90 hp Top Speed

[StingRay_90V4]

I have a 1993 StingRay ( 16.5' ) with a V4 90hp crossflow on it. I am running a aluminum prop that is 13.25d x 17p. We just picked the new to us boat up in August of last year. So we didnt have much time with it before pulling it out of the lake for winter. After finally getting the boat in the water this weekend. I decided to do a few wot pulls and test the boat out with just myself in it. At 6000rpm i am seeing 42mph. But that seems to be a peak speed every once in awhile. But I will always see 41mph at 5900rpm. These speeds are GPS confirmed at both 41 and 42mph on my Garmin. This boat is deffinitly faster then our old 3cyl 60 hp rude that would only see 32-34mph TOPS.. None the less. I am wondering if the 41-42mph I am seeing are good wot speeds for a 90hp on a 16ft boat and also WOULD i pick up any EXTRA top speed AND bottom end pull for tubing with a SS prop ?? I would love to see 43-44 mph with a little extra pull. Im getting greedy !! lol... Any suggestions on SS props and what if any extra speed I would see ? Or is my 41+ mph as good as it gets for a 1991 90hp ? Thank you !

 

[StingRay_90V4]

I will also add that the person we bought the boat from also gave us a seond prop. An aluminum Solas 13.5dx13p. That prop makes the boat FLY out of the water but tops out at about 30-32mph at 6000rpm. I find it is a massive bottom end power prop. And nothing more. The boat feels like it could pull a 500lbs person water skiing and still not bog down even with a full boat of people.

 

[johnson89]

i have a 90 on a 16ft bass boat,14x17 alum.prop wot 5600 and 41 mph with 2 people,3 batteries 18 gal. gas.... my set up is a 1989 model

 

[emdsapmgr]

That 90 runs out of breath around 5800 or so. Twisting it to 6000 gets it out of the torque band. 17 is a good all around prop, but not made for high speed. You might try a 19 pitch prop-it might pick up a mile or two on top end-the prop should drop the rpm's to 5600-5700-in a good torque spot. If you start experimenting with stainless props, keep in mind that they are usually cupped and may have a nice rake angle. They bite the water better than an aluminum. A 17 pitch stainless will act more like an 18 pitch aluminum. If you go to a stainless, you may be able to further improve your performance by re-mounting your engine one hole further up on the transom.

 

[StingRay_90V4]

I checked where my engine is mounted at on the transim yesterday. It is mounted in the very bottom hole. So moving it up one hole sould help top speed ?

 

[fhhuber]

Adjusting height may help or it may just cause the prop to pull air as soon as you get up on plane. Then it will almost immediately have the engine rev up and top speed will go down.

its obvious when you move up too much.

 

[jakedaawg]

In my experience, other than failure to do basic maintenance, the leading cause of engine lifespan is asking it to do too much. A boat should be proped properly for wot rpm range, after that wot should be used only for short times. Stay within the cruising range and you will get longer life out of all the parts.

SS props cause a lot of failure up where I live. Hit a rock or stump and now you are replacing lowers and vertical shafts in stead of props and hubs.

Just my 2 cents from a guy who has seen several people repower after trying to get an extra MPH or two out of a perfectly fine motor. I doubt there are many people that dont have extensive performance boating/race experience that can tell the difference between 42 and 43 without looking at a gauge.

 

[StingRay_90V4]

So really the 41-42 mph i am getting is decent and on the realm of what other similar 90hp do at top speed ? I really dont want to blow it up. So really its not like i shoild be seeing 45+ mph and im getting 41mph kinda thing..

 

[emdsapmgr]

Maximizing the setup of the engine is important. It's free hp. Make sure the engine is not mounted too low on the transom. If the anti-ventilation plate is dragging in the water, you will see tons of water spray and poor performance and fuel economy. Start there first, get the setup (engine mounting height) correct-then fiddle with the props.

 

[V153]

Maximizing the setup of the engine is important. It's free hp.

Amen. I'd guess ya could go up a hole or two.

Dunno if your '93 hull is Stingray's 'Z-Plane' design or not. But if so i'd expect a lil better performance.

What is the 'max' hp rating? What does the hull weigh? Where is your propshaft in relation to the 'keel'?

 

[StingRay_90V4]

Its is indeed stingrays zplane hull. It is a 1993 hull. It weighs 825lbs WITHOUT engine. Its max hp rating is a 90hp. And currently it has the engine mounted in the bottom hole on the transim. I thought 41 mph was respectable for a old 90hp. i dont really notice a lot of spray from behind the boat pionting to a dragging anti-ventalization plate. But. I will double check.

 

[StingRay_90V4]

A little more info on this old thread. The boat is actually a 1992 StingRay 501Zp. Not a 93 like i had thought. The dry weight of the boat is 865lbs according to Stingray. So woth motor some gear and myself. I would say around 1400 to 1500 lbs total. I have not experimented with props yet. But i did raise the motor up one hole on the transom .which makes it up only one hole from the bottom last whole. It deffinitly picked up aboit 150 to 200rpm more at top speed. No performance loss in the handling department. My current Solas 17p prop still grips the water well at wot on a hole shot and at top speed as well as while turning at high speeds. My top speed went from 41 to 41 and a hlaf mph. Lol... I have on occasion seen 42 mph on my gps. My next goal is to raise the motor one more hole again and re test. If it starts to decrese performance. Then i will look for a 16 p ss.

 

[interalian]

My boat is an 880 pound (no motor) aluminum sport boat with no 'pad' and a less than optimal hull profile for speed. With the original '82 90hp and one peron it would do 42mph all day long at around 5200 turning a 13-1/4 x 17 aluminum prop.

The 90 is now a 140 (not fully dialled in) turning the same prop. I can take it over 6000 but it doesn't do much more than 44. I'll be trying a 19" prop and finalize the timing (it's a couple degrees retarded now).

 

[StingRay_90V4]

Sounds fairly close to about the same speed. I was durprised when i used a gps to see what the actual real speed was. Come to find out the in-accuracy of the boats speedometer is not liner. At one spedd it is dead on. At anither speed it reads slow. And yet at another speed it reads fast. Not what i expected. Either way. When my boat says 35 mph . My gps says 33 mph. And when my boat says 41 mph. My garmin gps says 42 mph. Thats the best in can get to date. And as of last night while testing our compression for the 5th time in a week. Lol... We dound out we have a weak cdi ( cd4 ) some call it. So i am going to be picking on up tomorrow to install. When i trsted its spark. It couldnt jump a 1/4 gap at all. On all 4 cylinders. And the spark tester bairly lights up once every 10 seconds. I will see how it works after a new cdi in a day or so. Maybe with a new stronger ignition o can get 42.5 mph. Lol...

 

[oldboat1]

If you are a performance guy, you might consider venting your prop or purchasing a vented prop -- better hole shots, and might be able to hit current speeds with slightly less motor stress, possibly cooler running.

sounds like some simple risk analysis is relevant, though -- 26 year old motor with some generic potential for ring issues. Puttering around on a pontoon would be one thing, but if you routinely run it balls to the wall, you increase the potential for failure. The decarb you mentioned in your other thread probably isn't going to add much insurance, and any overheating might do it in. (Get an open air spark tester, btw.)

Might just do a ring job on it over the winter -- prep it for Spring. JMO

 

[StingRay_90V4]

I used both a closed spark tester with a light in it. As well as an adjustable open air spark tester. As far as im comcerned. The dpark failed both tests. The light bairly lights up on the 90 v4 . Yet on my 60 hp rude it is a almost a constant bright red. Using the open air spark tester the spark wouldnt jump over a quarter of an inch.

I have to ask. Why does everyone keep tellimg me to take apart a good running engine to re ring it when the boat has great compression and works very well. I understand the crossflows like to do rings in after awhile. I just dont think im there yet with compression on ALL four cylinders 130 psi after the decarbing last night.


As for how we drive the boat. It would be fair to say it spends 50% of its time at or near wot.