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  1. #1
    Cadet
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    Default 3.0 Mercruiser performance options

    Has anyone heard of any performance options for a 3.0 merc 140 horse? My boat is a 18 ft Sea Ray and it runs WOT at 44-4600 and it does 38-40 which is plenty enough for skiing ect. My problem is I need that extra bit of UMMMMPH for getting across the lake fast or for pulling my larger sized bro on law without boggin down. I have read about guys who build outrageous stockcar engines using 3.0 parts and apparently make like 250 hp. I don't want to go that far but maybe 50-75 more ponies. Any advise or URL would help. I have 14 years experience working on cars so technical style answers are ok.

  2. #2
    Lieutenant Commander bomar76's Avatar
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    Default Re: 3.0 Mercruiser performance options

    Easy to do.......pull drive, yank engine, etc, drop in SBC (ZZ4 crate are great. watch for reversion), install new drive w/ correct ratio, and away you go. Any other attempts at performace mods to the Industrial engine that is the Merc 3.0 are spitting in the wind.Real world answer:Sell boat, buy one with adequate power fo what your intended useage is.
    The last time religion controlled the world it was known as the Dark Ages

  3. #3
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    Default Re: 3.0 Mercruiser performance options

    Have you ever heard of power to weight ratio? I don't want to have a 500 lb engine(not to mention more fuel usage, extra parts ect) just to go 15-20 mph faster. The lighter I am the faster I go. I want to keep it that way and really the reason is that I love the boat.(and don't want to spend the $$$ for a different one)

  4. #4
    Lieutenant Commander bomar76's Avatar
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    Default Re: 3.0 Mercruiser performance options

    16 HP per ONE MPH gain is a good rule of thumb in the marine world.....Again, your solution is above.There is no magic answer.
    The last time religion controlled the world it was known as the Dark Ages

  5. #5
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: 3.0 Mercruiser performance options

    Originally posted by Scott Atwater: Have you ever heard of power to weight ratio? I don't want to have a 500 lb engine(not to mention more fuel usage, extra parts ect) just to go 15-20 mph faster. The lighter I am the faster I go. I want to keep it that way and really the reason is that I love the boat.(and don't want to spend the $$$ for a different one)
    You are not dealing with automotive here Scott, what you want is impossible.Deal with it.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
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    Only forum/moderator issues will be answered in PM's.

  6. #6
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    Default Re: 3.0 Mercruiser performance options

    I am basing my findings on a friend of mine who has the same boat(year, length ect) but with a 170 engine in it. He is actually only a tad bit faster. I think weight has everything to do with it. Why else would they make carbon fiber race hulls which weigh 800 lbs vs standard heavier fiberglass weight? It's true with cars and planes I also feel with boats this is also true. Less weight means less drag=go faster. Now I know what someone is going to say gut the boat and weigh less which is NOT an answer so don't go there.As for the engine doesn't anyone know of cams, pistons(high compression)maybe some porting, a small four bbl ect which will work? Sound like you guys are the v-8 block is the best in the world guys and frankly I don't think that is true anymore. The old 4.3 liter vortec makes 190-210 hp and it's 3/4 of a smallblock. Look at how they make so many beter products with more power ect than the years prior with better technology ect. Also is the alpha 2 3.0 a higher hp engine?

  7. #7
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: 3.0 Mercruiser performance options

    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

  8. #8
    Seaman Apprentice
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    Default Re: 3.0 Mercruiser performance options

    i wish i had a dollar for every time i've seen a post about "more hp out of a 3.0". then i'd have enough money to pull my 3.0 and get a v-8
    1985 Wellcraft 170 American / 3.0 Alpha 1

  9. #9
    Admiral tommays's Avatar
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    Default Re: 3.0 Mercruiser performance options

    About the only way to make MORE HP in a small motor is to spin it really fast problem is that the outdrive really really does not like driveshaft RPM above 5000And just study that mess of a combo intake/exaust manifold NOT really a lot to work with tommays
    If a dirty bottom slows you down what do think it does to your BOAT

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  10. #10
    Moderator Bondo's Avatar
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    Default Re: 3.0 Mercruiser performance options

    Ayuh,........ You can make a Race Car engine turn 10,000rpms to get Big HorsePower.......You Can't do that to the Tractor Motor that the 3.0l IS.........With 14 Years of being a Mechanic,....... You Seem to be Missing the Basics of Building USABLE HorsePower.......You Could use 12/1 350 Pistons,.... But it Still Won't Work...........Nobody is Arguing that Lighter is Faster,......
    Any Grease is Better,..... Than No Grease at All.......

  11. #11
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    Default Re: 3.0 Mercruiser performance options

    What they said...the curve is not linear...My 17.5 foot boat had a 140 3.0 and it went 40mph,My other identical hull (see avatar) has a 3.8 V6 @170 HP and it goes 50 mph, but with a SS prop. It's capable of almost 2X the fuel consumption.The weight of the V6 obviously is not too serious an issue.The first thing I would look at before upping HP is the fuel tank size... I just sized up some tanks for a retrofit...not looking forward to it tho'

  12. #12
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    Default Re: 3.0 Mercruiser performance options

    trade your boat or sell it.get what you want with factory aplication and youll have no troubles.or better yet--tell bro in law to get a boat and ride with him a while.

  13. #13
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    Default Re: 3.0 Mercruiser performance options

    here is the solution, build yourself a v-8 using all alumimm parts, block, heads intake , you can even get the exhaust logs in alum. now you dont have a weight problem, and since money is no problem here, get this thing fuel injected. at 75-80 mph, you will be asking how to make that hull, which is designed to do just what you are doing, handle better..... the perfect boat is not there yethave a great holdiay

  14. #14
    Vice Admiral Tail_Gunner's Avatar
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    Default Re: 3.0 Mercruiser performance options

    Doing a lot a reading on this subject and i afraid it useless. Basically if i have this right the 3.0 has been tuned to run @ high rpm's (4800) leaving it a tad weak in low end tourqe. Now if some one could find a way to increase the tourqe dramatcally on the bottom end and still maintain the top end then a bigger prop would seal the deal... Good luck on that one. Hmm maybe fuel injection.....$$$$$$$$. Notta
    Stickly a opinion your milage may vary.

    Speed is how fast you hit the wall
    Torque is how far you move the wall"

  15. #15
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    Default Re: 3.0 Mercruiser performance options

    to go along with "stock car racing engines" i raced a 4 cyl class for many years. we ran a pinto with a 2.3 liter. it produced around 250 h.p. but it didnt really "wake up until 6000 rpm's. with a spare engine still in the garage, i thought id look for a bayliner that also used a 2.3, and put mine in. upon calling OMC, they said the outdrive bearings would explode before the motor ever reached its "desired" rpm. thats the end of that idea.
    1985 Wellcraft 170 American / 3.0 Alpha 1

  16. #16
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    Default Re: 3.0 Mercruiser performance options

    LOL a car guy like me. Spray it. I think a small 50HP shot of N20 should get you put the hole a little quicker.
    -Mike

    1995 SeaPro
    Mercruiser 3.0LX
    Alpha 1 Gen II

  17. #17
    Moderator Bondo's Avatar
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    Default Re: 3.0 Mercruiser performance options

    Originally posted by IcantDo55: LOL a car guy like me. Spray it. I think a small 50HP shot of N20 should get you put the hole a little quicker.
    Shoot it with N2O,+ the Only Hole-Shot will be the Holes in the Pistons.............. Most All Boat motors,... Atleast 99% of the 1s We talk about here at iboats,.....Are designed to Pull,.. Hard,.. From Idle, to the Mid to High-4000rpms,....... Then they Fall on their Face.......With Most of Our Drives,....... Anything much over 5000rpms,+ You'll be $pending Big Coin$ to put the Pieces Back Together,.......Run what ya Got,+ Enjoy it.......... If it Ain't Enough,......Trade Up,........ Chances Are,...... You'll $pend More Hot Rodding the Hull you've got,....Than a Newer Big Faster Boat would Co$t......
    Any Grease is Better,..... Than No Grease at All.......

  18. #18
    Petty Officer 2nd Class
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    Default Re: 3.0 Mercruiser performance options

    I have played with porting head on my 3.0 and tried many of tricks I have had work on sbc in racing even found some total seal rings found I got a total of 3 mph faster for around 25 or 30 hrs worth of work and I do this stuff alot so these guys are telling you right go with stock or change boats just not enough there... I do limit my max rpms to 4800 too

  19. #19
    Seaman
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    Default Re: 3.0 Mercruiser performance options

    Scott Atwater What prop are U using? My best all around was a 3 blade 19P I've tried 4 blade 18P and lost a little top end, I want to find a 4 blade 20P to try.

  20. #20
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    Default Re: 3.0 Mercruiser performance options

    harveje, I have a 19' bayliner 2002 with the 3L 135hp. It has a 2:1 drive ratio and my oem prop is 14x21. I've tried a stilletto stainless 4-blade 14.25x20 on the boat and maybe loose 1 mph at top end, not really noticeable, but the holeshot is completely different. The prop has so much more bite that you can hear the engine really work in the mid range when the boat climbs out of the hole. It's sort of the opposite of what you want, because you're lacking low end torque with the 4 cylinder. You're better off having a 3-blade that'll slip more and allow the motor to rev higher. Not that I'm trying to talk you out of trying props, just don't go spending a couple hundred and get stuck with a prop you won't like. If you're running a 3-blade 19" prop and you're holeshot is so-so I can guarantee you a 4-blade 20" prop will be worse but you may be happier with mid-range performance.for the original topic, there's pitch-shifting props which have lower pitch at lower rpms for holeshotting and the pitch changes higher as rpms climb for top end speed. They're not cheap but may be a good solution to your problem.As for motor mods short of a v-6 or v-8, don't know what year you have but maybe upgrade to the newer style heads, find a custom set of heads, weber carb, look at thinner head gaskets if they're available, change over the valvetrain to roller fulcrums, modify your valve lift or have a custom cam made, pull the whole motor and do new pistons with new cam. And reducing weight in the boat is always a good idea.

  21. #21
    Master Chief Petty Officer
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    Default Re: 3.0 Mercruiser performance options

    For starters -- how often do you really go over 35 mph? If you are looking at more pulling power for a skier, maybe look into getting a lower pitch prop for when you are pulling people skiing, and a higher pitch prop for when you want to go faster...

  22. #22
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    Default Re: 3.0 Mercruiser performance options

    My future boat purchases will be basically based on this:15' to 16.5' 3.0L ok17' to 18' V6 4BBL18' to 22' 5.7 V8 4BBLOver 22' Big BlockThat way you arent always trying to squeeze every last HP out of the thing.When the thing gets older and has lost 5 or 10% of it's power, or you have one plug wire sorta going bad, or you didn't maybe buy the most awesome gasoline, or use the slipperiest synthetic oil... it'll still be fun.

  23. #23
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    Default Re: 3.0 Mercruiser performance options

    Thanks,I've tried ss and alum. 3 and 4 blade 17p,19p,21p and 23p the al 3 blade 19 is the best all around, the al 4 blade 18 is best for playing and pulling.

  24. #24
    Petty Officer 2nd Class
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    Default Re: 3.0 Mercruiser performance options

    Scott:The 3.0 liter GM engine is a fine powerplant for your application, and has the added advantage of much better fuel economy than any of the other engines mentioned, hystat's opinions notwithstanding (I think a V6 is called for on boats larger than 19.5 feet, dude! )If you want some more uummmph from your 3.0, check out this link: http://www.remanufactured.com/Inboar...ne_Engines.htm (1-800-575-6998)Dave Schaffner can hook you up with some added HP, to the tune of 165-180 hp (quoted), depending on the mods and carburetor. I'm sending him my engine for a reman/upgrade in June (fixed a long-standing problem with a sticky valve only to have the rod bearing on the adjacent cylinder disintegrate, and LOUDLY) .

  25. #25
    Seaman
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    Default Re: 3.0 Mercruiser performance options

    I agree with the fuel efficiency, I had a 79 cobalt 19.5' with a 305 and MAN it sucked the juice...We can cruise all weekend on a tank now with the 3.0

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