Mercury V6 2.0-2.5 litre powerhead interchanging.

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Jwsav

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Joined
Dec 31, 2011
Messages
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I will try to make this as breif as possible. This will let you know what powerheads you can put on what midsections.

This discussion is for all powerheads except the 77-78 175 with Large Open Exhaust Wiindows.

On all of the 150 Midsections they have an adapter plate with the larger rectangular Ports.
Most of the 175 and 200 Motors had a smaller Rectangular Port.

all 2.0-2.4 Litre Powerheads can be bolted to the 150 midsection. If you are using a 2.5 Litre Powerhead it is suggested that you use a 1992-up midsection OR use the adapter plate for 92-up Motors. The water Jacket area on the 2.5 Litre exhaust adapter flows more water required to keep the larger motor cool. You can use the older adapters but the cooling would be better with the newer adapters.

The 2.4 and 2.5 Litre 200 Exhaust adapters have the smaller exhaust ports so if you were to install a 150 or 2.0 Litre powerhead you would be blocking some of the exhaust flow. You can open the ports up if you know what your doing and you are handy with a Die Grinder.

So......
1979-up 150 Midsection can be used with all 1979-1991 2.0 (150) and 2.4 (175 and 200) Powerheads straight up, minimal headaches.
If you are Running a 92-up 2.5 Litre 150-200 on the ol;der midsection/adapter, You should replace the exhaust adapter with the newer style to accomodate water flow.
All 1992-up 2.5 Litre Midsections can be used with all of the powerheads 1979-up. Remember 150 ports work with all powerheads. 200 ports need to be opened up to accomodate the larger ports on the older 150 powerheads.

Now onto the important part!
The 150 and some older 175 powerheads used a 2:1 gear ratio in the lower unit whereas all of the 2.4-up 175 and 200 motors used the 1.87:1 ratio.
if you drop a 150 powerhead onto the 200 mid Lower you will have to Lower the prop pitch which is not a good idea, You would be better off with the 2:1 ratio lower unit gears. All of the 2:1 Lower units can be used with any of the powerheads including the 2.5 Litre 200 (you may need to pitch up on your prop).

So......
If you are moving up from a 150 powerhead to a 175 or 200 everything is straight forward and easy whereas if you are downgrading to a lower horsepower powerhead you will run into headaches.

Hope this helps you guys out. Confused? Drop me a line and i will give you better details. If you are experiencing any technical or troubleshooting problems with any 2.0 - 2.5 Litre powerhead including race motors, drop me a line. I have seen it all and can most likely help you diagnose your problem with a fuel simple questions. Enjoy your boating season!!!!
 

shadow21

Recruit
Joined
Apr 19, 2012
Messages
3
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

As you said , i am asking you something than ..

A problem i am encountering .. I have a 2.5 Ltr 200 HP 1998 EFI ...
with shaved heads 34cc .average compression is now 136 psi for the 6 pistons
and with brucato svs plus ACU adjustable unit as well
Last thing is it got a BOBS TUNer and Exhaust releiver from BOBs as well..
and Alien Cowling

This combination did not do any damage anywhere in the outboard..


Last week i decided to take off the EFI system and install Carbs instead ...

What happened was that the noise of the outboard was heard even louder than that with EFI... but it did not last long that the GASKETS between the Block and Mid Section was blown off..

we changed with New Gaskets and went testing again NOW what happened was that the Exhaust TUNER from BOB broke .. and fell low in the mid section

Am i rite saying that with the CARBS the engine made made power ...)) ???
and could be that the gas temerature now is too High to handle for the BOBS Tuner ???

and that is the reason why we are breaking down ???

Please note FUEL used at 97 octane ...

What could we do ???

Is it worth changing the midsection from the original 2.5 Ltr to the 2.0 Ltr XR2 one.???

Any ideas will help

Thanks

Clyde

SHADOW21
 

Jwsav

Cadet
Joined
Dec 31, 2011
Messages
7
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

As you said , i am asking you something than ..

A problem i am encountering .. I have a 2.5 Ltr 200 HP 1998 EFI ...
with shaved heads 34cc .average compression is now 136 psi for the 6 pistons
and with brucato svs plus ACU adjustable unit as well
Last thing is it got a BOBS TUNer and Exhaust releiver from BOBs as well..
and Alien Cowling

This combination did not do any damage anywhere in the outboard..


Last week i decided to take off the EFI system and install Carbs instead ...

What happened was that the noise of the outboard was heard even louder than that with EFI... but it did not last long that the GASKETS between the Block and Mid Section was blown off..

we changed with New Gaskets and went testing again NOW what happened was that the Exhaust TUNER from BOB broke .. and fell low in the mid section

Am i rite saying that with the CARBS the engine made made power ...)) ???
and could be that the gas temerature now is too High to handle for the BOBS Tuner ???

and that is the reason why we are breaking down ???

Please note FUEL used at 97 octane ...

What could we do ???

Is it worth changing the midsection from the original 2.5 Ltr to the 2.0 Ltr XR2 one.???

Any ideas will help

Thanks

Clyde


SHADOW21

A properly tuned EFI setup will alway produce more power than carbs. Are you saying that the bobs tuner broke? Are you using the stock blue powerhead gaskets?
 

sschefer

Rear Admiral
Joined
Nov 13, 2008
Messages
4,530
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

Which carbs were you trying to run. Do you have EGT's on it? Why did you decide to go to carbs? Who cut the heads?

I'd take one of Tony's SVS setups over carbs for overall performance any day. On a drag motor I'd be running WH's with a 1" spacer plate is that where you're trying to go with this motor.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

You also forget to list that the tuners are different between the 150 and 200.........The ACU if dialed in will make more power than carbs.
 

Jwsav

Cadet
Joined
Dec 31, 2011
Messages
7
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

You also forget to list that the tuners are different between the 150 and 200....

Yes, I was just touching the surface on powerhead interchangeability. Did not want to get too detailed or create more confusion than necessary.

So, yes. The 2.0 litre large port adapter uses a straight non-flanged tuner whereas the smaller port 175,200 uses the "bell" style or flanged tuner. The Bob's tuner is basically a replica of the old style 2.4 High Performance tuner most commonly used on the 2.4 Bridgeport and mod vp powerheads. I would like to hear some more details about your engine woes and thought I would mention that 136 psi cranking compression is fine on 91-93 pump premium fuel. If you are going to continue to run 97 + octane fuel you should use the thinner head gasket and try to bump your compression a little higher. Are you using the stock 2.5 200 head gasket now ?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

The Bobs tuner is just a stock 200hp tuner that's been lengthened a inch and flared, the Mod Vp and Bridgeport tuners where just stock tuners but bolted to a 1 piece adapter plate.
A problem i am encountering .. I have a 2.5 Ltr 200 HP 1998 EFI ...with shaved heads 34cc .average compression is now 136 psi for the 6 pistons and with brucato svs plus ACU
What rpm are you trying to turn? Is this the Shadow Tunnell hull? Did you recut radius on head after shaving?
 

shadow21

Recruit
Joined
Apr 19, 2012
Messages
3
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

The Bobs tuner is just a stock 200hp tuner that's been lengthened a inch and flared, the Mod Vp and Bridgeport tuners where just stock tuners but bolted to a 1 piece adapter plate.

What rpm are you trying to turn? Is this the Shadow Tunnell hull? Did you recut radius on head after shaving?



Thanks to all of you for your reply,

What you mean by ( Did you recut radius on head after shaving ? )

I am sending you more accurate information ...

I re done Compression test today..of 2.5 ltr outboard

pistons on PORT side No1 130 psi
No3 136 psi
No5 140 psi

pistons on Star Board side No2 142 psi
No4 148 psi
No6 149 psi

Both heads have the 1mm thin gaskets from Brucato and Rings done new ( just a month ago)

Both Heads checked and shaved at 34cc

The rpm i am trying to turn is not more than 6400 rpm

we are turning it rite now at 6200rpm with the EFI system ..SVS and ACU adjustable unit from Brucato..
with a 9% slip and we can turn it 6000rpm with a 6% slip using the same propeller being a 25 Pitch HRB series from POWER TECH the difference is adding a 2" spacer from BOBs ..to an existing 8" Jack Plate from BOB s this puts the slip down by 3% but still run the same speed

By the way i am replacing the carbs and go back to EFI, much safer ....

and of course i am replacing the existing BOB s broken TUNER with a new one from BOB s ..

Whilst checking the Plugs BUHW , i discovered that the engine came a bit lean , with the 200HP carbs WMV and perhaps thats why at first it blew away the gaskets betwen the Block,Alien Cowling tray and Mid section and
as someone of you guys noted the High Temerature was the cause of the BOBS Tuner to Fail...the propeller even showed evidence of the outboard being Lean , with the EFI the part of the propeller from where the exhaust comes out used to look BLACK with the carbon ..

While after trying the Carbs WMV on the propeller seems more cleaner with a lot less of carbon

I guess i was lucky not to make any damage to the outboard ..

By tomorrow i will install the EFI system and even a 1" intake spacer . done at alocal CNC shop

What you think about the 1" intake spacer ??? will it help with Torque only???

I will contact Tony Brucato and buy an EGT system with Probes so i will monitor the EGT temp and perhaps wil help more for a safer set up .

Any more suggestions on how to improve the power with an EFI set up as i got is appreciated ...

Thanks

Shadow 21
 

Jwsav

Cadet
Joined
Dec 31, 2011
Messages
7
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

Thanks to all of you for your reply,

What you mean by ( Did you recut radius on head after shaving ? )

I am sending you more accurate information ...

I re done Compression test today..of 2.5 ltr outboard

pistons on PORT side No1 130 psi
No3 136 psi
No5 140 psi

pistons on Star Board side No2 142 psi
No4 148 psi
No6 149 psi

Both heads have the 1mm thin gaskets from Brucato and Rings done new ( just a month ago)

Both Heads checked and shaved at 34cc

The rpm i am trying to turn is not more than 6400 rpm

we are turning it rite now at 6200rpm with the EFI system ..SVS and ACU adjustable unit from Brucato..
with a 9% slip and we can turn it 6000rpm with a 6% slip using the same propeller being a 25 Pitch HRB series from POWER TECH the difference is adding a 2" spacer from BOBs ..to an existing 8" Jack Plate from BOB s this puts the slip down by 3% but still run the same speed

By the way i am replacing the carbs and go back to EFI, much safer ....

and of course i am replacing the existing BOB s broken TUNER with a new one from BOB s ..

Whilst checking the Plugs BUHW , i discovered that the engine came a bit lean , with the 200HP carbs WMV and perhaps thats why at first it blew away the gaskets betwen the Block,Alien Cowling tray and Mid section and
as someone of you guys noted the High Temerature was the cause of the BOBS Tuner to Fail...the propeller even showed evidence of the outboard being Lean , with the EFI the part of the propeller from where the exhaust comes out used to look BLACK with the carbon ..

While after trying the Carbs WMV on the propeller seems more cleaner with a lot less of carbon

I guess i was lucky not to make any damage to the outboard ..

By tomorrow i will install the EFI system and even a 1" intake spacer . done at alocal CNC shop

What you think about the 1" intake spacer ??? will it help with Torque only???

I will contact Tony Brucato and buy an EGT system with Probes so i will monitor the EGT temp and perhaps wil help more for a safer set up .

Any more suggestions on how to improve the power with an EFI set up as i got is appreciated ...

Thanks

Shadow 21


I am not happy with your compression readings. You should be 5 psi diffrence between cylinders. Is it completely broken in? Who cut the heads? You need to cc them. Sounds like one head is not cut the same or possibly 2 different head gaskets? And yes, the bobs tuner is pretty much a replica of the 2.4 mod-vp/Bridgeport tuner. The first gen Tuner was longer than the 200 tuner etc. the 2nd gen towards the end of production of the 2.4 mod vp/ bridgeports had the longer tuner with the flared end just like the Bobs. It's a great add on to your setup if your using the stock 2 piece adapter. Is this block stock? Or has it had any exhaust cavity mods or porting? The spacer is good for bottom-midrange it will hurt you on the top end though. When I have a second I will explain what the purpose of the spacer is for the perf motors. I have been building and modifying these engines for 28 yrs. I will help you with whatever I can. You need to find out what the deal is with those heads. Are the casting numbers the same on both heads? What is the number on the carbs after the WMV? You can email me at 247erepair@gmail.com. Faster responses and easier for me to type it out. I have about 10 questions for you so email me as soon as you get a chance so I can reply.
 

shadow21

Recruit
Joined
Apr 19, 2012
Messages
3
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

I am not happy with your compression readings. You should be 5 psi diffrence between cylinders. Is it completely broken in? Who cut the heads? You need to cc them. Sounds like one head is not cut the same or possibly 2 different head gaskets? And yes, the bobs tuner is pretty much a replica of the 2.4 mod-vp/Bridgeport tuner. The first gen Tuner was longer than the 200 tuner etc. the 2nd gen towards the end of production of the 2.4 mod vp/ bridgeports had the longer tuner with the flared end just like the Bobs. It's a great add on to your setup if your using the stock 2 piece adapter. Is this block stock? Or has it had any exhaust cavity mods or porting? The spacer is good for bottom-midrange it will hurt you on the top end though. When I have a second I will explain what the purpose of the spacer is for the perf motors. I have been building and modifying these engines for 28 yrs. I will help you with whatever I can. You need to find out what the deal is with those heads. Are the casting numbers the same on both heads? What is the number on the carbs after the WMV? You can email me at 247erepair@gmail.com. Faster responses and easier for me to type it out. I have about 10 questions for you so email me as soon as you get a chance so I can reply.

Hi Thanks once again

First answer ?
YES the engine is completeley broken in by now ?90 minutes since new rings and first 60 mins done at 3500rpm only
Heads cut a local shop .he is stating that they have been cut to 34cc .. the number on the heads are both the same being 18488-05
Perhaps I take them to be rechecked to another engineering shop to be sure they bare the same
YES we are using the stock 2 piece adapter
YES block is stock as well
Carbs are WMV 3326 8282-72-0
Do you mean the 1? spacer will increase midrange but will decrease top end revs ? therefore speed will decrease or stay as it is ???
I am changing back to EFI again .and going to install the 1? spacer As well ? do you recommend /
As timing for this outboard what do you recommend in degrees please ???
Another thing is I am interested to buy the 52K REX2, ???..from Brucato

it comes with a two display head unit and two EGT probes, rifle bolts, extension leads, tach lead, and software.

I guess it helps me with the maximum EGT it can handle .

i am advised not over do it and keep it around 1200 degrees fahreneit
What you think ???
crownfibre@waldonet.net.mt
Clyde
 

fullon627

Recruit
Joined
Jun 2, 2012
Messages
1
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

I will try to make this as breif as possible. This will let you know what powerheads you can put on what midsections.

This discussion is for all powerheads except the 77-78 175 with Large Open Exhaust Wiindows.

On all of the 150 Midsections they have an adapter plate with the larger rectangular Ports.
Most of the 175 and 200 Motors had a smaller Rectangular Port.

all 2.0-2.4 Litre Powerheads can be bolted to the 150 midsection. If you are using a 2.5 Litre Powerhead it is suggested that you use a 1992-up midsection OR use the adapter plate for 92-up Motors. The water Jacket area on the 2.5 Litre exhaust adapter flows more water required to keep the larger motor cool. You can use the older adapters but the cooling would be better with the newer adapters.

The 2.4 and 2.5 Litre 200 Exhaust adapters have the smaller exhaust ports so if you were to install a 150 or 2.0 Litre powerhead you would be blocking some of the exhaust flow. You can open the ports up if you know what your doing and you are handy with a Die Grinder.

So......
1979-up 150 Midsection can be used with all 1979-1991 2.0 (150) and 2.4 (175 and 200) Powerheads straight up, minimal headaches.
If you are Running a 92-up 2.5 Litre 150-200 on the ol;der midsection/adapter, You should replace the exhaust adapter with the newer style to accomodate water flow.
All 1992-up 2.5 Litre Midsections can be used with all of the powerheads 1979-up. Remember 150 ports work with all powerheads. 200 ports need to be opened up to accomodate the larger ports on the older 150 powerheads.

Now onto the important part!
The 150 and some older 175 powerheads used a 2:1 gear ratio in the lower unit whereas all of the 2.4-up 175 and 200 motors used the 1.87:1 ratio.
if you drop a 150 powerhead onto the 200 mid Lower you will have to Lower the prop pitch which is not a good idea, You would be better off with the 2:1 ratio lower unit gears. All of the 2:1 Lower units can be used with any of the powerheads including the 2.5 Litre 200 (you may need to pitch up on your prop).

So......
If you are moving up from a 150 powerhead to a 175 or 200 everything is straight forward and easy whereas if you are downgrading to a lower horsepower powerhead you will run into headaches.

Hope this helps you guys out. Confused? Drop me a line and i will give you better details. If you are experiencing any technical or troubleshooting problems with any 2.0 - 2.5 Litre powerhead including race motors, drop me a line. I have seen it all and can most likely help you diagnose your problem with a fuel simple questions. Enjoy your boating season!!!!


I have a 1988 Sea Ray that has a 135hp V6 built by Mercury with a blown powerhead. It has it's own paint scheme. I would like to keep it original, but would like to upgrade to more power.Will the powerheads fit under my original cowling? My boat is just like this one: http://boats.iboats.com/1988-sea-ray-seville-18/766537.html

Thanks for any info.
 

Jwsav

Cadet
Joined
Dec 31, 2011
Messages
7
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

The boat you showed me has a mid 90's motor on it. If you have a 1988 motor then you will have the cowl that looks like a split clamshell style but it is a 1 piece liftoff hood. If your looking to keep it simple a 2.0 litre 150 powerhead would drop right in its place. Just remember the carbs you are running are only good for a 135. If you want to up the power you need a drop on powerhead. Everything but carbs and exhaust divider plate can be used with another engine. If you wanted to run a 175 or 200 powerhead you would need to swap out the tuner in the midsection sounds like a 150 would be a good replacement for you.
 

riversbluff

Recruit
Joined
Jun 27, 2011
Messages
4
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

Ok..great thread.

Its sounds like I have a similar situation..but would like just a little more peace of mind.
I have a 96 2 liter 150 hp merc...blown powerhead..I want to replace the powerhead with a 2000 model..2.5 liter 200hp. merc.
If I have read correctly..this should be a simple bolt on project.
Please correct me if I am mistaken.

Excellent info...thanks
 

Helton 18

Recruit
Joined
Mar 27, 2013
Messages
1
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

Can I put a '95 Merc 200 2.5 L EFI powerhead on a '88 Merc 200 2,4 midsection? I have a '98 Merc 200 2.5 L exhaust plate to put on the 2.4 midsection.
Thank you.
Helton 18
 

pnestor1

Recruit
Joined
Apr 22, 2013
Messages
1
Re: Mercury V6 2.0-2.5 litre powerhead interchanging.

I will try to make this as breif as possible. This will let you know what powerheads you can put on what midsections.

This discussion is for all powerheads except the 77-78 175 with Large Open Exhaust Wiindows.

On all of the 150 Midsections they have an adapter plate with the larger rectangular Ports.
Most of the 175 and 200 Motors had a smaller Rectangular Port.

all 2.0-2.4 Litre Powerheads can be bolted to the 150 midsection. If you are using a 2.5 Litre Powerhead it is suggested that you use a 1992-up midsection OR use the adapter plate for 92-up Motors. The water Jacket area on the 2.5 Litre exhaust adapter flows more water required to keep the larger motor cool. You can use the older adapters but the cooling would be better with the newer adapters.

The 2.4 and 2.5 Litre 200 Exhaust adapters have the smaller exhaust ports so if you were to install a 150 or 2.0 Litre powerhead you would be blocking some of the exhaust flow. You can open the ports up if you know what your doing and you are handy with a Die Grinder.

So......
1979-up 150 Midsection can be used with all 1979-1991 2.0 (150) and 2.4 (175 and 200) Powerheads straight up, minimal headaches.
If you are Running a 92-up 2.5 Litre 150-200 on the ol;der midsection/adapter, You should replace the exhaust adapter with the newer style to accomodate water flow.
All 1992-up 2.5 Litre Midsections can be used with all of the powerheads 1979-up. Remember 150 ports work with all powerheads. 200 ports need to be opened up to accomodate the larger ports on the older 150 powerheads.

Now onto the important part!
The 150 and some older 175 powerheads used a 2:1 gear ratio in the lower unit whereas all of the 2.4-up 175 and 200 motors used the 1.87:1 ratio.
if you drop a 150 powerhead onto the 200 mid Lower you will have to Lower the prop pitch which is not a good idea, You would be better off with the 2:1 ratio lower unit gears. All of the 2:1 Lower units can be used with any of the powerheads including the 2.5 Litre 200 (you may need to pitch up on your prop).

So......
If you are moving up from a 150 powerhead to a 175 or 200 everything is straight forward and easy whereas if you are downgrading to a lower horsepower powerhead you will run into headaches.

Hope this helps you guys out. Confused? Drop me a line and i will give you better details. If you are experiencing any technical or troubleshooting problems with any 2.0 - 2.5 Litre powerhead including race motors, drop me a line. I have seen it all and can most likely help you diagnose your problem with a fuel simple questions. Enjoy your boating season!!!!

Hello -

I bought a used powerhead. I had this powerhead installed on my lower unit. I saw the mechanic start the motor: rev, forward, reverse. I was told later today that the motor was running hot because the exhaust plate does not match the replaced powerhead. He says he needs to pull the powerhead back off and get the correct exhaust plate.

I believe one powerhead to be a 1981 and the other (Bad One With Thrown Rod) to be an early 90s. How can I isolate whether:
1) He is being totally up front
2) That both units are 2.4

I read your post and purchased the used powerhead believing it would interchange because the years span so long for this subject. Thanks in advance for any help with this.
 

RTB87

Cadet
Joined
Jul 16, 2014
Messages
17
Hi their so I want to try and get this straight My father in law has a blown 2.4 carb power head and has a running 2.5l alien style cowl power head from what I've read I can swap the 2.5 onto the 2.4 mid without a problem I just have to use the exhaust plates and tuner from the 2.5...not sure of the year of the motors I'll have to get that for ya if it makes a difference Thanks
 

Dukedog

Captain
Joined
Oct 6, 2009
Messages
3,235
Yes it can if your using tha 2.5 adapter plates (both pieces) makes it easy. Be sure tha get power head and adapter plate gaskets for tha 2.5......
 
Last edited:

RTB87

Cadet
Joined
Jul 16, 2014
Messages
17
Thanks dukedog I'll let you all know how it works out for me when I'm done
 

Starquesttsi

Recruit
Joined
Mar 22, 2019
Messages
1
I will try to make this as breif as possible. This will let you know what powerheads you can put on what midsections.

This discussion is for all powerheads except the 77-78 175 with Large Open Exhaust Wiindows.

On all of the 150 Midsections they have an adapter plate with the larger rectangular Ports.
Most of the 175 and 200 Motors had a smaller Rectangular Port.

all 2.0-2.4 Litre Powerheads can be bolted to the 150 midsection. If you are using a 2.5 Litre Powerhead it is suggested that you use a 1992-up midsection OR use the adapter plate for 92-up Motors. The water Jacket area on the 2.5 Litre exhaust adapter flows more water required to keep the larger motor cool. You can use the older adapters but the cooling would be better with the newer adapters.

The 2.4 and 2.5 Litre 200 Exhaust adapters have the smaller exhaust ports so if you were to install a 150 or 2.0 Litre powerhead you would be blocking some of the exhaust flow. You can open the ports up if you know what your doing and you are handy with a Die Grinder.

So......
1979-up 150 Midsection can be used with all 1979-1991 2.0 (150) and 2.4 (175 and 200) Powerheads straight up, minimal headaches.
If you are Running a 92-up 2.5 Litre 150-200 on the ol;der midsection/adapter, You should replace the exhaust adapter with the newer style to accomodate water flow.
All 1992-up 2.5 Litre Midsections can be used with all of the powerheads 1979-up. Remember 150 ports work with all powerheads. 200 ports need to be opened up to accomodate the larger ports on the older 150 powerheads.

Now onto the important part!
The 150 and some older 175 powerheads used a 2:1 gear ratio in the lower unit whereas all of the 2.4-up 175 and 200 motors used the 1.87:1 ratio.
if you drop a 150 powerhead onto the 200 mid Lower you will have to Lower the prop pitch which is not a good idea, You would be better off with the 2:1 ratio lower unit gears. All of the 2:1 Lower units can be used with any of the powerheads including the 2.5 Litre 200 (you may need to pitch up on your prop).

So......
If you are moving up from a 150 powerhead to a 175 or 200 everything is straight forward and easy whereas if you are downgrading to a lower horsepower powerhead you will run into headaches.

Hope this helps you guys out. Confused? Drop me a line and i will give you better details. If you are experiencing any technical or troubleshooting problems with any 2.0 - 2.5 Litre powerhead including race motors, drop me a line. I have seen it all and can most likely help you diagnose your problem with a fuel simple questions. Enjoy your boating season!!!!






So can the 150 powerhead with the large rectangle ports be used with the 77-78 175 (large open exhaust window) midsection?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Yes as long as you use a rectangle exhaust adapter plate....it will not if you use the 175 large port.
 
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