Mercruiser 120 Upgrades

Jamepc

Seaman
Joined
Dec 2, 2003
Messages
57
I have an '85 17'Chris Craft Scorpion with a 120 HP Mercruiser motor.<br />Is the 120 and 140 block interchangeable?<br />Is it the same block bored and stroked?<br />Can I bore my 120 and use a 140 crank and, viola, a 140 motor?<br />Do they use the same head?<br />Assuming I will be removing the engine for a rebuild, what other upgrades can be done to my 120 for some extra ponies (cam, higher ratio rockers, head porting etc.)?<br />Thanks for any suggestions, ideas and input!<br />James
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: Mercruiser 120 Upgrades

hello<br /> change the engine decal and run an extra 200 rpm on the tach.<br /> for 20 hp it is not worth the money.<br /> most of the 2.5 and 153 cid blocks were the same for many many years.
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: Mercruiser 120 Upgrades

hello again<br /> the 3.0 litre is a different animal as far as the block is concerned.<br /> good luck and keep posting
 

Walt T

Lieutenant
Joined
Mar 16, 2002
Messages
1,369
Re: Mercruiser 120 Upgrades

The difference between the 120 and 140 is the carb set up.
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: Mercruiser 120 Upgrades

hello<br /> there are at least 9 carbs. 4 intake assy's and 3 heads with different port configurations on the intake and exhaust. the 153 CID was made in 110,120,135 and 140 hp marine versions that I am aware of. the 3.0 or 181 cid was made in 135,140 and a FI 150 version that I know of and there could be more. this 4 banger is probably the toughest yet worst motor ever marinized. it works well but does not like many mods and there have been many many carb mods in the past few years . when you start swapping parts you will find a lot physically fit but now the engine runs like a wounded monkey. some swaps will allow water intrusion so be careful with mix and match. like I said if your 120 runs well run it. unless you are positive what year and head configuration you have try not to mix and match. <br /> good luck and keep posting
 

Jamepc

Seaman
Joined
Dec 2, 2003
Messages
57
Re: Mercruiser 120 Upgrades

Thanks for the replies guys.<br /> <br />"The difference between the 120 and 140 is the carb set up." DieselWalt, you didn't mean that's the ONLY difference, did you?<br /><br />rodbolt (or anyone else), How was 140 horses squeezed out of the 153 CID block? If it was bored and stroked, it wouldn't be a 153, would it?<br /><br />I would probably rebuild mine to stock specs, but I was just curious.<br /><br />Thanks again,<br />James
 
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