Faster

[Fieldsken1]

87 Malibu with a 175v6. WOT is 41mph @ 4900 rpm prop is a 14.8x17
Question I want to go faster Can I go faster?? What prop can I use.?? Should I just leave alone???

 

[jimmbo]

What is the Full Throttle RPM range for you engine? 4000 - 4400? 4200 - 4600? 4400- 4800? You say 4900 is what you are currently getting. So based on that, you may be over revving 100 rpms or more. A prop in the same lineage with more pitch will lower rpms, whether or not you gain any speed is maybe yes, maybe no. Drop rpms too much and you can end up going slower even with more pitch. Rule of thumb, One inch change in pitch generally results in a change of 200 rpm To add to the confusion/excitement are higher performance prop lines. These when properly matched may yield better top speed, again what works on one boat might not on another. Stainless props can be found as Heavy Duty props or very high performance props. Usually most SS are a compromise of more a bit more performance and a bit more strength.
What is your current prop, material, manufacturer and model? When I mean model, I'm not asking dia. and pitch. Black max, Vengence, Raker, Viper, Ballistic, Hustler, are models. Mercury, Qiuicksilver, Michigan, OMC/BRP. Solas, Turning point, are some manufacturers/brands.

 

[Scott Danforth]

assuming your tack is correct (verified against a shop tach) and your speed is correct (verified with GPS) you are getting 16% prop slip. slightly high, however still in the normal range

a prop change may get you 1-2mph.

you may need to add more motor along with a prop change. the motor you have would respond favorably with a head and intake change

 

[ahicks]

Is this an I/O, an inboard, or an outboard? Are you looking for just a couple mph to out run a buddy? Anything more dramatic may not be realistic.

17" pitch 3 bladed props are generally a pretty good compromise prop with a nice split between pulling power and speed (top end). They are a compromise though. If you want more pulling power, it will likely cost you some top end. Or, more speed will cost you some pulling power.

 

[Texasmark]

If a Mercury outboard, I have a 1997 Mercury sales brochure that says the 175 EFI V6 (only 175 for that year) is 5000-5600. Considering that most 2 strokes are 1 cu in per hp, they need their rpms to get the hp so they like to run at the top of the recommended range.....or so (mine anyway). With that said, you have something dreadfully wrong at 4900 WOT. If an I/O would guess you are in pretty good shape and I'll bow out of the responses.

 

[jimmbo]

Good Catch Tex. I assumed an I/O

If it is running 4900, that is below the RPM range, and a lower pitch prop would gain rpm and might raise the mph to boot

 

[Fieldsken1]

It's an I/o v6 2 barrel carb. I was told if I change heads and manifold and carb I would only get about 40 or so more HP. That would not be worth it.
The prop is alumium and a SOLAS. AND MAX RPM is 4600/4800 for this motor.

 

[Scott Danforth]

40hp for about $500 and a weekend is cheap hp

Its also a 23% increase in power

 

[ahicks]

OP, I think you're pretty much all the way home. A good prop guy may be able to find another couple miles per hour with some prop tricks (like cupping, smaller diameter and a hair more pitch, trick props, etc,). Depending on how you have it loaded, removing anything from the boat that's not necessary may be a help as well. Goes without saying a clean hull would be at the very top of the list.

IMHO, the mods, if not matched perfectly, and used with a properly calibrated carb, could easily cost performance. I'd leave that kind of stuff to pretty dedicated engine guys willing to spend the time necessary getting a package like that all dialed in.

 

[jimmbo]

Your not going to get that much of an increase, unless the 2bbl is very small. Even at 5000 rpm a 4.3 liter isn't going to flow more than 310 cfm, so a very small 4 bbl, like Holleys 390 cfm would be more than enough

 

[Fieldsken1]

40hp for about $500 and a weekend is cheap hp



Its also a 23% increase in power

Not to agrue but 500 for heads,manifold and carb?? From where??

 

[Scott Danforth]

Used heads, $50 from a pull-a-part yard, $150 to clean them up. Intake and carb from ebay for $200. Gaskets and carb kit for $100

If you did new, heads are $450 a pair. Intake is about $250, carb is $450, gaskets about $50