Mercruiser 5.0L or 5.7L

[thumpar]

Re: Mercruiser 5.0L or 5.7L

If the ratio, pitch and speed was GPS and correct I would have to think the tach may be off.

 

[Walt T]

Re: Mercruiser 5.0L or 5.7L

The loss of paint or finish on the props will not cause that slip. Consider that a prop repair shop will spray paint them on a hanger but the manufacturer will paint them with a much more durable system. Those painted props are aluminum, you might try stainless, you will generally get better all around performance. Funny thing, I have found my aluminum B5 propset is better than stainless for pulling kids around all day, and the stainless just seems less forgiving. So I sold the F5 stainless and bought F6 for cruising. Now with the Stroker I still use the B5 aluminums for towing, the motor is just loafing all day long. I am currently looking for F7s and am interested to see if that works with the stroker. My point is, you should experiment with props if you can. I know these propsets are not cheap but sometimes you can get a used reconditioned set from a propshop who will let you try them for a nominal fee, 25-50 bucks or so. Just don't break them.

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

The loss of paint or finish on the props will not cause that slip. Consider that a prop repair shop will spray paint them on a hanger but the manufacturer will paint them with a much more durable system. Those painted props are aluminum, you might try stainless, you will generally get better all around performance. Funny thing, I have found my aluminum B5 propset is better than stainless for pulling kids around all day, and the stainless just seems less forgiving. So I sold the F5 stainless and bought F6 for cruising. Now with the Stroker I still use the B5 aluminums for towing, the motor is just loafing all day long. I am currently looking for F7s and am interested to see if that works with the stroker. My point is, you should experiment with props if you can. I know these propsets are not cheap but sometimes you can get a used reconditioned set from a propshop who will let you try them for a nominal fee, 25-50 bucks or so. Just don't break them.

The bravo 3 come only in stainless props. I'll have to get another tach and try it out in the spring time.

 

[Scott Danforth]

Re: Mercruiser 5.0L or 5.7L

if you have a DMM that reads frequency, you can use that to read RPM if you do not have access from an optical tach. FWIW, many automotive stores have a diagnostic tach they can loan

 

[Cptkid570]

Re: Mercruiser 5.0L or 5.7L

Moosehunter - What is the diameter of your props? Maybe test out something with a large diameter?? I just think that if you could have a prop shop let you try out different props, you may find the best prop for your situation. I have a 15x17 prop on my 24' boat and probably get better cruising speed than you.

Oh, I also like the idea of checking the accuracy of you tach.

With as much as you use your boat, even 1/2 mile per gallon more efficiency could save you a lot of money.

 

[HT32BSX115]

Re: Mercruiser 5.0L or 5.7L

Hi Rick, I bought this package off a friend of my that the haul was cracked. He gave me all the paper work when he bought it new as a package. The drive says its 2.20:1 and my props say 24 pitch. I had 22 pitch that came with the drive. I took it for a test run and opened it up and I hit 5300 rpm wot. So I bought (used) 24 pitch which dropped my rpm down to 4800 rpm wot. Like I said earlier my props were matte finish but it's all worn off and now it's all shinny. Would the loss of the matte finish off the props cause the slip to be up at 26%? All my readings are off my chart plotter and GPS. Also it's a 2 barrel carb that's on my 5.0L. The boat is a bayliner 2159 trophy Alaskan bulkhead

Ok, First of all, no. the props aren't shiny because you just ran it normally. (Did you run it through water with a LOT of sand in it?) I have had those props in my rotating picture for 5 years and they're STILL a 'matte' finish........

I had to go back and look at your year model engine and drive.

Mercruiser 5.0L Marine Engine Specifications | Performance Product Technologies

You (should) have a Thunderbolt V ignition system on that engine if no one modified it....... your maximum RPM is rated at 4800 RPM, the rev limiter should be set 5000 RPM or so.

For example, my 1997 454 has a rated RPM range of 4200-4600 RPM. The REV limiter is set at 4700 RPM. Regardless of the prop pitch, the engine WILL NOT turn faster than 4700....and you can tell when you reach the limit...

I really think your TACH is defective if you can rev to 5300 indicated RPM (the rev limiter would prevent it)

You're going to be spinning your wheels trying to get this right if you don't get a known tach, speed measurement and VERIFY your drive ratio.
(sounds like you have the speed covered if you're using GPS)


Just because it says 2.20:1 on the drive, doesn't make it so........someone could have rebuilt the "upper" and only had the "high alt" gears etc.

An easy way to verify would be to pull the plugs and turn the engine. If it really is 2.20:1..........22 engine revolutions will result in exactly 10 prop revolutions.

If you want to turn the engine 2.2 revolutions, 0.2 revolution would be exactly 72 degrees (so 2 end revs + 72 degrees would be 1 prop rev) but you'd have to use a protractor or other degree measuring device to measure it. (with a 2.43:1 drive 0.43 rev = 155 degrees.........just a little shy of 1/2 turn)

In any case, you need to know for sure what your RPM, speed, ratio and prop pitch is......... since tachometers are frequently defective, that's where I would start.



Cheers,


Rick

 

[dan t.]

Re: Mercruiser 5.0L or 5.7L

Were telling you no,because that is the correct answer.If there was a magic answer then all the boat and car mfgs. would be using it.Why do you think the car people put so much into aerodynamics ? Because they can't do any more with the tranny and rear gear ratios.Every little 4 banger **** box gets about the same mileage if the gears etc are close,THEY can't do anything more with the internal engine to increase mileage. I will say this again it takes X amount a fuel to produce a single HP and that fuel goes into basically the same combustion chamber,they all operate under the same principal. You may be able to cruise at a lower rpm but it is still going to take the same amount of hp/fuel to meet that number.The displacement is bigger on the 5.7 so even though the rpms are less you still need the same amount of fuel to reach the needed hp. YES the engine is turning over slower but you have bigger cylinders to feed and that's when it evens out.Putting a higher pitched prop will only make the engine work [suck more fuel ]to reach your desired cruising speed. The 5.7 vs 5.0 or anything else is not going to give you any better mileage with all things being equal,even when perfectly propped to your hull.Like I said I would be working on where to put extra fuel tanks than trying to squeeze 10 more miles out of a 5 hour trip.

Well I beg to differ. I swapped my Bayliner 2452 from a 305 to a 350 and gained about .5 mpg. The original 305 with a 1.65 gear ratio and a 16x16 prop got around 2 mpg (imperial gallons) the 350 same gear ratio with a 15.5 x19 prop gets around 2.5 mpg. These millages were checked over 2 whole summers using the trip log in my gps and the total amount of fuel used.Sorry to rain on your parade but the figurs dont lie

 

[mr 88]

Re: Mercruiser 5.0L or 5.7L

^ Quite a difference in props,the one you ran with the 305 ,16 x 16 sure seems like it was under pitched. So unless you were propped correctly your numbers are skewed.The 305 sounds like it should of been a 17" with a smaller diameter than your 16". Who knows what speed you were cruising at with the 305 vs the 350 over the course of a season.You went up 3" in pitch with a increase of 30-40 hp in the power plant which also tells me you were under pitched to begin with.Were the props both made by the same company and were they both aluminum or SS and cupped ? Did you go from a carbed engine to EFI or are they both the same? You have a lot of variables that may affect your numbers and that will throw the scientific comparison out the window. IF by putting a larger engine in a boat or car for that matter increased fuel mileage every car and boat would have a 7.4 in it. I will say it again it takes X amount of fuel to generate one HP and in order to cruise at say 23 mph you are going to use Y amount of hp. So not matter what engine is in there you still need Y amount of the available hp to meet that goal.It is going to use the same amount of fuel in any engine to produce Y.

 

[HT32BSX115]

Re: Mercruiser 5.0L or 5.7L

I will say it again it takes X amount of fuel to generate one HP and in order to cruise at say 23 mph you are going to use Y amount of hp. So not matter what engine is in there you still need Y amount of the available hp to meet that goal.It is going to use the same amount of fuel in any engine to produce Y.

Exactly. It's abbreviated "BSFC".......... Brake Specific Fuel Consumption. There are "things' you can do to change (slightly) the BFSC of any engine. but for most "stock" marine type gasoline engines, the BFSC doesn't change much..... 2 identical boats loaded exactly the same will take the same HP to push them at a particular speed. two different engines that happen to exhibit the same BSFC will require approx the same fuel to produce the same work.

There are a LOT of variables but you don't automatically burn more fuel just because the engine is "bigger" if the boat is loaded the same.

You burn more fuel because you have additional power and you uswe it!! No one wants to hold back and not use it!

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

My engine is a 1998. The props I bought used and the matte finish was worn already so I have no idea what the previous owner did to it. Now for the tach, I'll have to check that out in the spring time. When I said I hit 5300 rpm's that was with the 22 pitch props that came with the package. Now I rev out at 4800 with the 24's. Why my rev limiter (if its not working or if I got one) didn't kick in. Going to have to look into that.
I looked up the power band on the 5.0 and 5.7 Blocks
5.0L- 220 hp @ 4800 & 270 ft @ 3600

5.7L- 290 hp @ 4800 & 355 ft @ 3200

I understand what people are saying about it takes X amount of fuel to make horse power but if I'm cruising at the top of my power band (3700 rpm) wouldn't it make sense to be at 3200? with the 5.7? You can't tell me that i'll be burnig the same amount of fuel doing 400 rpms and probably going a lot faster at the same time at a lower rpm

 

[thumpar]

Re: Mercruiser 5.0L or 5.7L

Exactly. It's abbreviated "BSFC".......... Brake Specific Fuel Consumption. There are "things' you can do to change (slightly) the BFSC of any engine. but for most "stock" marine type gasoline engines, the BFSC doesn't change much..... 2 identical boats loaded exactly the same will take the same HP to push them at a particular speed. two different engines that happen to exhibit the same BSFC will require approx the same fuel to produce the same work.

There are a LOT of variables but you don't automatically burn more fuel just because the engine is "bigger" if the boat is loaded the same.

You burn more fuel because you have additional power and you uswe it!! No one wants to hold back and not use it!

I will vouche for that. I went from a 120 to a 260. It is hard to not use it. :laugh:

 

[Walt T]

Re: Mercruiser 5.0L or 5.7L

Maybe you will burn less fuel, only one way to find out. I can assure you the burn rate difference is going to be very small. Boats like ours get 2-3 mpg and there's not anything we can do about it

 

[mr 88]

Re: Mercruiser 5.0L or 5.7L

Yes we can tell you.......As mentioned by a few,the 5.7 is turning over slower BUT has BIGGER cylinders to fill with gas and that translates to equal mileage.It is less wear on the engine at equal speeds vs the 305.The most economical cruising speed is about 28- 3000 rpms for V-8' & 6's.So what your looking at in cruise speed is gonna suck gas no matter what. HOW much more gas are you looking to save by this. In other words your heading out fishing and you have a 60 ?gallon gas tank and carry 20 gallons in reserve tanks? and have to travel 150 miles round trip ? Then troll using 15 gallons ? So at the end I am looking to save how many gallons by this swap ?

My engine is a 1998. The props I bought used and the matte finish was worn already so I have no idea what the previous owner did to it. Now for the tach, I'll have to check that out in the spring time. When I said I hit 5300 rpm's that was with the 22 pitch props that came with the package. Now I rev out at 4800 with the 24's. Why my rev limiter (if its not working or if I got one) didn't kick in. Going to have to look into that.
I looked up the power band on the 5.0 and 5.7 Blocks
5.0L- 220 hp @ 4800 & 270 ft @ 3600

5.7L- 290 hp @ 4800 & 355 ft @ 3200

I understand what people are saying about it takes X amount of fuel to make horse power but if I'm cruising at the top of my power band (3700 rpm) wouldn't it make sense to be at 3200? with the 5.7? You can't tell me that i'll be burnig the same amount of fuel doing 400 rpms and probably going a lot faster at the same time at a lower rpm

 

[HT32BSX115]

Re: Mercruiser 5.0L or 5.7L

My engine is a 1998. The props I bought used and the matte finish was worn already so I have no idea what the previous owner did to it. Now for the tach, I'll have to check that out in the spring time. When I said I hit 5300 rpm's that was with the 22 pitch props that came with the package. Now I rev out at 4800 with the 24's. Why my rev limiter (if its not working or if I got one) didn't kick in. Going to have to look into that.
I looked up the power band on the 5.0 and 5.7 Blocks
5.0L- 220 hp @ 4800 & 270 ft @ 3600

5.7L- 290 hp @ 4800 & 355 ft @ 3200

I understand what people are saying about it takes X amount of fuel to make horse power but if I'm cruising at the top of my power band (3700 rpm) wouldn't it make sense to be at 3200? with the 5.7? You can't tell me that i'll be burnig the same amount of fuel doing 400 rpms and probably going a lot faster at the same time at a lower rpm

If you still have the Thunderbolt-V ignition, and it runs, the rev limiter should work.

You MAY not be making it to 5300 because the tach is faulty. You may actually be only turning 4900-5000 because that's where the rev limiter *should* be working.

You will not burn the same fuel with the 5.7L engine if you run it "harder" but to go the same planing speed, it'll take a little less throttle to do it (but probably approx the same fuel flow)


I would STILL want the 5.7L engine over a 5.0 in a boat that size! (my 21' Four Winns Liberator is that size! and I wouldn't want an engine smaller than my 454!!........ Actually, I want a stroked 496 or 502 :thumb:

 

[dan t.]

Re: Mercruiser 5.0L or 5.7L

^ Quite a difference in props,the one you ran with the 305 ,16 x 16 sure seems like it was under pitched. So unless you were propped correctly your numbers are skewed.The 305 sounds like it should of been a 17" with a smaller diameter than your 16". Who knows what speed you were cruising at with the 305 vs the 350 over the course of a season.You went up 3" in pitch with a increase of 30-40 hp in the power plant which also tells me you were under pitched to begin with.Were the props both made by the same company and were they both aluminum or SS and cupped ? Did you go from a carbed engine to EFI or are they both the same? You have a lot of variables that may affect your numbers and that will throw the scientific comparison out the window. IF by putting a larger engine in a boat or car for that matter increased fuel mileage every car and boat would have a 7.4 in it. I will say it again it takes X amount of fuel to generate one HP and in order to cruise at say 23 mph you are going to use Y amount of hp. So not matter what engine is in there you still need Y amount of the available hp to meet that goal.It is going to use the same amount of fuel in any engine to produce Y.

You seem to have lots of excuses to defend your theory. FYI the 305 was perfectly propped,4400 wot, I tried a 15x17, poor hole shot, lots of slippage,anyone who has one of these boats with the 305 (and I personly know 4 and have talked to several others at the dock)run the 16x16 quicksilver prop. The 350 gets better milage because because it isnt turning as many rpm for the same speed nor is it working as hard. At 22 knots, where I cruise the 305 was turning 3600 rpm pulling 3 in of vacuum, the 350 is at 3350 pulling 7 in of vacuum. At 7 in of vacuum the power enrichment system on the Q-jet is closed. The 305 (220 hp)was working hard, the 350 (280 hp) is loafing. BTW 7.4s are fuel pigs, I wouldnt have one if it was given to me.

 

[Cptkid570]

Re: Mercruiser 5.0L or 5.7L

I still want to know what diameter prop you are using. Is it stainless steel or aluminum?

If "the differences between a 350 and 305" generated this much discussion, some saying it will make a difference and some saying it won't, then I would think that any difference it would make on your sized boat would be slim. Bascially, your boat is not underpowered.

But, just because you go from a 22 pitch to a 24 pitch doesn't automatically mean that you are going to get 24 pitch performance. I depends on the diameter, cupping, material (aluminum vs stainless), etc.

Kind of a summation of all of your answers tells me that there are other factors such as prop and drive ratio to really look at before deciding to swap engine size.

I don't know much about Bravo IIIs, is that a dual prop? Is that drive ratio proper? As I said, I come from Alpha one where the gear ratio is typically around 1.50 for V8s, 1.81 for V6, and 1.94 for 4cyl.

All that said, how long until you think you will have to replace your block? I mean really have to because it gets too worn.

 

[mr 88]

Re: Mercruiser 5.0L or 5.7L

To Dan T,what is scientific about your swap and numbers,nothing. Are you running with a measured tank hooked up direct to the carb and under the EXACT same conditions ? This is not " my theory" and no excuses are being offered. So you are telling me the BSFC formula created by engineers,you know the guys with multiple degrees, is BS and your right because you checked your fuel usage over a couple seasons.Again nothing scientific in your record keeping as far as sea conditions,wind,cargo and currents go. To the OP again,how much fuel are you looking to save for your fishing trips by doing this. You use auxiliary tanks what is the total amount you leave the dock with?

 

[HT32BSX115]

Re: Mercruiser 5.0L or 5.7L

Kind of a summation of all of your answers tells me that there are other factors such as prop and drive ratio to really look at before deciding to swap engine size.

I don't know much about Bravo IIIs, is that a dual prop? Is that drive ratio proper? As I said, I come from Alpha one where the gear ratio is typically around 1.50 for V8s, 1.81 for V6, and 1.94 for 4cyl.

Just an FYI, the 'rules' for prop size, pitch, aluminium/stainless steel, gear ratio that apply to an Alpha, VP SX, Cobra, etc, DO NOT APPLY to a boat using a Bravo III

Is it a dual prop? see below

Moose,

For your first question, can you change from a 5.0L engine to a 5.7L engine? Absolutely.

With the "correct propset" will it burn LESS fuel at the same planing boat speed as before?

NO.....................

Will it burn the approx the same fuel? Probably........................ I think Mr88 answered that pretty well.

Will you be tempted to use that extra power? I think so! and you'll use a little more fuel in the process

BUT you'll LOVE it!

BTW 7.4s are fuel pigs, I wouldnt have one if it was given to me.

Don't know where you get that.......Four Winns made many Liberator 211 boats (21' roughly 5000lb) with the 260 Mercruiser Alpha and OMC Cobra installed. they burn approx 10 gal per hour running around 30 mph with the SBC installed.

I installed a Lowrance LMF-200 fuel flow indicator in my 454 (bravo III) powered FW 211. At 30 mph, I burn about 10 gallons per hour.

It's only a "Fuel Pig" if you push really hard with your right hand.........






Cheers,

Rick

 

[Cptkid570]

Re: Mercruiser 5.0L or 5.7L

HT32B - thank you for your answer. As you could tell, I don't know anything about Bravo and was trying to educate myself as I follow this thread. Do all Bravo III use the same diameter props? Just the pitch changes?

 

[HT32BSX115]

Re: Mercruiser 5.0L or 5.7L

HT32B - thank you for your answer. As you could tell, I don't know anything about Bravo and was trying to educate myself as I follow this thread. Do all Bravo III use the same diameter props? Just the pitch changes?

Pretty much! Until recently, you could only buy props from Mercury.........AND they were (both) only 3 blade.

Now they have a new style propset that has a 4 blade "front" and 3 blade rear prop.



And I think an even newer style that is 4 blade for both of them!


Big Bux though!

I think they're all the same diameter.....