Should of bought a V6...

[_chris_]

I keep hearing/ reading people talk about their V6's cruising in the mid 50's. Is this correct? I have the 5.0 OMC V8 and I can maybe reach 48 and mine is setup with the right prop and has no issues. Is it true the smaller motors are outduing the V8's? Did I buy the wrong boat for speed?

 

[WAVENBYE2]

Re: Should of bought a V6...

Chris my cruising speed or what I call my cruising speed is 30mph at 3000rpm(half throttle) my rpms pretty much match my speed, I do about 48mph on average with the right trim on plane, that was with a hydrofoil, I can't wait to install the smart tabs and see what she does. I also use a 19p.

 

[_chris_]

Re: Should of bought a V6...

Yeah I cruise about 34 at about 33oo RPM but my WOT is 48 MPH at 5000 RPM with the right trim, if I don't trim I can only hit about 42, I am also running a 19p with no foil. I just keep reading post of these guys that can do 55+ with the 4.3 liter and am amazed.

 

[WAVENBYE2]

Re: Should of bought a V6...

I just keep reading post of these guys that can do 55+ with the 4.3 liter and am amazed.

I would probably get close to that with 21p. Weight of the boat probably plays a big role and prop slipage too. I also have a 30gl tank. when I am alone It doesn't even feel like I am in the water just skimming the top, It sounds like your right on the money, if your not worried about hole shot and go with 21p you will probably get a little better once on plane and get better fuel efficiency. I only push it when I am alone though, with my wife and dogs I just cruise at 30mph

 

[Bart Sr.]

Re: Should of bought a V6...

I just keep reading post of these guys that can do 55+ with the 4.3 liter and am amazed.

Those that say they are getting 55 are probably in a 16' bowrider/runabout.Mine gets 44/45 with a 3 ltr.

 

[windsors03cobra]

Re: Should of bought a V6...

Most are probably using the ridiculous pitot tube speedometer anyway.
I will say for me say in an old Chev truck or even a boat 4.3>5.0. A three fitty is always best in my book, but what a fuel pig those are......

I run mine at WOT from time to time but couldn't imagine doing that for any length of time, just don't seem right to run an engine at a tick below redline for long periods to me.
We usually cruise right around three thousand revs also. Good plane, nice speed and fuel sipping. :redface:

I watched a youtube video yesterday of a boat with twin 1075hp engines running both engines at 6000 revs, the speedo showed 130 mph. Think a half million dollar boat is using a gps on that super speedo or pitot?.............

 

[superpop]

Re: Should of bought a V6...

You have to compare apples to apples when it comes to speed. Weight, prop and gearing can all have an effect on speed. I went from a 19 foot Wellcraft open bow run about to a 21 foot Chaparral open bow, both heavy boats and the Wellcraft had the v-6 and the Chap has the V-8. Now the Wellcraft with half a tank of gas and me in it alone on smooth water would break 55MPH with a 23P prop on it. The Chap will do this as well with the same prop so I think a lot of it has to do with prop pitch. The V-6 was a Vortec 4V carb motor and the 5.0 is MPI but both have the same drive. I do know that I would never go back to a carb motor again but that is a whole other discussion. Your boat with a similarly aspirated motor would be a dog with two less pistons. I am not sure what all the hub bub is with top speed anyway, unless you boat where the water is glass all the time and you have long distances to travel, top speed should not be that big of an issue. A 19 foot boat is no fun to ride in at 50+ MPH when the water is rough, you get the crap knocked out of you pretty quick, and if the missus is on board, forget about it. I currently run a 17P 4 blade prop on my boat and it jumps out of the water but tops out at 40MPH, fast enough for me. See my sig line below.

 

[a70eliminator]

Re: Should of bought a V6...

Yep, 6 cyliders do the job pretty good, it's with a load of people and gear when your 8 cylinders will pull.
I have a 20' chaparral bow rider 351 CID, I put an 18P ss prop on it to slow it down a little 50MPH was too fast for my comfort, I have to be careful with the RPM's but with a full load of people it's a blast.

 

[_chris_]

Re: Should of bought a V6...

I personally don't need or even rarely hit my WOT speed but it is just one of those things just knowing that I can.

 

[haulnazz15]

Re: Should of bought a V6...

Top speed of your boat can only be compared with your exact boat and load. Then take a 4.3L and a 5.XL engine and compare. Even though both boats have an Alpha II or Bravo I outdrive, they are sometimes different gear ratios inside. That makes things even harder, because then the prop pitch doesn't have the same ratio. Assuming you have the same boat, and outdrive ratios, same prop pitch: the V8 will haul you out of the water faster and get to TOP speed faster at the same RPM's. Top speed would be limited by RPM's and then by engine power.

I'll take the V8 every time. Mine tops out at 50mph, but after I rebuild the engine this winter to 300HP instead of 233, I doubt that I'll see more than 1-2 mph gained. The redline will still be the same, but I'll sure as hell get out of the hole quicker. (although I'm already on plane in less than 3 seconds).

 

[dg512055]

Re: Should of bought a V6...

My boat has done 52 in still water and no wind with 3 on board and nearly full fuel. My MPH and RPM usually nearly match. I always measure speed with a GPS. The factory speedo is close up to about 40 MPH and then it pulls ahead of the GPS. It will show 55 - 56 when GPS is at 50.

 

[fixb52s]

Re: Should of bought a V6...

My Chapp has done 57 on GPS... calm day, 2 people, 1/2 tank fuel. With a full load of fuel and 10 people, I was lucky to break 46. But the real numbers I look at are the cruise speed. On plane at 32 is where most boating is done. I could have got similar top speed numbers with a smaller engine, but it would have some problems with the extra load.

The larger engine is sure nice to have. It will burn more fuel, but at cruise, it is not much worse than it would be with something smaller. Having that extra HP comes in handy if you are loaded and trying to outrun weather.​

 

[45Auto]

Re: Should of bought a V6...

This is the internet. Talk (or rather typing) is cheap. If it makes you feel better, post that your boat cruises in the mid-80's by GPS while burning 1.3 GPH. If people choose to believe you without researching your claims, that's their problem.

If everything else is equal (drag due to air and water), top speed will be determined by max HP. A carbed 5.0L is 220 HP, same as an EFI 4.3L. So the EFI 4.3L in a smaller boat with less drag will be faster. Of course, you'll probably pay more for the smaller EFI motor. Your decision. To make a legitimate comparison you need to compare the top speeds of IDENTICAL boats equipped with a 260 HP 5.0L EFI vs a 220 HP 4.3L EFI. Or a carbed 5.0L (220 HP) vs a carbed 4.3L (190 HP). In either case, the motor with the most HP will be faster.

Did I buy the wrong boat for speed?

Simple answer: YES.

If top speed is that important to you, get the most HP you can in the longest, skinniest, lightest boat you can find.

In the real world, I wouldn't worry about it unless the 4.3's are buzzing past you like flies. Find a buddy with a 4.3L in his boat and run them side-by-side for a while before you decide to get rid of your 5.0L .........

 

[deadstick]

Re: Should of bought a V6...

22 ft. 3750 lbs 5.0 efi volvo penta

my boat
wot: 55 mph @ 4800 rpm
cruising speed: 30 mph @ 3000 rpm
best mpg: 33 mph @ 3.6 mpg


this my two cents (this may make no cents), if you are are running i/o, wot is usually 4800. if you have a v6 turning 4800 or v8 turning 4800, the output on the rear of the motor is the same 4800 rpm. (please correct me if im wrong) if this is correct, the outboard ratio, or prop would be the only diff in speed.
hp has to do with how fast you reach this speed.

someone please correct me, i may be overboard on this.

 

[45Auto]

Re: Should of bought a V6...

if you have a v6 turning 4800 or v8 turning 4800, the output on the rear of the motor is the same 4800 rpm. (please correct me if im wrong) if this is correct, the outboard ratio, or prop would be the only diff in speed.

You're correct. That's why the larger motors have lower gear ratios in the sterndrive, they don't need as much gear reduction to multiply the torque delivered to the prop. Typical Alpha ratio for a V8 is 1.47:1, a V6 is 1.81:1, and a 4 cylinder is 1.94:1. So on a V8 at 4800 RPM, the propshaft is turning at 4800/1.47 = 3265 RPM, while on the V6 at 4800 RPM the propshaft is only turning at 2652 RPM. If you have the same size prop on each boat, the V8 will be faster. If the V6 has the horsepower to turn a higher pitched prop and still reach 4800 RPM, it could be as fast or faster than the V8.

hp has to do with how fast you reach this speed.

Actually it's excess available horsepower that determines how fast you accelerate, which is a direct result of how much excess torque your motor has available at the particular RPM it's currently operating at.

This thread from a couple of years ago has an explanation of how it all works:

http://forums.iboats.com/showthread.php?p=1509890#post1509890

 

[Bronc Rider]

Re: Should of bought a V6...

You're correct. That's why the more larger motors have lower gear ratios in the sterndrive, they don't need as much gear reduction to multiply the torque delivered to the prop. Typical Alpha ratio for a V8 is 1.47:1, a V6 is 1.81:1, and a 4 cylinder is 1.94:1. So on a V8 at 4800 RPM, the propshaft is turning at 4800/1.47 = 3265 RPM, while on the V6 at 4800 RPM the propshaft is only turning at 2652 RPM. If you have the same size prop on each boat, the V8 will be faster. If the V6 has the horsepower to turn a higher pitched prop and still reach 4800 RPM, it could be as fast or faster than the V8.

Do you mean higher gear ratio? Your explanation of how it works is spot on.
I only point this out for clarity purposes.

 

[a70eliminator]

Re: Should of bought a V6...

Do you mean higher gear ratio? Your explanation of how it works is spot on.
I only point this out for clarity purposes.

Yea I caught that too. Higher ratio is a lower number and people usually say it wrong.

 

[45Auto]

Re: Should of bought a V6...

Do you mean higher gear ratio?

Nope, definitely meant LOWER gear ratio for the bigger motors.

When you're talking gear RATIOS, like I was, 1.47 to 1 is lower than 1.94 to 1.

When you're talking GEARING, a low gear means a high reduction RATIO.

For example, if you're talking gears in a transmission or rear end, (NOT RATIOS), then the lower GEARS have higher RATIOS. The 4L80E transmission in my Suburban has a 1st gear of 2.48:1, 2nd is 1.48:1, 3rd is 1.00:1, and 4th is 0.75:1. The lower gears have higher ratios.

If you're talking rear end gears in a car, it works the same way. People call a high ratio rear end "low gears". For example, a differential with a 4.11:1 ratio is considered a low-geared differential. A 2.73:1 differential ratio is considered "high gears".

Higher ratio is a lower number and people usually say it wrong.

Nope, higher RATIO is a higher number, what you're talking about is a higher GEAR which is a lower number (or ratio). A high-RATIO reduction is considered to be GEARED low. And you're right, a LOT of people do say it wrong!!

You have to be clear whether you're talking about GEAR RATIOS or GEARING, I was clearly referring to GEAR RATIOS.

 

[lindathayer]

Re: Should of bought a V6...

To Bart S.

Thank-you for your service and my freedom. I pray for all the men and women to come home safe. My father was in the Navy. I teach my son to respect and remember all those who served. God Bless

 

[skargo]

Re: Should of bought a V6...

Nope, definitely meant LOWER gear ratio for the bigger motors.

When you're talking gear RATIOS, like I was, 1.47 to 1 is lower than 1.94 to 1.

When you're talking GEARING, a low gear means a high reduction RATIO.

For example, if you're talking gears in a transmission or rear end, (NOT RATIOS), then the lower GEARS have higher RATIOS. The 4L80E transmission in my Suburban has a 1st gear of 2.48:1, 2nd is 1.48:1, 3rd is 1.00:1, and 4th is 0.75:1. The lower gears have higher ratios.

If you're talking rear end gears in a car, it works the same way. People call a high ratio rear end "low gears". For example, a differential with a 4.11:1 ratio is considered a low-geared differential. A 2.73:1 differential ratio is considered "high gears".



Nope, higher RATIO is a higher number, what you're talking about is a higher GEAR which is a lower number (or ratio). A high-RATIO reduction is considered to be GEARED low. And you're right, a LOT of people do say it wrong!!

You have to be clear whether you're talking about GEAR RATIOS or GEARING, I was clearly referring to GEAR RATIOS.

Say WHAT?!?!?!?!?!?!?!?! Gearing and gear ratios are the same thing.