XL 1200 mods, special project

[88workcar]

First of all, hello to all. I am new to the site but not new to makeing an engine faster, 2 or 4 stroke. I build a lot of outboards, a lot of banshee and other 4 wheeler engines and I have a street car 88 Mustang the runs 10.70s on radials. My best toy of all is a 1980 Allison 14R race boat with a 90 yamaha on it. With a stock 90 it runs 67mph. With a mod motor I built it has gone 78mph.

My interest now are for more power. Has to be 3 cyl and 2 stroke. I have decided on a 98 Yamaha XL 1200 PWC engine. Yes not as much power as a 1300R but cheaper to find. I will be going from 90hp to 155hp. This is just the start, I have no limits or rules, open space instead of the confines of a ski. So pipes will be one of the first mods, that and Vforce reeds. I will sorce out the porting because for a one off project it is far more economical that chancing ruining a set of jugs with out the knowledge of what really works. I am here to ask advice and gain knowledge about mods to these engines and to find some parts. Thanks to all and I allready love the site. Jason.

[Glenn Briglio]

Check out Group K website and read. 98 XL not exactly the best ski to build for speed. But hey that could be a challenge. Welcome to the hulk.

[WFO]

98 XL not exactly the best ski to build for speed.

Big +1

[88workcar]

Keep in mind I will be using the engine only. It will be inverted and used as a outboard. Run with no cover, so any pipe configuration, carb, ect.... No motor restrictions either.

[jim mcgreehan]

Ebay is a great place to shop for used/new Gp1200 parts. I have a friend who still might have his used triple pipes which will add 50-75 horses. Plan to pretty much change the entire ignition system/timing, which is what you're probably planning to do anyway. PM me if you want... . Sounds like a cool project!!!

Just curious, are you planning on over 160 compression, raising the exhaust ports, etc. and race gas?

[Glenn Briglio]

Keep in mind I will be using the engine only. It will be inverted and used as a outboard. Run with no cover, so any pipe configuration, carb, ect.... No motor restrictions either.

Sry missed that engine only. What is it going on? Good luck with project.

[88workcar]

This is the boat, a 14' Allison, 1980 model. The pan and hood can be changed/modified to cover the new engine or can be left off, don't really matter. With a 90 that I built at home it has gone 78mph @ 7500rpm. I am not interested in going over 80mph. I am quite sure that the 155hp will far exceed that. That is great, then I can prop to accellerate harder. That is the main/root cause of the project. I will add the pipes, porting, head, reeds, aftermarket ignition, ect.... What you guys tell me to do, That is why I am here. I have found a donar PWC. A 98 yammi XL1200. If anyone needs any other parts including the hull, it will all be sold.

[jim mcgreehan]

Very Cool! Being a 2-stroke outboard advocate/owner myself, this is an exciting project. I'm hoping other's will chime-in, as there are some very experienced builder's/tuner's here that would be proud to help and see this thing get developed... . Not to be a 'debby downer'...why not just take a typical small displacement outboard, bore it, port it, add compression, (add pipes-might be a little harder to do) and ignition, etc. etc... ? I'm sure you mulled all that over; just curious.

[88workcar]

THE ROOM, there is none. My 90 has no room for additional ports. I do have fingers in it but no wheres close to the typical PWC, snowmobile, banshee, dirtbick ect.... This motor was never built with preformance in mind. It was built as a 90hp workhorse. My other option is to use half of a V6merc. It's been done a bit, the baddest one in the country makes 162hp and it's heavy. This thing makes 155hp STOCK. Then the dollar is the limit. I will not stop development of the 90 yammi but this project has to be done. I am on a mission. The best part of it is I was always the one that had to be diff. On the weekends I cruze with about 20, 90 - 120mph boats. All with V6 motors. Yes I am the slowest but I have respect. Quite a few of our gang have new rigs because of me. Our first ride, I was 3rd from the front of the pack. The way I see it I can't loose. If they beat me they are suppose to. But if it's even close they get a rash from everone.

[jim mcgreehan]

Totally get it! Sounds like you got it covered-turn it up on it's side/fabricate mounts and shaft, etc. etc. As far as the motor itself, in general, sounds like one approach without specific numbers is to take it to someone like Group-K/Arizona or your local tuner and discuss the following: 1.Add triple pipes 2. Add MSD ingnition/Advent to give you the ability to change timing and increase rev. limit. 3. Port and/or turn down cylinders-guessing you should raise the exhaust port for more top-end. 4. Purchase R & D race gas head/+30cc/cut head and domes for more compression and better squish angle. 5. Install carbon fiber reeds for more top-end. 6. Add flame arrestors for more intake flow. 7. Go one-size up on the oem Mikuni SBN carbs for more top-end. Those are just a few motor mod ideas, alot of which are bolt-on's that can be purchased on-line here, or from Riva and R&D performance products.

One challenge will be getting the triple pipe stinger(s) onto the lower unit... . Just trying to help move things along...