / friendly about it. Guess ya never know till ya ask...

 

[drivehard]

Re: Prop choice challenge

I'm in the middle of Iowa, and the local shops I have visited do not lend props.

I have heard a Turbo I in a given pitch will give a lower RPM than a competitor prop with the same pitch. Any truth to this? What is the hole shot like with Turbo props? I do like to ski.

 

[walleyehed]

Re: Prop choice challenge

The T1 is vented for better hole-shot and the drop in RPM is typical of the technology of this prop compared to others, but don't let that make you think it's slower...My 19P T1 runs the same RPM as a competitors 19P SS, yet the T1 is about 3mph faster, the midrange is much better and I don't notice but a very small difference in hole-shot...less than .5 secs.
I set up a buddy's Lund 1800 fisherman on which he had been running a 17P aluminum of about 3 different makes....to show him a point, I installed a T1 in a 15P.
Top speed was about 2mph faster, RPM actually slightly lower, hole-shot and mid-range sold the prop.

 

[LeftFeild]

Re: Prop choice challenge

Safe bet 23p Tempest Plus exteme 25p Tempest Plus,Total unknwon is your wot,it seems your grossly under pitched..

 

[walleyehed]

Re: Prop choice challenge

To me, a safe bet would be to get your hands on a Known good 23 or 25 alum., and we can go from there. I've got some pretty good cross-over data of actual runs if you can get a prop to try without spending 500 bucks, we can fine-tune for much less.