Mercruiser 5.0 Performance Boost

[DMaxum]

Hey All,

Im new to the forum and am looking for some sound advise. I have a 92 Maxum 19' ski boat with Merc 5.0 (305) 220 H.P. Alpha 1. Im looking to get a little more performance from the boat out of the hole and through the existing RPM. range. Does anyone have a good suggestion. I have been throwing around the idea of adding a cam and possibly heads with an intake. I have already upgraded the carb to a Holley. Does anyone know of a good combo with Cam etc... that they have actually proven out. Please no speculation. Also, the prop is stock and i am looking to upgrade that at the same time. Any experiences with the HighFive prop or something comparable?

Thanks!

 

[Thad]

Re: Mercruiser 5.0 Performance Boost

Do a search of the site and you'll a lot of threads that will show you that there is little you can do to get big noticable performance with that motor.
Most will tell you to pull the engine and drop a 5.7 in.

The best way to get performance is with props. I have several for my boat and each one hass a specific performance that it gives to the boat.
For instance, one is for pulling skiers and big tubes, one for cruiseng, one for when I want to be a kid again and go fast, etc.
If you post in the props section and ask, there are people that have all the formulas to figure out what prop you need to do what you want.

 

[Philster]

Re: Mercruiser 5.0 Performance Boost

You start playing with cams are you are pretty much committed to addressing any and all exhaust system design issues. High Performance cams require an exhaust that is set up properly to prevent water reversion (the engine sucking water via the exhaust due to valve overlap.)

I'd think about the prop and nothing more. Takes gobs and gobs of horsepower to make a difference you can notice, and you introduce a heap load of drive-ability issues. You can always make more power, but to have it show up as friendly, usable power ain't that easy. Sounds like that is your goal.

Think prop and think "keep this baby tuned perfectly".

 

[Bondo]

Re: Mercruiser 5.0 Performance Boost

Also, the prop is stock and i am looking to upgrade that at the same time.

Ayuh,... Drop in a 350,+ Then, after the power boost, figure how much more Prop it'll take...

 

[PitchFork]

Re: Mercruiser 5.0 Performance Boost

I would make sure the timing is right and that the engine is running in top shape first. I bought my boat 3 years ago and had it was slow getting to plane. I helped it out with a hydrofoil the first season. The second season my neighbor gave me a SS prop which I already had but it was a 15 1/4" x 17". Before I beat up 14" x 19" SS and that improved my hole shot. But the biggest increase out of the hole was getting the timing dead on 8? BTDC, installing the correct plugs, and trimming the drive up after takeoff.

I have about the same boat as you do a 19' Chaparral Bowrider and it now screams right out of the hole with no problems. Tops out at 49MPH at 4600RPMs.

Welcome to the forums they are great I find myself reading them for the fun of it as well as the knowledge.

 

[HT32BSX115]

Re: Mercruiser 5.0 Performance Boost

you'll a lot of threads that will show you that there is little you can do to get big noticable performance with that motor.
Most will tell you to pull the engine and drop a 5.7 in.

Yup. If you want a REAL performance boost, get a 383 cu-in "stroker"!


The below is from US Engines in Kent, Wa.
http://usengine.us/mercruiser.html

[FONT=Arial, Helvetica, sans-serif]

Yes You Can Replace Your Mercruiser 5.7 Marine Engine with A 383 Stroker Marine Engine Just Call US ENGINE and We Will Tell You How

[/FONT][FONT=Arial, Helvetica, sans-serif]383 Stroker 350 h.p 1985 - 1995 12 Bolt Intake Manifold [/FONT] [FONT=Arial, Helvetica, sans-serif]$2,495[/FONT]
[FONT=Arial, Helvetica, sans-serif]383 Stroker 400 h.p 1985 - 1995 12 Bolt Intake Manifold [/FONT] [FONT=Arial, Helvetica, sans-serif]$2,695[/FONT]
[FONT=Arial, Helvetica, sans-serif]383 Stroker 360 h.p 1996 - 2006 8 Bolt Intake Manifold [/FONT] [FONT=Arial, Helvetica, sans-serif]$2,895[/FONT] [FONT=Arial, Helvetica, sans-serif]
383 Stroker 410 h.p 1996 - 2006 8 Bolt Intake Manifold$2995[/FONT]

I am thinking about using them for my 454 "rebuild"

That's what I would do! There's probably a engine rebuild company near you that can do the same thing......


Cheers,


Rick

 

[mkast]

Re: Mercruiser 5.0 Performance Boost

You might be better off trading the boat in on a different boat.
After the dust settles (read "Your wallet is closed") the amount of money and time you will spend will be more than you think. You won't get that money back when you sell the boat.

 

[HT32BSX115]

Re: Mercruiser 5.0 Performance Boost

You won't get that money back when you sell the boat.

You mean a boat is NOT an investment?

Cheers,


Rick

 

[DMaxum]

Re: Mercruiser 5.0 Performance Boost

Thanks for the responses so far. I just want to clarify a little further. I am in no way unhappy with the current performance. The engine is running good. Pushes the boat to 52-54 mph depending on water conditions. Im just looking to "crisp" it up a little out of the hole. Being such a heavy boat it struggles just a little at times to pop out of the water. My thoughts on the engine mods were a cam is about $130 plus gaskets which is fairly cheap for the gains it will produce. Comp Cams makes some good marine specific grinds for stock application. I would only do heads if there were another "stock" G.M. head that was fairly inexpensive to pick up and do a re-bulid on that works better. Im thinking that I will do the prop for sure based on the feedback recieved, just need to do more research for what I need. I would love to drop a different engine in, but don't want to go that expensive or extreme at this time.

 

[SeanMcl]

Re: Mercruiser 5.0 Performance Boost

I would make sure the timing is right and that the engine is running in top shape first.

I'd do this too. It's not a sexy as new heads and a cam, but remember you don't exactly have a low restriction exhaust system.

If you already know you are getting all you can out of the current package, then find out if the high flow heads are going to matter when bolted to that exhaust manifold and flowing through the outdrive, and propped to keep your WOT RPM correct.

 

[PitchFork]

Re: Mercruiser 5.0 Performance Boost

I would guess since he is running 52-54 MPH that his engine is running great just needs to drop down a prop size or two. My local boat store offered to me a try out a prop but I already have a neighbor that has many for me to choose from. Maybe your local boat shop will let you try a prop out?

What prop are you running now? My 15 1/4" x 17" SS performs well and is within the RPM range spec'd for my engine.

 

[HT32BSX115]

Re: Mercruiser 5.0 Performance Boost

Well,

After you determine that your engine is running correctly and before you go swapping props around, You need to get some accurate numbers FIRST.

You need GPS measured top speed......Do not rely on your pitot speedo. They are notoriously in-accurate.

Next, you need the WOT RPM. That also needs to be accurate.....A tach can be upwards of 300-500 RPM OFF at the upper end of the range...

Do this at the load (fuel, number of people, gear, etc) you would run the boat on a regular basis.

The engine should be turning (RPM) at the top of the range for recommended for your engine. (probably up around 5000 rpm)


If your engine is NOT turning up near the max at WOT you need to "prop down" to a lower pitch.

You can use a prop-slip calculator to get in the ball-park.

There's a lot of info there on propeller selection etc....


Cheers,


Rick

 

[Bondo]

Re: Mercruiser 5.0 Performance Boost

Im just looking to "crisp" it up a little out of the hole. Being such a heavy boat it struggles just a little at times to pop out of the water. My thoughts on the engine mods were a cam is about $130 plus gaskets which is fairly cheap for the gains it will produce.

Ayuh,... I'd leave the Cam alone,... No real gains to be had there....

Finding a set of Vortec heads is pretty much the Only Hop-up that'll be at all Noticeable, if it is...
Just don't get the bright idea of having Big valves installed in them,...
The Big valves won't clear the cylinder walls...

 

[achris]

Re: Mercruiser 5.0 Performance Boost

..... Im just looking to "crisp" it up a little out of the hole. ....

Camming it for more power you will LOSE hole-shot. I'd throw the Holley in the bin. Hateful carbs, NOT for boats! Merc stopped using them a LONG time ago, and for good reason! Go back to the Quadra-junk....

For hole-shot pulling tubes and skiers, get a High 5 or a Laser II and pull the vent plugs out. These props will pull your arms off! They are designed specifically for what you want.

Chris........

 

[180shabah]

Re: Mercruiser 5.0 Performance Boost

Unless we are talking about BIG power gains, the effect on hole shot will be minimal, if any.

Props can make a HUGE difference though, more blades and or venting as mentioned above.

 

[mkast]

Re: Mercruiser 5.0 Performance Boost

Im just looking to "crisp" it up a little out of the hole.

Two speed or shifting propeller.
A lot cheaper than engine work, no maintenance.

 

[ENSIGN]

Re: Mercruiser 5.0 Performance Boost

Put a 5.7 in it.

 

[Bondo]

Re: Mercruiser 5.0 Performance Boost

I'd throw the Holley in the bin. Hateful carbs, NOT for boats! Merc stopped using them a LONG time ago, and for good reason! Go back to the Quadra-junk....

Ayuh,... Which is Why I like the Carter AFBs,...
Just the fact that Holley uses fore,& aft fuel bowls,...
Hammer the throttle,+ the fore jets go dry,+ the aft jets flood...

Atleast the Rottenchesters,+ AFBs with the side bowls are more tolerant to the angles of the hull at various throttle settings...

 

[mkast]

Re: Mercruiser 5.0 Performance Boost

Hammer the throttle,+ the fore jets go dry,+ the aft jets flood...

You have that backwards.
The front bowl jets can't flood, only fuel under ambient pressure can move through the jets.
The rear bowl, if the hull is moving that fast out of the hole, slosh tubes will prevent that from happening.
I notice Nascar has been using Holleys, and these cars come out of the hole a little faster than the original poster's boat.
http://sports.espn.go.com/rpm/nascar/icons/news/story?id=3473499

 

[DMaxum]

Re: Mercruiser 5.0 Performance Boost

Thanks everyone for the feedback. Right now I think im going to just upgrade the stock prop after reading alot of posts on the prop boards. Currently running a 21 pitch 3 blade aluminum so there should be ample room for improvement. Now the next question is do I drop to a 19 high five to preserve my RPM? Or should I get a shifting prop?