Mercury XR6 150 2.5

**Jnorris3** · 04-11-2021, 12:43 PM

What makes each engine different that uses the 2.5 block? Am I mistaken that the crank and bore are all the same on a 150, 175, and 200? Trying to figure out the differences.

**rock** · 04-11-2021, 03:01 PM

Welcome to the site. Ports, exhaust, tuner, and carbs or injection.

Rock

**Jnorris3** · 04-11-2021, 03:55 PM

Rock, Thanks. So you can put 150 parts on a 175 or 200 or visa versa in any configuration to make what engine you want?

**rock** · 04-11-2021, 05:37 PM

If you want to change ports, machine exhaust, and swap to correct fuel supply. It's not just bolt on stuff.

Rock

**Jnorris3** · 04-11-2021, 06:42 PM

Rock, when I look up power heads online it says for a 150,175,200. How can that be if the heads off of either 3 would bolt on? I understand there would be restriction if going backwards but wasn’t that the design to reduce horsepower?

**bullet123** · 04-12-2021, 04:31 AM

The blocks are out of the same mold. The difference is internally. porting sizes and locations. Not really financially feasible to turn a 150 block into a 200 block

**Smalltownbassin** · 04-12-2021, 06:13 AM

What everyone has already said is true, but...the xr6 is a special kind of 150 from the factory. Straight off the assembly line it makes close to 165HP being just inside the +-10% rated HP. If my crappy memory serves me right, Merc made these to suit the professional angler who at the time had a max HP limit of 150 in tourneys. The xr6 gave them an edge.

**Jnorris3** · 04-12-2021, 07:00 AM

Thanks for the comments. So the engines are different based on porting on the inside. Which would mean the 150 heads wouldn’t match 175 or 200 ports or visa versa? What about the carbs and ignition and things like that? The same? Interchangeable? Would a 200 power head run with 150 carbs or visa versa?

**rock** · 04-12-2021, 07:03 AM

Say you look at the inside of the exhaust chest of the 3 motors you will see how the 200 is less restrictive than the lower hp. If you look at just the tuners you will see the 200 is the shortest therefore the less restrictive. That is just the exhaust side and the same holds true for the intake side, combustion chambers in the heads, differences in the ecu on injected motors, sizes and locations of the ports and timing yet they all bolt together in the same patterns. Totally different on the inside yet look identical on the outside and are same physical size. The motor with mismatched parts would probably run just not correctly. Hope that ain't too confusing.

Rock

**bullet123** · 04-12-2021, 07:29 AM

Originally Posted by Jnorris3

Thanks for the comments. So the engines are different based on porting on the inside. Which would mean the 150 heads wouldn’t match 175 or 200 ports or visa versa? What about the carbs and ignition and things like that? The same? Interchangeable? Would a 200 power head run with 150 carbs or visa versa?

The heads are same bolt pattern. They are interchangeable. the only difference would be the cc volume in combustion area. ignition systems are identical if they are in the same era. carbs have same bolt pattern, but have different jetting and venture sizes.

**bullet123** · 04-12-2021, 07:30 AM

heads are basically flat pieces of aluminum with 3 depressions machined into them

**LakeFever** · 04-12-2021, 07:36 AM

Originally Posted by Jnorris3

Thanks for the comments. So the engines are different based on porting on the inside. Which would mean the 150 heads wouldn’t match 175 or 200 ports or visa versa? What about the carbs and ignition and things like that? The same? Interchangeable? Would a 200 power head run with 150 carbs or visa versa?

two stroke heads are not like four stroke heads. Two stroke heads are for compression and holding the spark plug. That’s it. Two strokes work on heat generated vacuum. The ports are in the walls of the cylinder and these are machined/ground to a size and shape pending hp. You can grind the small ports open to the same or more than a 200 but the shape and consistency has to be precise or you won’t have an engine that runs for bird poop. It take enormous time for the most seasoned pro to do this work. As an amateur this process is daunting, not impossible mind you but it is very labor intensive.

based on your posts and the advice above if more power is what you want? Sell the xr6 and buy a 200 or promax etc.

**25two.stroke** · 04-12-2021, 10:14 AM

Originally Posted by LakeFever

two stroke heads are not like four stroke heads. Two stroke heads are for compression and holding the spark plug. That’s it. Two strokes work on heat generated vacuum. The ports are in the walls of the cylinder and these are machined/ground to a size and shape pending hp. You can grind the small ports open to the same or more than a 200 but the shape and consistency has to be precise or you won’t have an engine that runs for bird poop. It take enormous time for the most seasoned pro to do this work. As an amateur this process is daunting, not impossible mind you but it is very labor intensive.

based on your posts and the advice above if more power is what you want? Sell the xr6 and buy a 200 or promax etc.

I think when Jnorris3 was saying the "heads" are all different he was referring to the powerheads not the actual bolt-on heads...what has the porting. Jnorris3, just for your info I wouldn't call the powerheads "heads" cause that can cause all sorts of confusion with the actual cylinder heads. If you are trying to ask about the differences in actual cylinder heads then that's a whole different conversation.

**Jnorris3** · 04-12-2021, 10:28 AM

If you blow a power head(rod through block) and put a new power head on, what have you put on? When advertised for sale on the internet they are listed as a 150, 175, 200. All being a 2.5. Now if you had 150 carbs and ignition and all to put back on it. It would be a 150? Same for a 175? And 200? I guess maybe I’m not understanding how it can be advertised at that if it wouldn’t work that way? Because the porting is different on a 200 and putting 150 parts back on it wouldn’t work correctly? Or would it? Just with restriction?

**25two.stroke** · 04-12-2021, 10:57 AM

Originally Posted by Jnorris3

If you blow a power head(rod through block) and put a new power head on, what have you put on? When advertised for sale on the internet they are listed as a 150, 175, 200. All being a 2.5. Now if you had 150 carbs and ignition and all to put back on it. It would be a 150? Same for a 175? And 200? I guess maybe I’m not understanding how it can be advertised at that if it wouldn’t work that way? Because the porting is different on a 200 and putting 150 parts back on it wouldn’t work correctly? Or would it? Just with restriction?

When you say post on the internet you gotta be more specific. Do you mean some random ebay listing claiming that its a rebuilt one-size-fits-all powerhead, or do you mean straight from mercury they are saying theres only one powerhead to put on? Mercury had different powerheads for the following (that had different porting)

135/150 tha same in 2.5
XR6/MagIII
175
200

If you have a specific part number for a block you are looking at we can help you id what it is.
And no, if you bought a 200 hp ported replacement powerhead for a XR6 and bolted all your stuff on you would not have a 150hp XR6 or a 200 hp...you would be somewhere in between and would want to re-jet to make that block happy.