What prop do you run on your 20'

[QC]

Re: What prop do you run on your 20'

the tach is brand new this summer

There is usually a setting for 4, 6 or 8 cyl on the back (OB setting too). I would check that first

There is still something wrong if she's not getting out of the hole with a 17, but trying to clarify stuff for you . . .

 

[Tail_Gunner]

Re: What prop do you run on your 20'

Between 2500 and 3000 rpm. That's when i'm trying to get up on plane. and i can peg it at 3000 and it stays there until the boat is up, and it seems to take a bit longer when that miss occures. In a previous post i thought it was a dead spot, in the throttle range.

Here is the problem or a suspected issue..When the motor is under a heavy load it experiences a slight miss or stutters..Not good sounds like detonation


(and i can peg it at 3000 and it stays there until the boat is up, and it seems to take a bit longer when that miss occures)

Again that sounds like the ecm is retarding the timing..which effectivley lowers the engines output

Until this issue is resovled there is no benefit to repropping....Unless dropping to a 15p is the answer...Now a 15p prop on a 20' boat with a 300hp engine .....Thats not a solution....

 

[msojjo]

Re: What prop do you run on your 20'

There is usually a setting for 4, 6 or 8 cyl on the back (OB setting too). I would check that first

There is still something wrong if she's not getting out of the hole with a 17, but trying to clarify stuff for you . . .

Tach is all set up correctly for an 8cyl. I appriciate the help, i'm just at my wits end with this boat. I know that it is a heavy boat and it will take a while to get up. The original owner that i purchased it from had a 22 pitch bravo four blade prop. After my repower i really had trouble getting the thing out of the water, and i was only at 4000rpm wot, then i went to a 21 pitch tempest plus three blade prop, no change as it was reworked so who knows what it was really pitched at. Now i have on that 17 pitch and at least my rpm are in the range that they should be. As far as the motor goes, i'm not sure what to do next, full tune ups have been done, fuel system has been redone from fuel pressure regulator to each and every injector. New exhaust manifolds. If there is predetonation what causes this, and how do i fix it. I'ts all computerized and there is no way to adjust the timing.

 

[msojjo]

Re: What prop do you run on your 20'

Again that sounds like the ecm is retarding the timing..which effectivley lowers the engines output

Until this issue is resovled there is no benefit to repropping....Unless dropping to a 15p is the answer...Now a 15p prop on a 20' boat with a 300hp engine .....Thats not a solution....

Why is the computer doing this? How do i fix?


I'm with you with the whole 20' boat with 300hp and already a 17pitch prop, everyone else with this set up is running lower 20's props.

 

[msojjo]

Re: What prop do you run on your 20'

Ok, got the boat out of storage this year and were going to try it again. Over the winter i have talked to several mechanics about my problem, some were telling me the motor is bad, i need to start from scratch, and the last one that i talked to said "just bring it in, its probably something stupid like timing or a bad sensor, it will take less than a half hour to look at." I liked this mechanic. He was very confident from the beginning that he could figure it out. So, i took it in last week monday, he said he would try to get to it at the end of the week or beginning of next. So i get a call this morning that it is done ready to be picked up. What was it.......well the timing was off "retarted" by 16 degrees. How the hell does that happen. And by the way tells me i need to get a different prop. He was testing in the "test pond" and was pushing the truck up the ramp at 2000 rpm. Finally someone got it done.

 

[rrhodes]

Re: What prop do you run on your 20'

Congrats. Sounds like you should have fun this season. Let us know how it turns out for you. Also if you have a smart phone there are several GPS apps that will give you MPH. GPS HUD is the name.

 

[craze1cars]

Re: What prop do you run on your 20'

LOL. Yeah...16 degrees retarded will destroy HP and holeshot. That's why when so many people post here with prop questions, many of my answers may annoy the owners because they have far less to do with props and much more to do with figuring out the state of tune of the boat...when was the latest comprehensive tune-up done by someone KNOWLEDGEABLE, becuase so many times the problem is somewhere in the motor compartment, and NOT in the prop.

Tail Gunner was right all along, your timing was retarded.

As for answering your latest "how the hell does that happen"...I quote you yourself...

The original owner that i purchased it from had a 22 pitch bravo four blade prop. After my repower i really had trouble getting the thing out of the water

There's your answer. Whoever did the "repower" is the person who set the timing last, and clearly that person set the timing 16 degrees retarded...water under the bridge at this point, but clearly someone who I wouldn't trust to do major work on my boat in the future...

As for what prop you need now? I will speculate that the original 22 pitch Bravo 4 blade might be a good place to get some start data, now that the boat is tuned properly...do you still have it?

FWIW, you own a 60 mph boat...easily. Maybe even 65. On GPS. It autta rip now...

 

[Robbabob]

Re: What prop do you run on your 20'

GREAT NEWS!

Sounds like tail_gunner hit it on the head.... kept you focused on motor and the right mechanic worked on it.

Probably going back to a 20+P. Let us know when you can get it out on the water and get some testing in. You should be jumping outta the water, and be careful about the higher revs... you'll probably only be able to get up to 3/4 throttle before max RPM is achieved.

~yup, great news~

 

[Mac525]

Re: What prop do you run on your 20'

Thats great as I was reading down this post I was thinking to write to check the base timing and all the vacum hoses glad to hear you found a great tech

 

[msojjo]

Re: What prop do you run on your 20'

I haven't gotten with the times to get a smart phone yet, but i do have a hand gelp gps, so i'll be taking that onboard to see what she does, just have to go find my new prop, now i'm going from a 17 back to a 21.

 

[msojjo]

Re: What prop do you run on your 20'

LOL. Yeah...16 degrees retarded will destroy HP and holeshot. That's why when so many people post here with prop questions, many of my answers may annoy the owners because they have far less to do with props and much more to do with figuring out the state of tune of the boat...when was the latest comprehensive tune-up done by someone KNOWLEDGEABLE, becuase so many times the problem is somewhere in the motor compartment, and NOT in the prop.

Tail Gunner was right all along, your timing was retarded.

As for answering your latest "how the hell does that happen"...I quote you yourself...



There's your answer. Whoever did the "repower" is the person who set the timing last, and clearly that person set the timing 16 degrees retarded...water under the bridge at this point, but clearly someone who I wouldn't trust to do major work on my boat in the future...

As for what prop you need now? I will speculate that the original 22 pitch Bravo 4 blade might be a good place to get some start data, now that the boat is tuned properly...do you still have it?

FWIW, you own a 60 mph boat...easily. Maybe even 65. On GPS. It autta rip now...

Well its my falt for assuming that a certified merc dealer would put my motor in the boat, and do it correctly. I did know that i had a motor issue when i dropped down to a 17 and still couldn't get out of the water, i think i had the boat back to the dealer who repowered it close to 10 times, while they were just replacing parts, and not checking out the easy basic things. Of course i don't still have the 22 pitch bravo prop, i sold it, and probably sold it too cheap, oops. When i purchased the boat the owner did say it was an over 60 mph boat, we'll just have to see how much over now.

 

[msojjo]

Re: What prop do you run on your 20'

GREAT NEWS!

Sounds like tail_gunner hit it on the head.... kept you focused on motor and the right mechanic worked on it.

Probably going back to a 20+P. Let us know when you can get it out on the water and get some testing in. You should be jumping outta the water, and be careful about the higher revs... you'll probably only be able to get up to 3/4 throttle before max RPM is achieved.

~yup, great news~

So, by the way thanks to tail gunner for keeping me focused on the motor, and that something just isn't right. I love this site......I'll be hopefully out on the water this weekend testing it out....thanks all......

 

[Tail_Gunner]

Re: What prop do you run on your 20'

Its hard to say where your at with that combo...Id try to find a 21p alum as a spare and take a read from there...Solas makes a good cheap 4 blade alum..That should net you 60...A 21p prop is a lot for a 1.5 ratio...maybe a 22 but i doubt it..Good luck

 

[steelespike]

Re: What prop do you run on your 20'

wow! Its allways great when you find a solution.Looks like Tailgunner had the right idea.
It seems you have found an honest mechanic that knows what he is doing.

 

[thejetman]

Re: What prop do you run on your 20'

What is an interupt switch? Why would i be experiencing predetonation? How do i solve it?

Put premium gas in it.

 

[msojjo]

Re: What prop do you run on your 20'

Its hard to say where your at with that combo...Id try to find a 21p alum as a spare and take a read from there...Solas makes a good cheap 4 blade alum..That should net you 60...A 21p prop is a lot for a 1.5 ratio...maybe a 22 but i doubt it..Good luck

I'm looking at 21 pitch mirage props on craigslist, i think that should be a good place to start, as when i purchased it he had a 22 pitch 4 blade on it. After the repower i was only pushing 4000 rpm wot, but now with the timing change, that should be cranked up quite a bit......i should probably run the 17 pitch thats on it and just see where i'm at, so i don't have to purchase too many props..................

 

[QC]

Re: What prop do you run on your 20'

If the engine is right, you will know immediately. I don't think you'll learn much though, as you will not be able to push it. Is there anywhere to just run a quick test? As TG pointed out you need two props, and yes this 17 can be your spare, but I love running my boat. So much so, that if I have an issue with anything I want it running right in 10 minutes, not the next trip. Spare props give you that if you are close on performance. You need some useful data, that will mean something, before you buy the final one.

 

[msojjo]

Re: What prop do you run on your 20'

If the engine is right, you will know immediately. I don't think you'll learn much though, as you will not be able to push it. Is there anywhere to just run a quick test? As TG pointed out you need two props, and yes this 17 can be your spare, but I love running my boat. So much so, that if I have an issue with anything I want it running right in 10 minutes, not the next trip. Spare props give you that if you are close on performance. You need some useful data, that will mean something, before you buy the final one.

Your right, i'll end up getting the 21 pitch prop right away this weekend and see where i'm at so i can dial it in before the summer starts.....

 

[msojjo]

Re: What prop do you run on your 20'

Well i went and purchased a 21 pitch mirage plus with the performance vent system for 175 bucks, and it's in great condition. I haven't been able to get it on the boat, because i wanted to try out the boat after being fixed and make sure that everything was in good working order. And boy is it, i had five adults sitting in the back of the boat with a 3/4 tank of gas, and it came on plane very nicely even with just easing into it and going to only half throttle. I didn't get a chance to go wot with it to see what it would actually do, but cruising at 4200 rpms i was going over 40 mph, so i should easily get 50 mph out of this prop. So the question is do i keep this 17 pitch prop on the boat for the small lake that i keep the boat on, and use the 21 for when i go to bigger lakes like castle rock lake and lake winnebego. Or do i just throw the 21 on and get a cheap aluminum for a spare, and sell the 17. Or do i sell both and get a 19 pitch prop.

 

[craze1cars]

Re: What prop do you run on your 20'

You won't know the answer to any of those questions until you have a chance to run WOT with the 21.

After that run, you can use the results to make a prop decision. No doubt in my mind that the 17 is way under propped for your rig. Holeshot will indeed be stunning, that's where the benefits end. If you leave the 17 on that boat you will burn more fuel than necessary, create more wear & tear than necessary, run the risk of over-revving when you have an opportunity to get on it (or hopefully first slam into the rev limiter if it has one), which will give you very limited top speed, etc...

For example, you say you need to spin 4200 rpm to go only 40 mph now. That's insane for a 300 hp V8 on a 20 ft runabout. Your motor should be more than capable of cruising that rig at 40 mph at only about 3000 to 3200 rpm. Currently you are doing the equivalent of taking your every-day driver vehicle out on the interstate, putting its 5 speed automatic transmission in 3rd gear manually (or maybe even 2nd gear), and then setting the cruise control at 75 mph and just letting the motor spin like that for miles and miles. Your throttle response would be fantastic, while everything else would suffer. I think you'd agree it would be rather senseless to do such a thing with your car on the highway...

And it makes no more sense to do it with your boat.

Run the 21 and report back. That 17 needs to be sold. It will serve as a fine spare to get you home in an emergency, but otherwise it has absolutely no place on your boat...sell it to someone with a 3.0L...many of them run 17's.

Like I said earlier, you have a 60 mph boat...EASILY. Many people on this board would kill for a boat that nice, and with so much extra power to spare. Now that you have it running properly, don't waste its fantastic potential by propping it like a 20 year old 3.0L runabout LOL...

Enjoy it!