1994 ( 90 HP V4 ) Help Please

[StingRay_90V4]

Sense 1987 my family has had a Sunray Bowrider with an Evinrude 60hp on it. It has been a great boat and has caused us next to zero problems over the course of the last 20+ years. It would pull myself up water skiing ( 155 lbs ) with a friend or two in the boat as well. It would turn a 13.25x17 prop to a top speed of 32-33mph ( no idea on rpm. No tach ) . Sometimes maybe 34mph on a nice clear day. But the time has come for us to purchase a new boat. So we picked up a 1996 16' StringRay 501zp bowrider with a 94 90 HP V4 on the back of the boat. I really love the way the 90 V4 works. It has a fair amount more bottom end for the whole shot to ski with and it turns the same sized 13.25x17 prop to a top speed of 40mph all day. At exactly 5000rpm. Im not speicifically on the hunt for more top speed per say. But lets just say I was . What size prop would you guys run to gain a few more mph and rpms ? And also , I am reading about things like jack plates. NLA rubber intake filler blocks. 1 5/16 carbs and bubble exhausts ? But I don't know what much of this stuff is or refers too. Can anyone help me out with any of these parts as to what they are , how much they cost , how to do ? and what they add to the motor as far as power or speed ? I am just learing about speed boats . BUT I am I car guy. And I am very mechanically inclined as I can work on my own cars 100%. I can even rebuild them . But boats, im just learning. If I wanted to see just a tad more bottom end and an extra 2-3mph so I could hot 42-43 mph. Would any of that stuff help ? And how and where do I get it ?

Thank you !

 

[StingRay_90V4]

Also I forgot to ask. Is 40 mph about what these motors should be doing on a 16 1/2' bow rider that weighs about 900lbs without motor ?

 

[emdsapmgr]

Before you do anything, you need to optimize your current setup with the 90. It's normal operating rpm band is between 4500 and 5500 rpm's. Current thinking is that you should prop it to run at the upper end of that operating range, or 5500. You are below that, such that at 5000 the engine is actually "lugging". You should re-prop the engine to pickup about 500 rpm's. So, you need to go down to the next lower pitch prop. That should pickup about 300 rpms. In addition, make sure the engine is not mounted too low on the transom. That can cause too much drag and lower boat performance. You may pickup a couple of mph once you get your setup dialed in, and the holeshot should be much improved.

 

[StingRay_90V4]

After watching my speed and tach this morning. It seems toi be hitting 41 ish miles per hour at exactly 5100 rpm. I looked at the motors location on the transem and the motor does apper to be at the very lowest hole. There is only three holes to raise the motor up some. If I was to raise it any, would I only raise it the next whole up ? Which would be the middle whole. Or all the way up to the top whole. Also , will that allow the boat to plain more allowing for a tiny bit more top speed ? And what are some of the pos and cons of raising the motor on the transem to the next whole up ?

Thanks

 

[StingRay_90V4]

Any thoughts on ANY of my questions ? :joyous:

 

[emdsapmgr]

I thought I was providing a number of relevant thoughts on post #3. 5100 rpm's is still too low. You are still lugging the engine with that prop. You might want to re-mount the engine: move it up one bolt hole and try it. Keep your eye on the telltale and listen for the overheat warning horn when you raise it. You don't want the engine to run out of cooling water while you test it in the lake.

 

[rothfm]

Follow EMDSAPMGR, knows his stuff.....Agreed, you are giving up some performance at 5-5100. Like he said get to that upper end. Between running the outboard at the highest point(safely), trying props you should be able to get toward that upper end.

Ensure the Link and Sync is followed in the OEM manual. Its important that timing is correct and the carbs are opening fully. I have several motors, and my 115 was loosing rpm's. The carbs were off, and the link/sync corrected it. That alone brought me up by 400, and raising the motor gained me another 200.

I"m not sure it is worth persuing different carbs, Jets and related parts..gains would be marginal. Folks that do this modify the block ports among other things. I would more concentrate leaving it original and fine tuning for optimal performance, while doing routing, and preventative maintenance.

 

[StingRay_90V4]

Okay...sounds good and makes sense. So I should only raise the motor by one hole then. And I assume by telltale you mean the pee port where the water shoots out of it from the water pump. As for the rpm of the boat at wot. I don't doubt anyone. But the local boat dealer that the boat came from new told us that the 90 should be between 5000-5500 rpm. And that 5100rpm was totally fine for the motor. Im no marine expert. So if I was to try another prop. What size pitch and diameter do i try. Because props sent all that cheap to be buying four or five to find the right one. It currently is running a 13.25dx17p and I felt like it works great. So if I was to gone down in pitch to a 13.5dx15p to gain 400rpm and be dead smack on 5500rpm. Wouldn't that smaller pitch prop cause me to have a slightly slower top speed . Say a drop from its current 40-41 to a slightly drop of 38-40. Or could it still possible hit 40-41 with a smaller prop and the few extra hundred rpm ? This is the part I really need help with. Or would a nice same pitch stainless or slightly smaller stainless give me the same too speed with more revs ?? Thanks for the input

 

[racerone]

Boat speed will stay the same with the 15" prop.-----Engine rpm will increase.

 

[FMJshooter]

No mention of trim settings each boat will have a different sweet spot have you played with the trim to try and raise rpm/speed? Can you blow the prop out by trimming up too high? Also for engine height the ventilation plate should just be skimming water or be barely out of the water when running, may be worth checking before you raise the motor just to see where your at and then pick which holes to mount in and as EMD said watch your tell tale and overheat alarms once you do raise it.

 

[emdsapmgr]

FMJ stated it well.