Engine swap. 305 to 400 sbc

[v8fieromatt]

Hey guys,

I'm new to this forum and to boating in general, I'm an auto mechanic by trade. What i do know is engines.

So what I've done is bought an 88' bayliner capri that measures right at 18 feet. The 260hp 305 chevy block is cracked from being stored though the winter with water in it. I pretty much hate 305s anyway and I didn't really want to do the average swap of just putting a 350 in it.

I just happen to have most of the parts laying around to make a bad SBC 400.

So my questions go like this. Can the OMC drive handle 425 lb/ft of torque and 325hhp? Will the boat be controlable? What about the flywheel? Can I use a stock 400 counterbalanced one in the boat? If not would a balance plate such as this one work with the stock one?

http://cgi.ebay.com/ebaymotors/ws/e...RK:MEWA:IT&viewitem=&item=180138403422&rd=1,1


Is there anything I should change while I have the motor out? Is there anything else I should know or consider before starting this engine swap?

Thanks a lot!

-Matt

P.S. How fast do you guys think my boat will go when I get it done?

 

[MikDee]

Re: Engine swap. 305 to 400 sbc

You do know that marine engines have different componets then an auto engine right? Such as brass freeze out plugs in the heads, & block, and stainless head gaskets, maybe even a brass, or non-corrosive oil pan, front timing cover, and valve covers. Plus the water pump has a stainless steel backplate (expensive puppy! bolt on, and use your old one) plus the starter, & alternator, are sealed, so as no spark can escape to cause an explosion. Also, an aluminum intake will self destruct quickly in salt water. You maybe able to use a lot of the "marine" parts off your old motor. These boats usually use a bonded rubber coupling as part of the flywheel, with a splined socket that the spline on the outdrive slips into (in place of a clutch or tranny). There maybe more that I can't think of right now, but proceed carefully.

That boat in stock form sounds like a 55mph boat, how fast do you want to go? a 350 will probably take you to 65mph, a 400,,, who knows? I'd be concerned about the hull, and it's components not being able to take the pounding abuse also. By the way, usually these motors are designed mostly for torque, and are never over revved, but fixed to run, & deliver their maximum power between 4200-4600rpm, using the prop as the final gearing to attain that. The more pitch, the less prop RPM, the prop will make, and vice versa, for less pitch. Good Luck, Mike

 

[v8fieromatt]

Re: Engine swap. 305 to 400 sbc

Thanks for the info!

Ok, so I was planning on using most of the marine parts off my current 305. I didn't know about the oil pan and valvecovers being special so I'll go ahead and swap the tin off this motor as well.

I was planning on having the engine make peak power at 4500 and getting a prop to match. I was going to use a com cams marine 262H extreme. .462 .477 lift. 262/268 duration.

It should have over 400 lbs/ft of torque from 2000-4000. I was planning on using an alumminum intake, but I only run in freshwater so will that be an issue?

The engine I'm building should be able to spin at 5000 all day long, but one guy told me that my outdrive shouldn't spin at over 4600 for any period of time, is that true?

How fast is too fast for this hull?

Thanks again,

Matt

 

[gcboat]

Re: Engine swap. 305 to 400 sbc

Your OMC drive might handle that amount of torque and horsepower if you don't pull skiers or go tubing. I'm replacing a tired ole' 5.7 with a 383 stroker and was told on numerous occasions not to do anything stupid like I mentioned. So, I'm going to replace with a VP duoprop - bulletproof stuff. It will make your piggybank empty in a hurry but well worth every penny (s).
As far as hull speed is concerned that is an issue that would probably be debated over many pages. Every manufacturer matches engines, h.p. to a certain hull for maximun efficiency and speed, but who's to say the envelope can't be pushed a little? It will definately handle differently, will want to wander to port a lot and may run with that pesky port rubrail in the water. Too many unknown variables for me to even entertain a guess as to the outcome. Another factor is hull strength, stringer strength, transom condition, etc. That boat better be in tip top shape for that much power. Adding additional strength to all of your critical areas would not hurt either. Just overwhelming to me.

 

[MikDee]

Re: Engine swap. 305 to 400 sbc

Thanks for the info!

Ok, so I was planning on using most of the marine parts off my current 305. I didn't know about the oil pan and valvecovers being special so I'll go ahead and swap the tin off this motor as well.

Probably a safe bet

I was planning on having the engine make peak power at 4500 and getting a prop to match. I was going to use a com cams marine 262H extreme. .462 .477 lift. 262/268 duration.

Ok, if you've got the money for fuel

It should have over 400 lbs/ft of torque from 2000-4000. I was planning on using an alumminum intake, but I only run in freshwater so will that be an issue?

Don't know how the OMC is gonna hold up to that? A king Cobra drive may handle it ok, Freshwater, the manifold you're probably fine

The engine I'm building should be able to spin at 5000 all day long, but one guy told me that my outdrive shouldn't spin at over 4600 for any period of time, is that true?

My Mercruisers I've run 5k RPM all day, no prob,,, some of the Mercruiser racing engines are made to run that high, and more to get the full power of the engine (checkout their website for comparible engine specs)

How fast is too fast for this hull?

I'm no expert, I think you'll know it when you get there. One boat I had was a 79'- 20' SeaRay bowrider, with a 228hp 305, no bottom paint, and thru hull exhausts, it would kiss 50mph when trimmed out, and it was a heavier boat with less horsepower then your bayliner, but it was strong, it could have handled a 350motor easy, but it did get a bit skittish ran this way, because of the hull design being bigger in the middle with a deep vee there, and having a small rather shallow vee at the back end.

Thanks again,

Matt

 

[John_S]

Re: Engine swap. 305 to 400 sbc

Unless your 305 was replaced with a new fuel injected pkg or was heavily modified, it was not 260hp. A stock 305 of that vintage would only be about 190-205HP. If it was upgraded to a carbed vortec, about 220-240HP. The point being you would make some gains with just a 350. I wouldn't bother with a 400. If you just have to do it, a 383 stroker. Heed the drive warnings given by others though.

Guessing you have the older 305, boat probably does mid to high 40's with light load. Maybe touches 50. A 350 vortec would probably get into the solid 50's. At high speed you will probably start to see some porpusing and handling problems. A set of smart tabs helped for me, in this area.

Now, before spending anything on the engine, I would examine the floor and transom very carefully. Capri's are noted for having floor/stringer/transom rot if not cared for. And given the frozen block, I'd be leaning toward the not cared for. If you find issues there, consider ditching/ebaying the boat or parts, unless you are looking for a good 1+ year project. Nothing wrong with a project. but can get fustrating to a new boater/first boat.

 

[MikDee]

Re: Engine swap. 305 to 400 sbc

Hey imported John S, Did you read this:

"I'm no expert, I think you'll know it when you get there. One boat I had was a 79'- 20' SeaRay bowrider, with a 228hp 305, no bottom paint, and thru hull exhausts, it would kiss 50mph when trimmed out, and it was a heavier boat with less horsepower then your bayliner, but it was strong, it could have handled a 350motor easy, but it did get a bit skittish ran this way, because of the hull design being bigger in the middle with a deep vee there, and having a small rather shallow vee at the back end."

Back in 79' The 305 2bbl was 198hp, 4bbl was 228hp, and the 350 4bbl was 260hp,,, and my boat did 45-50 regularly, neither engine had the vortec heads back then.
By the way, The 4.3 V6 was rated 190hp with a 2bbl, and 205hp with a 4bbl, not the 305, I just sold a 1986 22' Celebrity Cuddy SS with twin - 205hp V6 OMC Cobra's in it, so I know.

 

[John_S]

Re: Engine swap. 305 to 400 sbc

MikDe,

The Standard head 2brl: 190HP and Standard head 4brl: 205HP I had checked in the Merc Service manual for another post. I figured they would be close enough for this discussion. Basicly same engine, different drive. The 70's numbers you have quoted are inflated because back then, rated at crankshaft and not prop. My main point was that current 305 HP (260)ratings are significantly different and he should recheck what he actually has.

As far as hull comparison, the Searay you described, sounds significantly differnent than a Capri hull. My assessment was based on reviewing the NADA guide for that year, and because no 18' models, assumed a 1900BR. They do not specify deadrise only beam. My experience with Capris, there are two main hull configurations. One that has a narrower beam and larger deadrise and the other wider and less deadrise, per model length. The latter is a faster hull. I believe he has the former, though.

Both of our speed calculations are guesses and comparisons to what each of us has experienced. In my case a 20' Capri (narrower beam/larger deadrise version) with 5.7. He will probably be somewhere in that ballpark we both have given. Now, if you are incorrect, he will be disappointed. If I'm wrong, he will probably be estatic!

 

[MikDee]

Re: Engine swap. 305 to 400 sbc

MikDe,

The Standard head 2brl: 190HP and Standard head 4brl: 205HP I had checked in the Merc Service manual for another post. I figured they would be close enough for this discussion. Basicly same engine, different drive. The 70's numbers you have quoted are inflated because back then, rated at crankshaft and not prop. My main point was that current 305 HP (260)ratings are significantly different and he should recheck what he actually has.

As far as hull comparison, the Searay you described, sounds significantly differnent than a Capri hull. My assessment was based on reviewing the NADA guide for that year, and because no 18' models, assumed a 1900BR. They do not specify deadrise only beam. My experience with Capris, there are two main hull configurations. One that has a narrower beam and larger deadrise and the other wider and less deadrise, per model length. The latter is a faster hull. I believe he has the former, though.

Both of our speed calculations are guesses and comparisons to what each of us has experienced. In my case a 20' Capri (narrower beam/larger deadrise version) with 5.7. He will probably be somewhere in that ballpark we both have given. Now, if you are incorrect, he will be disappointed. If I'm wrong, he will probably be estatic!

You mean the 4.3 motor was 190 hp with a 2bbl, and 205hp with a 4bbl. The 305 was 198hp-2bbl, and 228hp-4bbl. Irregardless of shaft, or prop horsepower, that's what was labeled on them, I know because I had these motors, and my speed calc. are actually what I got, not guessed, but then again, on my SeaRay I also richened out the carb mixture screws, ran synthetic blend oil, installed thru the hull exhaust, and had no bottom paint (a former lake boat).

So tell me then, I am curious, what kind of hull is on my 89'-19' Bayliner Capri Ski boat?

 

[John_S]

Re: Engine swap. 305 to 400 sbc

"You mean the 4.3 motor was 190 hp with a 2bbl, and 205hp with a 4bbl. "

No, my service manual is only for 5.0 and 5.7 mercruisers. While merc manuals are specified by serial number, it generally covers '87-'97 305 and 350s. It has no information on 4.3L. I will recheck tonight to make sure I did not misread/mistype.


"The 305 was 198hp-2bbl, and 228hp-4bbl. Irregardless of shaft, or prop horsepower, that's what was labeled on them, "

Yes, when mfgs rated thier engines at the crankshaft they labeled them accordingly. I forgot which year mfgs changed but it was around mid-80's. Do a search, it effected all marine powerboats, including outboards. My point is, there wasn't any real differnce in output, just labels and ratings.


"I know because I had these motors, and my speed calc. are actually what I got, not guessed, but then again, on my SeaRay "

Yes, what I meant was we both did that, but we are only guessing on how it would work with "his" hull. Neither of us own the exact hull with the same power package.

 

[John_S]

Re: Engine swap. 305 to 400 sbc

Mercruiser Service Manual #17, Book 1, Chap 1, Page 1B-7

MCM 5.0L Alpha 2brl carb: 190HP, 141KW

MCM 5.0LX Alpha 4brl carb: 205HP, 152KW

Propshaft rating: Power rated in accordance with National Marine Mfg Assoc rating procedures

 

[MikDee]

Re: Engine swap. 305 to 400 sbc

Really? and what year is this referring to? because the engine specs I gave you from 1979 must have been for previous years to this, as at the time I don't believe there was even an Alpha drive yet.

 

[John_S]

Re: Engine swap. 305 to 400 sbc

" and what year is this referring to? "

The answer is already in the posts above.

Doesn't matter what drive, they haven't invented the zero loss drive yet.


BTW: I wouldn't mind seeing your analysis on how to gain 10 mph (55 to 65) between the 5.0 and 5.7, especially since he reported having 260hp to start with. A 40HP gain to 10mph would be incredible for any hull.

 

[MikDee]

Re: Engine swap. 305 to 400 sbc

Guessing you have the older 305, boat probably does mid to high 40's with light load. Maybe touches 50. A 350 vortec would probably get into the solid 50's. At high speed you will probably start to see some porpusing and handling problems. A set of smart tabs helped for me, in this area.

I got 50mph out of my 79' SeaRay 20', which is about 500-1000lbs heavier then this Bayliner, I would say his could do 55, at least I could probably get it to! Then a worked 350 pushing it to 65, is not really out of the question!

And I'm talking apples, and you're talking oranges, the early hp ratings on the 305 are what I said, and no, it wasn't propshaft hp, and it used a type 3, or 4, outdrive, not an Alpha which was better, newer, smaller, & lighter.

 

[FORMULA FAST]

Re: Engine swap. 305 to 400 sbc

Hey guys I'm kinda new to the boating thing aswell. I have lots of engine knowlage but manely with GM muscle cars. I have a 1980 20' formula thunder bird that I have been up grading. I did a hull nuber trace and found it used to have a 454 360 hp big block in it. When i purchased the boat three yrs ago it had a 1978 mercruiser 305 ingine in it with 198hp 2bl carb. I put a 4brl on it,through hull exaust and ran it one full season. the boat has the narrow beem and it weighs 3,400 lbs
On a light chop day and a tail wind of about 5mph it would run 50mph on a gps trimmed out with 1/4 tank of fuel and light a light load. I blew up the 305 this summer by playing with differant props and over reved the engine.(I hate the 305 engine also!)
I too am installing a new engine I went with a 375hp LT1 350 vortec engine and have found out the hard way that some of the things form the 78 305 won't work. The flywheel starter engine coupler combonation seems to my problem!!
The guy that started this post asked if the 400 sbc needed the 400 flywheel and the answer to that question is YES!! It needs to be a exteraly ballanced standard stick shift flywheel and not a flex plate. The engine I bought is a vortec engine and takes a exteraly ballanced flywheel much like the one a 400 sbc takes which i'm having a great deal of trouble being able to locate. The standard votec sbc flywheel is for an exteraly ballanced crank but I can't seem to find anyone who knows what to use. I do know the marine flywheel seems to be the same as a chevy truck. I bought a vortec sbc flywheel but my bellhousing won't fit. I'm told the truck flywheel is the corect one but my new engine coupler that I bought for the vortec engine won't fit it and neither will my starter. (which is the 305 marine starter)The 305 uses a 12" dia flywheel and the chevy truck is a 14" flywheel so any ideas here?

Formula told me my boat has a hull speed rating of 75mph and it should be able to reach that with no problem if I can get this engine to work. It is going to run a rpm range of 4,500 to 5,000 max and I do know you have to have a really good engine oil cooler and a deep sump oil pan to run a long time at that rpm!!
By the way up here in Traverse City MI we have a groupe of guys that put monster engines in little boats like the bayliner and others with a silly amount of hp
I saw a 19' bayliner last summer on torch lake that had a 1,200 hp 640cubic inch mountain motor with a blower and n.o.s. and it would run 100mph+!! on gps which is insane!!

 

[Rob454]

Re: Engine swap. 305 to 400 sbc

I put a 4brl on it,through hull exaust and ran it one full season. the boat has the narrow beem and it weighs 3,400 lbs
On a light chop day and a tail wind of about 5mph it would run 50mph on a gps trimmed out with 1/4 tank of fuel and light a light load. I!

You have a hull made for speed. If its a fast hull it wont require as much HP to get the same MPH out of it as you would of a slower hull with more HP.
Rob

 

[FORMULA FAST]

Re: Engine swap. 305 to 400 sbc

Well nearly a yr has passed and I do have my boat running now!
Boy did it ever take some work to get the newer 5.7 vortec to work in this boat. First I had to have an electric fuel pump because the LT-1 engine used to be fuel injected and there is no spot on the block for a mechanical fuel pump. Second the pump had to wired so in the event of an engine failer the fuel pump would shut off. Third, the flywheel engine cupler combo took some work to get figured out. Fourth the newer engine makes it's power at 4,500 to 5,000 rpm so an engine oil cooler had to be installed. Fith a remote engine oil filter had to be used to run the oil lines into the remote cooler!! Fifth the old style ignition would't run up to 5,000 rpm it would start to miss fire at 4,200 so I installed a mallory electronic ignition with a MSD marine rev protector. Sixth, with the engine running trimed up @ 5,000 rpm the boat gets abit scary... so i added bennit trim tabs wich made a HUGE difference in the attittude of the boat in ruff water and now is much more controllable.

All in all the engine swap was sucsess but it sure had it's trail and errors!

Now on a 1ft to 2ft chop day with 1/2 tank of fuel two people and some tools and a cooler she will hit 75 mph!!! ........

 

[MikDee]

Re: Engine swap. 305 to 400 sbc

Well, Good for You! I'll just Drool I do find it hard to believe it does 75mph? But, I do believe it is "Scary Fast!" Apparently you had a lot of issues, but overcame them all, I'm glad to see you got it all working, and replied with good useful info, as well as letting us know the final outcome

It seems we haven't heard how the O.P. made out?

 

[FORMULA FAST]

Re: Engine swap. 305 to 400 sbc

Thanks Mike,
I did forget a few details......lol
I installed a nose cone kit on the outdrive and sreamlined the leading and trailing edges of the lower unit. I also replaced the input and out put shafts for sronger ones as the origanal one broke!! I have a 15" 23pitch cleaver prop. I have the older 898 MR outdrive and had to modify it alot I ended up builing my dive shower kit to keep the outdrive temps down.

Formula states the boat has a haul speed of 85+ mph and gave me some tips
It is the narower beam of 7.5 not the 8' one.

The outdrive is the week link here I still have breakage problems and I'm checking into installing a alpha 1 gen 2 ourdrive I have been told it will bolt up to my alpha MR transom plate.

I will put some pics on here when I figure out hot to add them

 

[sully73]

Re: Engine swap. 305 to 400 sbc

how did you get around the 350 being internally balanced and the 400 externally? i started reading the post and thats the first thing that i thought of. are the marine balancer and flywheel externally balanced too?