How to coax out a few more RPM

YYZRC

@212rowboat I think you should do a cross-country boat mod roadshow. In the mid 2000s there was a guy from Europe who would fly to the US a couple times a year and install all of the euro mods on Benzs - crazy retrofits like HID lighting and air suspension. 

I would be in for rockers and injectors!! 

212rowboat

Its exceedingly uncommon for injectors to go bad.  Mechanics who work on engines all day will disagree but they see only engines with trouble for the most part... its like people venting on forums about a bad product and swaying opinion when there are thousands working just fine nobody thinks to go brag about.  

Swap the baskets if you run into dirty or wet fuel... new orings... done... tip: use a non petroleum based oil to lube the orings... i bought a tube of ky jelly for that specifically... i got a strange look from the cashier... fortunately I still have that tube somewhere so I only had to endure that once.  If my wife ever finds it I bet there will be questions... 

Black_Diamond

I’ve looked into this for my boat. In a car pretty simple job as described. A lot of stuff to take off to get the valve covers off on mine. That’s my pain. lol. Most all say you need tall valve covers it seems and that is a 100% no go on my set up.  🤷🏻‍♂️

Ian

Trying to follow some of these technical/mechanical terms in this thread has my eyes glassing over and rolling back in my head......

reneechris14

212rowboat said:

Its exceedingly uncommon for injectors to go bad.  

Both of the motors on my 342 needed to be fixed we I purchased the boat. Not the same symptoms mine was popping when throttle up but idled fine. Boat was 11 years old when purchased 296 hours. 10 hours after I had it I had the problem. The more you run the boat the better it runs.

YYZRC

Black_Diamond said:

I’ve looked into this for my boat. In a car pretty simple job as described. A lot of stuff to take off to get the valve covers off on mine. That’s my pain.

I was wondering the same thing - and how do you run the engine with the valve covers off and parts removed? I think I would need to remove the shift linkage bracket and the entire top bracket with the Deutsch connector, relays, etc. 

212rowboat

wiggling the covers out presents some problems, but it's doable.  

you can purchase the rockers without the fancy hex cap and the stack height is hardly greater than the stamped guys...







you don't have to have those locking caps, but they are nice.  piece and peace of mind... you don't need the thick bodied ones either- which are usually aluminum.. stainless are considerably smaller- seen in the second picture above and compared with a stock stamped rocker.. you can certainly go for the harland and sharp, which are pretty good roller rockers (used them in 1.7 in mopar LA block 360s and 408s) in the last picture, but you can start to see the stack height becomes an issue, especially with oil baffles and those locking caps.  

and these are the ones i used on mine- kinda in between in stack height, and self aligning- notice the little tabs outside the roller which disallows them to walk off the valve stem (which would only happen if you were hitting some silly high RPM's and didn't have them set correctly- but hey- piece and peace of mind, and i already had them). 



i can't remember if mine were 7/16 or 1/2... there are at least three sets of vortec heads.. one has a round journal for the pushrods to drop through, another has the rounded rectangle, and yet another has an oval... some are 7/16's and some are 1/2.... 

Dream_Inn

you can keep the oil from flying if you use the little clips that attach over the rockers.  I agree with row that it is a pretty easy thing to do, even for those not familiar with it.

Michael T

@Dream_Inn.....I have ALWAYS been proud of you - now you (and your buddy) are official members of the Sea Ray Humiliation Club. SR owners are like some dogs with porcupines - they just don't learn - even when it hurts.....every time. Unfortunately, where I boated, word of Rinkers spread pretty fast and the SRs didn't even put-up token resistance. Give a Rinker the right engine and no "normal" boat can touch it! BTW @Dream_Inn.....your Admiral has a point about that trawler or you do know they make some pretty mean supercharged/turbocharged diesels?  :-)

davidbrooks

So this goes down in the "dont ignore the basics" category. I did check the throttle and it was good.  Any tweaks and i also raised my idle which wasnt acceptible. Changed spark plugs and cleaned out the flame arrester and that took me to 4700 rpm and just under 40mph wot.  I can live with that. Last time i did plugs was 3 yrs ago. From the looks of them i am thinking i have a valve job in my future....and new rockers. Right row is my port engine. Left row is starboard or my problem child.

Michael T

@davidbrooks what is the OEM specified WOT band for your engines? 4700 @WOT seems low and could cause lugging with oil blow-by and rich fuel mixture.

aero3113

If it a 350 Mag MPI the max RPM range is 4600-5000 RPM’s.

davidbrooks

Everything i can find states it is 4800-5000. I am def not hitting 4800. Getting close though.

aero3113

https://www.perfprotech.com/blog/tech-specs/mercruiser-v8-marine-engines-specifications

Willhound

That chart is great @aero3113.
We need to pin that somewhere.

Handymans342

The rest is prop

Michael T

I would not be remotely happy unless I was within 100 RPM of my top WOT RPM otherwise IMO you are lugging the engines. On every boat I can remember having I could hit top rated RPM at WOT and even tickle the rev limiter on a good day. No way would I accept 4700 RPM on a 4800-5000 OEM RPM data point. No way.