how to get boat from 0-25mph faster?

[conk3416]

I have a 1985 I/O with a 302 Mercruiser. The carb on it is a 300cfm 2bbl Holley. I would like for the boat to have a little more power from the start to around 25mph. I was thinking of putting on a 2bbl 500cfm carb. Would that make takeoff better? And if so would it be a noticeable difference? Or if anyone has any other ideas please let me know.

Thanks Andrew

 

[WizeOne]

Re: how to get boat from 0-25mph faster?

You've hardly given enough information about your setup and boat for anyone to even hazard a guess!

 

[cr2k]

Re: how to get boat from 0-25mph faster?

Unless you can find a marine carb, I wouldn't do it.

Try a DolFin or some kind of Whale tail deal. It will get you on plane faster.

Or one step lower prop, but with this you could over rev. So you need to know what your WOT RPM is so and don't exceed specs.

 

[Bondo]

Re: how to get boat from 0-25mph faster?

I have a 1985 I/O with a 302 Mercruiser.

Ayuh,... Mercruiser was Not using Fords in 1985....

 

[conk3416]

Re: how to get boat from 0-25mph faster?

I just found out that the engine is a '73. The previous owner took out the original 4 cyl and put the 302 in. The WOT RPM is 2500. Does the DolPhin or Whale tail work good? I have heard they dont make much of a difference.

Thanks Andrew

 

[wca_tim]

Re: how to get boat from 0-25mph faster?

something is way wrong.....

can you post some more detailed information? also, if it is out of tyhe hole you're worried about more than top end, once you make sure your engine is in good tune and running on all 8 cylinders, prop changes are going to be by far the most cost effective way to approach what you sound like you want.

 

[WizeOne]

Re: how to get boat from 0-25mph faster?

If they put the 302 on an outdrive that was meant for a 4 cylinder, the gear ratios are all wrong. They are so wrong they might not even be reasonably corrected by different props.

The whale tale at best is a stop gap measure and has certain benifits and many drawbacks.

 

[wca_tim]

Re: how to get boat from 0-25mph faster?

If they put the 302 on an outdrive that was meant for a 4 cylinder, the gear ratios are all wrong. They are so wrong they might not even be reasonably corrected by different props.

The whale tale at best is a stop gap measure and has certain benifits and many drawbacks.

depending on how heavy the boat is might get away with 1.98 and a 302, but that's not what's happening based on above - his rpms would be through the roof if he was running that much gear and typical pitch prop.

no on the whale tale. it won';t even help. you ned to address either an engine problem or a propping problem... or.. ????

 

[conk3416]

Re: how to get boat from 0-25mph faster?

the outdrive is a MERC 888.

 

[conk3416]

Re: how to get boat from 0-25mph faster?

I am not sure what the pitch of the prop is..... How can i find out? I only use the boat for tubing, wakeboarding and kneeboarding, so i am just looking to get on plane faster or at a lower speed.

Thanks Andrew

 

[cr2k]

Re: how to get boat from 0-25mph faster?

You may be looking at a 23 or 25 pitch prop to cure the drive ratio problem you have. But this could give you new problems getting up to speed, like cavitation.

Some dealers have a prop test program and will rent you a prop for a day to see if will work for you. i would check in to this.

Prop pitch should be stamped on the side between the blades or cast on the hub.

 

[WizeOne]

Re: how to get boat from 0-25mph faster?

Find a prop repair business in your area. They can measure the pitch on your prop.

As for other performance issues, tubing, wakeboarding and knee boarding are the most demanding circumstances for any boat, even those with proper gearing and propping.

They all occur at speeds that are difficult to keep the boat on plane without increasing speed beyond what is desired.

For that, you need Smart Tabs. They will let you plane at a lower speed, keep the nose of the boat down and give you great throttle/speed control right in the area that you need it most.

http://www.iboats.com/Boat_Parts_Accessories/dm/*******.707929972--keywords.smart%20tabs--**********.078225272--submit.x.37--submit.y.2

 

[wca_tim]

Re: how to get boat from 0-25mph faster?

I am not sure what the pitch of the prop is..... How can i find out? I only use the boat for tubing, wakeboarding and kneeboarding, so i am just looking to get on plane faster or at a lower speed.

Thanks Andrew

before you go buying anything get what you got right.

prop: if it's not marked anywhere on the outside, then pull it off and look at the hub. many are marked or stamped... the one on the floor next to my desk says 14.5 x 27 - meaning 14.5" diameter and 27" pitch. if you only have a serial number often times you can figure that one out.

I would be shocked if your running a high gear ratio like from a 4 cyl and turning max 2500 rpms on a 302. unless your tach is way off, you're running a lower gear (ie 1.5 or the like) or have engine "issues" unless it's a barge of a boat and way overpropped.

How does it sound when you run it at max rpm? couild it just be the tach? If you have a friend with or can beg borrow, steal a timing light with electronic advance and an rpm reading on it, do it and check your tach. might as well check the timing as well while you're at it. give it a complete tune up while you're at it (unless been done recently), make sure it's running on all cylinders and so on. Not saying this will fix the problem, but if it needs done do it and it'll remove some questions you need to answer anyhow.

imho...

 

[Don S]

Re: how to get boat from 0-25mph faster?

the outdrive is a MERC 888.

GUYS, he has an 888 Merc outdrive. An 888 outdrive IS a Ford 302.
He has the correct gear ratio.

He also has a max WOT of only 2500 rpm, had he been using a 4 cylinder gear ratio, he would be getting too many rpms and not enough speed.

I would suggest you read the thread below, you have to find out why you have such a low WOT (Wide Open Throttle) rpm.
http://forums.iboats.com/showthread.php?t=295070

 

[conk3416]

Re: how to get boat from 0-25mph faster?

I am sorry i gave the wrong number for WOT RPM. With roughly 600-800lbs in the boat the WOT RPM is around 3500-3700 rpm's. Should RPM's be higher then that or is that normal? I just did a complete tune up (plugs, wires, distributor converted to HEI, coil, carb rebuilt) The engine runs good and goes good once on plane. Just trying to get on plane faster.

 

[WizeOne]

Re: how to get boat from 0-25mph faster?

I am sorry i gave the wrong number for WOT RPM. With roughly 600-800lbs in the boat the WOT RPM is around 3500-3700 rpm's. Should RPM's be higher then that or is that normal? I just did a complete tune up (plugs, wires, distributor converted to HEI, coil, carb rebuilt) The engine runs good and goes good once on plane. Just trying to get on plane faster.

Read my post above regarding SmartTabs. The will get you on plane quicker, at lower speed and with much more throttle control. Forget a whale tail.

Here is a link to the manufacturer's website. They have some good comparative vids.

http://www.nauticusinc.com/smart_tabs.htm

Also it sounds like you could be significantly underpropped for the load you are carrying. This all assumes that you are well tuned and have good compression. What is your WOT rpm with just you in the boat? Should be, give or take, around 4400 rpm which is the maximum operating rpm. A small boat with a big load can change that rpm easily. For best performance and to make the engine perform most efficiently, you need to be propped to reach maximum rpm considering the load you are carrying.

As loads can vary, depending on what you are doing, many people would have several props to fit the varying needs. I would wait to select a heavy load prop until you have installed your Smart Tabs. I believe each pitch number that you drop picks up about 200 rpm.

 

[conk3416]

Re: how to get boat from 0-25mph faster?

With only me in the boat WOT is around 4100-4200 rpm. I am probably going to get the smart tabs everyone seems to say they work. Thanks for the help

 

[frank246]

Re: how to get boat from 0-25mph faster?

Dont forget that the v8 is way heavier than the 4 cyl and only delivers 48 hp more than the L4 but with more torque.
I also have a 302 ford (888) rebuilded into my boat that originally had the 140 4 cyl engine.
I had to set the tacho to 8 cyl (selecter screw on the back) instead of 4 cyl to get the tacho gauge right.
I run a 23P cleaver prop for more sternlift to compensate the heavier engine in the back, boat is a 16' and gets 63mph@4600 (with chinewalk, hi-ha)
using an alloy edelbrock rpm intake and 600cfm marine Holley and Hei ign. and got rid of the 140 lbs log style exhausts.
The 888 is rated at 188 hp but with the 4bbl set up makes it a 225hp, go for the 4bbl set up, find some lightweight alloy or ss exhausts and start off with a 23 P prop.

 

[PiratePast40]

Re: how to get boat from 0-25mph faster?

JATO is the way to go, check out "Fat Albert" :http://www.youtube.com/watch?v=jTf0n5hn5s0&feature=related

 

[WizeOne]

Re: how to get boat from 0-25mph faster?

No, that is too low. You may well have a prop that is too steep. I like smart tabs as much as the next guy but your putting a bandaid on it instead of finding the real issue.

A low power hole shot and failure to reach proper WOT RPM(4200 to 4600) tells me its either over proped or isn't performing correctly.

I'll give another thing to kick around. You can realistically get another 30 HP or so out of that little 302 by going to a performance intake and a 4Bbl. carb. (600 - 650 CFM) Coming out of the hole you will really feel the difference.

Bubba, I hope you did not think I recommended Smart Tabs as a fix for his expressed problems? I clearly stated that he was under propped, at least for the load he was carrying, and that needed to be remedied. I do agree with you that even 41-4200 rpm, unloaded, is still too low an rpm. Add all the weight to that and you have a hopeless slug, trim tabs or not.


I brought up the SmartTabs in answer to his claim that he could not keep the boat on plane, at the speeds he performed those various sporting activities. That could well happen even with a correct prop. I then suggested that he wait to select a proper prop until he had the smart tabs on, as they could alter the equation.