XP big bores - lets compare

[tntm7]

heat soak is a big problem with sled motors, not such a problem with MX, look at all the time you spend in the air!
I have never seen a motocross race where you loaded the motor in high gear for 2 min.
The comment MX bikes dont have big bores, they have big bores. CRF450 has a 96mm bore, what sled has that size bore?
Heat soak is the big problem with sleds, long heavy pulls and deep snow.
Race gas mix's are a great insurance and consistancy for heavy loads and will increase the time it takes to heat soak the motor. Pretty common to see a 170hp motor loose 25hp when heat soaked.

 

[longhairfreak]

heat soak is a big problem with sled motors, not such a problem with MX, look at all the time you spend in the air!
I have never seen a motocross race where you loaded the motor in high gear for 2 min.
The comment MX bikes dont have big bores, they have big bores. CRF450 has a 96mm bore, what sled has that size bore?
Heat soak is the big problem with sleds, long heavy pulls and deep snow.
Race gas mix's are a great insurance and consistancy for heavy loads and will increase the time it takes to heat soak the motor. Pretty common to see a 170hp motor loose 25hp when heat soaked.

I think detonation is far more likely on a two stroke than a four stroke. I run 13-1 and the crf is 12-1. I have a 98mm bore on my two stroke.

 

[Trashy]

Why are snowmobiles so different?? Higher octane fuel DOES NOT build more power. Octane is the fuels resistance detonation. If you dont have a deto issue, you dont need better fuel. Agreed??

Because you just don't load up a bike engine the way a sled engine loads up in deep snow...

 

[Dano702]

Well, One MAJOR issue BRP will NOT discuss about the xp's is electronics !

When the 09 xp snoxers were deliverd to me prior to Duluth, I noticed right off that they WOULD NOT pull the 08 clutchs ???

Marcel assured me I was a bad tuner,,,lol ..I then informed him the pipe was longer at diffuser 2 and the timing was 3-4 + from 08..

YOU ARE INCORRECT !

That was November,,
March,25 2009. BRP racer e mail, Timing on 09 stockers is off by +4 and on Mod boxs Off by +5-7..

They are getting a very nice,, no foul language fairwell from our teams..
John,
I brought BRP 12 class championships in the RMR series and 2 ISOC national pro wins this season without so much as a thank you..

and their 3 foot tall nepoleon's..lol can kiss my arse..


off the rant..

A pump gas low low comp turbo is only producing about the same power as most big bores..MOST that is.

just because it has a turbo does not mean it is a brute, just another way of gettin to the same place..per say.


Gus

I would agree , i enjoy a silky smooth 7 lbs myself .

 

[triple7]

heat soak is a big problem with sled motors, not such a problem with MX, look at all the time you spend in the air!
I have never seen a motocross race where you loaded the motor in high gear for 2 min.
The comment MX bikes dont have big bores, they have big bores. CRF450 has a 96mm bore, what sled has that size bore?
Heat soak is the big problem with sleds, long heavy pulls and deep snow.
Race gas mix's are a great insurance and consistancy for heavy loads and will increase the time it takes to heat soak the motor. Pretty common to see a 170hp motor loose 25hp when heat soaked.

No, you're right a bike is never loaded as hard. But out playin in the dunes with a paddle loads it pretty damn hard.
Can anyone tell me why a "heat soaked" engine loses so much power?? What happens to have all the power evaporate?? I agree it happens, I dont know why. The hotter we ran our race cars the more power was built.

And just to clarify, I have tried good fuel blends and my inconsistent xp continued.

And is anyone else having ring issues with doo XP's??

 

[tntm7]

Nickel plated alum cylinders have reduced heat soak by 20% or more on some eingines.
they loose hp from heat soak for multiple reasons, inconsistant expansion, hot vapors taking up more space, increased ring land clearance, inconsistant ring seal.
Most race cars make more hp with high engine temps because the bore of a hot block is larger then with a cold block, you get less friction with a bigger bore, and heat soaked pistons are larger then cool pistons. You also get a more constistant combustion at higher temps, but also narrow the margin of safety.
Piston is the hottest part of the engine with only a thermocoupler conntected to the cylinder through the rings and oil bonding. so fuel, oil and ring contact are the only way the piston can transfer heat.

I have done over 100 dyno tests on two strokes with oil ratios, so far not once has less oil made more peak HP after 5 seconds, and I have seen 20to1 make 20hp more then 40to1 after a 7 second peak hp loading.
you may gain snap with less oil but you will loose much more at the top of the hill!
and I have made the most peak hp at 16to1 but cant jet it to run clean.

I run pump gas in my 450's at the track always, and mix 50/50 or run straight race gas in the dunes, motor rattles and gets smoking hot in the dunes on pump gas. stays crisp and my vent tube stays almost oil free with race gas.
my Kawi 450 in the dunes vents oil bad with pump gas, motor just gets to dam hot. I also find that i have to adjust the clutch much more in the dunes with pump gas to compinsate for the hot engine cases.

 

[tntm7]

I think detonation is far more likely on a two stroke than a four stroke. I run 13-1 and the crf is 12-1. I have a 98mm bore on my two stroke.

Most people dont account for the compression ratio of a two stroke with valves closed, which makes for a much greater chance of detonation.
some of the corrected compression ratios valve closed are 17to1.
and there running pump gas?

 

[Original Tetonice]

Loading up a snowmobile motor vs a dirt bike motor can happen to both just under differant condition.

if you ride alot of hot desert cross country or as mentioned sandune riding the hot heat can lead thei heat soak. Also those dirt bikes struggle when those air filters begin to get caked with fine dirt that prevents your dirt bike from breathing....Similar to how deep snow plugs up your sled from breathing.

OT

 

[tntm7]

plugging the filters will reduce power and cause a rich condition, both will reduce engine heat soak.
I ride in the dunes, grew up in the desert and its dam hard to load a bike motor like a sled, specially a sled in 2ft or more of fresh powder.
didnt say it wasnt possible to load a dirt bike, just real hard for a mx bike on a mx track to get even close to the load of a sled, simple math. wheels vs track, 500+ LBS vs 230lbs,
how bought we say its very common for a sled to see much higher loads then a mx bike. better choice of words?

 

[Norway]

Hang in there Dave!!!

Sorry to hear about your problems guys...

How much can you bypass on those engines? We heard the ECM could be programmed to just keep going. What else? If there is a temp sensor affecting things that should be possible to solve with the right resistor.

Some of the new sleds really haul a$$ in the pow and I like them, specially the M series, but I'm starting to fear the electronics. It's starting to become so complicated that even a dealer dont know all the inns and outs on sleds anymore.

Got my stator and cdi; period! Measure some ohms and done with them.

Luck guys..

RS

 

[Original Tetonice]

plugging the filters will reduce power and cause a rich condition, both will reduce engine heat soak.
I ride in the dunes, grew up in the desert and its dam hard to load a bike motor like a sled, specially a sled in 2ft or more of fresh powder.
didnt say it wasnt possible to load a dirt bike, just real hard for a mx bike on a mx track to get even close to the load of a sled, simple math. wheels vs track, 500+ LBS vs 230lbs,
how bought we say its very common for a sled to see much higher loads then a mx bike. better choice of words?

Again under certain condition you can load up a dirt bike....Can you load up a dirt under the the same snowload as a sled in 3 feet of powder ? Perhaps......Peps are converting ther MX bikes to run in deep snow.... The kit is available

OT

 

[BIG JOHN]

a few tips...

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..

DPM solenoids operating as they should....

I had 2 2008 sleds run in "safety" mode all winter..over the phone tuning didnt help, local dealer said everything was fine, MY dealer plugged in the BUDS and it was in deto/safety mode for the last 25+ hours (nice dealer HUH??)...cleaned up ECM with updates and now its on like donkey kong...

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????

As for Dave Trygstad (not Trigstad you dolt)..does build solid race/trail motors...but for $2600+ with no base line jetting/clutching??? I prefer a complete pump gas package that I know makes good power and can help 100% of my customers...if you want MORE HP I can help too, its just more than $1995...

I'm racing this weekend and I'm sure there will be a couple trygger motors..we'll see how mine does...BJ

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...

 

[NoSecondChances]

..... but I'm starting to fear the electronics. It's starting to become so complicated that even a dealer dont know all the inns and outs on sleds anymore.

Got my stator and cdi; period! Measure some ohms and done with them.
.....

Amen to that. This is the vey reason I keep hanging on to my mod sleds. I'd like to buy something new off the showroom floor but you need a fancy electronics degree to be able to tune them, and most of my stuff works just as good but I can fix it in the backcountry with a piece of wire and bailer twine.

You're comment on the new M series is understandable, but they are just as bad as some of the others. If you burn out the ECM in them, its a minimum $1500 and they are all different, lots of guys having issues with them and not being able to get a new one.

NSC

 

[Insaneboltrounder/sjohns]

Swest quote of the week !!!

"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... " BJ

 

[tntm7]

all the big bores xp's running on cali oxidized fuel need 540 or larger mainjets.
Few have tried smaller and they burned down, even with a little race gas.
But there race gas was 100 sunoco which is also oxidized.
Few are running 540's with power jets as well. EGT's are 1150 with stock pipe.

 

[turboal]

the single pipe bb i make uses 490 and .010 shim on needle with stock pipe and intake air box on the carbs modified slightly.
the twin piped unit with jaws twins ran 540's and .040 on the needle
it is only a handful that display the eratic running and low rpm top end that arent able to completely offer up a why to there ill condition ,

the twins really make a bb out of it .Good job Greg

the check valves in the power valve system , highly suspect, wont take much contamination to leak .
as the guys mentioned above the dpm has issues of contaminatiion to..
made me wonder were it is coming from and made me think of the check valves
yank them out Dave and see what they look like .

 

[Tuesday]

I've kept my "quest to make it run" off the main forums...just some PM's. I don't think the issues are anything to do with what Split Second built....I think it's a Doo problem and I didn't want to send any bad vibes at Ralph. This thread came up, and I thought that I better mention that between mine and several others I have talked with this season, it appears that the 800R big bores are hit and miss.

I see a turbo 1200 4S in your future!

 

[DaveB]

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.

 

[triple7]

"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

 

[triple7]

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??