new heads

[sabastianunf]

I have a 1978 mercruiser 120 sterndrive. I have been looking into cheap ways to improve my engine performance. I saw a complete head off a mercruiser 140 including rockers and valves but needs to be rebuilt. They say it will fit a 2.5 L or 3.0 L - could that be correct and would this fit on my engine? How expensive would it be to get these rebuilt?

 

[Don S]

Re: new heads

No such thing as a cheap way to improve a marine engine, especially a 120.
You will have to increase the HP by approximalty 10 HP to gain 1 mph. Is it worth all that.
If the head needs rebuilt forget it. If it needs valves, seats and valve guides, you could buy a complete 140 (3.0L) cheaper.

 

[sabastianunf]

Re: new heads

Would a 3.0 L head fit on my 2.5 L motor without any other changes? Would this increase my HP from 120 to 140?

 

[Bondo]

Re: new heads

Ayuh,......

The Head will Fit, But it Won't Raise the HP,.... At All....Might even Lower it.....

Your motor is 153cid, 2.5l....... A Head change doesn't Change That.....
You'll need the 181cid, 3.0l Block to find the 140hp..........

 

[Don S]

Re: new heads

I don't know if that head will fit or not, never tried it.
But the 3.0L had a larger bore, possibly a longer stroke, different cam etc.
You may be able to change the head, but I know you won't see any difference in speed or performance. You might try to talk yourself into seeing something, but it's not going to happen with changing a head.

 

[sabastianunf]

Re: new heads

Thanks for the info. Any reccomendations on how to improve performance of a 120 mercruiser?

 

[Don S]

Re: new heads

Replace the engine with a bigger engine. If you go to a 6 or an 8, you will need a different gear ratio in the drive, different exhaust setup, and differnt 'Lots of things' at great expense.
If you want a more powerful boat, find one with the power you want.
It's not cheap to upgrade.

 

[sabastianunf]

Re: new heads

Sounds like the cheapest thing to do is get a 140. Do you know how they compare in size? Would I be able to use the same gear ratio, exhaust setup and engine mounts? What would need to be changed? Carb was recently rebuilt 2 bbl carter, also have new starter, exhaust manifold and riser - would they fit on a 140?

 

[Don S]

Re: new heads

What is interchangable all depends on the year 140 you get. The gear ratio for the drive won't change, but that's about the only thing I would say would be the same.
Those engines are being sold brand new by Volvo and Mercruiser, and they look nothing like your 120.

 

[Reel Poor]

Re: new heads

Like Don said in an earlier post, you need approximently a 10hp increase to gain 1 mph. I don't understand spending the time and money here for a measly 2 mph. If you want to go 2 mph faster with the 120, just go boating by yourself, leaving your family/buddies on the dock.

 

[Bondo]

Re: new heads

Ayuh,..........

A Couple Thou$and Dollar$ for 20hp seems like a Pi$$ Poor Inve$tment to Me.......

Enjoy the boat you Have,.....
If it's Not Enough,....... Trade Up,........
There's No Easy way to Hop-Up the 4 cylinder motors,.....
Matter of Fact,...... There's Not Much you can do if you choose the Hard Way Either......