Indy Project Sled - Engine Modification

Nov. 01, 2005 By ORC STAFF
Cost: The sky's the limit
Risks: If you have to ask, don't do it!
Benefits: More power! *argh* *argh* *argh*
Tools Required: Depends on how much you do yourself
Parts Required: See price
Mechanical Skill Required: Depends on what you do yourself

When sledders begin talking about engine modifications, the conversation can take about eight million different turns. Everyone has an opinion about engine mods and most are different. One school of thought says modding is stupid, just buy a sled with a bigger engine to begin with. Another says that every stock sled has a lot left "on the table" and you should try to wring every last foot-pound of potential torque from your motor. Some people like to tinker, some like to ride 'em and forget 'em, some like to have sleds that aren't like what everyone else is riding.

But sticking with the theme of this article, if you have an older Indy that you still like or that you want to keep riding for one reason or another and you'd like to have a little more power to keep up with your buddies on their newer sleds, there are a bunch of ways to go about it. You could mod the stock motor. There is no shortage of aftermarket shops who know the Fuji piston-port motors and no shortage of performance parts. You could swap out the stock motor for a more powerful Polaris motor. The Polaris Engine Shop is a great place to find a bargain and swapping, for example, an XLT 580cc triple into an Indy 500 chassis is about as simple a swap as you'll ever have a chance to do. The new domestic twins are becoming more readily available too, although a swap like that is a pretty big job because of the size of the new twins relative to the old Fuji twins. The third option, the one I chose, is putting in another manufacturer's engine. I chose a Rotax twin because it is a relatively well known swap and I was able to find expertise at several shops. Let's look at each option a little more closely. I'm going to put the details of my Rotax swap in a separate article. Now that the project is complete and I know what it takes from start to finish, I realize that it deserves it's own article.

Modifying the stock motor has it's advantages and disadvantages. If you have a lot of miles on an original motor, it might be getting close to the end of it's life span. If that's the case, if compression is down, if there's excessive crank runout, if it's just not running too hot anymore and a rebuild is in the offing, a case could be made for doing some porting at the same time while the engine is in the shop anyway.

On the other hand, what is the power potential of a Fuji 488cc twin? Don't get me wrong, I think that motor is one of the all-time best sled engines, it makes good, trailable power and is rock- solid dependable, all while getting great fuel mileage. Still, when you compare it to the new twins, it comes up way short. If you spend eight hundred or a thousand dollars on it, it's still going to be short on power and you may end up with an undependable motor that still won't run with the new 500 and 600s.

But it's your money. Many shops will port and polish, cut the head, sell you twin pipes and a clutch kit, bore the carbs, etc. If you get 85 HP, consider yourself very lucky.

The Fuji triples are another story. There is a lot of potential still on the table with those motors and lots of shops who can make them run really strong. But it'll cost you. 130 horsepower is not beyond the realm of possiblity for even the piston-port Fuji triples, but think about what you are planning: a new XC 700 is low 120's, that thousand or fifteen hundred you are going to spend on a 10 year old motor would make a great downpayment on a '99 XC 700.

But like I said, it's your money.

Buying a newer Polaris (or Fuji) motor from the Polaris engine shop is another option. Usually their engines come with electrics and carbs, everything you'll need except a motor plate and a clutch. If your old motor is still in good shape, you can sell it to recoup some of the cost of the new motor and end up with a relatively inexpensive upgrade. An Indy 500 with an XLT triple in it would make quite a sleeper.

A Rotax swap, even though it's a "known quantity", is still a big job. Unless you're a real gear-head who rebuilds engines just to have something to do on weekends, a motor swap is a serious mechanical project. I approached it with a rather careless attitude, thinking it would be "no big deal." I got through it, but it *was* a big deal.

First piece of advice for those considering the Rotax swap, start with a newer chassis Indy. Precision Performance Products will sell you everything you need to do the swap and will even provide phone consultations, as long as you don't take up too much of their time, but they no longer sell the motor plate for the old Indy 500 chassis. Before you buy the first part or even make the first solid plan, make a list of *everything* you'll need and make sure you can get it. Don't leave anything to chance or leave anything to the last minute, because you might find you've done a lot of work for nothing or even worse, that you'll have to undo something you thought was finished.

Not following my own advice above, I assumed I would have no problem getting a motor plate for my chassis from PPP. Imagine my surprise when they told me they didn't sell them anymore. Vruwink's, another shop that at one time specialized in Rotaris swaps, has stopped selling any related parts. After some frantic scrambling, our very own Dan Canfield saved me when got me in touch with Jack Jensen of Jack's Upholstery in Salt Lake City Utah. Jack is a vertitable fount of information about the Rotaris swap, he saved me hours of improvisation and untold headaches as well as selling me a motor plate for my chassis.

Finding a motor is a project in it's own right. Unlike ordering an engine from the Polaris Engine Shop or having a reputable shop modify your stock motor, buying a Rotax is something you'll probably be on your own doing. Price of the rotary-valved motors has begun to come down recently, probably because Ski Doo's newest motors are reed valved and because the new Polaris motors are every bit as good as the 583 and 670 Rotax twins. Still, I was determined to do this and I was lucky enough to find a motor from a sled that was wrecked early in it's life. Based on availablity and price, I decided to go with a 583 twin. The fact that I found a '96 with only 400 miles on it had a lot to do with that. I was also able to get other parts from the sled. At the time of purchase, I didn't think that would be a big deal, but it turned out to be one of the smartest things I've done on this whole project. You'll have to read the swap article to find out what I mean. One of the best things about this is that now that the swap is done, if I find a great deal on a 670 twin, it's a true "bolt-on" to put it in in place of the 583.

So there are some options, I'm sure there are more. The questions you have to ask yourself are what do you want out of your sled? What are your financial resources? What is the best use of your financial resources? Do you want to learn how to do this kind of stuff? Why do you want to learn it? Do you have the time for a project like this? Will you end up wrenching instead of riding? How do you feel about that idea?

I guess, to sum up this long article based on an even longer project, I'd have to say that if all you want to do is ride, then forget the mods. If you want to go faster, buy a new sled with a bigger motor, it'll be easier and cheaper in the long run. But if you are a true hot-rodder at heart, then the older Indy chassis is a great sled to start with, the aftermarket is loaded with all sorts of goodies to make your sled unique.

See ya on the trails!

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