evenrude 88 special torque tab

[Bret Casselman]

I have a 93 Evinrude 88 special mounted on a 87, 17 ft Boston Whaler Montauk. I reciently mounted a 10 inch CMC manual Jack Plate along with converting the steering to a NFB Safe-T II system.

The boat performs very well under this new configuration. I do have a question about the torque tab (behind prop) on this engine using the NFB steering. Is it safe to remove this tab and replace it with a machined plate.

There is a water intake hole on the leading edge of the tab but its not connected to anything in lower unit. Is there a reason for water to be shot up the lower unit? I cant find any information on this.

With the price of gas nowadays and this engine getting around 4 miles to the gallon, I know any drag you can take out of the water cant hurt. HAHA. If anyone could give me any comments on this i would appreaciate it

Thanks

Bret

 

[tashasdaddy]

Re: evenrude 88 special torque tab

can't answer the question about the tab. but i have a 1988 88spl. on a comparable weight boat, can run at around 40 to 42 mph and get 7-8 gallons an hour. if you are running wot all the time it will burn max fuel. these engines have a cruise control feature, since the 1960's. that if you go to full power, then drop the throttle back to 7/8 to 3/4 throttle the timing stay advanced, but the fuel flow drops, you may loose 2 mph. be gain significant mileage. how are you propped, are you getting optimum rpms, or is the engine lugging and not getting turned all the way up.

 

[Bret Casselman]

Re: evenrude 88 special torque tab

Thanks for the reply.

At max, im running at about 41 mph at plus of minus 5100 rpm. I usually run at around 30 mph at 3500 rpm which is a comfortable speed, and slower in rough water. The Whaler is a very rough boat in choppy water, the boat can take it its the person who cant, HAHA.

My milage figures come from a full fishing trip which includes idle, slow etc, with a few 5 to 10 mile jumps at speed. I fish a lot of marsh area where it is slow putting around. A trip of 45 to 50 miles will burn 12 gallons of gas.

My last trip going by my garmin gps, i went a total of 48.27 miles, max speed of 40.6 mph, avarage speed of 19.6 mph with a total runing time of 2 and 1/2 hours.

So as you can see i do a lot of starting and stopping, so this is a overall average.

One day i plan to do a better test of my milage, using a certion amount of gas and testing consumption of fuel at a fixed speed.

Again, thanks for the reply.

Bret

 

[ob]

Re: evenrude 88 special torque tab

You didn't mention which diameter and pitch prop you're pushing the rig with.One thing you'll want to do is insure that the engine is mounted to it's optimal height on transom.This will reduce drag and allow the engine to attain its optimal rpm as propped.I'd be looking for at least 5500 rpm at wot with an average load aboard.This will optimize fuel efficiency and engine life.The anti-ventilation plate above the prop should be roughly even with the boat pad when the engine is trimmed down level.This is a rule of thumb starting point.

 

[Bret Casselman]

Re: evenrude 88 special torque tab

I will have to get back to you on the prop size, i cant remember off hand. Reminder, i have the moter mounted on a jack plate with a 10 inch setback. I was able to raise the engine 3 to 4 inchs.

Running on plane, trimed out for best speed at rpm, the trailing edge of the av plate is almost on surface of water. That was the highest i could get the engine before it started to cavitate. I may need to drop it a turn or 2, in rough water, it is at the verge of cavitating if i hit a big wave.

Ill keep experminting with the configuration, This is just a trial and error type of thing. But with the set back, the performance has improved, just getting the engine further away from the back of boat helped. Ill even put the fin back on, i tried it without and with and found it gets up faster with it on and seems to help keep the rear of boat up in rough water.

Bret

 

[ob]

Re: evenrude 88 special torque tab

Yep. I overlooked you mentioning the jackplate.If all of your carb flaps are opening fully horizontal at wot setting,then I'm guessing you are slightly overpropped if 5100 is all you can squeeze out with the engine trimmed at wot.

 

[Bret Casselman]

Re: evenrude 88 special torque tab

Ill do some more checking on this as i run it next time, i know my tach was acting up my last trip a few days ago. Ill get back to you on this.

I really appreaciate your input on this matter.

If anyone does have any coments on the torque tab, i would appreaciate it, with NFB steering, there is no need for the tab.

Thanks

Bret

 

[ob]

Re: evenrude 88 special torque tab

The tab produces an insignificant amount of drag.That said ,its primary function is to offset the rotational torque that the engine places on the steering.No feed back steering simply dampers the feel or feedback to the operator.It does not diminish the torque steer.It is my opinion that you should leave it in place.The trim tabs function is purely dynamic and has no mechanical or flow effect on the engine or it's components.

 

[Bret Casselman]

Re: evenrude 88 special torque tab

The reason i ask is i have noticed, most boats around here with 90 plus engines which have either NFB or hydrolic (power) steering dont have the tab on them. I even noticed some new boats at dealierships, which are water ready dont have the tabs.

 

[ob]

Re: evenrude 88 special torque tab

Dunno.I'm running a 96' model 15 dauntless with a 70 hp Rude with NFB steering and a whale tail and have left my trim tab in place.I never felt I had any reason to remove it.

 

[emdsapmgr]

Re: evenrude 88 special torque tab

Believe the hole is to divert water back up into the gearcase for cooling. May even provide cooling for the carrier and prop hub, which has hot exhaust around it. At the height of my engine, coupled with the trim angles, not much of the skeg is in the water to cause drag anyway. Suggest you leave it on the engine..

 

[Dhadley]

Re: evenrude 88 special torque tab

Yes, the tab supplies water to the exhaust to cool the prop hub. You'll want to keep it on.

The torque is still there, you just can't feel it. That's the downside of hydraulic or NFB steering. The gearcase is still torqued to one side and adding drag regardless if you feel it or not.

Adding a 10" plate means you raise the motor 2" just to get back where you were when the motor was transom mounted. Play with the engine height to try and gain rpm. At 5100 the motor is lugging. Since it's been running like that it might be a good idea to decarbon if you haven't done that in a while.