what are you guys doing with performance mods? so far ive put a couple clutch kits together, and carbon tech with frett bros spacers.

im thinking of a r t k head would that alone give more hp?

what are you SNEAKS up too?

As of know on my '02 MXZ 800 I have done the following:

RK Tek head with 13.1/1 domes
1.2mm base gasket
Art dual ring Pro-X pistons (modified by Kelsey at RK Tek to work in the doo motor)
Mild porting
Boyseen Reeds
Reed spacers
Boost Bottle Delete
Stock Pipe and HPS Stinger
1.25 Snowcross track with 144 Woody's down the middle
26/44 gearing
clutching that doesn't work

Things that I am working on are:

Chassis blueprinting
different clutching
exhaust change. Not 100% sure what I am changing to
Carburation...stock 40's are worthless. Idooski is working on a fix.
new custom hood
want to try some different gearing
polishing eveything that will polish.

I am hoping to prove to some that you can get over 150hp on pump gas with these series III 800"s.On paper, I should be at or above 160, but thats on paper. I will be doing some dyno pulls before the season starts to see where I am at.

Brian

What I'm dooing is pinned. Stay tuned! :D

As soon as Idooski's parts arrive, we'll be starting in the basement an working our way up to the attic. Hopefully we can shoo out the bats from this mill's upper end without getting too drastic. The superflow tells all !. :sly:

Originally posted by mxzwfo@Jul 16 2003, 11:37 AM
exhaust change. Not 100% sure what I am changing to
Carburation...stock 40's are worthless. Idooski is working on a fix.
I am hoping to prove to some that you can get over 150hp on pump gas with these series III 800"s.On paper, I should be at or above 160, but thats on paper. I will be doing some dyno pulls before the season starts to see where I am at.

Brian
With the combination of large bore size / tight wall clearance (less than .005"), lean midrange fueling and moderate CR, I'd hold off on the exhaust flow improvements unless you have a secret fuel injection system you haven't told us about (Holtzman??). I think it may be a quick path to part throttle seizure. :nervous: Keep in mind, were working against a miserable Rev limiter here. :angry:

Thanks Doc! What would you recommend for squish on the 800 doo motor? I think I will follow your advise on the pipe, until we can figure out what to do with the timing and carburation.


Thanks again,
Brian

!!! Rotax racing recommends a chamber / piston squish clearance @ .054" (minimum)measured parallel to wrist pin on both sides of the chamber. This gives you some wiggle room if you find some poor quality gas or use Canadian gas which has a oxygenate octane-enhancing additive called mmt - methylcyclopenadienyl Manganese Tricarbonyl :doh: (sorry for the chemistry lesson) which shortens the life of spark plugs and my guess would be, 800 series 3 piston rings too :nervous: . The rotax 800 HO uses a head which goes down to .038" squish but this is restricted to high altitude operation or use of racing fuel. This is not a very good design head for everyday full power high load conditions. I understand that you are using a RK Tek head which the same squish band properties may not apply. I would follow their recommendation and perhaps cc the chamber and crown volume to get a real world CR. Keep in mind, flame propagnation differs between subtle changes in combustion chamber design. Since you are no longer using stock items, some compromises are to be expected. I expect to cc some stock '03 800 pistons soon to get better knowledge on their compatability with different chamber designs. Stay tuned!. :sleeping:

Hey Brian:

You mentioned above that you are considering gear changes. What are your thoughts? I'm looking at using the same track and stud setup you have. Are you planning on gearing down or up to start off with?

I happen to have a leftover 24 tooth that i was thinking of tossing in when i change the track. I know when i was running a 1.5" on my 670HO. The 25 tooth was more effective than the stock 26. My buddy who ran a 1.25" on his ZR 800 claims gearing up 1 tooth on the small sprocket worked best for him...

Thanks for the info
Jon

Originally posted by skidoomaster@Jul 23 2003, 08:59 AM
Hey Brian:

You mentioned above that you are considering gear changes. What are your thoughts? I'm looking at using the same track and stud setup you have. Are you planning on gearing down or up to start off with?


Jon, I have tried the gearing up thing with no luck. I am now at 26/44, or 1.69 ratio (stock is 26/43, 1.65) which works better. My next gear change will be 25/44, a 1.76 ratio to see how much top end I will lose. If I get the clutching spot on, the top end should not fall off much.
Time will tell! Just waitin' on the snow to do some tuning!!


Brian

What I did last year on my 800 REV was DNE's porting,boyseen reed petals,spacer. The reed cage had the center support taken out for better flow. RKT head 13/1 compression with 2mm gasket. HPS can (love it), Bickford racing clutch. This thing ripped out of the hole and midrange. Around 90 it lost its pull and I would get passed by a one armed rider on a stock 800 REV. ??? My sled topped out at 105 on the sleds speedo. Took the sled to a track dyno north of Detroit. I was getting 82hp at the track, but falling off on top end. What I didn't know at the time was the sled was getting harder to start during the testing. Of course a couple of hundred miles later I found my compression down to 120. Might of seen more hp if I had the right compression. For fear of high compression causing detonation, I called DNE and asked them what they do to the stock head so I can put it back on. They told me to mill it so many thousands (I forget) and install a .8 mm base gasket. I checked the squish and had .058-.059. I always ran premium gas. Running the RKT head my egt would read 1325 at a steady 60mph. I did have a little pitting on the top dome of my mag side piston. I know 1300 is the max I want to go on my egt's. I let of the gas to about 40mph and the temps dropped to around 1280. If I gave it more throttle speed up to 80mph the temps would start do drop. There is still a problem with the mid range leaning out. It's not as bad as the 01,02 sleds but its still there. With the stock head back on with DNE's suggestions my egt's at 60mph were hitting 1375. This pretty much tells me the stock head has a #### poor combustion chamber compared to RKT. I have not taken the top end apart to check the new rings. I have a little over 500 miles on the new ones. I need to change my pistons either with Weisco or RKT modded ART. don't know if I should drop compression down to 12 or 12 1/2 to 1. I need to get the RKT head back on and have the domes recut to whatever I decide. Don't know weather to stay with the .8mm gasket that DNE suggested, or go with 1.2mm that RKT (from what I here) is suggesting now.

New this year could be Team secondary roller clutch, Crankshop twins, Boondocker nitrous, and looking into the turbo crank. I'm in so deep that I will have this sled for life :D

WOW! you guys spend some serious cake on components.

That RKT head is so effecient it's scary. I have a '01 800X and have dropped mains to 410's. MY egt's are still rich at WOT. May be able to go to 390's This has been the best investment for me to date.

I feel I have cured MY midrange lean spot. In fact I had it so rich is was only 900 deg. at about 6500 or 60 mph. Could hold it there all day. Riding tight trails it would load up and foul a plug. I slowly stepped it back and can now hold the throttle steady at 6500 and get about 1100deg on egt's. I still need to lean down more, but feel very safe with it now. My recalled pistons look great. Almost all the moly is still on and the ring surfaces look good.

My bud has 4000 miles on his recalled pistons and it still has 140 lbs. compression and runs fine.

I'm confused on all these piston problems. Was there a major issue after the '01 models?? Seems more talk than ever about replacing pistons.

The reed cage had the center support taken out for better flow.
Can you elaborate on the center support removal? Are you saying that since the Boyesens are a 2 stage that you were able to remove both of the petal supports and have just the outside frame left?

RKT head 13/1 compression with 2mm gasket.
JMHO...13:1 is just too high for us guys here in Michigan. I believe that 12:1 is what to use as a maximum. Lifting the cylinders is a great way to find out whether or not there are gains to be found. I don't think that 2MM is too much to lift the exhaust, but I do think it's too much to lift the intake. You're giving the pipe way to much time with the intake open. I think that the pulse to stuff the gas back in just before the exhaust closes is getting back early enough to find the intake still open. The crankcase is the low pressure area at this point due to the rising of the piston. Combine that with the early arriving exhaust pulse and you have the unburned gasses in the pipe along with more than the normal amount of burned gasses getting pushed into the cylinder and right on into the crankcase through the open intake. This dilutes not only the gasses in the cylinder, but also the mixture in the crankcase. This causes a serious lean condition which fools us into thinking that we are running rich. Just remember, this is just my opinion. You should lift the cyl in no more than .6MM increments. If you find a gain you like, grind the top of the exhaust port the .6MM and drop the cyl back down. I know that can get expensive. I don't know yet, but I believe that raising the top of the exhaust port about 1MM is where we want to be. I'll let you know. Didn't mean to ramble. ???

Don't know weather to stay with the .8mm gasket that DNE suggested, or go with 1.2mm that RKT (from what I here) is suggesting now.

I'd go with the 1.2MM as recommended by Kelsey.

Brian: I'd like to hear your results on the gearing/cluthing once you go to the 1.76 ratio.

What type of stud are you running on your 1.25" track? do you remember the size? did you add tunnel protectors?

Thanks
Jon

I'm running 1.375 Woody's Golddiggers on my 1 1/4". 144 down the middle. Don't expect a lot from them as far as traction for launch goes though. They shine in the corners and for stopping.

Keith, did you add any tunnel protectors or other modifications for that setup to fit?

Originally posted by skidoomaster@Jul 24 2003, 12:04 PM
Brian: I'd like to hear your results on the gearing/cluthing once you go to the 1.76 ratio.

What type of stud are you running on your 1.25" track? do you remember the size? did you add tunnel protectors?

Thanks
Jon
Yes, my set up is the same as Keiths (idooski's) and we both are running tunnel protectors, I will let you know on the gearing!!! :D

1.325 Woody's Golddiggers set to a pattern like this:

[]0 00 []
[] 0 00[]
[]00 0 []
[] 00 0[]


Brian




SWRules

[quote]Can you elaborate on the center support removal? Are you saying that since the Boyesens are a 2 stage that you were able to remove both of the petal supports and have just the outside frame left?

Yes, DNE takes the stock cage and removes the support brackets.