Speed Question, 21' Triton w/225 Optimax

[WB4IUY]

Been helping a friend with the conversion of a '99 Triton to a '04 225 Mercury Optimax EFI. Changed to a QuickSilver surface mount transmission control and uses a Hotfoot, pile-o-wiring changes for that and the smartcraft transducers. Engine had a new power head installed. We also installed a SmartCraft guage system. It's just come off of the break-in period, runs great, nice and smooth, not dropping cylinders, no alarms on the smartcraft. He installed a 4-blade prop he had on the previous '99 Optimax 225. Boat runs about 60mph, will not turn over 5000rpm.

 

He said his previous '225 Optimax engine turned way over that. I'm lost, this is way outside of my wheelhouse and my experience with my little Johnson 70 ? . I felt like if it were a fuel delivery problem it would be going into alarm and not running good, but that's just my opinion. Any ideas?

 

Dave

Edited October 20, 2019 by WB4IUY

[MN Fisher]

2 minutes ago, WB4IUY said:

Boat runs about 60mph, will not turn over 5000rpm.

Don't know what year it is - but the 2012 Product Handbook states that the 225 Optimax has a max RPM of 5000-5750.

https://www.mercurymarine.com/static/pdf/product-handbook/Mercury-Outboards-links.pdf

 

[WB4IUY]

It's a 2004 engine. Thanks for the tip. I'm searching for 2004 info now on google.

 

Dave

 

[WB4IUY]

OK, I found the Factory spec as being 5000-5700 rpm at WOT. With a 4-blade, I'm guessing it would be on the lower end of that. I know the previous engine had a different lower unit. I see the factory spec on the lower unit for '99 & '04 is 1.75:1. Wondering if there's a different lower with different ratio that might have been swapped onto it, if that's even doable? We don't really know that the '99's lower end (the motor that pushed the boat faster) is the original, it was destroyed in a log crash on the lake, so we can't swap to it to test. I never rode on the boat with the old engine, but he said the boat was considerably faster with the previous engine, and also rev'd higher with the same prop.

[Russ E]

Number of blades is not the main factor in rpm.

blade pitch is what determines how fast the motor will turn at WOT. a higher pitch is the same as a higher gear ratio. 

Sounds like there are a lot of unknowns in the new motor. a different lower unit gear ratio, would definitely change top speed.

If it were my boat I would try a prop with one or 2 inches lower  pitch. That would raise your rpms.

It may or may not increse top speed, but it will give you better acceleration.

some shops will let you try a different prop. they will hold yours, until you bring it back.

they will also reccomend a prop, if you tell them what is going on.

 

I am not a mechanic. I am just speaking from my own experiences.

I am sure others with more knowledge will chime in shortly.

[WRB]

Do you have a jack plate? standard equipment for most 21' Tritons. If you changed lower units make sure it's the same length as the original, standard is 20" shaft.

what pitch and prop? 4 blade isn't enough detail, ie 24" Fury 4.

This boat should run 70+ mph @ 5700-5800 rpm's IMO.

Tom

 

 

 

[Jig Man]

Motor height is very important. You need to measure your p2p ( prop to pad).  If you are more than 4” then try raising the motor.  Do that about 1/2” at a time then take it for a run.

 

When I bought my current boat I was told that it would turn 6000 rpms and run 70.  It turned 5500 and barely ran 65.  The prop to pad was 6 1/2”.  I have it at 3 1/2”.  Now it turns 6000 and runs 70 with 55 gallons of gas and 2 people.

 

If you guys aren’t very experienced operators, be careful as chine walking may occur and that can get you killed.

[WB4IUY]

Thanks for the tips, guys. We're pretty sure the P2P is too deep. He's used to dealing with the chime walking thing, the previous setup on his Triton was a '99 225 Optimax w/4-blade (same prop as now), and would push the boat around 78mph on the GPS. He's gonna check the P2P and adjust that.

 

Just can't get the motor to turn past 5000 rpms /60 mph with the current setup. Runs great, no misfires, no alarms on the SmartCraft, throttle body looks to be almost 100% open with the hot foot all the way down. Power head has passed the break-in period. Everything seems OK otherwise.

 

Still looking ?

[WRB]

Plane surface to centerline of prop shaft parallel is 3 1/2”. I assume no jack plate? Fast boats chine walk is usually the driver skill.

Tom

[Further North]

I love topics like this.  Always learn things. 

[WB4IUY]

On 10/22/2019 at 5:27 PM, WRB said:

Plane surface to centerline of prop shaft parallel is 3 1/2”. I assume no jack plate? Fast boats chine walk is usually the driver skill.

Tom

Thanks Tom. He's checking the jack plate settings now. It's a manual version where you move bolts into different holes to set the height. He said it was a bit low and working on that. Still wondering why it won't rev above 5000. Runs great, thinking it would be misfiring if it were starving for fuel on the top end?

[WRB]

On October 25, 2019 at 6:39 AM, WB4IUY said:

Thanks Tom. He's checking the jack plate settings now. It's a manual version where you move bolts into different holes to set the height. He said it was a bit low and working on that. Still wondering why it won't rev above 5000. Runs great, thinking it would be misfiring if it were starving for fuel on the top end?

When the engine is set at the correct height and the prop pitch* is optimized for the 225 hp the boat reach 70 mph speeds. Just take it easy with the trim so you don't start chin walking, a fine edge on the pad and balance.

Tom

* 4 blade prop is a little tricky to max performance with over 24P

[Way2slow]

If the motors have the same style lower unit, with same gear ratio and he's running the same prop on the 2004 motor he had on the 1999, their performance should be about the same. 

Has a compression or preferably a leak down test, been done on the motor.  Sounds like he has just bought himself a nightmare.

The first thing I would do is find a shop that has a good dyno and knows how to use it, and have the motor checked out because it sounds like the performance is way down on that motor.

[WRB]

Agree, new power head doesn't mean it's a good new power head.

Tom

[Way2slow]

I noticed in one of your other post you said the throttle body looked "almost" 100% open.  Almost is not good enough, it has to be 100% open.  

Prop height being low will only cause a couple of mph slow down from the extra drag the LU is creating, it's not going to make that big of a difference (unless it's way down and the anti-cav plate is dragging under water) but even at that, shouldn't cause that much of a slow down.

 

Another thought, someone may have put a 200 ecu on it.  I'm not a black motor mechanic and know little about them, but I think the main difference between the 200 and 225 is the programming in the ecu.

Unless it was from one of the few, reputable, engine builders, there is no telling what it's got for a powerhead.  I've seen builders go through and only repair damaged parts, not even bore the whole block, slap a new set of rings in and call it a remanufactured power head.  Several years back, when I was more involved in this stuff, I know one guy that over the years changed company names three times because he would do that and when enough people got the word out, or looking for refunds, he would disappear and show back up later with a different name.  Scream and fly banned him from their sight every they found out he owned the company he was doing business under, and he was a major builder.  

Remanufactured means all machined surfaces have been inspected and checked for tolerances and/or machined and all wearable parts have been replaced.

Rebuilt, can be as little as just having any broken parts replaced and maybe a new set of rings. Basically, they got it running again. 

If you are not doing the work yourself, outboard engine repair is one of the biggest rip offs going.  If you can find an honest, reputable mechanic, your lucky, and don't complain about what he charges, he's worth it.  They are hard to come by.

[Mason Bohland]

Having an issue with my 04 Tr-21x w a 225 opti as well, not sure what the original prop was, but we ran about 68 top speed, that prop has since been replaced and we now have a 26 pitch turbo, but we somehow run higher RPM 5900(which is too much) and only 55-60 top speed. I’m really not sure what is going on with this and it has me concerned, but the motor runs great, just not near the speed we had before. Any help would be appreciated 

[MN Fisher]

Contact Triton, ask them what the OEM prop was - diameter, # of blades and pitch.

[Michigander]

29 minutes ago, Mason Bohland said:

Having an issue with my 04 Tr-21x w a 225 opti as well, not sure what the original prop was, but we ran about 68 top speed, that prop has since been replaced and we now have a 26 pitch turbo, but we somehow run higher RPM 5900(which is too much) and only 55-60 top speed. I’m really not sure what is going on with this and it has me concerned, but the motor runs great, just not near the speed we had before. Any help would be appreciated 

I've got two props for my Merc 250 on a TR-21. One runs way higher RPMs and lower top speed but better hole shot. The other is lower RPMs and higher top speed but worse hole shot. Probably just your prop's properties.