Tune-Up for performance

[WanabeBoater]

Is there a way to tune a boat motor for maximum performance the same way you can tune a car? I'm not talking a typical tune-up, but more on the end of maximizing the carb, maybe switching out from a two barrell to a four barrell or just tuning the two barrell. I know in a car the electonics are tuned for performance, but since my boat doesnt have this I was wondering what more I could do if anything. I have a 1994 Starcraft 2010ss with a 5.7L Alpha 1. The WOT is 4400 to 4600. Just looking for information so I appear to be ignorant while speaking to a mech. thanks

 

[Haut Medoc]

Re: Tune-Up for performance

You are in the ballpark with your WOT......
What kind of top end speed are ya getting?......​

 

[WanabeBoater]

Re: Tune-Up for performance

I am at the top of my WOT at 4600 (maybe a little over) reading from Speedo not GPS around 55mph with normal load. I have to check into getting a GPS for next year.

 

[John_S]

Re: Tune-Up for performance

Assuming you have a 2brl 5.7L, you have two "reasonable" choices. Get a 4brl manifold and carb and get to about 250HP, or add vortec heads to the mix for about 280HP. If your bottom end is tired, just wait and do it with the engine replacement/rebuild.

 

[Gary H NC]

Re: Tune-Up for performance

At 55 mph i would be happy! If it runs good don't mess with it.There is always those small things that cause problems when you start changing out parts.

 

[ron7000]

Re: Tune-Up for performance

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[Maclin]

Re: Tune-Up for performance

55mph at 4600 rpm sounds about perfect for a 20 footer like that with normal load. I would leave it alone! Some would spend money to get up to what you already are seeing.

 

[WanabeBoater]

Re: Tune-Up for performance

Hey guys,,,I truly appreciate the help...I'm just looking for better response when I hit the throttle. Top end is great...but my accleration is sluggish. I wonder if my cable adjustment could be the culprit? I do have a 2inch play before engagement.

 

[Manipulator]

Re: Tune-Up for performance

I would be more than happy with those numbers! My 22.5 with a 5.7L and the 4BBL is lucky to hit 35-40MPH with no added weight. It runs great, I keep telling myself my speedo has to be wrong but deep down I know its probably right. As long as it continues to give me lots of fun with no breakdowns I'm happy.

 

[Maclin]

Re: Tune-Up for performance

By play, if you mean the lever travels that far after going into forward and before the engine throttle starts to open, then that sounds about right.

What you may be experiencing is over-propping, where the prop pitch is a bit too high for good holeshot. If over-propped you will get a great top speed at the expense of a not-as-peppy holeshot.

What pitch prop do you have now?

Also, are your top speed and tach rpm readings accurate. That will help determine if a lower pitch prop will get the balanced performance you are seeking.

 

[Maclin]

Re: Tune-Up for performance

Propping is almost always a compromise between good acceleration from a dead stop and the top speed available. I think my perf numbers are relevant to the issue. My boat is a 22 foot Cuddy Cabin with a 270HP 5.7 4bbl Volvo and 290DP DuoProp drive.

I run a B5 set of props now, this is in the higher end of the pitch range available for my drive (B1-B7), I am sorry that I cannot provide a comparable pitch number like non-DuoProps have. The boat will hit 47+ mph at 4600 rpm. It has a great holeshot, and can hit the top speed in 7 or 8 seconds. Cruising speed is a very comfortable 35 mph at 3500 rpm.

There are two pitches higher than the ones I have, a B6 and a B7. By the Volvo prop chart the B7 set will go 53mph an 4600 rpm. By comparison on the same chart the B5 set shows 46mph at 4600 rpm. The B6 set shows 49mph at 4600 rpm. Very subtle changes between them, but much different feel from a dead stop.

I changed from a B7 to the B5 set because we are usually loaded and doing water sports. Also the lakes I go on are small and do not allow for a long range cruise, and 50+ mph speeds are not my thing in a boat anymore. As you can tell from my numbers my current prop set is right on the money as far as speed and rpm, and I can tell you the thing pulls like crazy from a dead stop. If I did put a B7 set back on it could probably break 50 at the expense of good acceleration from a dead stop. As in most things in life you usually have to compromise.

 

[John_S]

Re: Tune-Up for performance

"I'm just looking for better response when I hit the throttle. Top end is great...but my accleration is sluggish."

With that clarification, I think you would be on the right track to try a prop with slightly less pitch. Another thing to consider, would be smart tabs. Lots of testimonials for you to read on this site. They will help your on plane time, lower the bow rise, and maybe get 1-2 mph increase at wot.

As far as a performance tuning, I would then stick to doing normal yearly maintenance. Do not try to rejet carb, or change ignition timing from stock. If you haven't done a good tune-up in a while, do that, and re-baseline your wot performance.

 

[WanabeBoater]

Re: Tune-Up for performance

The props i'm running are a SS Turbo 1 14.5x17 Three blade and for watersports a Alum Michigan Wheel 14.25 x 18 Four blade. I have given my boat regular maint and complete tune-up each year. Complete oil and lube change each year. But I have never touched the carburator since I have owned the boat. I thought maybe I have neglected a very important part of the system and you say about two inches of play in the throttle (yes, going forward before engagement) is normal?

 

[f_inscreenname]

Re: Tune-Up for performance

Boats are not sports cars. They are like trains and need some room to get up to speed. Also making a boat jump out of the water is bad on the transom, drive and motor. With that said there is lots of things you can do. Intake, carb, ignition........just depends on your wallet. As for just making what you have better. Sounds like you are close to perfect now.
This boat;

with a 454 and a 14X24SS prop only does 55mph (GPS).

 

[John_S]

Re: Tune-Up for performance

From your description, its sounds like you are talking about the throttle cable doesn't move until you pass the forward gear selection. That is the way it is suppose to work. You can check to make sure the throttle is openning fully. With engine off, remove flame arrestor and advance throttle lever to full throttle. Look down carb and make sure butterflies are fully open.

I only adj idle mixture and idle speed during yearly tune-up. If your acceleration problem is a bog and hasn't always done it, then it might be time to look at the carb. You might be experiencing accelerator pump problems.