90 Hp Rude ( Raised height results )

[StingRay_90V4]

So last year after i pulled our boat out of the water. I descided to raise the engine on the transom. It was sitting on the lowest possible holes. I only raised the engine up one hole. There are 4 holes in total. It now is on one hole up from the bottom. The anti cav plate sits pretty mich exactly level with the bottom of the boat. I am wondering if i should raise it up one more hole again. My results from raising the motor only one hole where very pleasing. The boat last year would get a top speed of 39 to 40 mph. Now , i am constantly seeing 41mph and it seems to creep up to 42mph once i awhile. So i deffinitly gained a mile per hour or two. More like 2 i would say. As well my tach seems to agree. I use to see a max of about 5400 to 5500 rpm. Now i see about 5800 to 6000 rpm at wot. Everything else seems to be exactly the same. Except i gained a few miles per hour at top speed. My hole shot is the same. No prop blowimg out at all. Even with the motor fully trimed up at top speed it will still take a good hard turn without slipping the prop. Which is why i think i could possible go one hole higher. Just a fyi. The boat is a 1996 16 foot Stingray 501 ZP. With a z plane hull. What ever that means. With a 1994 evinrude v4 cross flow 90 HP on it with a Solais 13 1/4D x 17P aluminum 3 blade prop. . That now will get 42 mph tops . the speed was confirmed by a Garmon gps. Surprisingly. The boats speedometer said 41.5 mph and the gps said 42mph. Strangly my gauage is slow. Where as i thought they would read fast. Does anyone think oli would gain anymore from raising my engine up one more hole ? Or if i should even bother trying it ? I mean.... How much more speed and performance can a 90 hp give out ? I think im probably at the top end for speed from this size of motor .

 

[jimmbo]

Raising the engine usually brings benefits(reduced chine walking) at speeds above 50mph. You are considerably lower than that. It also reduces leverage needed to raise the bow. If you keep raising the engine a prop with more rake and cup will be of benefit. You are already exceeding your engines RPM range, and the 90 makes its best power in the 5000 rpm range, so I would say you need more prop.

 

[emdsapmgr]

Raising the engine is a solid performance trick. Normally, the water flowing from under the transom should run back to just under the antiventilation plate (just above the prop.) That minimizes drag and performs well. You might call that a "factory" setting. As you've seen, raising the engine one hole will yield further improvements. Usually that's about as far as you can go with an aluminum prop. If you go yet another hole upward, you will probably start to see ventilation/slippage. However, you can go up that next hole if you are running a stainless prop. Those props are made to run in slight surface-piercing environments. The stainless props have lots of cup/rake to "hold" the water when the engine is running high. One, thing to be careful of when going the next hole higher. It's possible that the engine will be mounted too high and will run with the upper water intake hole out of the water. This can be a disaster-if some of the water bleeds back out of the top hole before it ever gets pumped to the powerhead. So, when you decide you want to move up a second hole, best to get a water pressure gauge and start to monitor the water pressure headed to the powerhead. Keep in mind that a 19 aluminum is not the same as a 19 stainless. The stainless props have more cup than aluminum, so the actual prop pitch on a stainless is about 1 pitch more than the prop says. Such as a 19 stainless functions more like a 20. As you keep raising the engine on the transom, at some point, you will have to consider moving up one prop size.

 

[StingRay_90V4]

I think for now im just going to leave the motor at the height it is right now. Which is only one hole up from the bottom. Its tops speed is faster then it has ever been in all the years we have owned the boat. And its handling did not suffer at all. So based off of what you are saying about the engine getting water or the lack there of , if it is raised too high. I will just leave well enough alone. Raising the engine the one hole already gave me nearly 2 mph. Not too bad for 45 minutes of work. As for a ss prop vs my aluminum. I have no idea which size stainless to get. My current aluminum is a 13 1/4 D x 17 P . It is about 8 years old and has a few dings and dents in it. As well as a few small pieces out of it. Maybe if the prop was brand new i would see even more top speed. what size stainless would you recomend i look at to be as close on the hole shot as my current aluminum but give me a tad more top speed ? Say a 18 P ? Or would that be going the wrong direction ? And i would need a 16 pitch ? I would love a ss that gives me even more hole shot and even faster top speed. If thats possible.

 

[StingRay_90V4]

Anyone able to recomend what type or sixe of stainless prop ro further my adventure ?

 

[emdsapmgr]

When you get ready to move the engine up another bolt-hole: You could go with one of the Bombardier 17 stainless. Called a Viper. Will run more like an 18. 763930

 

[jimmbo]

RAKER is one of the better props for raised engines and it will lift the entire boat out of the water. BRP does make them for the V4s

 

[emdsapmgr]

The Raker line is made in even pitches only. Lowest pitch Raker is an 18. Since it's a high rake, high cup prop, it is going to perform more like a 19. Whether you can spin this 18 Raker or the 17 Viper will be the result of your testing both of them Swapping and testing for the correct prop is a tedius, but really fun part of searching for optimum performance. Start checking to see if any of your buddies will let you try their props on your engine. Fun times ahead!