1978 Mercruiser 898 Repower

[smokeonthewater]

Re: 1978 Mercruiser 898 Repower

I have had real good luck with performer cams but otherwise you have listed basically the specs for a stock merc 260....

 

[BlueBayouV8]

Re: 1978 Mercruiser 898 Repower

And thats fine... With that basically stock Merc 260 cam, an edelbrock performer intake, 650 carb. Flat top pistons, I should be about to pull close to 300hp. I got my 305 out today, the block was cracked, BAD.. I knew it was cracked, but it was worse than I saw while it was in the boat... Also I broke out the side of the block to see how it looked, and the water jackets were filled at least half way up with rust, and sandy looking sh*t. Im supprised the thing even worked at all. I used it 5 times last year like this! the heads that were on it, have small valves 1.76 and 1.5 i think. with 60cc chambers. With the flat top pistons, my compression would be close to 10:1, I suppose I should use the heads off the 350? would there be any benifit to using the 305s heads?

 

[Bondo]

Re: 1978 Mercruiser 898 Repower

I suppose I should use the heads off the 350?

Ayuh,... No benefit in the 305 heads...

 

[BlueBayouV8]

Re: 1978 Mercruiser 898 Repower

I didnt figure so... I am just stuck in the mindset that i want high compression, even though that i know i dont.

 

[smokeonthewater]

Re: 1978 Mercruiser 898 Repower

high compression is fine..... you will need to buy 110 octane race fuel for $5-7 a gallon and be real carefull in the lower rpm's pulling tubes and such...... When I said 86 the 305 heads it was because they have small valves smalll runners and the chambers are too small to run pump gas with flat top pistons... you can call it 300 hp if it makes you feel good but the STOCK 260 has flat top pistons a good cam and a decent cast iron intake........ it's already 70 hp more than an automotive engine of the same year

260 hp will make your boat run WAY stronger than ever before.... don't sweat it

 

[BlueBayouV8]

Re: 1978 Mercruiser 898 Repower

il have to see whats in my 350 when i get it opened up. i hear ya on the high octaine fuel. I Just want to go fast. its a big old boat, and I woult love to see it stand out on the water. I pulled about 40 before, which I didnt think was too bad considering its 32 years old, Tired as hell, and weighs almost 2000lbs. I would like to see it go around 55-60. and my current prop is a 21. Am I correct in thinking that I want the engine to get me going and the prop for top end? If I build a good engine, with a lot of low end power, I could go with maybe a 25-27 prop, and raise my top speed? I know props are a whole other mess, and im sure we'll get into that later. Just a thought?

 

[Bondo]

Re: 1978 Mercruiser 898 Repower

I would like to see it go around 55-60. If I build a good engine, with a lot of low end power, I could go with maybe a 25-27 prop, and raise my top speed?

Ayuh,... Now you're DREAMIN'...

That's in the 1000hp+ territory...

Be Happy with mid-40s to Maybe 50mph...

 

[BlueBayouV8]

Re: 1978 Mercruiser 898 Repower

I dont know much about boats, what can i expect for an inprovement on my top end with an almost 100hp gain in my engine. I would think that would be good for at least 7-10 mph. with a bigger prop too.

 

[smokeonthewater]

Re: 1978 Mercruiser 898 Repower

you are not going to gain 100 hp with a 45 cubic inch increase.... NOT GONNA HAPPEN..... If that were the case at 100 hp/50 cu/inch your 350 would be a 700 hp engine. You can't build boat engines the same way as car engines because (to simplify) of the way the power is used and because there is water in the exhaust that you don't want reverted into the hot exhaust valves.... these are facts to live with.... Also You may be familiar with the saying that air gets thick at 80 mph so gaining above that in a car takes alot more power than below.... well water gats thick at about 5 mph..... the drag of the water on your hull goes up much faster than the needle on your dash.... every ounch of speed on the top is very expensive.
You will gain a bit on the top end and alot on the bottom end.... build your engine and THEN we'll work on the prop with ya

Horses hate when you put the wagon in front of em

 

[BlueBayouV8]

Re: 1978 Mercruiser 898 Repower

I wasnt expecting 100hp form the Displacement alone, but while i was in there i was going to build it a little. Today i was out at the farm and descovered an old TPI 305 I forgot about. I think the tuned port injection unit would be pretty sweet to add to the engine..

 

[BlueBayouV8]

Re: 1978 Mercruiser 898 Repower

scratch the TPI. as it is not Marine rated, and I understand that it cannot be safely put on.... also another question... do I have to run the water through the exhaust? can I not do that, and fab up some headers?

 

[smokeonthewater]

Re: 1978 Mercruiser 898 Repower

ur not fixin to ask if you can put a transmission in are ya?

 

[Bondo]

Re: 1978 Mercruiser 898 Repower

do I have to run the water through the exhaust? can I not do that, and fab up some headers?

Ayuh,... In an enclosed boat,..?? Absolutely Not.... It'll be a ball of Fire 1st trip out....

Build your 350 with a set of Vortec heads on it,... A set of "D" dish pistons to lower the compression ratio to about 9.5:1...
A decent cam for idle to 4800rpms,...
A decent 4bbl. carb.... Eldebrock performer at 650cfm would be My choice....

That'll give you slightly more power than your outdrive is going to like,...
And, you'll probably need a new bigger prop to use the extra hp....

You be Flyin' at probably the lower 50s,..... Havin' a Ball...

 

[smokeonthewater]

Re: 1978 Mercruiser 898 Repower

that'll make a good combo........when he says vortech.... those are not the tbi heads... just a fyi since it's a common misconception

 

[BlueBayouV8]

Re: 1978 Mercruiser 898 Repower

I know that. My buddy totaled his 98 silverado. Maybe ill see about getting those heads. I could get the whole engine, and a carb setup on it. It should get me where I want. Edelbrock makes a performer for the Vortec heads I think.