Not enough power

[Cptkid570]

Hi everyone,

I installed the reman 260hp longblock in my 26' searay and I'm not getting the speed that I think I should be getting. Yesterday, with a 14x 17 prop, I was going 16 miles an hour at 4000 rpm. I have trim tabs and did use those.

I'm trying to figure out what the problem is.. the engine runs smooth and doesn't sputter or anything with it's at the 4000 rpm. I'm going to check and see if the boat is water logged and if it's just too heavy of a boat for the engine to push. I'm also going to maybe try a 15 pitch prop.

I came across the list in this post: "engine won't reach operating RPM"
http://forums.iboats.com/showthread.php?t=201320

Of the items in this list, will any of these cause the engine to run poorly and sputter and stuff? -- like if it isn't getting enough gas or air? or if the timing was off?

 

[Haut Medoc]

Re: Not enough power

Something is wrong.....
You should be able to get 4200-2600 out of a 14x17 prop....
Granted, it is a lot of boat for a 350, but it should do better than that....
I would start with making sure the timing is right & all of the plug wires are in the correct position & functioning.....
This is a TBIV ignition?......​

 

[Cptkid570]

Re: Not enough power

Yes, Thunderbolt IV. The thing is, it runs smooth...if the timing were off that bad, wouldn't it sputter and backfire?

Is 4000 rpm the same regardless of how the engine runs to get to the 4000 rpm? As in -- if I have a 14x17 pitch prop spinning with the motor at 4000 rpm, shouldn't I be on a plane? I tried a 14x19 prop too, and wasn't getting the 4000 rpm.

I'll go over the timing again -- because the timing may be a little off.. but, I was thinking that it should still push the boat if the engine will get to the 4000 rpm.

 

[Haut Medoc]

Re: Not enough power

Yeah, it should......
The prop is in good shape?....
It is possible that the hull is waterlogged.....
Do you have access to a different prop?....​

 

[Cptkid570]

Re: Not enough power

It's definitely possible that the hull is waterlogged.

I've only tried the 17 and 19 pitch props... I may try a 15 pitch if I can get my hands on one.

 

[180shabah]

Re: Not enough power

17' prop, 4000 RPM and 16 MPH, just doesn't jive. Zero slipage would equal 43 mph, so your speed should be double what you have now at 4000RPM. Is the tach accurate, how are you measuring speed?

 

[John_S]

Re: Not enough power

I doubt the prop is the issue, but you might consider buying the 15" diameter series once you figure out what the true issue is. Most larger boats, like yours, run that diameter. The 14" diameter is "generally" more for the I/O runabaouts. The 15" will give you more bite on acceleration.

Since its a new motor, check the easy stuff first. Throttle plates opening all the way, base timing and total advance timing, plug wires, etc. Scale the boat and hopefully it isn't water logged. Then go through the rest of Don's list.

 

[QC]

Re: Not enough power

I'm with Shabah. Something is initially wrong that is not engine or even boat related. I am going with a 1.32 gear ratio and the numbers aren't even close. One or more of the numbers ^^^^^^ is wrong. 4000 RPM with that ratio is indeed over 40 MPH, with 20% slip it is 39 MPH . . . Although I am not sure why a slipped hub would allow for only 4000 RPM that number could be off too. We need the tach verified, the prop hub checked, the gear ratio confirmed and the speed verified by GPS. Without that we are chasing this with very bad info or we are looking past the obvious . . . I guess it could be a monster ventilation issue, but either those numbers are wrong, or this thing is slipping somwhere to the tune of over 67%

 

[whywhyzed]

Re: Not enough power

Is 4000 rpm the same regardless of how the engine runs to get to the 4000 rpm?

to answer that question- yes.

 

[Cptkid570]

Re: Not enough power

Speed was checked by GPS... not positive if the tach is 100% accurate, but just from the sounds of the engine speed, I would bet that it is..

I'll check the outdrive and make sure it's the proper drive.

What gear ratio am I supposed to have??

 

[Haut Medoc]

Re: Not enough power

!.5 : 1.......​

 

[whywhyzed]

Re: Not enough power

It ran fine before the longblock? Did goblins come to the marina at night and switch outdrives with you?

 

[Cptkid570]

Re: Not enough power

I bought the boat at a project and it didn't run when I bought it.. so, I don't know what it was like for the prior owner...

 

[QC]

Re: Not enough power

I am getting a 1.32:1 ratio, but am using an unreliable source . . . Where do you get your info Messr. Medoc?

 

[Coors]

Re: Not enough power

An '88 is 1:41...

 

[QC]

Re: Not enough power

The numbers are sooooo far off the ratio really doesn't matter much at this point . . . need to find out why your are getting RPM (at least we think so) and the prop isn't turning as fast as it should (RPM divided by gear ratio). . . Maybe it is, but it isn't doing it right . . .

 

[Cptkid570]

Re: Not enough power

If the engines timing was off, could it hurt the performance this much?

If it's not that, I'm thinking that the boat foam is waterlogged and the boat is too heavy.

 

[180shabah]

Re: Not enough power

If the engines timing was off, could it hurt the performance this much?

If it's not that, I'm thinking that the boat foam is waterlogged and the boat is too heavy.

Stop worrying about power. If you are spinning 4000RPM and only getting 16 MPH while doing it, something is slipping. Three possibilities, coupler, prop hub, and prop/water(ventilation/catitation). I would be looking at the last one first.

What is the height of the anti-ventilation plate in relation to the bottom of the hull?

Do yo have any through hull fittings?, If so, where are they in relation to the drive?

What items do you have mounted to the transom, where are they in relation to the drive?

 

[QC]

Re: Not enough power

^^^^^^ Yes, yes, yes!! ^^^^^

 

[SuperNova]

Re: Not enough power

Lime4x4 has an '86 Searay Weekender 26' with the exact same problem. We are going to experiment with props, I think he's not getting enough bite in the water to push the boat.
--
Stan