Power Increase for Mercruiser 165

[FreeBeeTony]

I recently completed a rebuild of a early '70s Mercruiser 165 IL6. Runs great so far! While I was in the process of the rebuild, I noticed that the manifold would accept a 4bbl carb. Does anyone know if this engine ever used a 4bbl? Would the cam need to be changed? Just thinking for the future..........

 

[FreeBeeTony]

Re: Power Increase for Mercruiser 165

bump

 

[Juancho]

Re: Power Increase for Mercruiser 165

I have never heard of a 4bbl carb being used with a 6 cylinder engine before. How would that work? I think 3 2bbl carbs would be the ideal hi performance setup for an I6.

 

[daveswaves]

Re: Power Increase for Mercruiser 165

Tony, 4BBl is more noticeable in a car engine since you are always accelerating. In a boat you are usually running at a steady rpm. The engine can only "breathe" so much with standard valve sizes, cam set up etc. Putting more air and fuel in would likely "bog" the engine and it will be hard(expensive) to find a marine 4bbl with low enough CFM to perform properly. Stick with the 2BBL

 

[DJ]

Re: Power Increase for Mercruiser 165

FreeBee,<br /><br />Daveswaves makes a very ggod point.<br /><br />That engine doesn't like anything over 4300 rpms. RPM's equals horsepower. You could probably get a little more torque out of it with a lot of expensive tweaking.<br /><br />Is it worth it, probably not.

 

[FreeBeeTony]

Re: Power Increase for Mercruiser 165

Thanks guys............<br />Like I said I was just thinking about it, I don't plan on doing anything major. I am satisfied with what I have done so far.

 

[Battlewagon]

Re: Power Increase for Mercruiser 165

I am in no way a pro with boats. I do however have a pretty good grasp on engines. I have a '69 Merc 160 with the 250 I6 Chevy. I am also searching for more power. My plan is as follows. For the carb, I my gonna replace my Rochester model 2G 2 barrel with a larger 2G. I have found that there at least 4 cfm sizes from around 360 to 430 cfm. I am going for the largest and of course using the marine gaskets for safety. I have spoken with Crane Cams about my 4100 rpm brick wall and have found a solution that will get me to 5000 rpm and still have some bottom end. The cam, lifters and springs are gonna run about $600. I can get you the part numbers if you are interested. I am also gonna get the exhaust valves replaced and hardened valve seats installed. I have also spoke with Kenny at Sterndrives.com and I am gonna replace my 1.68 geared Mercruiser 1 outdrive with a 1.50 ratio Alpha drive.<br /><br />My boat is a 1978 17' Silverline trihull. I have clocked it at 43.5mph on the GPS by myself, full tank, and flat water. I am shooting for 50-55.

 

[FreeBeeTony]

Re: Power Increase for Mercruiser 165

Battlewagon, let me know how you make out. I would be interested to know.

 

[horndog]

Re: Power Increase for Mercruiser 165

geez, well, if you were to go that route might as well get a 4.3L reman engine. <br /><br />Cam, lifters, valves, go with roller rocker arms, that will increase horsepower by about 5-10% alone, carb, 430cfm is about max on that engine before it starts to bog done and run really rich.<br /><br />I wouldn't spend that much money in a motor, I would get a new boat first, something a little bit up to date, like one with a 5.0 or 350 in it, then tweak the chit out of it!

 

[Doug Durako]

Re: Power Increase for Mercruiser 165

Battle----you might want to check the specs on the boat hull design of your 1978 and compare to something built in the 90s.<br /><br />You might not be able to get enough of that old boat trimmed and up out of the water to reach the speed you want.

 

[Battlewagon]

Re: Power Increase for Mercruiser 165

I'm gonna do it I am. I only need 6.5 mph more to hit 50. As far as cost, just parts and head work, the rest I do myself. I will move to a newer hull when I finally sink this one. As far as my I-6, well, I have 4 vehicles including the boat with I-6's, I luv'em! Modding the Chevy is not near as complex as doing the 4.0 MPI motor in my Jeep. Fixing to stroke that one from 242ci to 275ci. Inlines forever!! I am gonna tackle the boat I-6 over the winter and I will keep ya'll posted.