1980 johnny/rude 140 WOT RPM

[ddbyrd3]

First of all allow me to appologize for starting a new thread, for the life of me I cant locate the other one I was on.<br /><br />I just wanted to post back in regard to the problem I have been chasing with the WOT RPM issue.<br /><br />I had my boat ran on the Dyno yesterday as I watched... Intereting process by the way.. I found my 2 year old teleflex vector series tach is off by 250RPM and fluxuates around the 5000k range.<br /><br />The motor sounded GREAT!!! timing was spot on (thanks DHadley for teaching me how to static time last season) sync and link was perfect as well.<br /><br />The motor pulled 5500k NO PROBLEM, fired perfect on all 4 cylinders, (no double firing) Everything went good.<br /><br />The bad part is I can still only pull 4800K RPM in the water full trim, standard load. So my next step is to raise the motor on the transum. It is set at the lowest point. (I posted pics but cant find my old thread) <br /><br />My prop is a SST 13x19 so my goal is 5500 RPM WOT right, am I heading in the right direction by raising the motor???<br /><br />Sorry for the book....

 

[Dhadley]

Re: 1980 johnny/rude 140 WOT RPM

Yep, absolutely.<br /><br />You might want to consider something a little higher than 5500 but let's get there first.<br /><br />Thanks for the update.

 

[ddbyrd3]

Re: 1980 johnny/rude 140 WOT RPM

Thanks "D".... You have been a HUGE help to me getting this thing dialed in... The Dyno run yesterday re-lit my interest in getting my old beater beating again...<br /><br />I will raise the motor 3 holes (there are 4) and start there. I wont replace my tach anytime soon now that I know how much it is off.<br /><br />So what should my target RPM range be??<br /><br />I was told yesterday during the dyno run that the 1980 140 V4 will blow up at 6k. (personally I have found the advise on this board to be the best) so I will go with what you guys recommend...

 

[walleyehed]

Re: 1980 johnny/rude 140 WOT RPM

I'd like to talk to the dealer that told you the engine would blow at 6k....

 

[emdsapmgr]

Re: 1980 johnny/rude 140 WOT RPM

You may not pick up all 700 rpm by raising the engine..you also may want to try a 17 pitch prop. The prop change will give you nearly 300 more rpm. The conbination of both changes should get you to the 5500 range.

 

[OBJ]

Re: 1980 johnny/rude 140 WOT RPM

Be careful how high you set the engine. I don't know how high the transom is but if you get the engine to high, you could starve the engine for water once on plane and the prop could blow out for venting. <br /><br />Just a little rule of thumb, start with the anti-cavitation plate (the plate right over the prop) about one inch above the keel of the boat. Most folks are surprised by the big difference this makes in performance.

 

[sycamore]

Re: 1980 johnny/rude 140 WOT RPM

I have a 1988 88hp that came with a 13X19 SS when I bought it used. The motor would only turn 4800 rpm and run right about 38 mph. I dropped down to a 13 1/4 X 17 cupped aluminum and picked up about 400 rpm (5200) and stayed at 37-38 mph, but the acceleration is much better. I am in the process of trading the 13X19 SS on a 13 3/4 X 15 cupped aluminum to further increase the rpm's.

 

[ddbyrd3]

Re: 1980 johnny/rude 140 WOT RPM

OBJ, the anti-cavitation plate is 1/2" -3/4" BELOW the keel of the boat right now.<br /><br />A quick glace and it looks like i can go up 2 or 3 holes on the motor.<br /><br />I would imagine that would be a HUGE help even if it doesnt get me all of the RPM i am looking for.<br /><br />The interesting thing is that when I install my Hustler 13x17 prop the RPM doesnt change according to the tach.... But my ear tells me differently and I loose about 4-5 MPH.<br /><br />Right now, the tach is off by 250RPM, it reads 4800 at WOT so figure 5050RPM with the 13 x 19 SST prop. With my motor hanging in the water approximatly 2" more than it should be, I would expect a rather nice increase in RPM and speed.<br /><br />Does this expectation sound reasonable???

 

[OBJ]

Re: 1980 johnny/rude 140 WOT RPM

I don't know the "in's and out's" like Dhadley, but I do know, the more of the gear case you get out of the water the better.....without jepordizing water to the engine. So....if you are raising the engine, start with the anti-cav plate about 1" above the keel. Even that will make a big difference in the way the rig performs.

 

[ddbyrd3]

Re: 1980 johnny/rude 140 WOT RPM

10-4 thanks for the input.... I am looking forward to how my boat will be effected by the change..

 

[ddbyrd3]

Re: 1980 johnny/rude 140 WOT RPM

Question, i am in the process of installing new t-stats. I know there is varying views on this issue and as many threads.<br /><br />One thing I havent heard mentioned in any is; would it be a benifit to install the t-stats and leave out the springs and white caps? (sorry I dont know the technical name)<br /><br />I run my boat strickly in the summer time in sunny Southern Calif, Nevada, and Arizona so the water is far from cold.<br /><br />Just curious as to your thoughts on this...

 

[ddbyrd3]

Re: 1980 johnny/rude 140 WOT RPM

By the way, I raised the motor up 2 holes on the transum. It is probably 1/2 to 3/4" above the keel.<br /><br />I have 1 more hole i could go if need be.

 

[Dhadley]

Re: 1980 johnny/rude 140 WOT RPM

I'm leary about leaving out the pressure relief valves myself. That just might allow the water to exit so fast that it might not completely fill the block causing some hot spots. Probably not a huge issue but it could affect the water cooled reg/rec if you have one.

 

[ddbyrd3]

Re: 1980 johnny/rude 140 WOT RPM

Interesting "D". So what would be the difference of running with no t-stats and pressure relief valves verses just t-stats... Again I have read many threads about running without t-stats but never the relief valves. I am just trying to understand the reasons for both views.<br /><br />Is your opnion; "if its meant to be there than install them" regardless?