OMC 1988 5.7 advice

I have a 5.7 260hp OMC and cobra outdrive. The boat is an 88 bayliner 2655.
The motor is out and on a stand. Had a headgasket leaking water between 2nd and 3rd cylinder on the right side.

I would like to get a little more power out of this motor. Sending the heads out to be redone. Should I think about a performance cam while the engine is out and being gone over?

Is 300hp unrealistic with heads, cam, performance intake and carb? Any input appreciated!

Re: OMC 5.7 advice

You have to be very careful with the cam, you don;t want water reversion.

Hopefully Rick will come bye, the right pistons the right heads and the right carb you should get over 300hp. Will empty your wallet at least 2 grand if not more.

Is it worth the extra 40 hp ?

Your running what carb. ? Say it's a 2 barrel the the cheapest way to 20 hp is a 4 barrel.

My carb of choice is a quardra jet. To me the rochester is bullet proof.

Others will disagree with my choice but none will disagree say if set up right they stay setup right.

Re: OMC 5.7 advice

The boat is an 88 bayliner 2655.

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This is a great fat wallowing cow of a boat and just on the verge of being too big for a single Chevy 350. I don't think you will be seeing any great improvements in either hole shot or top end even if you were to get another 50 ponies from that lump. It's more a matter of hull shape than anything. Even with a big block engine you will have some degree of difficulty getting that thing up on plane. I would aim for reliability and fuel efficiency which means pretty much factory settings.
Maybe your next boat will have twins (not the bikini kind, but they help too) which will give you that manly boost you crave when you push the lever forward.

Your post begs the question of why you took the engine out to replace a head gasket?

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Thanks for the feeback.
I have a Quadrajet on it and will be keeping it with a rebuild kit. I am on the same page with the worth it question.. we just want it to run good and take the time now and get it right.
As for why I pulled the whole engine.. to have it rebuilt at a shop and take the boat home to work on the rest of it. I plan on keeping this boat for a while, it was less expensive to have the motor rebuilt than buy a new one. Also have the drive out for rebuild. I am restoring the boat, not much needed really but going over the entire boat. We dont really have any interest in anything bigger better newer dont really care much about the neighbors brands and so on, it is what it is and we like it.. it will be fine for my family boating needs. I would like to have it perform as well as can be expected. Getting on plane was my main concern as I know these to be slugs.. so I wanted to try to do something. I read that these modifications did wonders for other 2655 owners.

Re: OMC 5.7 advice

Welcome aboard !

I like the attitude you have. It's the same as the one i have.

It's a rare day i have more then my son and myself on the boat. Sometimes my friend and his son.But he has a boat and most day's he's on his boat with his son, and i'm on mine with my son.

We like to buddy up that way if something happens to one boat we have the other to tow us in.

Sometimes we have 5 friends with boats out the same day, we spread out on the bay looking for fish.

To get back to your boat. If your rebuilding completely then it's possible to get way more then 300 hp.

But will your drive handle the extra hp thats the question.

So heres what you have to go over with your rebuilder:

I would not overbore more then 30 thou.. What sorta pistons you will use. What cam he wants to use. Do not use a hv oil pump. Stock will do.

What heads?

You need a expierenced marine motor rebuilder who understands marine motors.

Good luck !

Re: OMC 5.7 advice

Ayuh,... The Best bang for the Buck is, Slap on a set of Vortec heads, 'n matching intake manifold...

Bigger Cams cause Problems...

Re: OMC 5.7 advice

Waterbender said:

Thanks for the feeback.
I have a Quadrajet on it and will be keeping it with a rebuild kit. I am on the same page with the worth it question.. we just want it to run good and take the time now and get it right.
As for why I pulled the whole engine.. to have it rebuilt at a shop and take the boat home to work on the rest of it. I plan on keeping this boat for a while, it was less expensive to have the motor rebuilt than buy a new one. Also have the drive out for rebuild. I am restoring the boat, not much needed really but going over the entire boat. We dont really have any interest in anything bigger better newer dont really care much about the neighbors brands and so on, it is what it is and we like it.. it will be fine for my family boating needs. I would like to have it perform as well as can be expected. Getting on plane was my main concern as I know these to be slugs.. so I wanted to try to do something. I read that these modifications did wonders for other 2655 owners.

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I mean no disrespect to you or your boat. As you know there are performance improvements that will get that hunk of arn up in the 600 hp range with some major modifications. Totally not in the picture of course. The other thing you should take a good look at is your prop. Like the tires on a car this is what gets the power to the pavement so to speak and having the wrong prop on there can make a slug even sluggier. When you get the thing back to the point that you can do sea trials then have a few props on hand to check whether a different one makes a difference. Once you get the propping tweaked, then start with the engine mods. Remember that marine engines are not like automotive engines. They must constantly push the boat "uphill" so the faster you go the harder it has to work. And the more gas it sucks down.

Re: OMC 5.7 advice

Waterbender said:

I would like to have it perform as well as can be expected. Getting on plane was my main concern as I know these to be slugs.. so I wanted to try to do something. I read that these modifications did wonders for other 2655 owners.

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I'm afraid that those mods alone will be dissappointing.
I think that o2batsea is being relalistic, rather than making a derogatory statment.
We sometimes need to hear what we don't want to hear.

Agree with o2batsea and Chief on this one.

Here's how I see it with the '88 SBC in that 2655 boat..... and it's multi-fold:
1... the OEM engine build....
2... 2655 the hull...
3... the single prop drive...

You could do extensive cylinder head work, and still not gain a tremendous amount of improvement due to the full dished piston choice that GM made. (shame on them).
Furthermore, you'd have to stay with the smaller 64cc chambers (of which is OK)

Agree with o2batsea re; the 2655 needing all the help it can get. I'm a BOC member, and this hull has been discussed many times.

Also, if you were to achieve 300 hp from this engine, you now place the Cobra at/near it's limits.... probably above it's limits.

Your best Bang-for-the-Buck on this particular hull, IMO...., will be the DP-S conversion.... hands down.... no questions about it!
Take what money that you'd be spending on over-hauling the obsolete single prop/dog clutch Cobra, and put it towards a good used 1.95:1 DP-S drive. Then purchase the conversion kit, and install it.
The DP-S will do more for this boat than a 377/383 will, while staying with the Single Prop Drive. There are a few BOC members who have done this, and with good results.

Engine:
If up for the task, and if an over-haul is eminent, then get as far from the full dished piston as you can.
This would also open up options for cylinder head chamber volume as well.
The cost to go with a Low Compression Q/E (quench effect), D-dished, or Reverse Dome piston will not break the bank. Shoot for a good deck height, and use the correct head gaskets that will render an approximate .038" quench.
There are no other major changes that are required. The piston selection will be the most difficult task.
Any good piston supplier can help with the piston selection, once the cylinder head chamber volume has been choosen.

In order take the best advantage of the 64cc chamber Vortec cylinder heads, these too need the correct pistons underneath them.
Not the full dished pistons!


My only other advice would be to use caution when taking suggestions/advice from the Automotive type guys when building a Marine version of the SBC.
The differences are subtle, but none-the-less, are very important..... the Q/E being one of them in my book!
It serves us best when these machinists/engine builders also have first hand experience at owning/operating their own Cruiser Style boats...... if not presently, at least a fair amount of past experience. These are the guys that you want.
Or...... you educate yourself, and have your engine built to suit!

Auto/Marine = Apples/Oranges!

Edit:
If your shop does not understand that the full dished piston is a poor choice for a SBC Marine engine, nor understand how to achieve the Q/E, yet offer the correct C/R with a given cylinder head volume......, then they may not be the right shop for you.

Your local library can bring in Dennis Moore's "SBC Marine Performance" book. I'd suggest that you do this.
Dennis offers invaluable information pertaining to a more correct SBC Marine build.... including piston selections, cam profile information, and some cylinder head casting #'s to steer clear of.

Re: OMC 5.7 advice

See why i said if Rick stops bye he can explain it better then i ever could.

Some guys have a knack for words don;t they.

Really what i would do if you enjoy this boat , and there is no reason you should not, then put the motor back together, and just go boating.

Down the road if your needs change, then sell it and get the package you want.

My 19 footer was enough for me all day of fishing and running i burnt 8-10 gallons.

But now i feel the itch for a twin motor boat, i want to fish the canyons of NY. I will not trust just one motor, nope a twin motor boat for me.

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o2batsea you know you mean no desrespect but seams like you always have something to say bad about people just wanting to ask advice about their probles with their boats.....What kinda piece of **** you own? I think you should clean up your own back yard before you condemn and knock other peoples boats!oh yeah your just kidding I forgot! well you could not afford a boat like mine and probly a lot of others here so if you truly want to give people some help and advice do so plzzzzzzzzz.........and dont condemn what they own, you seem to be know alot about boats ! so why dont you stay with that and keep your smartass attitude to yourself.......

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Them Texas boy's can get nasty. I know my brother lives there 40 years, as i did for over 7 years.

Wait Wisconsin, boy's can get nasty. I never lived there but it's g-ds country.

I am trying to diffuse a situation that i just went thru on a different site.

Please , please, please, did i say please ?

Let it stop right here, please !

Re: OMC 5.7 advice

Thanks kewl I just dont like a wanta be thinking hes all that! It piss"s me off with the comments I have see him leave including to one of my supid questions! But thats what we all are here for is to learn from one another and not to have what we own knocked down! yes I agree on honest advice but not with the lilttle bit added in.That is uncalled for and he knows it! Hes not all that! maybe hes got a self complex? are was picked on as a child and fells like he can be a bully and make other people feel like ****. and no I am not taking this out of context! I am reading it like it is Thanks

Re: OMC 5.7 advice

Whoah there Texas60........
Your comments not only show some signs of taking things out of context, but of bringing an "old bone" into a thread that's not even yours! Why not simply ignore comments that do not pertain to you or your boat?
While o2batsea's delivery may have not been finely polished, he was referencing Waterbender's boat......... Not your boat!
In fact, it had nothing to do with YOU!
Fair nuff?

Basically, you've needlessly interrupted Waterbenders's thread!

(take it OFF Forum!)


.

Re: OMC 5.7 advice

ok fair enuff! I relize hes your buddy and I was just looking throu the threats for information and I relize its not my threat but I just have gotten tired of seeing just about every time I see a comment by him it at first puts down ther boat! thats not right and Rick if you dont Like me commenting on your buddie just get ahold of the moderator and get me booted off! Hes wrong and you know it I just apolize that I spoke up about his rude comments! If you dont like it do what I said get me booted! Actaually you are invaded a threat! think about it,by protecting your lil buddie! this is the last Time I will respond to this, I can see it wont do me no good to voice my opinion on him I guess he will get away will demeaning other peoples boats you go Rick join him

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o2batsea and I are not buddies, per se'. We have not spoken, nor have we exchanged any emails over the years.
Nor am I demeaning to others or other people's boats...... truthful....YES!

And what "Threat" could you possibly be speaking of? Do you mean "thread", as in this thread of postings?

BTW..... You're always welcome to voice your opinion, as are any of us!
Just keep it on topic, related to YOU (if threatening or demeaning), and ignore that which does not pertain to you.

Re: OMC 5.7 advice

sorry I meant" Tread" or post Rick my mistake for typying so fast but just pissed off

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YIKES! Its all cool.. Ricardo, I am on BOC.. Have a current thread in the projects area. Anyway, thank you for the advice! I think you helped a friend of mine last year on BOC who was getting a 2550 into the water from a long time sitting. I will take what you wrote to the mechanic doing the work for me. Thank you for taking the time to explain this. I think I need to make a decision to either go for this or just rebuild to stock. My wallet is saying stock however. The results of the investment are looking like something that may not warrant my financial investment. So.. I am going to think it over.
The guys that work on my boat are good at what they do, I have confidence in them, they have actually said much of what I am reading here.

o2batsea its all good, No offense taken.. I have heard it a thousand times if not more about my boat and bayliners in general, being that this is my third bayliner, but I will say, I would be hard pressed to buy anything else.. especially the way the economy is now and has been. I have had very little problems with my boats. I take care to see that they are maintained and that seems to help. I have full confidence I will not take a bath on a Bayliner if I "have" to sell it as the investment was never too much to begin with. I am the same with cars and trucks.. I love those nice shiny ones.. but, I never lost money on a mid 90s f-150 and the one I currently own doesnt owe me a dime

Chiefalen, thanks for your input as well.. it sounds like we see eye to eye on much I can take the heat from this.. I realise I am not very knowledgeable about these things and sorta knew I might catch some noob heat.. but this is not what I do.. now ask me about shoeing horses, different story.. lol.

Texas- its all good like I said but thanks for stepping up.

So- You know it was coming.. what prop should I get for this? I have read on another forum.. stainless 15x15 and the shop guys told me same thing... This is a purchase I will be making asap. soon as I know what to get for sure.

Re: OMC 5.7 advice

Hey....., You are very welcome.

NOTE: whether building to OEM specs, or id donig a Q/E SBC, does not mean spending much more money..... I just want to be clear on that for you.
The gain is well worth it!
Like said, this involves a piston selection change ONLY.
While we can make additional changes, nothing else absolutely needs to be done or changed....., other than taking advantage of the Q/E by using the correct deck height and head gaskets.... of which must be done anyway.
(no one puts an engine together without checking deck height)

Read up on Quench Effect to better understand what this means.
Here is a great article on "Quench Effect" by Jeff Smith. (lots more if you were to search this topic)
Jeff speaks primarily of automotive.... and I'll be the first to suggest that we NOT use Automotive build info when building a Marine SBC!
However, this is one area that nicely crosses over into SBC Marine.
One difference being that for Marine, we can close the Quench down to approximately .038", due to the lower operating RPM.
Other than that, Jeff's info is worth reading.
See Dennis Moore's book also. Well worth the read!

BTW, the 5.7L engine can use a single valve relief F/T pistons, when used with the 76cc chamber heads.
This gives us the Q/E (or "squish"), yet maintains the correct C/R for Marine use.


Something like this Low Compression Quench piston, or a "D" dished piston, can be used with the smaller 64cc chamber heads.... of which you likely have.
Again, the C/R remains correct for Marine use, as long as the correct piston p/n is used.
(i.e., dish volume. The smaller chambers require that the dish volume control C/R)


With any Quench Effect combustion chamber, C/R can be increased some, yet with little to no affect re; Detonation potential..... of which is what we're combating in the first place.
The Full Dish piston w/ ZERO quench, offers very little resistance to Detonation.
Quite frankly, it's the worst piston that could be used in a SBC Marine Engine!


As for Bayliner..... this is not a typical Bayliner issue. It just seems to be more so with that particular model, and a few others only. Otherwise, it's a non-issue .... no more/no less than with other boats!

As for the word "Investment" and "Boat" being used in the same sentence.... Hah!
Boats are rarely investments, and are almost always expenses only.
We just use it up in the form of enjoyment as we watch the smiles on our children's faces.... (if you have kids!)
If you were to look up Boats as an Investment, and search the words "Financially Up-Side Down".... you'd see a cartoon with a picture of me and my old restored 2850 SDN F/B boat..... LOL!
But I knew this going in.... I don't mind it one bit!

As for Prop selection:
You won't be able to correctly prop this, until you have all your ducks in a row. I.E., engine in full tune, hull clean, drive ratio correct, etc.
(you may want to pitch down for your break-in duration!)
Then you must perform a WOT RPM test, just as you would with any boat. Stay within your OEM WOT RPM specs, and you'll have the correct prop pitch.
(you are limited to diameter with the Cobra drive.)
I would find a prop shop that will allow you to test several props.
Anything else is a crap shoot that may damage your engine by over-burdening it.


Keep us updated!

.

Re: OMC 5.7 advice

I'll tell you the standard procedures for testing props and you can go from there.
The quick and dirty rule of thumb get-you-in-the-ballpark method is to look in the owners manual and see what the wide open throttle (WOT) engine speed is supposed to be. Then you go sea trial the boat and firewall the throttle and see what the rpms are. If the prop that is on the boat is getting you within a few hundred rpms then you are golden and you can go spend that money on tanning oil for when you are hosting the Swedish Bikini Testing Team. If the RPMs are too high then you need to go with more pitch. One step for every 500 rpms. Too Low then you need less pitch. My personal feeling is to fit the largest diameter prop. If you can stuff a 15 in there, do it. Others may disagree with this, which points out that prop science is less science than it is black art. You can get into all kinds of discussion about cupping, blade shape, three four five or six blades, aluminum or stainless, blah blah blah.
There is another method that involves testing over a measured mile and stopwatches and all kinds of bother, but this is probably too much hassle for your average weekender.

Re: OMC 5.7 advice

If I may, I'll add to Mr. Trouble Maker's comments! (BTW, o2batsea.... dinner tonight? 7:00 PM? our house?)

He'll be breaking in a fresh rebuild, correct?
If we're going to error, we need to error on the side of being "Under-Pitched" for this break-in duration. The very last thing we need, is a prop that is too aggressive for break-in!
From there.... we do as suggested, but we make certain that the boat is loaded as we would normally intend to load it.
If not, all bets are off, and the selected propeller may not be correct for when more heavily loaded.

He may find that he needs two props........ cruising -vs- tubing/skiing, etc.

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Yes of course I was describing general practice and not speaking directly to Waterbender's specific case. If he's like me he's got a whole prop 'effin LIBRARY on the shelf to work with. I am always buying bargains and haven't yet seemed to figure out that I can only use one on my boat at any given moment, but that's another story. Anyway, you won't get any arguments from me that you need more than one prop. If for no other reason that you can always foul your prop while under way and find you need to put on your spare. We have nothing but mud here in the Chesapeake but almost 500 years of people chucking garbage in it as well as oyster beds. Seems that hitting bottom will always get you some dings or dents regardless of the mud. Having a spare is a must.

If I may, I'll add to Mr. Trouble Maker's comments! (BTW, o2batsea.... dinner tonight? 7:00 PM? our house?)

Click to expand...

I love Portland, too bad there's all this dirt in the way or I'd be right over.

Re: OMC 5.7 advice

I too recommend talking to the shop and tell them you need to try 3-4 props.

You must never go over wot. So if you reach wot and you still have throttle lest then you have to little pitch. I think the golden rule is 200 rpm for ever change in 2 degree pitch.

My gut feeling is 15 pitch is a good starting point.

Re: OMC 5.7 advice

Prop Pitch is measured in inches.
Theoretically, and minus slip, a 19" pitch propeller slices and moves it's way through 19" of jello in one full revolution.
Add marsh mellows if you want to!

chiefalen said:

..........

1. You must never go over wot.
2. So if you reach wot and you still have throttle lest then you have to little pitch.
3. I think the golden rule is 200 rpm for ever change in 2 degree pitch.

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1. I think this needs a little clarification. WOT RPM is a TEST RPM ONLY, and should never be a sustained rpm, no mater what we're doing. Test ONLY to see if we're propped, geared and tuned correctly, hull clean, etc. Nothing says that we can't run a prop that takes us over WOT RPM, as long as we do not run within, or sustain, this high rpm. Skiing/Tubing, for example: When not towing a skier/tuber, there's nothing wrong with cruising at well bellow WOT RPM. In fact, we should be somewhat under-propped during a portion of new engine break-in, IMO.
2. Agreed!
3. Chief, that may be close. Some will suggest as much as a 400 rpm change. Some also depends on prop diameter (such as the smaller Cobra props), also rake and cup. Chief, I'm no expert at taking a stab at which prop should be used. I'd seek out a starting point, and just test for WOT RPM as anyone would.

Regarding #1 :
We DO NOT want to run at even the lower RPM range, if WOT RPM cannot be achieved due to being over-propped.



If you want a real brain tickler....., try to figure out Volvo Penta's Duo Props.
There is no pitch mentioned, just a code. And each prop is different in both diameter and pitch.

Re: OMC 5.7 advice

I have an 89 donzi with 5.7 liter it has overheated and no the starter won't turn the engine over what next?

Wow talk about reviving a 6 year old thread!
If you overheated it and it won't turn that is very very bad. You probably spun a bearing or something. Likely fix is a new long block.