I have a 521 plus engine which I am building for a vintage sno-x sled. It's apart right now for a top end rebuild. What mods can I do to this engine to gain more torque, and possibly a couple hp? A 583 top end? Would my 521 carbs, and pipe work with that combo?

I would think the 40mm mikunis would work perfect. Get it ported, and cut the rotary valve. If ya use a 583 top end you'd prolly want a 583 pipe. (If it's bigger than the 521). Or some D&G TWIN PIPES-

What do u have for a stinger dia, 30mm works good for 86-88
207 RV plate 62* atdc
mill head to achieve .050 squish ( max cr for 92-93)
Taking .012 off the base of each cylinder is good for 13:4:1
timing .080-.090 btdc
They like 44mm carbs

Every time i tried DG twins ( 3 differrent sleds) they were quicker for 300'
lost 10-12 mph on top compared to stock single
sent pipes back, got another set, same result
threw them out in the end

DG twins make 12-14 hp less than stock....

I don't think I would go for twin pipes anyways. I believe you get a better low to mid with a stock pipe. Maybe I'll get a stinger (to save some weight) or open up the stock can to try and get a little more mid.

have a 521 from a 9700 bliz with 44 mikes and i am going to fit 2 mach z 780 pipes using the original head pipes in a ss 25 some day when i get to it. i think it will be a cool project, be a vintage radar runner.

Any one tried a fatboy 583 single on 521 engine.

DG Pipes were, and are a joke, stick with fine tuning the stock setup.

I'm going to just fine tune the 521. In the vintage classes, we are not allowed to run any studs, so extra hp will just be wasted I feel. Losing weight, and improving the handling of the PRS chassis will be the best modifications which I will make.

Just picked up a complete with screwed con rod bearing 583 rave from a 96 mxz ...cheap! Brand new never installed pistons included!

Dude- send them to me!

I ended up picking up another 583 for parts. I now have my motor ready to assemble. What heads should I use? I have a milled 470, a stock 521, an early 583 casting #955, and a newer style #150. The earlier 955 does look smaller than the newer 150, but looks to have a maybe deeper combustion chamber. Also, how do I eliminate the oil pump?

yeah as for the pipes your not gona beat ski-doo's stock setup those motors are really perticuliar about there exhausts, there factory tuned and dialed in for the max hp with stock ide run a stock setup so the backpressure is just right plus it saves you like 400.00 for a aftermarket pipe.

Is formula plus single better then blizzard 9700 twins?

It has longer legs but usually a bit slower off the line. Atleast from what i remember. but yeah it's probably a better overall pipe.

OK, so what about my original topic?

People didn't seem to mess with it as much as other motors.

I think in post 11 u said it best
do u have the 27mm stinger and curl form the 85, the smaller can also?
builds heat quick they increased Dia thru the years
preformance starts from the crankshaft up(make sure u have a good one)

The motor is now sitting in the sled. 583 rave topend on a 521 bottom. I used an early 583 head, as it looked like it would cool better due to the larger passages. Which pipe, and can should I use? I have both a 521, and a 583 system. Carbs measure 42mm.

The 583 system.

Will the 583 topend simply bolt on top of the 521 bottom end? I thought I tried this years ago and found that the intake side of the 583's cylinder skirt was to wide for the 521 cases......it's been a long time so I may be mistaken.

Yes, it does bolt right on BUT you have to cut clearance in the face of the upper case for piston skirt clearance.