503 Upgrades

Aug 18, 2009
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Vermont
I was wondering about any type of performance upgrades for the 503. Like pipes, silencers, and anything else you guys may of come across out there to make this sled have a little more performance. Any advice for performace upgrades would be nice.
 

TLKDPROD

Well-known member
Jan 25, 2008
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Salmon Arm, BC
Hahahahaha !

503 guys don't want to share their tricks :beer;:beer;:beer; !!! They all want to show up at Hawkfest in UT next season and say "Oh, i've only worked on my clutching as you can see! " Hahahahaha !

Man, there's an array of stuff you can do on a 503 and I think we can go further than the sleds on fan cooled mods because the 503 hawks have an open outside air intake for the fan compared to sleds who have nothing and blows underhood temperature air.... but none of us (as far as I know) has really gone far enough in the motorwork (how much can you shave off the head before you screw up, can you go agressive on the porting, bore carbs, Y-Pipe port match...) to see where you can do it safely...

As far as aftermarket stuff for the 503, the stock Jaws pipe you got is already amazing, you may get a silencer custom built by Alan from The Sled Shed in Revy, BC. Besides that : Clutching. This is where 85% of the potential sleeps.

2 other stuff you can free an HP or two with : track porting and bigger idler wheels at the back.

One more thing I'd personnally give a try would be the gearing. I'd go down on the gearing because of the low power that the motor's got. To do so you need to dump that belt drive and get a chain drive...

Or you can put a 550F motor in there !

Now you know everything :D Hahahahaha !
 

off road rider

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Jan 2, 2008
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Got any Idea of the 550 hp #s Im thinking that swap isnt worth it..Ive got a line on used 550 motors.. Mines coming apart in a few weeks...I know its going to fly for at least a few seconds:face-icon-small-win
 

TLKDPROD

Well-known member
Jan 25, 2008
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Salmon Arm, BC
Claimed HP of the 552 Type Engine on Rotax's site : 57
http://www.rotax.com/en/Engine/2004/Snowmobile/Engine.Models.htm

Claimed HP for the 503 Aircraft Engine (same as previous sled's) : 49.6
http://www.rotax.com/en/Engine/2004/Aircraft/Engine.Models.htm

Of course these are "raw" measurments. Which setup (Exhaust/Jetting/Carbs) you put on each motor will really make the difference.

The real person to ask on this is Roo of course. He tried them both. What I'd do personnally is I'd start off with a 550 and do all the mods on the 550, not do mods on a 503 to make it run like a 550 ! There has to be more tourque all the way on the powerband on the 550 and this is a super interesting thing when comes to clutching... Of course there's a bit of frame mod to do but someone has done most of the R&D on this and you may get most of the info you need. Personnaly I'd go with the 550...
 

off road rider

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Jan 2, 2008
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Claimed HP of the 552 Type Engine on Rotax's site : 57
http://www.rotax.com/en/Engine/2004/Snowmobile/Engine.Models.htm

Claimed HP for the 503 Aircraft Engine (same as previous sled's) : 49.6
http://www.rotax.com/en/Engine/2004/Aircraft/Engine.Models.htm

Of course these are "raw" measurments. Which setup (Exhaust/Jetting/Carbs) you put on each motor will really make the difference.

The real person to ask on this is Roo of course. He tried them both. What I'd do personnally is I'd start off with a 550 and do all the mods on the 550, not do mods on a 503 to make it run like a 550 ! There has to be more tourque all the way on the powerband on the 550 and this is a super interesting thing when comes to clutching... Of course there's a bit of frame mod to do but someone has done most of the R&D on this and you may get most of the info you need. Personnaly I'd go with the 550...
The aircraft motors are detuned for reliability.. I really dont think this swao is worth it..I didnt notice roos machine having anything huge over the other 503s.. Theres only one way to tell and we cant get that done for a few more months.. Im a believer that you can build the small mill...
Roo would you do it again???
 

roo

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May 12, 2008
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sedro woolley WA
503/550

The aircraft motors are detuned for reliability.. I really dont think this swao is worth it..I didnt notice roos machine having anything huge over the other 503s.. Theres only one way to tell and we cant get that done for a few more months.. Im a believer that you can build the small mill...
Roo would you do it again???
thiery is right on with the numbers I have for h.p.(although everyone that has run a 550 on a dyno "claimes" their closer to 70?????), my machine has very little clutch work done, (as in next to none)running 100/290 primary with all small weights removed, have not even touched secondary. running zx2 with track WAAAAAAY to tight too utilize the horsepower, only way to keep it from ratcheting. Motor has way more torque than 503. compared to harleys 503, (which has an amazing clutch system dialed in as good as it can get) It is not that much of an improvement! but after i get done- anti ratchets and hopefully getting harley to help me set up new clutches, we will see?????

everyone that i talked to about building either motor said no way! anything that you are going to do to really push the hp up is also going to cause over heating!!!!(which is the nightmare of a fanner) The large amount of cash that you will dump into it will get you up in hp but not enough to even come close to a 440 water cooled motor and maintain any kind of reliability. Have talked to a couple guys that have done it and they both recomended the same thing, clean up the ports, try to get a good pipe on it, get the jetting right (which you do not want to run anywhere near to lean, they burn up in the mid rpms because of over heating) spend your money on clutching or put a water cooled motor in!

so.............. compared to stock 503 with stock clutching definatly way more torque, runs like different motor. If you are a die hard fanner and you can come up with a 550 motor it is the best place to start (I got mine for $400). If you have the dream of building a high hp fan like i did in the beginning just go to rotax website and look at the hp numbers, this should be enough to change your mind!
 

off road rider

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The only issue with using the HP #s from the rotax website is that they are not the same motors.. An AC motor is detuned for reliability.. plain and simple..
I still dont think its worth it. We will see this season... I am with you guys on the torque specs , but its not enough to do all the work on a transplant.. might as well go liquid
 

ozzydog

Member
Dec 17, 2007
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503f Engine Mods

Ok guys,
I recently found a fellow that claims he can boost the power on the 503f significantly. He also claims he can eliminate the cooling issue associated with it. But and there is a but. It will cost you $2,700.
Bruce Kahlhamer at PSI Powersports. He is the man when it comes to exhaust also. Many of you may be familiar with the PSI Genesis engines, he makes those.
His number is 801-393-1010

But like many of us have mentioned you will get more power but is the time and effort spent and the money worth the gains when you can just go to a liquid cooled engine and really see some gains.

Roo, call me sometime on your clutching. Now would be the time to be picking up your parts and pieces. You rode mine with just the secondary completed, I now have my primary done with a thundershift kit installed. I now need to get the weights right and it should be dialed in.
 
May 30, 2011
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63
Ames, IA
A 2004 550F uses 9.6cr, Twin 34mm Carbs, Dynoed 70hp@7000rpm! Later 550F's come with Smaller 30mm Carbs, and later ones even have Smaller Port Cylinders, rated 58hp@6800rpm. A 550F (76mm x 61mm) 553.6cc.

A 2 Stroke using 11.5cr and turned 6500rpm, Carbed right, with a Good Tuned Pipe it takes on Avg 7cc to make 1hp. A +/- 1.0cr = Avg 1-1.5hp. So 553cc/7cc = 79hp. A 503F is 496.9cc/7cc = 70.9hp.

A 503UL, same Core Engine as a 503F, they use 10.8cr and 36mm Carbs and uses a Muffler, not a Tuned Pipe, and is rated 50hp@6500rpm. The Sled 503F uses 34mm Carbs and was rated around 58hp@7000rpm. A 503UL with an R&D Aero Tuned Pipe made 62.3hp@6500rpm, and that's a very Mild Tuned Pipe! 50hp + 22.5% = 62.5hp.

A 521, 583 use 38mm Carbs, so a 550F could also use a 38mm Carb. More Air = more hp.

Cylinder & Case Porting can add 10-15% more hp.

So to answer your question.
1. For Maximum hp Gain use an After Market Tuned Pipe.
2. Use Bigger carbs.
3. Do Cylinder & Case Porting.
4. Raise the CR.
5. Do all of these plus a Big Bore. Max Bore with a Custom Sleeve is 82mm. The 277F, 503F, 550F, and 521 to 670 All use a 4 or 6 Bolt Pattern based on a 100mm Bolt Circle. The 670 has been Big Bored to 82.5mm.

277F uses 11.8cr
377F uses 9.6cr
440F uses 9.6cr
503F uses 10.8cr

All Water Cooled 470 to 670 use 11.5cr
670HO uses 12.5cr.
 

Hawkster

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Apr 22, 2010
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:) that little guy comes with a Jaws pipe , had Aaen performance do a head shave , they actually cut a groove on the perimeter of the head otherwise it would not squash back to the jug , and some porting on hers . It pulls over like a big liter liquid when it's cold but different because it doesn't have the big fly weight to assist threw the pull .
 
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