View Full Version : Mercruiser 330 or 310hp cam at idle?

09-08-2011, 11:00 AM
I have never owned a stock I/O. My Scarab 1 with a 350 had a cam, carb and intake and it showed at 62mph. My 240 Baja had a 440 cam, 502 intake and carb but stock heads so she made roughly 400hp and sounded mean. I know nothing about this engine except it just says 7.4L and has the oval port heads and looks stock but....she has a pretty darn lopey idle for a stock engine and is an animal. Reason I ask is I am getting about 5k swinging a 23 Mirage and 65+ w/ 2 people and 3/4 fuel which some say here is not possible with a 330 or 310 454. My mechanic thinks I might be able to swing a 25" after go for a ride with me. So again do stock low hp 454's have a lopey idle or smooth like truck engine?

09-08-2011, 03:37 PM
they have a smooth idle,,maybe the old owner did some internal work,looks are deceiving.

all else fails go to youtube and have a listen of a 330 running.


09-09-2011, 11:02 AM
Oh no mine sounds NOTHING like that. Now that you mention it(and shown it), that is what my friend's SeaRay sounds like with stock 454's. You can hear both exhausts at the sme time. Mine you hear left & right almost individually....sounds more like this 365hp, maybe even more lopey. http://www.youtube.com/watch?v=JNIJKsqw86k&feature=related

I have the same intake and valve covers, did 365's have oval ports? When did they go to the plastic valve covers? Mine are plastic like the 365's not metal like the 330 but that is probably an age thing. I am starting to believe I gots me a 365, not a 330/310. I will do some more investigating. Maybe Donzi can shed some light on it like Boston Whaler does when you give them your HIN.

09-10-2011, 12:58 PM
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the gen 6 engines had the alunimum valve covers,,also if you look at the intake manifold on the 365 mag the intake manifolds ports were higher then the head were the valve cover sits,,the 310-330 round port intake ports were a little under where the valve cover sit on the heads..got a pic?

Barry Eller
10-08-2011, 05:56 PM
365 hp was the 454 HO. Rectangular ports. That is what my 1993 OMC King Cobra came with. Click on the bottom link on my page to hear my current 502 idle.

10-08-2011, 09:55 PM
I found out what I have....330/310 oval port but not peanut oval ports. Nothing fancy and not a Magnum, no problem! The rects are great for high end like in cars. The ovals are for low/mid in boats. For some who want speed, rects are great, for me I want the ovals.