XP big bores - lets compare

[diamonddave]

call me...send me that top end...SHR will keep you in the sport...BJ

Sounds like a great idea. Sometimes a fresh set of eyes can make all the difference!! Can't hurt if your season is over.

ALL 2008/2009 XP stock or BB get the 2009 "update" for a less sensitive knock sensor...its on the BUDS screen in bold letters saying UPDATE...the dealer should be aware of this...my 2009 needed this update so dont assume its OK..

This really made a difference for a stocker 09 in our group!

Extra safe jetting on some BB's is killing hp...with mine I've been from 500 mains down to 430's...460/470 is consumer safe...stock needle plus .030" is consumer safe...as in 90% of all motors are running this spec with solid/clean fueling/mileage...540 or 560 mains????

This is what really suprises me reading about these bigbores. There seems to be a very wide range of jetting being used. I've read as low as 430's to as high as560's?? What gives. Is it all in the head being used? Any of the experts have an opinion on why there's such a drastic swing?

BTW- OT, if you knew 25% of what think you do I'd be impressed...but you keep opening your mouth and proving me right...

Classic!!

 

[byeatts]

Sounds like a great idea. Sometimes a fresh set of eyes can make all the difference!! Can't hurt if your season is over.



This really made a difference for a stocker 09 in our group!



This is what really suprises me reading about these bigbores. There seems to be a very wide range of jetting being used. I've read as low as 430's to as high as560's?? What gives. Is it all in the head being used? Any of the experts have an opinion on why there's such a drastic swing?




Classic!!

I can tell you the Cali. fuel will require two jet sizes by itself. A pipe can be two sizes as well , The intake signal plays a "huge" factor with airbox/pod mods and the porting ,base gasket,port timing ,head all are factors.I,ve recently seen some really poor porting jobs as well which must be considered,Not really that suprizing when you look at the big picture.It leaves a lot of room for poor tuning,I know how long it took me to dial in. My 880 was flat on the top when running lean.Gain HP with the addition of fuel.most likely specific to my motor

 

[fatguy1]

"how bought we say its very common for a sled to see much higher loads then a mx bike. better choice of words?"

Agreed. So what you are saying is that cutting oil out of the motor can cause it to drop rpm under a sustained pull?? And I would have to reread your explanation of heat soak power loss but it sounds like basically you are saying that as internal temps rise, power falls off on a sled engine?? But not in a race car?? Not nit picking but why do race cars fall under different parameters than sled motors??

I am just trying to get ahold of some reasons why we have erratic behavior in some of the XP's

Not trying to speak for tntm7, IMO the two stroke has a more difficult time getting rid of the combustion heat. The piston sees a ton of heat and it gets transfered through the ring to the cylinder where the coolant can do it's job.(also through the head) By increasing the ability for the piston to get rid of the heat (by maybe using oil to transfer the heat) then there is less cylinder expansion/distortion/fade.
I know I'm not explaining the best so maybe some one else can. (Or call Bull $hit) Another thing is most race cars are four strokes, they don't see the heat of combustion every other cycle like a two stroke.

 

[Tuesday]

I see a couch in my future. I don't want to hex the 4 strokes....they would suddenly turn into poor-running unreliable piles of dung like everything else I own.

haha....

How did you BB run that you had in your rev?

 

[MARCUSO]

forgive me if I missed it, but.

Dave, Did you send your MPEM to get reprogrammed when you got the BB?

 

[tntm7]

"how bought we say its very common for a sled to see much higher loads then a mx bike. better choice of words?"

Agreed. So what you are saying is that cutting oil out of the motor can cause it to drop rpm under a sustained pull?? And I would have to reread your explanation of heat soak power loss but it sounds like basically you are saying that as internal temps rise, power falls off on a sled engine?? But not in a race car?? Not nit picking but why do race cars fall under different parameters than sled motors??

I am just trying to get ahold of some reasons why we have erratic behavior in some of the XP's

Engine block temps and heat soak are not the same. you can have a 240 deg engine that is not heat soaked, heat soak is when the bore and piston are above engine water temps by more then 200 deg.
Another words, you can have a engine water temp at 120 or 280 and they both can heat soak.
When the piston and cylinder are surface temps above base engine temp, then you are heat soaked, another words you have more heat in them than what can be evacuated through the cooling system and need a shut down period to stabilize.
ANd no race car engine and sled engine are no different in terms of suffering from heat soak,

 

[tntm7]

One other ?? on the oil thing. If a motor is being run at 40:1, and that is causing a loss in horsepower under sustained load as opposed to running that engine at 20:1, shouldnt the motor show signs of lack of oil inside it during tear downs??

NO you may see a slight bit more wear then you would with 20to1 but without two comparisons you cant see it.
You are just loosing thermocoupling to be able to remove heat, so its not going to show more wear to say, and almost never lubrication related issues.
Just heat soaks faster and wont make quite the hp on top after few seconds of peak load.

 

[tntm7]

Not trying to speak for tntm7, IMO the two stroke has a more difficult time getting rid of the combustion heat. The piston sees a ton of heat and it gets transfered through the ring to the cylinder where the coolant can do it's job.(also through the head) By increasing the ability for the piston to get rid of the heat (by maybe using oil to transfer the heat) then there is less cylinder expansion/distortion/fade.
I know I'm not explaining the best so maybe some one else can. (Or call Bull $hit) Another thing is most race cars are four strokes, they don't see the heat of combustion every other cycle like a two stroke.

What two stroke guys call squish band was really designed to be a quench band, to trap cool fuel and air and quinch the surface of the piston, so yes head design plays a big part in how fast you can loose heat or build it.
All though a two stroke fires every 360 a 4 stroke usually traps more heat in the piston then a 2 stroke, you have to remember it has to do an exhaust stroke and push out hot spent gas exposing the piston to high temps longer then a 2 stroke, it also has a full 180 deg power stroke, port doesnt open halve way down and gets a cooling wave of new fuel 180 deg before a 4 stroke.
I think that theory came from the old days when two strokes burnt down much faster when lean compaired to 4 stroke, thats def true.

 

[SMT860]

I hears ya Al. I am firmly convinced that there is something in the ECM itself holding it back. My dealer and his #1 Tech think the same....it's just impossible to prove. I know they tried a different ECM on Jack's and that wasn't the problem. His ended up being the one-way valves leaking. I have elliminated this as a source of problem thanks to Byeatts....but I am out of season. Will have to continue next year. Boy....that's gonna be nice to look forward to: start my 09/10 season bye STILL working on a brand-new sled. LOL.....maybe I'll get lucky and my garage will burn down while I'm out camping this summer....

I feel your pain Dave. I too have had a winter full of less than satisfactory tuning and still not the stellar BB I was expecting from SS. I also thought it must be the clutching from the start and have also tried numerous set ups and have one that works well and will hold any RPM but I am still looking back to see if a stocker is going to high mark me. This machine has also run well all season with 2000km on it with no engine, belt or frame issues. However I want more as my 05 860 will make the 09 look silly with a shorter track.
The first sign of trouble I noticed was I ran the stock eng on the first trip and found to be able to hold RPM and everything was good with clickers on 6. I then left all the same and did the BB and went for the next ride w/o doing anything thinking I would be able to lower clickers - not. Then played with clutching pretty much all year to make better but still not seeing the power. Here is my set up: Running 460 mains, 07 needles on middle setting with 17thou shim, VF reeds, HPS can, SW secondary w/ stock spring, 160/320 primary w/ 15.4g pins and 412 ramps and 20T top gear. Holding Rs OK. Had troubles getting mid temps down but now running 1240 in mids and 1180 WOT. Kinda stumped from here - like you I'm tired of messing with it and should just say F it and have fun riding (I do anyways - just sucks to get beat is all).
Ralph asked me to check the squish as he thought there may have been too much but came up with 60 thou which seems Ok as it is the same as the 05.
It must be those CAT pistons!!! Damn I knew that was a bad idea to stick them in there.
Anyways, good luck with yours and if you come up with the answer let me know!

 

[fatguy1]

What two stroke guys call squish band was really designed to be a quench band, to trap cool fuel and air and quinch the surface of the piston, so yes head design plays a big part in how fast you can loose heat or build it.
All though a two stroke fires every 360 a 4 stroke usually traps more heat in the piston then a 2 stroke, you have to remember it has to do an exhaust stroke and push out hot spent gas exposing the piston to high temps longer then a 2 stroke, it also has a full 180 deg power stroke, port doesnt open halve way down and gets a cooling wave of new fuel 180 deg before a 4 stroke.
I think that theory came from the old days when two strokes burnt down much faster when lean compaired to 4 stroke, thats def true.

Thanks for the explanation, does the fact that polaris and artic cat have dual ring pistons help them transfer or loose heat quicker??? or is that a myth?

 

[MARCUSO]

HOw about something as stupid and simple as this??

Scroll down to "feeling fat?"

Just kinda stumbled onto this... could this be a factor??

 

[tntm7]

Thanks for the explanation, does the fact that polaris and artic cat have dual ring pistons help them transfer or loose heat quicker??? or is that a myth?

single ring will heat soak faster and loose more power when heat soaked, but will make more power in short run.
I asked Franko Detorie, why he is using the single ring in the 800r motor, he said there was to many failures in testing with double ring pistons and 91 octain gas, they wholed pistons, so he went with the single ring to reduce heat soaked hp and give the motor longer life,
OH, Franko is Rotax Engineer who designed the 800r engine.

 

[fatguy1]

single ring will heat soak faster and loose more power when heat soaked, but will make more power in short run.
I asked Franko Detorie, why he is using the single ring in the 800r motor, he said there was to many failures in testing with double ring pistons and 91 octain gas, they wholed pistons, so he went with the single ring to reduce heat soaked hp and give the motor longer life,
OH, Franko is Rotax Engineer who designed the 800r engine.

Good to know the above... The problem I have with it is that my sled doesn't make any "Short Runs" and it seems like right when I need it, 45 sec into a long pull in the mountains that is when you get that seat of the pants feel that the sled has stopped pulling and is turning into a turtle.

 

[BIG JOHN]

NO you may see a slight bit more wear then you would with 20to1 but without two comparisons you cant see it.
You are just loosing thermocoupling to be able to remove heat, so its not going to show more wear to say, and almost never lubrication related issues.
Just heat soaks faster and wont make quite the hp on top after few seconds of peak load.

I'm gunna piggy back TNT's post...NOT that I did dyno tests to prove each ratio...but from the field I have been recomending 32-1 with oil injection (1 qt oil per tank of fuel) for yeeeeears...thanks for verifying my gut...I was shooting for longer crank bearing life...LOL-BJ

 

[BIG JOHN]

single ring will heat soak faster and loose more power when heat soaked, but will make more power in short run.
I asked Franko Detorie, why he is using the single ring in the 800r motor, he said there was to many failures in testing with double ring pistons and 91 octain gas, they wholed pistons, so he went with the single ring to reduce heat soaked hp and give the motor longer life,
OH, Franko is Rotax Engineer who designed the 800r engine.

1 more time...LOL

IMHO...nothing more...the rings werent the reason, the extreme ignition timing and very small exhaust port (with valves closed at cruise speed, read slow traffic) was/is the problem...

At WOT with full fuel/less timing and a full exhaust port wasnt/isnt the problem...

In my 860 kit I modify the valves (bigger opening when closed), modify the side port valves (alot bigger than stock when closed), better head design (IMHO), alot larger exhaust port/sub ports and with a bigger bore stock timing becomes less...I actually bump it 1 degree to match my motor...BJ

 

[Dynamo^Joe]

single ring will heat soak faster and loose more power when heat soaked, but will make more power in short run.
I asked Franko Detorie, why he is using the single ring in the 800r motor, he said there was to many failures in testing with double ring pistons and 91 octain gas, they wholed pistons, so he went with the single ring to reduce heat soaked hp and give the motor longer life,
OH, Franko is Rotax Engineer who designed the 800r engine.

Franco Dettori & Claude Fortin he he he

 

[fatguy1]

Franco Dettori & Claude Fortin he he he

I can see lots of people who hate the 800 R using the names of these guys in vain everytime they run into a problem. LOL

 

[tntm7]

If you new Franko you would have a hard time doing it. That guy put a smile on your face at anytime.
Few yrs back he got a nice flash burnt face in my shop working on a seadoo.
HE looked like he had a 4 day sunburn. He was working on a flooded seadoo that the had a bad needle in seat in one carb and cranking it over with plugs out and had his face over the engine compartment with a cig in his mouth and whooooosh it went up like a roman candle, SHop smelt like burnt hair for two days.
The look on his face with a charded sig in his mouth and freshly flashed hair and mustache, still makes us chukle today.

 

[CBX]

This Thread is almost Tack worthy at the top of the forum.

TNTm7: Thank you for sharing your wealth of info and all your years of experience with us. You are obivously in the know.

Guys like you, Big John, Joe Imhoff really make these forums one of the greatest knowledge libraries for sledders.

You guys Rock!

 

[fatguy1]

This Thread is almost Tack worthy at the top of the forum.

TNTm7: Thank you for sharing your wealth of info and all your years of experience with us. You are obivously in the know.

Guys like you, Big John, Joe Imhoff really make these forums one of the greatest knowledge libraries for sledders.

You guys Rock!

I second that!, when I first saw the 860 BB title on this I thought to myself "Isnt that horse already Dead?". But Everyone has given excellent info and brought up good questions.

thanks