partlowr

Hey, I hope I don't get flamed too badly but you guys know your engine performance mods on this site so I thought I would give it a shot. The general recreational boating forum guys don't really have much knowledge when it comes to engine and performance topics. My boat is not technically an "off shore" boat, I own a Rinker 232 Captiva Cuddy. The boat has a carburated 5.7 on it. The motor has somewhat extensive modifications, Edelbrock intake manifold, Edelbrock valvetrain/heads, Edelbrock cams and carb. It's a fairly heavy boat 4200lbs but still scoots along at 58mph according to GPS, lol I know some of you guys boats can idle at that speed. The previous owner claimed it makes 380hp but had nothing to really back up that claim and the motor stock made only a claimed 250 by the manufacturer. I know a lot about car engines and making an additional 130hp with heads and cams and bolt-on's sounds like a stretch to me. My boat also has the Corsa through hull exhaust but from what I have read the Rinker through hull does not net as much gains as a traditional through hull because it exits out the sides rather than the transom.

..so on to my question. I am running a 17p stainless prop, as I stated I can pull 58mph on the gps and that is at 4900rpm. 4900rpm, from what I have read is the highest I want to rev this motor. The boat will actually rev much higher when I play around with trim and throttle, I have had it up to 5200rpm for a few seconds but since I didn't want to grenade my motor I shut it back down. When I had it up to 5200 it felt like it still wanted to keep pulling. Can I rev it higher safely? Would a different prop benefit me? Are there rev limiters available so I don't grenade the motor? Any advise would be appreciated.

partlowr

Also, I am not looking to make this boat a rocket, I know what I have is not a super high performance boat and not designed for huge speed. Some of these boats came stock with 454 mags so I know I have a little room to play with as to what my hull can handle. I bought this boat a year ago with a 1 year old daughter at home, when most guys have to sell their toys I convinced the wife to let me buy a toy lol. My goal is to get the wife and kid into the boating lifestyle and then move up to something bigger, sportier and faster in another year or so. Growing up my dad had a Donzi Z25 so I have had a taste of real performance.

Mr Maine

17pitch, 4900rpm, 1.47:1 outdrive, and 12% slip comes out to about 47mph. If you are truly running 58, something is off. Also, if your wide open speed is at 4900, how do you turn it to 5200?

Trash

This...

We need more data. Comp ratio, head runner size, cam size, valve size etc...

If the motor was EFI changing the rev limiter is relatively easy with the appropriate software.

SB

iTrader: (1)

http://www.boats.com/reviews/prime-choice/

Above link is a boat test in which the Rinker 232 Captiva Cabin ran 55.7 with 320hp 5.7...so I believe his speeds. OP's prop info makes no sense though..althouh I haven't run the math with a 1.36 gear outdrive.

To the op, a stock cheapo parts 260hp Mag shortblock will survive the 5200 WOT no problem. Cruise speeds are typically say 3800-4000 rpm anyway.

As stated Since none of know your engine build, we really can't answer any of your particulars. Find your prop manufacturer, model, pitch and diameter and get that 2" Pitch larger and see what happens. If your WOT is at an okay rpm, then no real need for a rev limiter. Edit in: If you are going by the sellers word on your current prop, the pitch, diam, and part# should be stamped on it.

BUP

iTrader: (9)

what ignition set up here ? And you have a built in rev limiter already ? or no ?

Merc T-bolt 4 oem stock ignition had no rev limiter

Mer T-bolt 5 carb apps depending has 4950 built in.

These were stock apps and carb apps

partlowr

Thanks for your reply. That is my very question/problem, it's not making sense to me either. The guy I bought the boat from told me not to rev past 4900/4950, various thing I have read on other sites say not to rev over 4900 but I have got it up over 5200. The 58 mph is gps confirmed and a couple of my buddies have boats much newer and nicer than mine and they were floored last summer when we were all out on Lake Michigan and I was keeping up with them. I would imagine if I kept it at 5200 it would exceed 58 mph but for fear of blowing it up I have never stayed in it. Should there be some sort of rev limiter on it like a Mallory ignition? The fact that I can rev it over 4900 is something possibly slipping? Am I leaving something on the table? Would a different pitch prop change what I am seeing.

partlowr

Unfortunately I don't think I have that info without opening up my motor. I can reach out to the guy I purchased the boat from last year to see if he has those details or the contact info for the shop that did the work. The seller told me the reason he had the motor "hopped up" was that the original motor had cold weather damage(not properly winterized) and he had to get a rebuilt so he added some performance parts rather than just going with OEM stuff for about the same price...makes sense I suppose.

Thanks again for everyone's insight, I appreciate it. I guess I was hoping there would be an "easy" answer, but that was just wishful thinking. One of my buddies just told me to experiment with different props but that sounds like an expensive experiment lol.

partlowr

Agreed, as I eluded to in my first post I did not put too much faith in what the seller told me, I questioned the 380hp figured, that sounded a bit optimistic to me. I know for sure the prop is a 17 because it is stamped or engraved right on the pro. The model is a stainless Mirage Plus which is also engraved on the body of the prop.

Mr Maine

The bottom end should take 5200 no problem. Would be nice to know where the engine makes max power, then prop for that.

What is the exact prop on it now? You need to spin a 17 close to 6k rpm to reach 57mph unless you have a 1.32 outdrive which would be unusual.