Building a rotax 503???

[off road rider]

Im looking to build a rotax 503.. Its already dual carbed.
would like to see around 90 hp and of course reliable. Anyone on here have experience with this?? shaved head? porting, etc???
Thanks

 

[dexter]

never get even close to that power, if you can find a pipe its the only mod i would do and maybe some jetting and clutching.

 

[leafspringer]

Those 503 were great engines. try to find a cdi version, then with a little porting, you should be able to get around 65hp. I think they were 52hp stock?

leafer

 

[Himark]

Those 503 were great engines. try to find a cdi version, then with a little porting, you should be able to get around 65hp. I think they were 52hp stock?

leafer

46hp in some books and 52 in others. Not sure how that is??? but I will say 52 since my ole one felt like it ran like crazy

 

[Sidehiller]

46hp in some books and 52 in others. Not sure how that is??? but I will say 52 since my ole one felt like it ran like crazy

Some were dual carbed (blizzards), some single carbed (everests)?

 

[off road rider]

Thanks for the reply's. The 503 we are trying to build is in a snowhawk. Its already cdi and dual carbed. good power stock, but....need more. want to keep the fanner motor, weight on these is everything.
Nos is going on for the climbs, but I would thgink with general hop up techniques we can get another 20 poinies.. Mill the head, porting, bigger carbs???
someone must have done it...

 

[d&mraceengines]

if i was you i would contact kelsey rkt or big john or some one in your area reputable and see what they say about porting and raising compresion on the 503 have a great day and good luck

 

[portgrinder]

I recently built up a 550 fanner in a backcountry. Its basically the 503 with a bigger bore and reeds instead of piston port.

Stock it dynoed at 60

Split Second did the engine work for me
NPP custom single pipe
Bored 30mm carbs out to 31.5 if I remember right

Dynoed 80hp on same dyno. It works awesome, but it was alot of work.

You're going to be hard pressed to make more than that. Lots of guys will promise you they can, they are either straight up lying or it will make more...for about 30 seconds until it gets too warm.

Fan engines cannot be overbuilt because they cannot get rid of the heat quick enough. If you are going to use nitrous (proper name for NOS) you should leave it stock, otherwise you will have BIG heat issues. Even with just nitrous, you will be looking for trouble.

If its in a snowhawk, the first thing you gotta do is get a TRA or P-85 clutch. Any engine that has some work done to it will struggle with the junker stock clutch. I've been there. It doesnt work. I run a TRA on the one we built. You need to find an old school TRA with the different taper. Back when SKI-DOO wasnt so cheap, they used them on the smaller sleds, like in 98 or so. Thats the clutch you need to find.

good luck

 

[off road rider]

I recently built up a 550 fanner in a backcountry. Its basically the 503 with a bigger bore and reeds instead of piston port.

Stock it dynoed at 60

Split Second did the engine work for me
NPP custom single pipe
Bored 30mm carbs out to 31.5 if I remember right

Dynoed 80hp on same dyno. It works awesome, but it was alot of work.

You're going to be hard pressed to make more than that. Lots of guys will promise you they can, they are either straight up lying or it will make more...for about 30 seconds until it gets too warm.

Fan engines cannot be overbuilt because they cannot get rid of the heat quick enough. If you are going to use nitrous (proper name for NOS) you should leave it stock, otherwise you will have BIG heat issues. Even with just nitrous, you will be looking for trouble.

If its in a snowhawk, the first thing you gotta do is get a TRA or P-85 clutch. Any engine that has some work done to it will struggle with the junker stock clutch. I've been there. It doesnt work. I run a TRA on the one we built. You need to find an old school TRA with the different taper. Back when SKI-DOO wasnt so cheap, they used them on the smaller sleds, like in 98 or so. Thats the clutch you need to find.

good luck

Thanks, great info.. I keep being warned about the heat issues, I wonder if anyones done anything to address that? The nos is only for the bigger climbs.
I hear you on the clutching if that doesnt work why mess with anything else..