The Merc XS1500 and the Mercury 150/1500 consumer outboard differences

[Scream And Fly]

As far as I've always known, the consumer model Mercury inline-6 150 horsepower engine was pretty much at the limit of its design. Aside from the midsection and gearcase, what were any specific powerhead differences between the consumer 150 and the Merc XS1500? Did the XS1500 make much more power than the standard 150, and if so, how? I suppose the Merc XS1500 had a lightweight flywheel, but did it have different carbs and ignition timing?

I would love to get a discussion going on that. Any technical information would be greatly appreciated. :)

Greg

[milkdud]

All the same except slightly higher port timing and the low water pick up lower unit and slotted cowl.

Mercury claimed 155 hp out of the J block xs motor. So 5 more hp. No light weight flywheel was used.

The midsection is the same 15 inch mid that the 1500 uses. 1973-1975 were the regular blue stripe short shafts as well as long.

1974-1975 the J block was produced for the blue short shaft motors. The slotted cowl was available as well. but the true xs came out in 1976 and added the lwpu.

1976-78 were the red 1500xs's (short) The long shaft blue 1500 was produced from 1973-1977.

The Carbs are the same as far as I know. Possibly jetted one step up.

Timing is the same as well I think. The first 1500's were max @ 23 deg. later they came back to 21.

Ignition is the same .

The early 1500 and 1500xs shared high dome power port pistons. People swear that the last 1500 and the last 1500xs motors came with low dome pistons.

My J block 1500 pulls up to 6500 RPM pretty well. I think a stock 1500 was rated at 5800 RPM and the xs @ 6000

On a normal boat you would be hard pressed to see the difference I think.

Conrad

[Capt.Insane-o]

I've had both on my Vixen and both have pulled within 200 rpm of each other dependent on weather before running out of steam @ 7200. I have 3 J blocks and 2 "consumer" blocks and on this boat there is zero difference. No the xs didn't come with a light flywheel or anything different than a slight campher on the intake ports by what I can visually tell. I'm pretty sure a few years ago I posted pics of the intake ports. On the average 80 degree day I've never been able to spin either over 7200 with a 30p inline chopper on a 180 lb Vixen plus 12 gallons of fuel, a 24 series battery and my 190lb ass with gear. :). And yes I can hang the ****er out.

[Raceman]

I have about 15 1500XS's in varying conditions from running engines to scattered and in boxes. I also own 4 std 1500's including a '73, a '74 and 2 '75's. The port configuration is slightly different in the '73 engines, although I don't recall off the top of my head what the difference is. My first 15' Ally had a '73 1500 shortshaft on it which was later changed to a J powerhead (same as XS). There is an old wive's tale that the '73 powerhead is somehow more desireable than even the later J block, but it's simply that, a rumor. To put a chronology on the engines, the configuration of the bottom powerhead bolt pattern and exhaust outlet placement and shape changed in 1972 with the 1400. 72 was an odd year because the 1400 had this new pattern while the 1150 retained the old one. 72 was also the only year that Mercury ever made a shortshaft 1150, presumably because they had shortshaft mids with the old pattern left over from the previous 2 years 1350 shortshaft engines. The 72 1400 was what the 73 1400 would become except for the power port in the side of the cylinder wall and the corresponding hole in the piston skirt for it. Interestingly in '73 when Merc added the power port with no other changes to the 1400 and upped the horsepower rating by 10, they did not use it in the T2 and T2X race engines of subsequent years. In 73 the shortshaft and std. length 1500's were identical except for the mid section length and the '74 production run started the same way. The '74 Merc catalogue shows a shortshaft 1500 on a tunnel boat without a louvered cowl. Sometime in '74 Merc began installing the higher ported J powerheads in all shortshaft engines and at that time went to the louvered cowls. The '75 model shortshaft engines retained this same configuration. At some time in this mix the fuel pump moved from duals on the side of the powerhead to the single unit mounted on the lower pan and also hex headed upper transom clamp bolts instead of the former T handles. All '75's had the pan mounted single pump and hex bolts and all 74 longshaft engines had the T handles, but I cannot recall about the mid year 74 shortshafts. All of the '74 and older inline 6's had the silver front faceplate, while all the inline 6's '75 and newer had the black one.

The 1500XS or J block will outperform a standard 1500 on a light fast boat, but as the weight increases and the hull efficiency decreases the differences become minimal. If I remember right putting a J powerhead on my 15 Ally made approximately a 3 MPH difference with all other things being equal. Jeff_G who doesn't seem to play here anymore for whatever reason is a former FormulaV world champ and has posted a lot on inline 1500 topics in the past and is very knowledgeable on all the inlines. He's said that J blocks in XS's as early as 77 had some of the lower domed pistons, however I have never been into one of mine that had the low domes installed. The difference between the low domes and the earlier high ones is .100 on the top of the deflector. Some time in about '77 the Sport J record jumped about 10 MPH suddenly and David Lee from Ala. and Doug Pearl from Florida were running those kinds of speeds. Some thought it was merely taking advantage of the newer cleaver technology and the sky high transom heights they could now run because of the cleavers and low water pickup gearcases, but we always figured Merc had found a few extra ponies there somewhere. I found it hard to believe that those guys were running the low domes in those engines, but never knew for sure.


The 1500XS is without a doubt one of the best looking outboards of all times.

A little over a year ago, after a search spanning more than a decade I finally found the old 18' Super Sidewinder that I bought new in 1974. It still had the '78 200 V6 that was the last engine that I had on it after 4 or 5 different inline 6's and also a '76 1750 V6. The years had not been kind to the boat and it is going to need a complete restoration. When this is completed I plan on powering it with a pair of 1500XS's just for the novelty.

[delawarerick]

Raceman congrads on the sidewinder any pictures? Rick

[crazy horse]

Don't forget the A25 switch box? I ran a A21 and a A25 box one day to see if I could find anything different about them. Never saw anything change. I still have two new A25 boxes settin on a shelf. Dave

[magcat16]

My first boat was a 1971 16' sidewinder with a 1974 1500 shortshaft inline merc. It had the louvered cowl. I had alot of fun in that boat.

[FUJIMO]

All the same except slightly higher port timing and the low water pick up lower unit and slotted cowl.

Mercury claimed 155 hp out of the J block xs motor. So 5 more hp. No light weight flywheel was used.

The midsection is the same 15 inch mid that the 1500 uses. 1973-1975 were the regular blue stripe short shafts as well as long.

1974-1975 the J block was produced for the blue short shaft motors. The slotted cowl was available as well. but the true xs came out in 1976 and added the lwpu.

1976-78 were the red 1500xs's (short) The long shaft blue 1500 was produced from 1973-1977.

The Carbs are the same as far as I know. Possibly jetted one step up.

Timing is the same as well I think. The first 1500's were max @ 23 deg. later they came back to 21.

Ignition is the same .

The early 1500 and 1500xs shared high dome power port pistons. People swear that the last 1500 and the last 1500xs motors came with low dome pistons.

My J block 1500 pulls up to 6500 RPM pretty well. I think a stock 1500 was rated at 5800 RPM and the xs @ 6000

On a normal boat you would be hard pressed to see the difference I think.

Conrad

That about wraps thing up.

[Robby321]

The 1500XS is without a doubt one of the best looking outboards of all times.

The under statement of the year! :thumbsup:

Had one on a 17SS Switzer, and I could simple look at the motor all day long. The Red decals, and the louvered wrap.......simple "too cool"!;)

[TNT Teen]

Does anybody know the port timing or increase in height over the stock ports? I read somewhere .045 higher, that didnt specify if it was on both intake and exhaust, or exhaust only. Anybody know?

[Capt.Insane-o]

.045 is a lot. I have 2 j blocks and a bunch of regular 1500 and none of them are that far apart. It would take longer to get the tools out and set up than it would take to make a non j block a j block.

[joyrider]

I have a 1977 150 XS striped down for re-ringing & a 1986 I6 also. I've taken port maps of both motors.
It appears both Intake and exhaust ports on the XS are higher than the stock block. Will post pics and port map later this week.
Wayne

[joyrider]

Merc XS 150 Inlet & Exhaust Ports366942366943

[joyrider]

Merc 1984 115 ADI Stock Inlet / Exhaust ports366944366945

[FMP]

Any numbers?

[Magcat 62]

That about wraps thing up. I HAD a blue stripe short shaft 1500 no xs your right on no real diff excpt l/w p/u they sure idled smooth but loud @ 6000! just reverse of omc v4 big bore short stroke hole shot omc was killer i raised my ports 1/16'' left exhaust alone raised reed stops .030 bored carb venturi 1/16'' combo really worked had fastest evinrude around gained about 30-40 hp back then the merc-omc hp wars were on! had a setof stacks but marine patrol didnt care for my dry exhaust that some times would flame-up from ra..w fuel build-up.they made a pit stop and talked to mom and dad and that was the end of arts lake X . HA HA

[ddh7691]

The A25 Switchbox had no rev limiter. That is the difference between an A21 and A25. Late model XS motors had low dome pistons. I was able to check engineering drawings on Part numbers.

[FUJIMO]

...everyone thats "J-Block" minded, never even thought to look at any of the 150's that were 20' shaft motors all those years...or have they?...

[25ss]

I talked with an old racer and he said when he got his first 115 DIS motor and he would race with
XS motors if it was a short course he could beat them.
Because it had a lot more low end torque and he could pull them in the corners.
But if it was a long course he could pull them in the corners but they would run him down in the straits.
I have worked on 115 DIs and other than the ignition system they seem like a low dome 140 with a longer tuner
Im guessing thats were the torque comes from great motors.
Dale