1978 Mercruiser 898 Repower

BlueBayouV8

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I am pulling out my cracked, junk, weak old 305, in favor for a stout new 350.. I am building this engine specifically for the boat. and this in new to me (boats not engines). Where do I want my peak HP and TQ? Do I want High Revving, or Low end Torque? also what do I need to know, about taking th old one out? can the outdrive stay on? is it easier to take it off? where should I start. I dont want to F*ck it up by just pulling it out?
 

Don S

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Re: 1978 Mercruiser 898 Repower

I would suggest you go up to the Adults only sticky, there are OEM service manual downloads for the engine and drive. Try to stick with the same vintage engine, or you will have problems getting things to fit. Remember, you need marine rated electrical and fuel parts for your newer engine, DO NOT use automotive starters, alternators, distributors, carbs, or fuel pumps.
 

BlueBayouV8

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Re: 1978 Mercruiser 898 Repower

The new engine is a 1981, out of a truck. I plan on using all the parts off the 305, just swaping the block and heads.
 

Bondo

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Re: 1978 Mercruiser 898 Repower

Ayuh,.. Pull the drive,... Pull the motor,...
Swap all the accessory parts from the old to the new, then put it back in...

Everything,... 'n I mean EVERYTHING, ya need to know can be found in the Adults Only section of this forum,...

Good Luck...
 

BlueBayouV8

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Re: 1978 Mercruiser 898 Repower

im gonna pull the drive tonight. the manual says to pull off the gear case(lower unit) first. does this need to be done? also, does the shifter need to be in any special position, when i changed the impeller last year, i had a hell of a time getting the shifter to line up when i put it back.
 

smokeonthewater

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Re: 1978 Mercruiser 898 Repower

outdrive can stay on but it should be removed.... you need to check alignment when you put the new engine in and you can't do that with the drive in place.... your 81 350 will be fine.... you want flat top pistons with big chamber heads and you want to build for all the low rpm torque you can get as far as cam and intake... think edelbrock performer..... While you are at it new gimbal bearing u joints shutters trim senders/wires (if you care) and bellows are a good idea if they are not recent ..... heck they may be 30 years old don't forget your impeller and drive oil
 

Bondo

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Re: 1978 Mercruiser 898 Repower

the manual says to pull off the gear case(lower unit) first. does this need to be done? also, does the shifter need to be in any special position, when i changed the impeller last year, i had a hell of a time getting the shifter to line up when i put it back.
Ayuh,... Pretty much when doin' Anything on an alpha, put Everything in forward....

Like I said,... The Adults Only section.....
 

smokeonthewater

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Re: 1978 Mercruiser 898 Repower

oh and besides the stuff from the 305 the two main things that differ from an automotive application are stainless head gaskets and brass freeze plugs

Also don't use any chrome anything.....It WILL get rusty....
 

BlueBayouV8

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Re: 1978 Mercruiser 898 Repower

thanks I didnt even think about the Stainless head gaskets. can I get them at summit or jegs, or is it a marina thing? and thanks but Chrome is lame! haha. anyway, the 305 has larger combustion chanbers than this 350 i have, so il probably use the old heads, the 305 already has an edelbrock performer rpm intake on it. Il have to look at the specs, but i think i might need just a performer not the RPM. i think the rpm i for 1500-5500, and im looking for idle to 3500.
 

Bondo

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Re: 1978 Mercruiser 898 Repower

I didnt even think about the Stainless head gaskets. can I get them at summit or jegs, or is it a marina thing?

Ayuh,... You can get Fel-pro's at any Better auto parts house...
 

smokeonthewater

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Re: 1978 Mercruiser 898 Repower

you can get stainless gaskets at oreily's but they are pricey.... they are all over ebay but I gave up after getting 3 sets of plain steel with epoxy coating and having to argue and sent back..... 86 the rpm stuff and 86 the 305 heads... you want under 10:1 compression.....having a brain fart here but wanna say 76 cc chambers.... not sure though
 

BlueBayouV8

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Re: 1978 Mercruiser 898 Repower

so what would be a good mark to shoot for with my HP and TQ? its a 19 foot deck boat, it weighs about 1700lbs..(a total guess.. but its heavy). I want it to be decently fast. It goes about 40 flat out now. i am pushing for about 50, with the same 21 pitch prop.
 

smokeonthewater

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Re: 1978 Mercruiser 898 Repower

I didn't look at the cam but if it is a low rpm cam with a smooth idle no loping max power down low then it will be good..... The stock mercruiser 260 hp is a good figure and is a 60 hp increase over your 305 ... you might get a couple more ponies than that but if the 21 was right 198 hp it will be wrong for 260..... that said, my old 78 arrowglass 20' cuddy ran mid 40's with an 898 and 1.5:1 ratio outdrive with a 19 pitch prop so you may be overpropped with the 21 and it may work alright with the new engine.... build the engine first and THEN worry about the prop
 

BlueBayouV8

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Re: 1978 Mercruiser 898 Repower

the cam has a smooth idle. idle-3500 power range. i have also been looking at one with a slighly rough idle, power range is 1300-5500.. the regular performer intake is idle-5500, my RPM intake is 1800-6500.. that one is as good as gone, Im going for the regular performer. With my edelbrock 650 carb, on a pretty much stock freshened up 350.
 

Bondo

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Re: 1978 Mercruiser 898 Repower

Ayuh,... Find some different Cam listings,... I didn't like Any of them...

You want Idle, to 4800....
 

BlueBayouV8

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Re: 1978 Mercruiser 898 Repower

Lift .437 /.454 Duration 250 deg /256 deg RPM Range Idle-5000
thats pretty close to stock. is it worth the extra $200?
 

Bondo

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Re: 1978 Mercruiser 898 Repower

Ayuh,... I'd just leave the cam in the new motor, In it...
 

BlueBayouV8

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Re: 1978 Mercruiser 898 Repower

the only issue is that the new engine stock is only 175hp. and 230 ft,lbs. I need to bump that up. I was thinking flat top 8.5-9:1, 72-76cc heads, the Lunati idle-5000 cam, the performer intake, and 650 carb. I am shooting for 270-300hp. is that too much?
 
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