which prop 19 or 22?

[chris0061]

Hello fellow boaters, I just bought a 87 GT 150 for my 17 foot v hull ski boat. My question is this. On the 22 pitch stainless I was getting around 58 mph at 4800 rpm. Now on the 19 pitch alum. I'm getting about 50 mph at 5200 rpm. Which is better the 4800 or the 5200 or would anyone recommend a 21 pitch prop???? Thanks, Chris

 

[walleyehed]

Re: which prop 19 or 22?

The GT150 needs to be turning 5700-5800 under normal load conditions......4800 for very long and you'll be looking for another powerhead.
I've got "roughly" the same engine as you, just a few years older....a 200 with GT heads and a few other mods. I've spent alot of time fine-tuning my set-up (when I'm not testing props, because I tune/adjust height for every prop)..Jackplate and higher tech SS props. I'm in an 18ft alum deep-V, but I've got a fair amount of weight.
The 17ft ski boat depending on hull design, should show alot better numbers.
One thing we need to verify is the tachometer....this is the most important instrument in the dash and it's the gauge we use to determine the right prop.
I "think" we either have tach issues or possibly a sick engine....I can spin a 22P close to 5700 and over 6100 with a 19P SS.
Unless your boat is REALLY heavy, we've got one of the issues stated above.

EDIT....something is wrong here..I just figured your slip ratio with the numbers you give.
At 58mph, a realistic 12% slip, your RPM would have to be 5700, not 4800, so I have to ask..is the speed by GPS? if it is, the tach is WAY off.

 

[chris0061]

Re: which prop 19 or 22?

The mph are from the speedo and I realize they are far from right. The boat is a deep v. Its a 87 Fabuglas. When I got it I ran double mix threw it and the plugs look well oiled now. The boat with load weighs about 2500 pounds. So you think something is wrong here????????? The range for this motor is 4500-5500 on rpm and I have read that you want to be at least in the middle for your wot. Maybe I should go down to a 17 pitch prop to get the rpm's.

 

[walleyehed]

Re: which prop 19 or 22?

First, the RPM range has changed from when this engine was built in 1987....we don't have the quality of fuel we had in '87 and we've found that by raising the RPM 300-500 from the TOP of the original range, the engines of this vintage tolerate the newer fuels better and the engines last much longer. The GT/XP series was designed to run above specs anyway.
I rebuild these engines and I can tell you first-hand DO NOT prop this one under 5500.
Your stock powerpack has a rev limit of 5800...a couple of years after that they went to 6100. I have no limiter on my pack...I've ran mine well over 7000RPM.
As for propping, I don't think your speed is as far off as your tach is...and you're lighter than me with a better hull for speed. If you could get the tach verified or barrow a GPS we can get one of the 2 variables exact and then we can pin-point the area we need to work on.
I don't know what brand of 22P you have or where your engine is mounted height-wise, but the 22 "may not" be far off....
Can you get your hands on a GPS???
We can determine the problem asap if you can.....

 

[chris0061]

Re: which prop 19 or 22?

The 22 pitch is a raker. About the power packs when I got the engine a couple weeks ago I had to replace one pack with original omc part though. I doubt weather I can land a gps and the tach is new when I had the mechanic put the engine on. It even sounds better with the 19 pitch prop. you know you can tell your turning more rpm. The hight of the engine- the cavatation plate is about 2 inches above the keel of the boat, maybe not that much, I took a picture of it today incase you asked let me try to get it here.

 

[walleyehed]

Re: which prop 19 or 22?

OK, the Raker gives me an added bonus of info because I use the Raker on a regular basis as a test comparison prop.
If all you can get is 4800 RPM, the 22P Raker will produce about 48mph on that boat...not 58.
What brand of tach did you have installed? what setting is the tach on?
We've still got something off here...I can spin a 26P Tempest close to 5100-5200 and I have a much higher drag boat.
Was does the tach read when you have the engine at Idle, in gear?

 

[chris0061]

Re: which prop 19 or 22?

I'm not sure of the brand or the setting, I can look. At idle and in gear it turns 700 rpm. I pulled my plugs last night and they are rich. I got me a 3 gal tank and filled it up so today I'll run the rest of my heavy mix out get to harbor on the 3 gal tank and mix 50 to 1 and put a new set of plugs in. Around the edges on the bottom four plugs seemed like there were a clear spot around the edge of the plug sleeve the top two were pretty soiled. I checked spark and have great spark. the compression is right at 90 on my gauge. Cheap outozone gauge.. The tach is a teleflex and I don't know what it is set at. Do I have to pull the dash and look behind there? If so could you tell me what it should be set at so when I pull the dash if it is'nt your setting I can set it there? Thanks, Chris

 

[chris0061]

Re: which prop 19 or 22?

Say walley, do you think maybe I'm not trimming it enough???????? I just read that your rooster tail should be as high as you cowling. On my trim gauge I just trim it to the middle were the boat level line is on the gauge, should I be trimming it all the way up till the needle gets to the top mark?????????????

 

[walleyehed]

Re: which prop 19 or 22?

The gauge for trim is....well, let's forget about it...
Trim out until we get porpoise or slight venting of the prop, then touch'r back in a hair...

 

[chris0061]

Re: which prop 19 or 22?

Just got back, I been trimming right. took it up till venting then back a hair. Put new gas in, premium if that makes a difference, put new plugs in, took it back out up river about 5000 rpm with the 25 gallons of added gas and about 48 mph till my speedy quit working. going back down river hit the 5200. The currant on the Mississippi is very very fast now and I put in right above a dam. Do you think I have a problem here?????? I think I may have underestimated the weight of the boat. I think loaded with me and my wife it might be closer to 3000 pounds, I think the 1600 pound I thought the boat weighed I read was just hull, no motor. It seems to vibrate a little in the no wake zone at the harbor going out to the river but just a little gas and that goes away and runs smooth. I went to the Johnson trouble forum and asked the guys there if they thought it could be more than a sick engine, You got me nervouse saying that earlier. Anyway IF i'm not pulling the right rpms should I go to a 17 pitch just to make sure?

 

[walleyehed]

Re: which prop 19 or 22?

"Put new gas in, premium if that makes a difference,"
87-89 octane is the max you need...anything higher can truely cause problems, long-term.
Another thing that puzzles me is how going up or down stream can change the RPM....it changes my GPS speed, but I've never noticed anything noticably different on RPM.
At any rate, we use the 150's and 17P on the larger 19+ft runabouts.
I have no doubt that your rig should give me a run for the money but the numbers you have lead me to believe there is something in the engine, or "with" the engine that just is not right.
Try a 17 and see what ya get...we'll go from there...

 

[chris0061]

Re: which prop 19 or 22?

OK will do. Thanks......

 

[jerryjerry05]

Re: which prop 19 or 22?

To do this you need to test with a loaded boat. Run it full throttle check RPM.
5500-5800 should be max. If you run a 22 and you hit 4800RPM then pitch down to 21 then 20 19.
So much depends on kind of prop:stainless or aluminum.cupped or not. OEM or aftermarket.
Raker props.chopper props. regular, they all affect your motor differently.
The selection of prop as to what kind of boating you want to do.Fishing and watersking compared to racing use different kinds of props.Decide which kind you want to run,then go from there.Jerry

 

[chris0061]

Re: which prop 19 or 22?

That's kinda what I'm doing here Jerry, I went from the 22 stainless to the 19 alum and am looking for a 17 stainless now calling to see if a prop shop would take my 22 pitch Raker in for a 17. I'm not out there racing, I like the speed but I want the best performance for my engine not me. No skiers right now mainly my wife and I fishing and site seeing. Thanks for your input. Chris

 

[walleyehed]

Re: which prop 19 or 22?

If you want a Raker, you'll have to go with an 18P...they are even numbers only...

 

[chris0061]

Re: which prop 19 or 22?

OK sorry about the long delay but after getting rid of the Raker I bought a Michigan stainless 19 pitch off eBay and a 18 pitch turbo, took them out to test the Michigan got me at 5700 rpm and the turbo was about the same only the Michigan ran allot smoother. I'm getting a GPS should be here this weekend so when the river goes down I'll have another update. I noticed the Michigan didnt have the 3 extra exhaust holes like the turbo and the raker does and I also noticed that in the no wake zone with the Michigan there was no vibrations as with the turbo and the raker there was. Could this be because of those exhaust holes?