Needs:

• Okay, Im looking at what I need for to get 200WHP from a 12a carbureted. I also need a 10k redline. To keep in mind also is size and as simplistic design as possible.

• Anything less than 200hp I might as well rebuild my 700 as is. When factoring the engine weight of the 12a Vs. the stock I would be better off this way.

• Must stay carbureted, as an EFI would pose to big of a hassle for this build.

The Twist:

• My plan is to convert 1999 Polaris 700Xc to a rotary powered sled. I started a thread here https://www.rx7club.com/old-school-other-rotary-63/rotary-snowmobile-12a-1006405/

• I have yet to find anyone who has done a swap like this and it thus, there is absolutely 0 information about it out there.
The Build:

• I know I will have to have a full bridge port along with the corresponding bearings, springs seals and lubrication systems to support a 10k constant RPM pass.

• My questions are what am I looking at for ports for 200HP. What seals should I use ceramics or RA classics (for durability over longevity) or a Racing Beat N/A carbon seal. What are some concerns you have about this build?

Thoughts So Far (pulled from above thread, for you thread-chasing haters):

• DriveTrain - I Found out the drive-train for the stock 700 has held up 220+ Hp. I feel confident that the drive pulleys should be fine.

• Power- I’m looking for ~200Hp from the 12A. i know that this will mean bridged Primaries and secondary’s. One plus is exhaust will be free flowing, no emissions, thank God.

• Heat - Cooling the 12A is going to be one of the hardest tasks, as i don't think the stock Radiator will cool the ~1100CC engine

• E-Shaft to Eccentric Clutch - I’m thinking I’m going to use a custom hub adapter from the E-shaft to clutch. I’m trying to use the stock clutch assembly and adapt it to the Shaft.

• Starting- I don’t think a hand pull will work. Maybe an AC start up like on the snow blowers? I’m stuck here lol.

o Update : Started and flywheel may be the best option thus far.

• RPM - I’m looking to increase the Stock 7k Red line to 10k. Guessing that Ceramic seals would be best for this, whereas; the RA classics/Black would be a secondary option (It’s not turbo, but i don’t think you can tune a snowmobile as well as a car lol) as longevity for a snowmobile is 6k where as 20-30k with the 12A on hard seals would still be a huge increase in longevity.

• Electric Power - Getting power for the spark, starter, lights, and sensors. I’ll have to do more research on the stator for the 700XC (if there is not started used or it is externally powered)

Please shoot me any ideas you have. This is just the brain storming stage I want to have a full plan so the build can go smooth.

 

To have the engine survive 10K you will need:

1. Hardened and pinned stationary gears

2. Higher oil pressure to support
Larger oiling jets in eshaft

3. Windowed bearings to get more of that oil around

4. External oil cooler, can't use the beehive

5. Balance the rotating assembly

6. Clearanced rotors

Probably a lot of other things too. Others I'm sure will chime in with more.

 

if you have the cash, get the hardened stationary gear tho my SP have seen 10k constantly on OEM gears and apex seals. If its my choice, semi-PP so the motor will last longer, can run OEM onternals and no need to worry about broken bridge.


In addition, there is no need to rebalance if your using rotors and front counter weight if these parts re from the same keg

 

i'm sure 10K has been done, however the competition book uses a 9000rpm redline, and then gives a life expectancy of something like 400kms, and @8500rpm its 600km's. this is on carbon seals. ceramics would last longer for sure.

200whp out of a full bridge is possible, it would be more like 8500-9000 though. you might also want to look at a P port, it'll be more HP, and its a little simpler to build.

cooling might be tricky, it helps you're gonna be in the snow!

it would be nice to balance the thing too, the factory balance is ok, but its one of the things they have improved over the years

for a starter, it would be simplest to use like a T2 bellhousing/clutch flywheel/starter, that way its all stock, but i'm not sure how the polaris works. the rotary is stupid simple to mount, and takes up very little room, so adapting it to the trans will probably be the hard part

i would also have a hard look at fuel injection, the carbs are cheaper to purchase, but once you've bought all the jets and other junk you need to actually have it dialed in, it adds up.

 

All parts will be coming from the same keg. So PP would be the best bet, But it is a little bit out of my price range and as i Dont have a full shop i wouldn't be able to do it all myself. Plus i would think using Devcon would shorten the engine life and would be a little to loud for a snowmobile lol as the exhaust would be very short.

Whats the stock RPM range for a 85 12A carb? 7k or 8k?

Farrell: I get i would need the oil pressure, jets and bearings, but by clearances do you mean spec tolerances or 3MM, the engine i plan on using is a fully working 12a 124k tho. Thats the reason I would rebuild it when I do the tear down for the porting. I also have a oil cooler from my 91 rx-7


My thinking is that as long as the engine is well cooled and oiled with the correct seals and springs 10k should be okay. Is the OMP for a 12a mechanical like the S4? This is my only weakness for the build, i never touched a 12A before.

 

Stockport 12A makes max power around 6700 rpm and can be pushed to 7-8000 rpm occasionally without issue. Constant load in those ranges would result in
accelerated wear and earlier failure.

At high rpm levels there is some side to side movement of the rotors and allowing
extra clearance of the rotors and the side plates keeps them from digging in and
causing failures. With an engine with that mileage on it make sure you spec
everything out to make sure its within specs, especially doing a high rpm motor
like this.

In this application it might make sense to premix but it should work ok.

 

Farrell: Gotcha, so would you suggest getting the sides refurbished? Extra tolerance will allow for more play at higher Rpms right resulting in more wear and less compression right?

I'm going to premix as well and use the omp.

Fd3s: how much less work is a pp. only 500kms on a full bridge at 200hp I was thinking 15k at least. As for other ways to get 30K-40k miles with 200hp at least what could I do for small forced induction. I dont need a "turbo" what about a high powered fan?

 

have a read thru the competition book https://docs.google.com/file/d/0Bzy-.../edit?hl=en_US

they make many minor changes in the engine to see 9k, and that's the engines they ran the Daytona 24 hours with starting in 79, so its a reliable combo.

the exhaust will just as loud on a P port, bridgeport, or even a stock port...

if you're planning on the engine lasting the max amount of time (and making power) you need to start with the best condition parts you can. so flat side housings, new or really good rotor housings. rotors with tight seal grooves, etc etc.

the bearings, oil pump, and stuff like that is to increase durability at high power and RPM