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!!!!
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!!!!