TOPIC: What's the difference between the 1500 and 1500XS?

One of my pals in MN asked a question, I advised this was the place to get the right answer!:
What's the difference between the 1500 and 1500XS?

All XS's were short shaft & had a low water pickup on the lower unit. The port timing was, I believe slightly different on the 1500 XS. There appears not to be a lot of other differences but they were possibly 'blueprinted' from the factory for optimum hp. Conrad will I'm sure pop up with a bit more info.

There were cosmetic differences of course including a vented wrap (only on the 1500).

The 850XS appears little different to the standard 850 apart from it's low water pickup & a higher max rpm.

The 650XS was a beast that went like stink - when it went. Light ali flywheel, one carb per cyl with (I think) external reeds & a really high max rpm (can't remember what it is - I have it at home). Developed 90hp (sometimes!)

**EDIT*** Reading the thread '74 Merc 1500 and 74 Vector' on here it looks like the 1500XS had hard mounts, different carbs & jets sizes and a different switch box.

Thank you sir, I'll pass it along.

According to my 1976 Merc catalog, the 850 and 1500XS motors featured the latest developments of the Power Ported pistons, in addition to the other changes mentioned above, and the 650XS was rated at 6000-7000RPMs.

Thanks Kerry.

When I checked my standard 1500 with my 1500 block noticed that the exhaust port timing is slightly raised. The new power port pistons were "new" before the 1500xs was made. They came out in 1973. I cannot find any difference between the older power port pistons and the ones used in the xs's.

Some may have been cherry picked and put together with weight matched parts. But my J block XS had a lot of weight differences in the rotating assembly. I balanced it during rebuild.

My 1500xs J runs up to 6500 easy. And will pull 7000 if needed.

Jets are 82's the same from a STD 1500 and a XS 1500. They came with rubber mounts I believe. I changed mine out for hard ones.

The 1500 xs was rated at 155 hp.
conrad

Thanks Conrad. If I ever get a chance to get back up to eastern Iowa to see my brothers, I'm gonna swing by and beg you to take me for a ride. (You gotta hold it down to 65MPH or so though, I'm getting old and scare easily.) I'd LOVE to hear that masterpiece sing!

I have all versions down in my shop.
Here is what I have found looking at differences and researching parts:
First is the 1500 short shaft has a lot more in common with the XS than the long shaft does. But I'll speak to the differences I have seen between an 1500 long and an XS.
As far as powerhead goes, I have measured port heights and they are near identical, I have done it on a CMM (big buck cordinate measuring system commonly used in big machineshops) with the block sitting on the parting line and measuring the port diameters and the height from the parting line. At least the two blocks were within what I would consider manufacturing tolerances.
I will speculate that the difference in a "J" block and a run of the mill 1500 block is that the ports are on the high side of tolerance, and selected at the factory. I do not believe that if they were decidedly different that they could be used for class racing as rules are strict about dimensions but again that is speculation on my part.
I have heard that the 5 h.p. difference listed between the XS and the stock 1500 is due to the short shaft exhaust tube length giving slightly better tuning at high RPM for exhaust scavenging allowing the XS to make a little more HP spinning a little more RPM, and that is the reason for the slight hp increase. I also heard that the rotating parts were weight matched better but Conrad has found otherwise.
Carbs on the XS are the non-backdraft style and have .082 Jets instead of the .080's in a 1500. (Early 1500's like 73, also had non backdraft carbs.)
The switchbox on the XS is a different part number and has the rev limiter set higher.
The rubber mounts used on the XS are higher durometer, they are still rubber but stiffer, this is also true of the shortshaft, H.D. mounts are listed for the short shaft versions too. There is a bumper that goes between the exhaust housing and the swivel bracket on the XS bolted in place using the same bolt that holds the "U" bracket on down in the same place, ditto short shaft 1500.
The lower unit on the XS has no water intakes on the sides, it has small grooves on the bottom side of the bullet. The bearing carrier is different to allow a water passage from these grooves to the area leading up to the waterpump intake.
The XS has the louvered cowl, which was also available as a Quicksilver item from the parts counter for many years prior.
The pistons are the same, high domes, power ported. Reeds etc. are the same.
I would say the XS is a tweaked version of the vanilla 1500 rather than a decided departure for more performance like say a Twister or a B.P. motor was. It really jsut allowed higher transom heights with better handling of the stiffer mounts and a few tweaks to let it run at higher RPM for a few extra H.P.
So no doubt the XS is one cool motor, the apex of the non full race versions of 99 cu direct charge motor but not too different than the "pedestrian" 1500.
The Hydrostream I just completed has what I would call a long shaft version of the XS. I used all the XS stuff listed above except I went with a later swept back lower unit. The XS lowers were rumored to be weak using bow lifting props becasue of the slots for water intake weakened the area supporting the propshaft carrier. The transom is 23 1/2 inch high but still allows stock water intake location to supply a good flow of water.
The Switzer I have runs a real XS but it runs a Super Speedmaster lower unit, a 1:1 direct drive with
a much smaller prop and above water exhaust.
Randy

That Hydro looks rel classy Randy. The Switzer looks fast. I like the color of it.

Hey MarkS stop by anytime:) That goes for everyone. I dont have much thats pretty, but I have a few runners.

Randy My 1500J port height was measured the same and I got a very small difference from my standard 1500. Ill have to look thru my notes . But it was very small, but measurable. I agree that they may have been selected from normal run motors.?.

My xsJ block has a larger intake runner. The cavity under the covers leading to the intake ports is something close to 1/10 of an inches wider. My 1500 standard the intake ports really cut into the runner. The J block with the wider entrance does not have to relieve cut into the runner at all. They are the same port height I believe on the intake.

The XS low water pick up had a problem. It was using bow lifiting props while needing positive trim the water inlets would starve. Running small positive trim to neutral trim they were fine. WHen you trimmed them up the inlets being so far back on the bullet would not get proper water flow.

I think the 1973-1975 1500 had 82 jets. Not sure after that. I thought they all had them I guess.

I just picked up a 1988 1150 block. I hope to do some measuring and see how it differs from a 1500. I bet its the same except pistons and reeds:)

Conrad

Thanks Jim, come for a ride sometinme, I doubt either of these will make it to the tip, but the Hydostream might using the back channel on a nice day.

Conrad, you are right about the trim angle and the pick-ups being starved, forgot about that. I run water pressure gauges on everything to watch for such a sudden death situation.
I'll have to look at those intake passages, I didn't measure them that way. I have a bare J (cracked damnit!) on my bench with a stock 1500 sitting next to it.
My manuals say 080's for the 1500's, all the carbs I have stripped off 1500 donor motors have 080's and 082's for the XS, but I'll bet the 1500 shorties ran 082's too. I put 082's in my Longshaft to prevent hi RPM lean out, along with running 21 total timing. Years ago I ran my original Stream with the stock .080 jets. My current one seems to run a bit better on the top end with the slightly richer jets. In general you have to richen for alchohol so now that gas is 10%, I'd guess this bit of richening helps. It's a little anecdotal where it was so long ago I had my original Stream but, I can say this motor runs strong on the top end and it idles like a dream which is not always the case with these. Plots I have seen on fuel air ratio vs power generally indicate that a slightly rich mixture makes more power, of course at the expense of fuel usage...but power is what we are after not best fuel economy . I have not even run the Switzer with the XS this year but I think I'll try 084's just to see, next time it see's daylight. Merc still has all these jet sizes available, one of my manuals had all the part numbers.
Too bad we are not closer, very few guys are into the earlier Mercs (Jim not withstanding) particularly on go fast stuff, around here to bomb around with. I do like your Carlson.
The Scream and Fly guys do a CT river cruise in the fall
that I'll probably go to but, they are not so into vintage stuff although they do enjoy seeing it once in a while.
I'll bet the porting on the late 1150 si the same, I think h.p. is lower due to low dome pistons rather than porting changes. Those ADI's do run good!
Randy