1985 150xp vs 1979 175

[1983 ercoa 21']

I have both of these motors im going to put one of them on my tritoon.
my question is which is the better motor?
both have good compression.
I'm bypassing the bro on the 150xp .
I know there is someone here that has experience with both motors your input would be greatly appreciated.

 

[Faztbullet]

Use it 150 as it almost the same as the 175.......

 

[boobie]

Use the 150 as there's not much difference between the two.

 

[emdsapmgr]

A 150 XP/GT makes 10% more hp than a base 150, or about 165 hp. It uses the 1 5/16" throated 175 carbs, but is jetted down to make just 165. They both should be crank rated those years, so the 10 hp diff is real. Same blocks, porting and rpm operating ranges. My guess is that the 175 has the old style 150/175/200 higher compression heads and also has the special (200/235) rubber intake filler blocks, worth 5-8 hp. The 175 may have the original high ring pistons, which can be problematic on this year's V6 engines, but is desired for their ability to make higher compression. Original 1985 power packs may be limited to 5800 rpm's, but original 79 packs are unlimted-tho it's unlikely that the engine may still have original packs on it. As the guys noted, the performance should be close, but I'd give the nod to the 175, considering the performance (heads/filler blocks) goodies on it. The XP has a better cowl decal and the unique side vents.

 

[1983 ercoa 21']

It was my understanding the 1985 150 XP was prop rated is my understanding wrong?
yes I had read somewhere the XP was more like 165 hp .
I do alot of boating and fuel economy is a plus to me with the lower compression heads I should be able to run the cheaper lower octane fuel rather than the premium shouldn't I?

 

[1983 ercoa 21']

Plus the XP has the higher amp alternator

 

[emdsapmgr]

Good catch! Some of the engines were rerated in the 1985 model year, that's correct. Possible that this XP was rated for propshaft hp. I know the 200 was re-rated that year down to 185 hp. That could make a 10-15 hp swing difference, a net of 5 hp, now in favor of the 150. The factory parts list are unclear as to which amp system/flywheel was used on the 150 engines. Both the 10 and 35 amp systems show as options for the 150XP for that year, hp. The 175 hp parts lists for 1985 V6 shows that the 35 amp was only on the 175, 185 and 235. Very confusing factory parts lists. One way to verify for sure: Visually check the flywheels. The vented flywheel is the 35 amp model. You will be able to run lower octane fuel in the 150. If I owned the 175 and ran it at the original factory set timing, original heads-I'd be running premium. I purchased a rebuilt 150 XP factory long block in 1985. Had low compression bathtub heads, but came with a tag indicating that the timing should be set at 30 degrees. Quite high-and a reason they would perform well-despite the heads.

 

[1983 ercoa 21']

Yes I have the vented flywheel

 

[Faztbullet]

Since its going on a toon go with the 150 as if the 175 is original the pistons it wont live long under lugging conditions. It was a bassboat mota for high end rpm..

 

[1983 ercoa 21']

Think I'm gonna pull the bypass covers on both motors and check for high or low ring gland

 

[emdsapmgr]

So, it is the larger 35 amp charging system. Should really keep up with the radio on the pontoon! It would be pretty unusual for the 79 to still have the original high-ring factory pistons. Agree-a good thing to check, tho.

 

[Faztbullet]

It will be hard performance wise to see the 10hp difference on a toon

 

[1983 ercoa 21']

Guess I'm not so much about the performance as I am the durability. I have always ran evinrude and Johnson motors but the have always been v4 s and down. I have never owned a. Good merc.

 

[Faztbullet]

The 150 will be your best bet for performance and durability as it has all the improvements/updates that the factory found that was needed from 1979 to 1985. As posted it will have the 35amp output which is great for dual battery set-ups or stereo/amp systems. Be aware that these are a little more thirsty on fuel than a looper motor and make sure you prop it for max top end rpm.

 

[1983 ercoa 21']

I'm assuming since your saying that I should prop it for max rpm your saying that is best so not to lug the motor and not because that's where it needs to be ran most of the time? I have always found a probably proper motor is more efficient than one that's not. I ran a cupped 3 blade 13 3/4 x 13 on my 115 crank rated motor that was on this boat before I'm starting with a 14 3/4 x 15 4 blade on this motor

 

[emdsapmgr]

Obviously the gear ratio in the V6 is different from the V4. Possible the 15 pitch will be ok. Good prop to start with as you test run it. Run a prop on it that will let the engine run up to 5500 rpm's. It's ok if it revs to 5600.

 

[1983 ercoa 21']

Out of all the things I have thought of the gear ratios being different wasn't one of them. I chose to start with the 15 simply based on similar boats running the same pitch. What is the difference between gear ratios?

 

[emdsapmgr]

The V6 gear ratio is much taller,even though it swings a larger prop. That V6 has the torque and power, so has a higher ratio (on the consumer models.) That's why a V6 with a 15 pitch will out run a V4 with a 15 pitch (at the same rpm) if they were tested on the same boat.

 

[1983 ercoa 21']

That makes sense I was scared that a 15 would be to low and over rpm the motor not so worried now