Which powerheads can I swap onto a 1989 2.0L 20" 150 HP Mid?

**pjbrownva** · 06-07-2018, 11:29 AM

Inspired by this post: https://www.screamandfly.com/showthr...0hp-midsection

I'd like some general advice about power heads that I can bolt up to my 1989 150HP 20" mid and lower unit.

Are there certain sizes and/or years that will work?

Can I get, for example, and 200 HP Optimax head and drop it on?

Can I drop an older (say 2005) 225 HP EFI head on this mid?

I'm not looking to cut or heavily modify anything. If you were to tell me that I could use a certain powerhead but would need
to purchase a different exhaust plate (assuming that the exhaust plates just mount up) that would be fine.

I know these are basic questions for the hard-core racers, but for a fishing boat guy like me, this is entirely new territory.

Thanks in advance for the info.

Sincerely,

-Philip

**bullet123** · 06-07-2018, 11:51 AM

Optimax no. 3.0 liter no. Any 2.0, 2.4 or 2.5 liter will bolt to that mid. Will have to change exhaust plates to match powerhead. The only other thing would be tilt and trim. Older (like yours) are 3 wire with solenoids and newer are 2 wire with relays. Its not a big deal. easy conversion

**rock** · 06-07-2018, 02:52 PM

A 2.5 Optimax will fit but you must either swap out your adapter to an Optimax adapter or you can modify your current adapter to allow for a water supply for the air compressor.

Rock

**pjbrownva** · 06-07-2018, 04:54 PM

Originally Posted by rock

A 2.5 Optimax will fit but you must either swap out your adapter to an Optimax adapter or you can modify your current adapter to allow for a water supply for the air compressor.

Rock

Thanks for the info on the 2.0, 2.4 and 2.5 heads. What is the adapter? Is this an inexpensive part that I can purchase?
If anyone has a link to the adapter part or could post a photo that would be awesome.

Once I see the parts, I can better determine what's needed. Modifying my adapter to allow for a water supply to the air compressor would also work... although I realize that
I'd need to learn more first.

also, is the adapter just a different name for the mid section?

I really like the idea of putting a 2.5 optimax head on it... that would be a dream come true!

-Phil

**vnemous** · 06-07-2018, 05:33 PM

The adapter is also called the exhaust plate. Its between the mid and block and contains the upper motor mounts

**bullet123** · 06-07-2018, 05:49 PM

I wasn’t trying to mislead you about optimax. Just trying to keep it simple. Maybe it’s because I’m not a big fan of the optibombs. Used Exhaust plates are relatively easy to find. I would think $50 would find you a set

**pjbrownva** · 06-07-2018, 05:55 PM

Originally Posted by bullet123

I wasn’t trying to mislead you about optimax. Just trying to keep it simple. Maybe it’s because I’m not a big fan of the optibombs. Used Exhaust plates are relatively easy to find. I would think $50 would find you a set

That makes sense. I certainly didn't think you were trying to be misleading. I'm interested in an optimax, because I like the idea of better fuel efficiency.

Even if I end up spending more on the motor, somehow, I just prefer to have lower consumables. So, the motor is a sunk cost (at least in my mind), but every time I take a trip,
the amount of fuel I burn is dependent on how far I go... and that's where the cheapness sets in... If I burn a lot of gas, I don't like to go far. If I end up with good fuel economy,
then the cheapskate in me will feel better about taking a long ride. :-)

Are Optimax motors really that unreliable? I know that you can have BIG issues if water gets into the fuel, and somehow gets into a part of the motor (the high pressure pump, or the injectors... I'm not sure), but I thought that a good filter, and using "quick klean" could help with that problem.

Plus, I like to fish and ski, so I'm not a speed demon (40 mph is fine for me), and I probably only put 20 to 40 hrs on a motor per season -- if that much!

**bullet123** · 06-07-2018, 06:13 PM

They had their problems. Maybe it was just the early years. Somebody else can give you better advice on an optimax.

**rock** · 06-08-2018, 06:59 AM

I have heard the stories about the opti's. Many are related to the early models and I think they revolved mostly around the air compressors. That issue was resolved by a change in design. The only one I owned was used for probably 10 years or more on my Allison bx02 and ran flawlessly. Fuel mileage tripled from the 200 efi I was running before and speed increased due to the extra torque. If you boat a lot the motor will pay for itself in fuel savings.

Rock

**vnemous** · 06-08-2018, 07:30 AM

^agreed^

**Onetime** · 06-08-2018, 07:48 AM

Don’t think an Opti powerhead will fit in the original cowl. Not enough room in the rear for the compressor.

**rock** · 06-08-2018, 07:52 AM

And you are most likely correct. Good point as alien cowls can be expensive.

Rock

**Onetime** · 06-08-2018, 08:16 AM

Even with an alien cowl it’s a special, unique to 200XS, bottom plate to move the cowl further back for compressor clearance.

**Fishinmymission** · 06-08-2018, 09:10 AM

I just put a 2006 175 opti head onto a 1995 carbed motor. You need to run either the EFi/carbed cowl(upper and lower) from 1996-1997 till end of life (135, 150 or 175), or an optimax cowl (135, 150, 175) 1998 till end of life. Around 2002 2003 optimax 2.5 L (135-175) upper cowl changed design and the upper cowl became 11 lbs lighter. Lower cowls from everything stated above are the same.
Of course all of the racing xs or alien cowls will also fit you just have to install them as you have the adapter plates exposed.
I happen to have an older heavier 135 upper optimax cowling I can let go for $50 plus shipping if interested.

I also messed up the adapter plates (had two mismatched plates. One year the thermostats return water were in the lower plates, another year they were in the upper plates, I of course had one of each plate and no where to plug in my cooling return lines) had to end up drilling and tapping after I installed the engine but it was easy to figure out and no worse for wear. I'm loving the efficiency fishing this year.

**pjbrownva** · 06-08-2018, 12:12 PM

Originally Posted by Fishinmymission

I just put a 2006 175 opti head onto a 1995 carbed motor. You need to run either the EFi/carbed cowl(upper and lower) from 1996-1997 till end of life (135, 150 or 175), or an optimax cowl (135, 150, 175) 1998 till end of life. Around 2002 2003 optimax 2.5 L (135-175) upper cowl changed design and the upper cowl became 11 lbs lighter. Lower cowls from everything stated above are the same.
Of course all of the racing xs or alien cowls will also fit you just have to install them as you have the adapter plates exposed.
I happen to have an older heavier 135 upper optimax cowling I can let go for $50 plus shipping if interested.

Thank you.I also messed up the adapter plates (had two mismatched plates. One year the thermostats return water were in the lower plates, another year they were in the upper plates, I of course had one of each plate and no where to plug in my cooling return lines) had to end up drilling and tapping after I installed the engine but it was easy to figure out and no worse for wear. I'm loving the efficiency fishing this year.

Thank you. I think I need to get an opti power head first, but if/when I do, If you still have the cowl, I'll reach out to you about purchasing it.