Mercruiser 3.7 Questions

[devisetek]

I just bought a 1989 Glassmaster S187 Bowrider. It is a 1900 lb boat with the 165 3.7 Inline 4. The boat seems to run out pretty well top end, but only gets up to about 40 MPH with my and my GF trimmed out.... It seems that this motor and my boat would run out a litter higher top end, I was thinking high 40s. The motor also sometimes doesn't idle perfect. I was thinking adjusting the idle a bit would be a temporary fix, but overall maybe cleaning the carb and changing plugs and wires would be good as well.<br /><br />What spark plugs would be best, and can I get them at Autozone, Advance, Pep Boys, etc? What part number do I give them?<br /><br />Where can I get plug wires?<br /><br />For a boat like mine, what pitch prop should I use? Any other suggestions? Hydrofoil?<br /><br />Its fun so far, but I am looking for a little more top it. Its fast enough out of the hole for me, at least 0-20 which is fast enough to pull up a skiier. <br /><br />One more thing, is it possible my speedo is just off?<br /><br />Oh yeah, and would putting on the 4BBL from the 180/190 HP version kill my gas mileage, is it hard, and are the HP/MPH gains worth it? Where can I find one? <br /><br />Thanks all, Im 20, and just bought my first boat!

 

[Bob_VT]

Re: Mercruiser 3.7 Questions

Welcome to iboats.<br /><br />Well that motor is running right and your top end is on the money. Changing over to a 4bbl will not give you much more speed but will hit your wallet pretty hard.<br /><br />The prop that is on it is probably fine as long as you are getting adaquate RPM's at WOT.<br /><br />The true diagnosis is... You have "two foot fever" wanting more speed.<br /><br />Remove one of the exsisting plugs and match it at any NAPA, Autozone etc. NAPA also has a good supply of marine parts...caps wires, plugs.<br /><br />The primary BEST investment you can make before you spend another nickle is on a Mercruiser Manual for your motor.<br /><br />Bob

 

[Northern Eclipse]

Re: Mercruiser 3.7 Questions

If the motor is turning within the top rpm range 4200-4600 rpm at WOT then its running right and the prop is correct, as far as a bit of rough idle, its a bit normal for that big 4 hole motor, Timming for that motor as been TSB'd by merc to be at 4* not 8* as stated on the valve cover label. The 4bbl would be up to you, fuel consumption may or may not increase depends on the boat and how you operate it.

 

[KaGee]

Re: Mercruiser 3.7 Questions

"with my and my GF trimmed out.... "

If your Girl Friend is already trimmed out, the only way to get more speed would be to throw her overboard.... <br /><br />Sorry, couldn't resist <br /><br />Got any pictures of her??

 

[QC]

Re: Mercruiser 3.7 Questions

Originally posted by KaGee:<br /> Got any pictures of her??

Fully trimmed, right? Sorry, I also couldn't help it

 

[devisetek]

Re: Mercruiser 3.7 Questions

<br /><br />Thats her<br /><br />And I am actually able to rev higher, like 5100 if Ill let it (which I dont)<br /><br />Does this mean I should go with a larger pitch prop? I have a 19 right now. 21, 23?

 

[Dunaruna]

Re: Mercruiser 3.7 Questions

The pitch and cupping look perfect

 

[tommays]

Re: Mercruiser 3.7 Questions

i would treat it like my grandma <br /><br /> old but still going and will for a long time if i dont expect miracles<br /><br />if you speedo was correct it would be rare GPS is usally the only thing thats on the money<br /><br />anything you do with the prop for top end is going to kill you skier pulling abilty unless you like draging them underwater for a long time<br /><br />tommays

 

[QC]

Re: Mercruiser 3.7 Questions

Originally posted by tommays:<br /> i would treat it like my grandma

For some reason that post and this thread are not meant for each other.

 

[KaGee]

Re: Mercruiser 3.7 Questions

Originally posted by Quietcat:<br />

Originally posted by tommays:<br /> i would treat it like my grandma

For some reason that post and this thread are not meant for each other.

The boat or the girlfriend??<br /><br />

 

[QC]

Re: Mercruiser 3.7 Questions

Well, if you have to ask . . .<br /><br />I am not treating his girlfriend OR my boat like tommy's grandma.

 

[devisetek]

Re: Mercruiser 3.7 Questions

Come on, more positive suggestions plz

 

[Dunaruna]

Re: Mercruiser 3.7 Questions

What is the maximum WOT for the 3.7? 2" increase in pitch will reduce WOT by about 400rpm, 2" decrease in pitch will increase WOT by about 400rpm. You need to know what your WOT RPM is now and what it should be - then decide on the prop.<br /><br />There ain't no substitute for cubic inches, a 3.7 will only ever do what it will do, you can spend thousands trying to squeeze 10 or 20 HP out of the little 4 banger.<br /><br />Speedos are often no accurate, a GPS will tell the truth. A foil may improve your holeshot but it will probably decrease your top end speed.<br /><br />Tune it right, prop it right, All you can do.<br /><br />Aldo

 

[devisetek]

Re: Mercruiser 3.7 Questions

Well, It seems that it can drop a few on the RPMs to get some more speed... How much is GPS and where can I find one?<br /><br />And It may be a candidate for a 5.0, 350, or even a 4.3 over the winter

 

[Bob_VT]

Re: Mercruiser 3.7 Questions

Continue to "cut your teeth" on this being your first boat...it's a learning process.<br /><br />Keep the RPM's to 4600 MAX or the engine will not last. You can re-prop but you might loose the pulling power in the bottom end.<br /><br />Borrow a GPS to check your speed I know quite a few people have them now.<br /><br />As for being a candidate for re-power??? Do your homework and you might find getting a differant boat cheaper and far less work.<br /><br />Good luck<br /><br />Bob

 

[rbarnesjr@nc.rr.com]

Re: Mercruiser 3.7 Questions

If your Girl Friend is already trimmed out, the only way to get more speed would be to throw her overboard....

Only perform this action if my boat is next to yours. <br /><br />On a serious note these guys know what they are talking about 4600 is the absolute MAX for a 3.7(470) if you want to get your moneys worth out of it. These "little" engines are suprisingly durable and reliable once the charging and cooling mistakes made by Mercruiser are corrected. I know several people that swear by the engines but I also know some the swear just by hearing them mentioned. If this is your first boat my recommendation is to make sure it's tuned up and you and your girlfriend enjoy. If you are only 20 you'll have plenty of time for speed. Boats are far different that cars in the way they drive. The biggest thing to remember is that if you swerve with a car you run in the ditch...with a boat you are already there.

 

[MrBill]

Re: Mercruiser 3.7 Questions

I've tried a 21 inch pitch with my 3.7L. It adds greatly to the top end, but reduces the hole shot a lot, a real lot. The real issue is the low (1.84:1) Aplpha gear ratio. Be happ y with 40 MPH, don't waste money on the 4 barrel...you'll need a new manifold and won't notice the extra 10 HP. You'd be wiser to invest in electronic ignition ($100) or conversion charging system ($375).

 

[captian Ozone]

Re: Mercruiser 3.7 Questions

I bought a used 4 bl with the manifold and did a swap out. One can only assume the oil cooler that was part of the arrangement also helps longevity. It idles better and gets better cruising and trolling and slightly better hole shots using the two smaller primarys. Much better operation in extended running in no wake zones @1000 to 1500 rpm
However anything over 4000 accellerating and 4200 cruising and those huge secondarys start opening on just a 224 cid motor. It sounds cool when vaccum gets to the point the 4bl opens. It makes this low pitch air sucking sound. It adds 200 rpm to the wot so if max cruise speed is 300 prm less than if you like to go fast one would assume the new 4 bl cruise point is just 100 rpm under the 2 barrel wot point and now you have added an oil cooler).
Overall I was happy but I got the items reasonable. My boat will plane at 3600 when it is pretty calm so I normally keep the secondarys closed. I suppose if you want to operate flat out it will cost you more but I figgure I came out ahead.

 

[thuff]

Re: Mercruiser 3.7 Questions

Where can I get one of these electronic ignition ($100) or conversion charging system ($375)? Are there ample instructions for converting from the old system?