TOPIC: New horse in the stable

I picked up a 75 or 74 mercury 150 20 inch leg for 200 hundred tonight. It came with controls and two old merc tanks and a thunder bolt tach. 5 props made trip to my house also. He had paper work showing a complete rebuild in 2003 and then the transom on the Hydrodyne broke in 04 leaving the motor untouched till 09 when the boat was bought taken for a hell ride and then removed to fix the transom. Then refitted with a V6 Jonnie 175. Compression and spark checked out good so I might have got a good deal on a motor it didn't need. horay Question how much better do you think this motor will preform over my 76 115 worth the swap? Thank for any and all input Mike ps anyone looking for a thunderbolt tach?

Sounds like you got a pretty sweet deal, congrats Mike. Which boat are you thinking about putting the 150 on? That's a lotta HP!

I am thinking that I will be putting it on my 74 MFG tri haul we love to tube off it it so it could be a nice set up for that. not sur if the extra hp would be needed?

I'm supposed to go look at a G'tron V186 after work tomorrow night, with no motor. May be looking for something for it real soon.....

The 1150 and 1500 are the same 99 cubic inch motor, same crank same pistons same most everyting..

The 1500 is ported differently letting it create more HP on the upper RPM band I believe.

I have heard that the 1150 had more torque low end for pulling skiers, but lacked the high speed power that the 1500 had.

If on a light boat and high speed is the key the 1500 will walk away if they are in equal condition.

If on a family boat lugging skiers out of the hole the 1150 may be a better choice.

Conrad

Hi,
I have swapped a 75 1150, for a 75 1500 it was on a Hydrostream so it was for top speed intentions. The 1150 did about 59 mph the 1500 did about 64 mph. Everything was the same including the prop. The speed difference will be smaller on a heavier boat.
Just to expand on earlier posts, Conrad is correct on most of his post except, The 1500 does indeed have differnet porting, the intake ports are larger on the 1500 and there is a third intake port that uses a hole in the piston as a transfer port, there is a corresponding groove in the cylinder wall to provide passage of the intake charge. The pistons are the same size but they are different with the addition of the hole, the skirt has an inside bulge to thicken the wall a bit around the hole, os it's not even as simple as the same piston with a hole added. The exhaust porting is the same. The 1500 porting breathes better so more HP on the top end but it does diminish the low end torque. Torque is what gets your boat up out of the water, not hp strictly speaking.
I found the 1150 a bit snappier at low speeds, but ran out of punch near the top end RPM. which makes sense, similar to a high torque cam vs a high rpm cam on a 4 stroke.
Personally I'd go for the 1150 for tubing etc. the extra low end torque would be useful, granted some of this loss could be made up with a lower pitch prop if you do use the 1500. The other thing to consider is the 1500 is a lot more fussy when it comes to fuel. Detonation damage is far more frequent on these motors that the 1150. Fuel consumption will be slightly worse with the 1500.
In my case it was a vintage high performance boat so I thought it only "right" to have the higher hp motor on it.
Good luck,
Randy

Randy,

So the early blue stripe 115's had no power port? This is the era that they had the 150's

Did the 115 become the 90 and the 150 become the 115 in the later years and did the power port only remain on the larger motor?
Thanks
Conrad

Hi Conrad,
So it is a little complicated but here it goes, I have the catalogs and manuals as well as taking many of them apart (in line 6's are my "thing") to piece this story together but still I may be off here or there but, essentially this is the progression. I'll stick to piston/porting/hp changes over time. starting in 72 there was the 1150 and the 1400, the 1400 had bigger ports but no power porting. In 73 Merc powerported the 1400 and it became the 1500 this line up of 1500/1150 remained unchanged till 76 where the 1150 and 1500 where similar except the previously mentioned power port and port sizes. This H.P. was measured at the flywheel. It should also be noted that during this time, there was a Merc Bulliten saying the total timing on the 1500 should be reduced to 21 degrees from the 23 degree specification to help with a problem surfacing with detonation.
I have seen no performance difference between 21 and 23 degree timing.
In 78 Merc had a 150 h.p. V-6 so the top inline became 140 h.p. or the 1400. Porting was unchanged BUT they went to lower compression pistons, so hp really did drop. This was both to jiggle the h.p. progression in the motor line-up as well as help fix the 1500 had problems with detonation which lowering the compression helped, the timing remained at the reduced 21 degrees total. When you hear about "high dome" or "low dome" pistons thisis what is being refered to. Merc lowered the compression by shaving the top of the deflector on the piston top down about .100 inch, you can see it when holding them side by side. The 1400 really was 140 h.p. at the flywheel, as a side note, the 150 h.p. V-6 was much stronger than advertised. It is unclear to me during this time if the 1150 also used unported low domes and Merc never changed the H.P. rating or if the stuck with high domes. In the years after this change the distributor went away on the inlines in favor of ADI. This in itself did not effect h.p. much BUT then H.P. started to be measured at the propshaft not the flywheel so the measured h.p. dropped due to h.p. losses in the lower unit. This is where the now "1400" became the "1150" so the later 1150's had power porting and the previous "1150" dropped to "90" still with no power porting.
The later 1150's with power porting all had ADI so it's easy to identify one.
As far as performance goes:

The 72 1400 and the 77 1400 are about equal but the later has power porting with lower compression vs. the earlier with no power port but higher compression.
The ADI powerported propshaft h.p. 1150's of later years would perform about equivalent to these.
The 1500 does make slightly more power than any of these but, at a cost of being very suseptible to detonation. It is about 1 to 2 mph faster due to the higher compression and slightly higher real h.p. but 10 h.p. isn't much. That is the difference I see on two fast hulls, a Hydrostream Vector (64mph) and a Switzercraft shooting star (84 mph).
You could put powerported high domes into a later ADI low dome 1150 for the ultimate in-line 6. As a side note I have not seen any perfomance increase using the much ballyhooed "J" block, (only done in distributor style) over a standard 1500. I have measured the porting and is as near identical as I can measure. My guess is the "J" blocks where destined to be used by racers obligated to use "standard" stock blocks but Merc cherry picked some with the porting, although within standard specs and therefore "legal" were biased towards the favorable side of port size and location to make more power. This is so slight that any real difference in perfomence is negligable.
Well I hope that helps some,
Randy

Thanks Randy, I appreciate the detail in your writing, I will save this. My main thing is the inline 6's too. But I am learning. I collect inline 6 short shafts, form the MK 75 up to the 1500.

I am putting back together my 1975 1500 short right now. It is a J block like you talk about. We measured the exhaust ports on it and a standard 1500 and found .045 higher exhaust porting on the J.

I hope to have it running before October!
Conrad

I think you would see an appreciable performance gain. 35 more HP carrying the same weight...propped correctly, i would imagine would pick you up another 5-10 MPH on the top end. But like others have said, it could come at the expense of loosing a little bit of your low end grunt and its going to drink a little bit more fuel.

The 115 got adi in the last half of 1979, but I don't think they got power ports until about '83.
The adi 140 in late '79 continued through about '82ish, had high dome power ported pistons and blocks, and as Randy explained, began to display 115 decals and the 115 began to sport 90 decals I'm thinking in about '83.
I'm not sure just when the low-dome pistons came on the scene, (maybe '83ish, but were definitely factory installed by about '85 and on through '88.
I have stuffed high dome power-port pistons into the later boost ported blocks, used 850 4 cyl reed stops, and installed early 1500 carburetors with .082 jets to make a real strong running Stack.
I acknowledge the concerns of detonation with today's disgusting quality of gasoline and max my beasts out to 21, but install low domes and time to 19 in customer rebuilds.
Unmentioned, but the 1150 and 1250 prior to '72 were different blocks, high dome, no p-ports. The 1350 is one hard running old Stack-6 and was the basis that Mercury Racing built the Twister I from.

Guys what is the highes PSI of compression these high domers produced when new,or when you rebuilt them. The two I have showed 150lbs on the good cyls that were not damaged. They must have produced a bit more when new???

Most of my other lower compression mercs run 130-140lbs of compression. My mk 75 runs good at 125lbs.

wow you guys are bringing some great merc info to light thanks very much. I enjoy reading and understanding how these motors work. I guess that is why I keep buying them. I am gonna place it on the tri haul and see what it does since it is a breeze to swap and I can post the results for all.

So last night I swapped the motors and today I took it out and beat it like it owed me money. I ran it with a 19 first and got 36 mph and it was a pig out of the hole. I switched to a 17 pitch got a 39 mph at 5100rpm. So back to a 15 and ran 39 mph at 5900 to 6000. Thinking that this haul isn't gonna run any faster but you never know this horse might be lame. I will check it all again but I think this 150 is in good shape compression wise and timing. Oh well though not trying to win any races just thought 35 horse would be more omg than, is that it.

Hmm, interesting...i would have though a 1500 would have pushed it a good bit faster than that!