Mercruiser 165 HP L6 beef up

[Mercdude]

Hi! I just bought a 1976 Ankor Craft 18' runabout. I pulled the motor (Mercruiser 250 CID, 165HP, in-line 6) to do a complete rebuild (winter project). Once I got the motor apart, I started thinking that I want to increase the power "just a tad". Since this is my first foray into marine engine modification, I thought I'd ask the experts. What would you suggest I do in the way of Camshaft/valvetrain, ignition, carb, etc... to give my little $300 raft some more UMPH? Any honest suggestion will be appreciated. Thanks

 

[achris]

Re: Mercruiser 165 HP L6 beef up

If you start playing with cams and valves, be aware that the torque curve will be affected. Sure you can possibly get another 100 ponies out of it, but at the expense of a 'usable' engine. About the most I would consider would be to open the head ports a little and put electronic ignition on it.<br /><br />Chris.........

 

[waterone1@aol.com]

Re: Mercruiser 165 HP L6 beef up

I agreee with achris. contact a reputable speed shop such as Lingenfelter Engineering (decatur Indiana) and talk to them about porting your heads for more flow. Looking into electronic ignition and fuel injection (if they make a system for an inline 6) would be about it. Once you start messing with cams, high compression pistons, etc., you will be affecting the usable torque and jepordizing the dependability of the motor. Besides you will find your options pretty slim when it comes to "speed parts" for an inline six.

 

[FreeBeeTony]

Re: Mercruiser 165 HP L6 beef up

I recently rebuilt an IL6 and asked the same question..........basically got the same answers. Not much to be had here. I added a petronix ignition and that was about it, other than the usual: bored out 0.030, new pistons/rings, new bearings, new oil pump/lifters, rebuilt head, rebuilt carb, etc....Runs great, great on gas, just not a speed demon!

 

[Rainmaker]

Re: Mercruiser 165 HP L6 beef up

The big limiting factor when hopping-up those marinized 250 ci Chevys is the one-piece intake/exhaust manifold. Unless you have the original manifold, you will have to go with an Osco, which only permits a two barrel carb. If you're good with a grinder, maybe you could adapt a higher CFM two barrel carb to the existing manifold. I would be very careful though. You don't want to cut into a water jacket and throw away a $500 manifold.<br /><br />There is a company called Clifford Performance that makes lots of HP parts for inline engines. These parts are generally geared toward high RPM power bands (drag racing), which you don't want in a boat. Maybe Clifford, Crane, or Comp can custom grind a cam for good low-end torque. But you will need to tell them lifts, duration, overlap, etc.<br /><br />With all that said, I agree with FreeBeeTony. These motors are great in stock form. They just aren't very quick.<br /><br />Have you considered a V-8?<br />mike